1
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Ewert M, Nunn BL, Firth E, Junge K. Metabolic Responses, Cell Recoverability, and Protein Signatures of Three Extremophiles: Sustained Life During Long-Term Subzero Incubations. Microorganisms 2025; 13:251. [PMID: 40005618 PMCID: PMC11858272 DOI: 10.3390/microorganisms13020251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2024] [Revised: 01/14/2025] [Accepted: 01/16/2025] [Indexed: 02/27/2025] Open
Abstract
Few halophilic strains have been examined in detail for their culturability and metabolic activity at subzero temperatures, within the ice matrix, over the longer term. Here, we examine three Arctic strains with varied salinity tolerances: Colwellia psychrerythraea str. 34H (Cp34H), Psychrobacter sp. str. 7E (P7E), and Halomonas sp. str. 3E (H3E). As a proxy for biosignatures, we examine observable cells, metabolic activity, and recoverability on 12-month incubations at -5, -10 and -36 °C. To further develop life-detection strategies, we also study the short-term tracking of new protein synthesis on Cp34H at -5 °C for the first time, using isotopically labeled 13C6-leucine and mass spectrometry-based proteomics. All three bacterial species remained metabolically active after 12 months at -5 °C, while recoverability varied greatly among strains. At -10 and -36 °C, metabolic activity was drastically reduced and recoverability patterns were strain-specific. Cells were observable at high numbers in all treatments, validating their potential as biosignatures. Newly synthesized proteins were detectable and identifiable after one hour of incubation. Proteins prioritized for synthesis with the provided substrate are involved in motility, protein synthesis, and in nitrogen and carbohydrate metabolism, with an emphasis on structural proteins, enzymatic activities in central metabolic pathways, and regulatory functions.
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Affiliation(s)
- Marcela Ewert
- Polar Science Center, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Box 355640, Seattle, WA 98105-6698, USA; (M.E.); (E.F.)
| | - Brook L. Nunn
- Department of Genome Sciences, University of Washington, Foege Building S-250, Box 355065, 3720 15th Ave NE, Seattle, WA 98195-5065, USA;
| | - Erin Firth
- Polar Science Center, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Box 355640, Seattle, WA 98105-6698, USA; (M.E.); (E.F.)
| | - Karen Junge
- Polar Science Center, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Box 355640, Seattle, WA 98105-6698, USA; (M.E.); (E.F.)
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2
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Tobie G, Auclair-Desrotour P, Běhounková M, Kervazo M, Souček O, Kalousová K. Tidal Deformation and Dissipation Processes in Icy Worlds. SPACE SCIENCE REVIEWS 2025; 221:6. [PMID: 39830012 PMCID: PMC11739232 DOI: 10.1007/s11214-025-01136-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/28/2023] [Accepted: 12/30/2024] [Indexed: 01/22/2025]
Abstract
Tidal interactions play a key role in the dynamics and evolution of icy worlds. The intense tectonic activity of Europa and the eruption activity on Enceladus are clear examples of the manifestation of tidal deformation and associated dissipation. While tidal heating has long been recognized as a major driver in the activity of these icy worlds, the mechanism controlling how tidal forces deform the different internal layers and produce heat by tidal friction still remains poorly constrained. As tidal forcing varies with orbital characteristics (distance to the central planet, eccentricity, obliquity), the contribution of tidal heating to the internal heat budget can strongly change over geological timescales. In some circumstances, the tidally-produced heat can result in internal melting and surface activity taking various forms. Even in the absence of significant heat production, tidal deformation can be used to probe the interior structure, the tidal response of icy moons being strongly sensitive to their hydrosphere structure. In the present paper, we review the methods to compute tidal deformation and dissipation in the different layers composing icy worlds. After summarizing the main principle of tidal deformation and the different rheological models used to model visco-elastic tidal response, we describe the dissipation processes expected in rock-dominated cores, subsurface oceans and icy shells and highlight the potential effects of tidal heating in terms of thermal evolution and activity. We finally anticipate how data collected by future missions to Jupiter's and Saturn's moons could be used to constrain their tidal response and the consequences for past and present activities.
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Affiliation(s)
- G. Tobie
- Laboratoire de Planétologie et Géosciences, UMR 6112, CNRS, Nantes Université, Université d’Angers, Le Mans Université, Nantes, France
| | - P. Auclair-Desrotour
- IMCCE, CNRS, Observatoire de Paris, PSL University, Sorbonne Université, Paris, France
| | - M. Běhounková
- Faculty of Mathematics and Physics, Department of Geophysics, Charles University, V Holesšovičkách 2, Praha, Praha 8 180 00 Czech Republic
| | - M. Kervazo
- Laboratoire de Planétologie et Géosciences, UMR 6112, CNRS, Nantes Université, Université d’Angers, Le Mans Université, Nantes, France
| | - O. Souček
- Faculty of Mathematics and Physics, Mathematical Institute, Charles University, Sokolovská 83, Praha, Praha 8 186 75 Czech Republic
| | - K. Kalousová
- Faculty of Mathematics and Physics, Department of Geophysics, Charles University, V Holesšovičkách 2, Praha, Praha 8 180 00 Czech Republic
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3
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Zhang Y, Kang W, Marshall J. Ocean weather systems on icy moons, with application to Enceladus. SCIENCE ADVANCES 2024; 10:eadn6857. [PMID: 39504379 PMCID: PMC11540039 DOI: 10.1126/sciadv.adn6857] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2024] [Accepted: 10/01/2024] [Indexed: 11/08/2024]
Abstract
We explore ocean circulation on a rotating icy moon driven by temperature gradients imposed at its upper surface due to the suppression of the freezing point of water with pressure, as might be induced by ice thickness variations on Enceladus. Using high-resolution simulations, we find that eddies dominate the circulation and arise from baroclinic instability, analogous to Earth's weather systems. Multiple alternating jets, resembling those of Jupiter's atmosphere, are sustained by these baroclinic eddies. We establish a theoretical model of the stratification and circulation and present scaling laws for the magnitude of the meridional heat transport. These are tested against numerical simulations. Through identification of key nondimensional numbers, our simplified model is applied to other icy moons. We conclude that baroclinic instability is central to the general circulation of icy moons.
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Affiliation(s)
- Yixiao Zhang
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Wanying Kang
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - John Marshall
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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4
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Rhoden AR, Ferguson SN, Bottke W, Castillo-Rogez JC, Martin E, Bland M, Kirchoff M, Zannoni M, Rambaux N, Salmon J. Geologic Constraints on the Formation and Evolution of Saturn's Mid-Sized Moons. SPACE SCIENCE REVIEWS 2024; 220:55. [PMID: 39036784 PMCID: PMC11255024 DOI: 10.1007/s11214-024-01084-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Accepted: 06/13/2024] [Indexed: 07/23/2024]
Abstract
Saturn's mid-sized icy moons have complex relationships with Saturn's interior, the rings, and with each other, which can be expressed in their shapes, interiors, and geology. Observations of their physical states can, thus, provide important constraints on the ages and formation mechanism(s) of the moons, which in turn informs our understanding of the formation and evolution of Saturn and its rings. Here, we describe the cratering records of the mid-sized moons and the value and limitations of their use for constraining the histories of the moons. We also discuss observational constraints on the interior structures of the moons and geologically-derived inferences on their thermal budgets through time. Overall, the geologic records of the moons (with the exception of Mimas) include evidence of epochs of high heat flows, short- and long-lived subsurface oceans, extensional tectonics, and considerable cratering. Curiously, Mimas presents no clear evidence of an ocean within its surface geology, but its rotation and orbit indicate a present-day ocean. While the moons need not be primordial to produce the observed levels of interior evolution and geologic activity, there is likely a minimum age associated with their development that has yet to be determined. Uncertainties in the populations impacting the moons makes it challenging to further constrain their formation timeframes using craters, whereas the characteristics of their cores and other geologic inferences of their thermal evolutions may help narrow down their potential histories. Disruptive collisions may have also played an important role in the formation and evolution of Saturn's mid-sized moons, and even the rings of Saturn, although more sophisticated modeling is needed to determine the collision conditions that produce rings and moons that fit the observational constraints. Overall, the existence and physical characteristics of Saturn's mid-sized moons provide critical benchmarks for the development of formation theories.
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Affiliation(s)
| | | | - William Bottke
- Southwest Research Institute, 1050 Walnut St, Boulder, CO 80302 USA
| | | | - Emily Martin
- Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, DC USA
| | - Michael Bland
- U.S. Geological Survey, Astrogeology Science Center, Flagstaff, AZ USA
| | | | - Marco Zannoni
- Dipartimento di Ingegneria Industriale, Alma Mater Studiorum – Università di Bologna, Forlì, Italy
| | - Nicolas Rambaux
- IMCCE, CNRS, Observatoire de Paris, PSL Université, Sorbonne Université, Université de Lille 1, UMR 8028 du CNRS, 77 Denfert-Rochereau, 75014 Paris, France
| | - Julien Salmon
- Southwest Research Institute, 1050 Walnut St, Boulder, CO 80302 USA
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Khawaja N, Hortal Sánchez L, O'Sullivan TR, Bloema J, Napoleoni M, Klenner F, Beinlich A, Hillier J, John T, Postberg F. Laboratory characterization of hydrothermally processed oligopeptides in ice grains emitted by Enceladus and Europa. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2024; 382:20230201. [PMID: 38736335 DOI: 10.1098/rsta.2023.0201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2023] [Accepted: 01/30/2024] [Indexed: 05/14/2024]
Abstract
The Cassini mission provided evidence for a global subsurface ocean and ongoing hydrothermal activity on Enceladus, based on results from Cassini's mass spectrometers. Laboratory simulations of hydrothermal conditions on icy moons are needed to further constrain the composition of ejected ice grains containing hydrothermally altered organic material. Here, we present results from our newly established facility to simulate the processing of ocean material within the temperature range 80-150°C and the pressure range 80-130 bar, representing conditions suggested for the water-rock interface on Enceladus. With this new facility, we investigate the hydrothermal processing of triglycine (GGG) peptide and, for the first time, analyse the extracted samples using laser-induced liquid beam ion desorption (LILBID) mass spectrometry, a laboratory analogue for impact ionization mass spectrometry of ice grains in space. We outline an approach to elucidate hydrothermally processed GGG in ice grains ejected from icy moons based on characteristic differences between GGG anion and cation mass spectra. These differences are linked to hydrothermal processing and thus provide a fingerprint of hydrothermal activity on extraterrestrial bodies. These results will serve as important guidelines for biosignatures potentially obtained by a future Enceladus mission and the SUrface Dust Analyzer (SUDA) instrument onboard Europa Clipper. This article is part of the theme issue 'Dust in the Solar System and beyond'.
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Affiliation(s)
- Nozair Khawaja
- Department of Planetary Sciences and Remote Sensing, Institut für Geologische Wissenschaften, Freie Universität Berlin , Malteserstraße, Berlin 12249, Germany
- Institute of Space Systems, University of Stuttgart , Stuttgart 70569, Germany
| | - Lucía Hortal Sánchez
- Department of Planetary Sciences and Remote Sensing, Institut für Geologische Wissenschaften, Freie Universität Berlin , Malteserstraße, Berlin 12249, Germany
| | - Thomas R O'Sullivan
- Department of Planetary Sciences and Remote Sensing, Institut für Geologische Wissenschaften, Freie Universität Berlin , Malteserstraße, Berlin 12249, Germany
| | - Judith Bloema
- Department of Planetary Sciences and Remote Sensing, Institut für Geologische Wissenschaften, Freie Universität Berlin , Malteserstraße, Berlin 12249, Germany
| | - Maryse Napoleoni
- Department of Planetary Sciences and Remote Sensing, Institut für Geologische Wissenschaften, Freie Universität Berlin , Malteserstraße, Berlin 12249, Germany
| | - Fabian Klenner
- Department of Earth and Space Sciences, University of Washington , Seattle, WA 98195, USA
| | - Andreas Beinlich
- Department of Mineralogy and Petrology, Institut für Geologische Wissenschaften, Freie Universität Berlin , Malteserstraße, Berlin 12249, Germany
| | - Jon Hillier
- Department of Planetary Sciences and Remote Sensing, Institut für Geologische Wissenschaften, Freie Universität Berlin , Malteserstraße, Berlin 12249, Germany
| | - Timm John
- Department of Mineralogy and Petrology, Institut für Geologische Wissenschaften, Freie Universität Berlin , Malteserstraße, Berlin 12249, Germany
| | - Frank Postberg
- Department of Planetary Sciences and Remote Sensing, Institut für Geologische Wissenschaften, Freie Universität Berlin , Malteserstraße, Berlin 12249, Germany
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6
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Lainey V, Rambaux N, Tobie G, Cooper N, Zhang Q, Noyelles B, Baillié K. A recently formed ocean inside Saturn's moon Mimas. Nature 2024; 626:280-282. [PMID: 38326592 DOI: 10.1038/s41586-023-06975-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Accepted: 12/14/2023] [Indexed: 02/09/2024]
Abstract
Moons potentially harbouring a global ocean are tending to become relatively common objects in the Solar System1. The presence of these long-lived global oceans is generally betrayed by surface modification owing to internal dynamics2. Hence, Mimas would be the most unlikely place to look for the presence of a global ocean3. Here, from detailed analysis of Mimas's orbital motion based on Cassini data, with a particular focus on Mimas's periapsis drift, we show that its heavily cratered icy shell hides a global ocean, at a depth of 20-30 kilometres. Eccentricity damping implies that the ocean is likely to be less than 25 million years old and still evolving. Our simulations show that the ocean-ice interface reached a depth of less than 30 kilometres only recently (less than 2-3 million years ago), a time span too short for signs of activity at Mimas's surface to have appeared.
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Affiliation(s)
- V Lainey
- IMCCE, Observatoire de Paris, PSL Research University, Sorbonne Université, CNRS, Université Lille, Paris, France.
| | - N Rambaux
- IMCCE, Observatoire de Paris, PSL Research University, Sorbonne Université, CNRS, Université Lille, Paris, France
| | - G Tobie
- LPG, UMR-CNRS 6112, Nantes Université, Nantes, France
| | - N Cooper
- Department of Physics and Astronomy, Queen Mary University of London, London, UK
| | - Q Zhang
- Department of Computer Science, Jinan University, Guangzhou, P. R. China
| | - B Noyelles
- Institut UTINAM, CNRS UMR 6213, Université de Franche-Comté, OSU THETA, BP 1615, Besançon, France
| | - K Baillié
- IMCCE, Observatoire de Paris, PSL Research University, Sorbonne Université, CNRS, Université Lille, Paris, France
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7
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Kang W. Nonsynchronous rotation of icy moon ice shells: The thermal wind perspective. SCIENCE ADVANCES 2024; 10:eadk2277. [PMID: 38266084 PMCID: PMC11804828 DOI: 10.1126/sciadv.adk2277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 12/21/2023] [Indexed: 01/26/2024]
Abstract
The ice shells of icy satellites have been hypothesized to undergo nonsynchronous rotation (NSR) under the influence of tidal torques and/or ocean currents. In this work, the author proposes that the thermal wind relationship can be combined with geostrophic turbulence theory to predict ocean stress onto the ice shell inside the tangent cylinder. High-resolution numerical simulations validate the prediction within a factor of 2. For the prediction to be valid, the rotation effect must dominate (Rossby number < 1), and the upper ocean should be stratified. The latter can be achieved with sufficiently large ice thickness variations [the threshold for Europa is O(100) m]. Using this framework, once the ice rheology, thickness variations and NSR rate are determined, one may be able to estimate the ocean overturn timescale and put constraints on the ocean vertical diffusivity or the heat flux originating from the silicate core.
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8
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Nimmo F, Neveu M, Howett C. Origin and Evolution of Enceladus's Tidal Dissipation. SPACE SCIENCE REVIEWS 2023; 219:57. [PMID: 37810170 PMCID: PMC10558398 DOI: 10.1007/s11214-023-01007-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Accepted: 09/19/2023] [Indexed: 10/10/2023]
Abstract
Enceladus possesses a subsurface ocean beneath a conductive ice shell. Based on shell thickness models, the estimated total conductive heat loss from Enceladus is 25-40 GW; the measured heat output from the South Polar Terrain (SPT) is 4-19 GW. The present-day SPT heat flux is of order 100 mW m - 2 , comparable to estimated paleo-heat fluxes for other regions of Enceladus. These regions have nominal ages of about 2 Ga, but the estimates are uncertain because the impactor flux in the Saturnian system may not resemble that elsewhere. Enceladus's measured rate of orbital expansion implies a low dissipation factor Q p for Saturn, with Q p ≈ 3 × 10 3 (neglecting the role of Dione). This value implies that Enceladus's present-day equilibrium tidal heat production (roughly 50 GW, but with large uncertainties) is in approximate balance with its heat loss. If Q p is constant, Enceladus cannot be older than 1.5 Gyr (because otherwise it would have migrated more than is permissible). However, Saturn's dissipation may be better described by the "resonance-locking" theory, in which case Enceladus's orbit may have only evolved outwards by about 35% over the age of the Solar System. In the constant-Q p scenario, any ancient tidal heating events would have been too energetic to be consistent with the observations. Because resonance-locking makes capture into earlier mean-motion orbital resonances less likely, the inferred ancient heating episodes probably took place when the current orbital resonance was already established. In the resonance-locking scenario, tidal heating did not change significantly over time, allowing for a long-lived ocean and a relatively stable ice shell. If so, Enceladus is an attractive target for future exploration from a habitability standpoint.
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Affiliation(s)
- Francis Nimmo
- Dept. Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064 USA
| | - Marc Neveu
- Dept. Astronomy, University of Maryland, College Park, MD 20742 USA
- Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771 USA
| | - Carly Howett
- Dept. Physics, Oxford University, Oxford, OX1 3PU UK
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9
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Roberts JH, McKinnon WB, Elder CM, Tobie G, Biersteker JB, Young D, Park RS, Steinbrügge G, Nimmo F, Howell SM, Castillo-Rogez JC, Cable ML, Abrahams JN, Bland MT, Chivers C, Cochrane CJ, Dombard AJ, Ernst C, Genova A, Gerekos C, Glein C, Harris CD, Hay HCFC, Hayne PO, Hedman M, Hussmann H, Jia X, Khurana K, Kiefer WS, Kirk R, Kivelson M, Lawrence J, Leonard EJ, Lunine JI, Mazarico E, McCord TB, McEwen A, Paty C, Quick LC, Raymond CA, Retherford KD, Roth L, Rymer A, Saur J, Scanlan K, Schroeder DM, Senske DA, Shao W, Soderlund K, Spiers E, Styczinski MJ, Tortora P, Vance SD, Villarreal MN, Weiss BP, Westlake JH, Withers P, Wolfenbarger N, Buratti B, Korth H, Pappalardo RT. Exploring the Interior of Europa with the Europa Clipper. SPACE SCIENCE REVIEWS 2023; 219:46. [PMID: 37636325 PMCID: PMC10457249 DOI: 10.1007/s11214-023-00990-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/24/2022] [Accepted: 07/20/2023] [Indexed: 08/29/2023]
Abstract
The Galileo mission to Jupiter revealed that Europa is an ocean world. The Galileo magnetometer experiment in particular provided strong evidence for a salty subsurface ocean beneath the ice shell, likely in contact with the rocky core. Within the ice shell and ocean, a number of tectonic and geodynamic processes may operate today or have operated at some point in the past, including solid ice convection, diapirism, subsumption, and interstitial lake formation. The science objectives of the Europa Clipper mission include the characterization of Europa's interior; confirmation of the presence of a subsurface ocean; identification of constraints on the depth to this ocean, and on its salinity and thickness; and determination of processes of material exchange between the surface, ice shell, and ocean. Three broad categories of investigation are planned to interrogate different aspects of the subsurface structure and properties of the ice shell and ocean: magnetic induction, subsurface radar sounding, and tidal deformation. These investigations are supplemented by several auxiliary measurements. Alone, each of these investigations will reveal unique information. Together, the synergy between these investigations will expose the secrets of the Europan interior in unprecedented detail, an essential step in evaluating the habitability of this ocean world.
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Affiliation(s)
| | | | - Catherine M Elder
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | | | | | | | - Ryan S Park
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Gregor Steinbrügge
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Francis Nimmo
- University of California, Santa Cruz, Santa Cruz, CA, USA
| | - Samuel M Howell
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | | | - Morgan L Cable
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | | | | | | | - Corey J Cochrane
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | | | - Carolyn Ernst
- Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA
| | | | | | | | | | - Hamish C F C Hay
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Paul O Hayne
- University of Colorado Boulder, Boulder, CO, USA
| | | | - Hauke Hussmann
- German Aerospace Center Institute of Planetary Research, Berlin, Germany
| | | | | | - Walter S Kiefer
- Lunar and Planetary Institute, University Space Research Association, Houston, TX, USA
| | | | | | | | - Erin J Leonard
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | | | | | | | | | | | | | - Carol A Raymond
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Kurt D Retherford
- Sapienza University of Rome, Rome, Italy
- University of Texas at San Antonio, San Antonio, TX, USA
| | - Lorenz Roth
- KTH Royal Institute of Technology, Stockholm, Sweden
| | - Abigail Rymer
- Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA
| | | | | | | | - David A Senske
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Wencheng Shao
- University of California, Santa Cruz, Santa Cruz, CA, USA
| | | | | | - Marshall J Styczinski
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
- University of Washington, Seattle, WA, USA
| | - Paolo Tortora
- Alma Mater Studiorum - Università di Bologna, Bologna, Italy
| | - Steven D Vance
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | | | | | | | | | | | - Bonnie Buratti
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Haje Korth
- Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA
| | - Robert T Pappalardo
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
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10
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Weber JM, Marlin TC, Prakash M, Teece BL, Dzurilla K, Barge LM. A Review on Hypothesized Metabolic Pathways on Europa and Enceladus: Space-Flight Detection Considerations. Life (Basel) 2023; 13:1726. [PMID: 37629583 PMCID: PMC10456045 DOI: 10.3390/life13081726] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Revised: 08/01/2023] [Accepted: 08/07/2023] [Indexed: 08/27/2023] Open
Abstract
Enceladus and Europa, icy moons of Saturn and Jupiter, respectively, are believed to be habitable with liquid water oceans and therefore are of interest for future life detection missions and mission concepts. With the limited data from missions to these moons, many studies have sought to better constrain these conditions. With these constraints, researchers have, based on modeling and experimental studies, hypothesized a number of possible metabolisms that could exist on Europa and Enceladus if these worlds host life. The most often hypothesized metabolisms are methanogenesis for Enceladus and methane oxidation/sulfate reduction on Europa. Here, we outline, review, and compare the best estimated conditions of each moon's ocean. We then discuss the hypothetical metabolisms that have been suggested to be present on these moons, based on laboratory studies and Earth analogs. We also detail different detection methods that could be used to detect these hypothetical metabolic reactions and make recommendations for future research and considerations for future missions.
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Affiliation(s)
- Jessica M. Weber
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA (B.L.T.); (K.D.); (L.M.B.)
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11
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Postberg F, Sekine Y, Klenner F, Glein CR, Zou Z, Abel B, Furuya K, Hillier JK, Khawaja N, Kempf S, Noelle L, Saito T, Schmidt J, Shibuya T, Srama R, Tan S. Detection of phosphates originating from Enceladus's ocean. Nature 2023; 618:489-493. [PMID: 37316718 PMCID: PMC10266972 DOI: 10.1038/s41586-023-05987-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Accepted: 03/21/2023] [Indexed: 06/16/2023]
Abstract
Saturn's moon Enceladus harbours a global1 ice-covered water ocean2,3. The Cassini spacecraft investigated the composition of the ocean by analysis of material ejected into space by the moon's cryovolcanic plume4-9. The analysis of salt-rich ice grains by Cassini's Cosmic Dust Analyzer10 enabled inference of major solutes in the ocean water (Na+, K+, Cl-, HCO3-, CO32-) and its alkaline pH3,11. Phosphorus, the least abundant of the bio-essential elements12-14, has not yet been detected in an ocean beyond Earth. Earlier geochemical modelling studies suggest that phosphate might be scarce in the ocean of Enceladus and other icy ocean worlds15,16. However, more recent modelling of mineral solubilities in Enceladus's ocean indicates that phosphate could be relatively abundant17. Here we present Cassini's Cosmic Dust Analyzer mass spectra of ice grains emitted by Enceladus that show the presence of sodium phosphates. Our observational results, together with laboratory analogue experiments, suggest that phosphorus is readily available in Enceladus's ocean in the form of orthophosphates, with phosphorus concentrations at least 100-fold higher in the moon's plume-forming ocean waters than in Earth's oceans. Furthermore, geochemical experiments and modelling demonstrate that such high phosphate abundances could be achieved in Enceladus and possibly in other icy ocean worlds beyond the primordial CO2 snowline, either at the cold seafloor or in hydrothermal environments with moderate temperatures. In both cases the main driver is probably the higher solubility of calcium phosphate minerals compared with calcium carbonate in moderately alkaline solutions rich in carbonate or bicarbonate ions.
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Affiliation(s)
- Frank Postberg
- Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany.
| | - Yasuhito Sekine
- Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, Tokyo, Japan
- Institute of Nature and Environmental Technology, Kanazawa University, Ishikawa, Japan
| | - Fabian Klenner
- Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
| | - Christopher R Glein
- Space Science Division, Space Sector, Southwest Research Institute, San Antonio, TX, USA
| | - Zenghui Zou
- Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
| | - Bernd Abel
- Leibniz-Institute für Oberflächenmodifizierung, Leipzig, Germany
- Institute of Chemical Technology, University of Leipzig, Leipzig, Germany
| | - Kento Furuya
- Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, Tokyo, Japan
| | - Jon K Hillier
- Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
| | - Nozair Khawaja
- Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
| | - Sascha Kempf
- Laboratory for Atmospheric and Space Physics (LASP), University of Colorado, Boulder, CO, USA
| | - Lenz Noelle
- Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
| | - Takuya Saito
- Institute for Extra-cutting-edge Science and Technology Avantgarde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kanagawa, Japan
| | - Juergen Schmidt
- Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
- Astronomy Research Unit, University of Oulu, Oulu, Finland
| | - Takazo Shibuya
- Institute for Extra-cutting-edge Science and Technology Avantgarde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kanagawa, Japan
| | - Ralf Srama
- Institut für Raumfahrtsysteme, Universität Stuttgart, Stuttgart, Germany
| | - Shuya Tan
- Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, Tokyo, Japan
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12
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Ni Z, Arevalo R, Bardyn A, Willhite L, Ray S, Southard A, Danell R, Graham J, Li X, Chou L, Briois C, Thirkell L, Makarov A, Brinckerhoff W, Eigenbrode J, Junge K, Nunn BL. Detection of Short Peptides as Putative Biosignatures of Psychrophiles via Laser Desorption Mass Spectrometry. ASTROBIOLOGY 2023; 23:657-669. [PMID: 37134219 DOI: 10.1089/ast.2022.0138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Studies of psychrophilic life on Earth provide chemical clues as to how extraterrestrial life could maintain viability in cryogenic environments. If living systems in ocean worlds (e.g., Enceladus) share a similar set of 3-mer and 4-mer peptides to the psychrophile Colwellia psychrerythraea on Earth, spaceflight technologies and analytical methods need to be developed to detect and sequence these putative biosignatures. We demonstrate that laser desorption mass spectrometry, as implemented by the CORALS spaceflight prototype instrument, enables the detection of protonated peptides, their dimers, and metal adducts. The addition of silicon nanoparticles promotes the ionization efficiency, improves mass resolving power and mass accuracies via reduction of metastable decay, and facilitates peptide de novo sequencing. The CORALS instrument, which integrates a pulsed UV laser source and an Orbitrap™ mass analyzer capable of ultrahigh mass resolving powers and mass accuracies, represents an emerging technology for planetary exploration and a pathfinder for advanced technique development for astrobiological objectives. Teaser: Current spaceflight prototype instrument proposed to visit ocean worlds can detect and sequence peptides that are found enriched in at least one strain of microbe surviving in subzero icy brines via silicon nanoparticle-assisted laser desorption analysis.
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Affiliation(s)
- Ziqin Ni
- University of Maryland, College Park, Maryland, USA
| | | | - Anais Bardyn
- University of Maryland, College Park, Maryland, USA
| | | | - Soumya Ray
- University of Maryland, College Park, Maryland, USA
| | | | - Ryan Danell
- Danell Consulting, Winterville, North Carolina, USA
| | - Jacob Graham
- NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - Xiang Li
- NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - Luoth Chou
- NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
- Georgetown University, Washington, DC, USA
| | - Christelle Briois
- Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, Orléans, France
| | - Laurent Thirkell
- Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, Orléans, France
| | | | | | | | - Karen Junge
- University of Washington, Seattle, Washington, USA
| | - Brook L Nunn
- University of Washington, Seattle, Washington, USA
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13
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Perera LJ, Cockell CS. Dispersion of Bacteria by Low-Pressure Boiling: Life Detection in Enceladus' Plume Material. ASTROBIOLOGY 2023; 23:269-279. [PMID: 36689196 DOI: 10.1089/ast.2022.0009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
The plume of Enceladus is thought to originate from the dispersion of a liquid source beneath the icy crust. Cryovolcanic activity on Enceladus may present a direct way of accessing material originating from the potentially habitable subsurface ocean. One way to test the hypothesis of whether life is present within the ocean of Enceladus would be to investigate the plume material for the presence of microbial life. In this study, we investigated the entrainment of Bacillus subtilis within Enceladus-like fluids under boiling conditions caused by exposure of the fluids to low pressure. We show that boiling, associated with exposure of a fluid to low pressure, works as a mechanism for dispersing bacteria in Enceladus plume-like environments. Exposure of Enceladus-type fluids (0.01-0.1 molal Na2CO3 and 0.05-0.2 molal NaCl) to low pressure (5 mbar) results in the dispersion of bacteria in droplets that evaporate to produce particles of salt. We find that, for particles with radius (r) ≤ 10 μm, the number of dispersed particles containing cells was between 7.7% and 10.9%. However, for larger particles 10 < r ≤ 50 μm, 64.4% and 56.4% contained cells for lower and upper end-member solutions, respectively. Our results suggest that the gravity-induced size sorting of plume particles will result in plume deposits closer to the vent source containing a larger volume of biological material than within the plume. If life is present in the ocean of Enceladus, we would expect that it would be effectively entrained and deposited on the surface; therefore, it would be accessible with a surface-lander-based instrument.
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Affiliation(s)
- L J Perera
- UK Centre for Astrobiology, University of Edinburgh, Edinburgh, UK
| | - C S Cockell
- UK Centre for Astrobiology, University of Edinburgh, Edinburgh, UK
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14
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Calapez F, Dias R, Cesário R, Gonçalves D, Pedras B, Canário J, Martins Z. Spectroscopic Detection of Biosignatures in Natural Ice Samples as a Proxy for Icy Moons. Life (Basel) 2023; 13:478. [PMID: 36836835 PMCID: PMC9960113 DOI: 10.3390/life13020478] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2023] [Revised: 01/29/2023] [Accepted: 02/04/2023] [Indexed: 02/11/2023] Open
Abstract
Some of the icy moons of the solar system with a subsurface ocean, such as Europa and Enceladus, are the targets of future space missions that search for potential extraterrestrial life forms. While the ice shells that envelop these moons have been studied by several spacecrafts, the oceans beneath them remain unreachable. To better constrain the habitability conditions of these moons, we must understand the interactions between their frozen crusts, liquid layers, and silicate mantles. To that end, astrobiologists rely on planetary field analogues, for which the polar regions of Earth have proven to be great candidates. This review shows how spectroscopy is a powerful tool in space missions to detect potential biosignatures, in particular on the aforementioned moons, and how the polar regions of the Earth are being used as planetary field analogues for these extra-terrestrial environments.
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Affiliation(s)
- Francisco Calapez
- Centro de Química Estrutural, Institute of Molecular Sciences and Department of Chemical Engineering, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
| | - Rodrigo Dias
- Centro de Química Estrutural, Institute of Molecular Sciences and Department of Chemical Engineering, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
| | - Rute Cesário
- Centro de Química Estrutural, Institute of Molecular Sciences and Department of Chemical Engineering, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
| | - Diogo Gonçalves
- Centro de Química Estrutural, Institute of Molecular Sciences and Department of Chemical Engineering, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
- Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
| | - Bruno Pedras
- Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
- Associate Laboratory i4HB—Institute for Health and Bioeconomy, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
| | - João Canário
- Centro de Química Estrutural, Institute of Molecular Sciences and Department of Chemical Engineering, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
| | - Zita Martins
- Centro de Química Estrutural, Institute of Molecular Sciences and Department of Chemical Engineering, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
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15
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Abstract
Saturn's moon Enceladus has a potentially habitable subsurface water ocean that contains canonical building blocks of life (organic and inorganic carbon, ammonia, possibly hydrogen sulfide) and chemical energy (disequilibria for methanogenesis). However, its habitability could be strongly affected by the unknown availability of phosphorus (P). Here, we perform thermodynamic and kinetic modeling that simulates P geochemistry based on recent insights into the geochemistry of the ocean-seafloor system on Enceladus. We find that aqueous P should predominantly exist as orthophosphate (e.g., HPO42-), and total dissolved inorganic P could reach 10-7 to 10-2 mol/kg H2O, generally increasing with lower pH and higher dissolved CO2, but also depending upon dissolved ammonia and silica. Levels are much higher than <10-10 mol/kg H2O from previous estimates and close to or higher than ∼10-6 mol/kg H2O in modern Earth seawater. The high P concentration is primarily ascribed to a high (bi)carbonate concentration, which decreases the concentrations of multivalent cations via carbonate mineral formation, allowing phosphate to accumulate. Kinetic modeling of phosphate mineral dissolution suggests that geologically rapid release of P from seafloor weathering of a chondritic rocky core could supply millimoles of total dissolved P per kilogram of H2O within 105 y, much less than the likely age of Enceladus's ocean (108 to 109 y). These results provide further evidence of habitable ocean conditions and show that any oceanic life would not be inhibited by low P availability.
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16
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Neveu M, Coker RF, Lorenz RD, MacKenzie SM, Lunine JI, Davila AF. Planetary Protection Assessment of Radioisotope Thermoelectric Generator (RTG)-Powered Landed Missions to Ocean Worlds: Application to Enceladus. ASTROBIOLOGY 2022; 22:1047-1060. [PMID: 35972349 DOI: 10.1089/ast.2020.2432] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Landed missions to icy worlds with a subsurface liquid water ocean must meet planetary protection requirements and ensure a sufficiently small likelihood of any microorganism-bearing part of the landed element reaching the ocean. A higher bound on this likelihood is set by the potential for radioisotope thermoelectric generator (RTG) power sources, the hottest possible landed element, to melt through the ice shell and reach the ocean. In this study, we quantify this potential as a function of three key parameters: surface temperature, ice shell thickness (i.e., heat flux through the shell), and thickness of a porous (insulating) snow or regolith cover. Although the model we describe can be applied to any ocean world, we present results in the context of a landed mission concept to the south polar terrain of Saturn's moon Enceladus. In this particular context, we discuss planetary protection considerations for landing site selection. The likelihood of forward microbial contamination of Enceladus' ocean by an RTG-powered landed mission can be made sufficiently low to not undermine compliance with the planetary protection policy.
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Affiliation(s)
- Marc Neveu
- Department of Astronomy, University of Maryland, College Park, Maryland, USA
- Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - Robert F Coker
- Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA
| | - Ralph D Lorenz
- Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA
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17
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Van Volkenburg T, Benzing JS, Craft KL, Ohiri K, Kilhefner A, Irons K, Bradburne C. Microfluidic Chromatography for Enhanced Amino Acid Detection at Ocean Worlds. ASTROBIOLOGY 2022; 22:1116-1128. [PMID: 35984944 PMCID: PMC9508454 DOI: 10.1089/ast.2021.0182] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Accepted: 04/18/2022] [Indexed: 06/15/2023]
Abstract
Increasing interest in the detection of biogenic signatures, such as amino acids, on icy moons and bodies within our solar system has led to the development of compact in situ instruments. Given the expected dilute biosignatures and high salinities of these extreme environments, purification of icy samples before analysis enables increased detection sensitivity. Herein, we outline a novel compact cation exchange method to desalinate proteinogenic amino acids in solution, independent of the type and concentration of salts in the sample. Using a modular microfluidic device, initial experiments explored operational limits of binding capacity with phenylalanine and three model cations, Na+, Mg2+, and Ca2+. Phenylalanine recovery (94-17%) with reduced conductivity (30-200 times) was seen at high salt-to-amino-acid ratios between 25:1 and 500:1. Later experiments tested competition between mixtures of 17 amino acids and other chemistries present in a terrestrial ocean sample. Recoveries ranged from 11% to 85% depending on side chain chemistry and cation competition, with concentration shown for select high affinity amino acids. This work outlines a nondestructive amino acid purification device capable of coupling to multiple downstream analytical techniques for improved characterization of icy samples at remote ocean worlds.
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Affiliation(s)
| | | | - Kathleen L. Craft
- Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
| | - Korine Ohiri
- Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
| | - Ashley Kilhefner
- Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
| | - Kristen Irons
- University of North Carolina at Chapel Hill College of Arts and Sciences, Chapel Hill, North Carolina, USA
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18
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McClain CR, Bryant SR, Hanks G, Bowles MW. Extremophiles in Earth's Deep Seas: A View Toward Life in Exo-Oceans. ASTROBIOLOGY 2022; 22:1009-1028. [PMID: 35549348 DOI: 10.1089/ast.2021.0120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Humanity's search for extraterrestrial life is a modern manifestation of the exploratory and curious nature that has led us through millennia of scientific discoveries. With the ongoing exploration of extraterrestrial bodies, the potential for discovery of extraterrestrial life has expanded. We may better inform this search through an understanding of how life persists and flourishes on Earth in a myriad of environmental extremes. A significant proportion of our knowledge of extremophiles on Earth comes from studies on deep ocean life. Here, we review and synthesize the range of environmental extremes observed in the deep sea, the life that persists in these extreme conditions, and the biological adaptations utilized by these remarkable life-forms. We also review confirmed and predicted extraterrestrial oceans in our solar system and propose deep-sea sites that may serve as planetary field analog environments. We show that the clever ingenuity of evolution under deep-sea conditions suggests that the plausibility of extraterrestrial life is much greater than previously thought.
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Affiliation(s)
- Craig R McClain
- Louisiana Universities Marine Consortium, Chauvin, Louisiana, USA
- Department of Biology, University of Louisiana at Lafayette, Lafayette, Louisiana, USA
| | - S River Bryant
- Louisiana Universities Marine Consortium, Chauvin, Louisiana, USA
- Department of Biology, University of Louisiana at Lafayette, Lafayette, Louisiana, USA
| | - Granger Hanks
- Louisiana Universities Marine Consortium, Chauvin, Louisiana, USA
- Department of Biology, University of Louisiana at Lafayette, Lafayette, Louisiana, USA
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19
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Wolfenbarger NS, Buffo JJ, Soderlund KM, Blankenship DD. Ice Shell Structure and Composition of Ocean Worlds: Insights from Accreted Ice on Earth. ASTROBIOLOGY 2022; 22:937-961. [PMID: 35787145 DOI: 10.1089/ast.2021.0044] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Accreted ice retains and preserves traces of the ocean from which it formed. In this work, we study two classes of accreted ice found on Earth-frazil ice, which forms through crystallization within a supercooled water column, and congelation ice, which forms through directional freezing at an existing interface-and discuss where each might be found in the ice shells of ocean worlds. We focus our study on terrestrial ice formed in low temperature gradient environments (e.g., beneath ice shelves), consistent with conditions expected at the ice-ocean interfaces of Europa and Enceladus, and we highlight the juxtaposition of compositional trends in relation to ice formed in higher temperature gradient environments (e.g., at the ocean surface). Observations from Antarctic sub-ice-shelf congelation ice and marine ice show that the purity of frazil ice can be nearly two orders of magnitude higher than congelation ice formed in the same low temperature gradient environment (∼0.1% vs. ∼10% of the ocean salinity). In addition, where congelation ice can maintain a planar ice-water interface on a microstructural scale, the efficiency of salt rejection is enhanced (∼1% of the ocean salinity) and lattice soluble impurities such as chloride are preferentially incorporated. We conclude that an ice shell that forms by gradual thickening as its interior cools would be composed of congelation ice, whereas frazil ice will accumulate where the ice shell thins on local (rifts and basal fractures) or regional (latitudinal gradients) scales through the operation of an "ice pump."
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Affiliation(s)
| | - Jacob J Buffo
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA
| | - Krista M Soderlund
- Institute for Geophysics, University of Texas at Austin, Austin, Texas, USA
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20
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Kang W, Mittal T, Bire S, Campin JM, Marshall J. How does salinity shape ocean circulation and ice geometry on Enceladus and other icy satellites? SCIENCE ADVANCES 2022; 8:eabm4665. [PMID: 35857831 PMCID: PMC9299536 DOI: 10.1126/sciadv.abm4665] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2021] [Accepted: 06/06/2022] [Indexed: 05/28/2023]
Abstract
Of profound astrobiological interest, Enceladus appears to have a global saline subsurface ocean, indicating water-rock reaction at present or in the past, an important mechanism in the moon's potential habitability. Here, we investigate how salinity and the partition of heat production between the silicate core and the ice shell affect ocean dynamics and the associated heat transport-a key factor determining equilibrium ice shell geometry. Assuming steady-state conditions, we show that the meridional overturning circulation of the ocean, driven by heat and salt exchange with the poleward-thinning ice shell, has opposing signs at very low and very high salinities. Regardless of these differing circulations, heat and fresh water converge toward the equator, where the ice is thick, acting to homogenize thickness variations. Among scenarios explored here, the pronounced ice thickness variations observed on Enceladus are most consistent with heating that is predominantly in the ice shell and a salinity of intermediate range.
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21
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MacKenzie SM, Neveu M, Davila AF, Lunine JI, Cable ML, Phillips-Lander CM, Eigenbrode JL, Waite JH, Craft KL, Hofgartner JD, McKay CP, Glein CR, Burton D, Kounaves SP, Mathies RA, Vance SD, Malaska MJ, Gold R, German CR, Soderlund KM, Willis P, Freissinet C, McEwen AS, Brucato JR, de Vera JPP, Hoehler TM, Heldmann J. Science Objectives for Flagship-Class Mission Concepts for the Search for Evidence of Life at Enceladus. ASTROBIOLOGY 2022; 22:685-712. [PMID: 35290745 PMCID: PMC9233532 DOI: 10.1089/ast.2020.2425] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2020] [Accepted: 01/21/2022] [Indexed: 05/07/2023]
Abstract
Cassini revealed that Saturn's Moon Enceladus hosts a subsurface ocean that meets the accepted criteria for habitability with bio-essential elements and compounds, liquid water, and energy sources available in the environment. Whether these conditions are sufficiently abundant and collocated to support life remains unknown and cannot be determined from Cassini data. However, thanks to the plume of oceanic material emanating from Enceladus' south pole, a new mission to Enceladus could search for evidence of life without having to descend through kilometers of ice. In this article, we outline the science motivations for such a successor to Cassini, choosing the primary science goal to be determining whether Enceladus is inhabited and assuming a resource level equivalent to NASA's Flagship-class missions. We selected a set of potential biosignature measurements that are complementary and orthogonal to build a robust case for any life detection result. This result would be further informed by quantifications of the habitability of the environment through geochemical and geophysical investigations into the ocean and ice shell crust. This study demonstrates that Enceladus' plume offers an unparalleled opportunity for in situ exploration of an Ocean World and that the planetary science and astrobiology community is well equipped to take full advantage of it in the coming decades.
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Affiliation(s)
| | - Marc Neveu
- Department of Astronomy, University of Maryland, College Park, Maryland, USA
- Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - Alfonso F. Davila
- Division of Space Science and Astrobiology, NASA Ames Research Center, Moffett Field, California, USA
| | - Jonathan I. Lunine
- Department of Astronomy, Cornell University, Ithaca, New York, USA
- Carl Sagan Institute, Cornell University, Ithaca, New York, USA
| | - Morgan L. Cable
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | | | - Jennifer L. Eigenbrode
- Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - J. Hunter Waite
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA
| | - Kate L. Craft
- Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
| | - Jason D. Hofgartner
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | - Chris P. McKay
- Division of Space Science and Astrobiology, NASA Ames Research Center, Moffett Field, California, USA
| | - Christopher R. Glein
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA
| | - Dana Burton
- Department of Anthropology, George Washington University, Washington, District of Columbia, USA
| | | | - Richard A. Mathies
- Chemistry Department and Space Sciences Laboratory, University of California, Berkeley, Berkeley, California, USA
| | - Steven D. Vance
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | - Michael J. Malaska
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | - Robert Gold
- Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
| | - Christopher R. German
- Department of Geology & Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
| | - Krista M. Soderlund
- Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas, USA
| | - Peter Willis
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | | | - Alfred S. McEwen
- Lunar and Planetary Lab, University of Arizona, Tucson, Arizona, USA
| | | | - Jean-Pierre P. de Vera
- Space Operations and Astronaut Training, MUSC, German Aerospace Center (DLR), Cologne, Germany
| | - Tori M. Hoehler
- Division of Space Science and Astrobiology, NASA Ames Research Center, Moffett Field, California, USA
| | - Jennifer Heldmann
- Division of Space Science and Astrobiology, NASA Ames Research Center, Moffett Field, California, USA
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22
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Styczinski MJ, Vance SD, Harnett EM, Cochrane CJ. A perturbation method for evaluating the magnetic field induced from an arbitrary, asymmetric ocean world analytically. ICARUS 2022; 376:114840. [PMID: 35140451 PMCID: PMC8819682 DOI: 10.1016/j.icarus.2021.114840] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Magnetic investigations of icy moons have provided some of the most compelling evidence available confirming the presence of subsurface, liquid water oceans. In the exploration of ocean moons, especially Europa, there is a need for mathematical models capable of predicting the magnetic fields induced under a variety of conditions, including in the case of asymmetric oceans. Existing models are limited to either spherical symmetry or assume an ocean with infinite conductivity. In this work, we use a perturbation method to derive a semi-analytic result capable of determining the induced magnetic moments for an arbitrary layered body, provided each layer is nearly spherical. Crucially, we find that degree-2 tidal deformation results in changes to the induced dipole moments. We demonstrate application of our results to models of plausible asymmetry from the literature within the oceans of Europa and Miranda and the ionospheres of Callisto and Triton. For the models we consider, we find that in the asymmetric case, the induced magnetic field differs by more than 2 nT near the surface of Europa, 0.25-0.5 nT at 1 R above Miranda and Triton, and is essentially unchanged for Callisto. For Miranda and Triton, this difference is as much as 20%-30% of the induced field magnitude. If measurements near the moons can be made precisely to better than a few tenths of a nT, these values may be used by future spacecraft investigations to characterize asymmetry within the interior of icy moons.
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Affiliation(s)
- Marshall J. Styczinski
- Department of Physics, University of Washington, Box 351560, 3910 15th Ave NE, Seattle, WA 98195-1560, USA
- UW Astrobiology Program, University of Washington, Box 351580, 3910 15th Ave NE, Seattle, WA 98195-1580, USA
| | - Steven D. Vance
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA 91109-8001, USA
| | - Erika M. Harnett
- UW Astrobiology Program, University of Washington, Box 351580, 3910 15th Ave NE, Seattle, WA 98195-1580, USA
- Department of Earth and Space Sciences, University of Washington, Box 351310, 4000 15th Ave NE, Seattle, WA 98195-1310, USA
| | - Corey J. Cochrane
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA 91109-8001, USA
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23
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Thompson SP, Kennedy H, Butler BM, Day SJ, Safi E, Evans A. Laboratory exploration of mineral precipitates from Europa's subsurface ocean. J Appl Crystallogr 2021; 54:1455-1479. [PMID: 34667451 PMCID: PMC8493616 DOI: 10.1107/s1600576721008554] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Accepted: 08/17/2021] [Indexed: 11/10/2022] Open
Abstract
The precipitation of hydrated phases from a chondrite-like Na-Mg-Ca-SO4-Cl solution is studied using in situ synchrotron X-ray powder diffraction, under rapid- (360 K h-1, T = 250-80 K, t = 3 h) and ultra-slow-freezing (0.3 K day-1, T = 273-245 K, t = 242 days) conditions. The precipitation sequence under slow cooling initially follows the predictions of equilibrium thermodynamics models. However, after ∼50 days at 245 K, the formation of the highly hydrated sulfate phase Na2Mg(SO4)2·16H2O, a relatively recent discovery in the Na2Mg(SO4)2-H2O system, was observed. Rapid freezing, on the other hand, produced an assemblage of multiple phases which formed within a very short timescale (≤4 min, ΔT = 2 K) and, although remaining present throughout, varied in their relative proportions with decreasing temperature. Mirabilite and meridianiite were the major phases, with pentahydrite, epsomite, hydrohalite, gypsum, blödite, konyaite and loweite also observed. Na2Mg(SO4)2·16H2O was again found to be present and increased in proportion relative to other phases as the temperature decreased. The results are discussed in relation to possible implications for life on Europa and application to other icy ocean worlds.
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Affiliation(s)
- Stephen P. Thompson
- Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, United Kingdom
| | - Hilary Kennedy
- School of Ocean Sciences, Bangor University, Menai Bridge, Anglesey LL59 5AB, United Kingdom
| | - Benjamin M. Butler
- Environmental and Biochemical Sciences, The James Hutton Institute, Craigiebuckler, Aberdeen AB15 8QH, United Kingdom
| | - Sarah J. Day
- Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, United Kingdom
| | - Emmal Safi
- Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, United Kingdom
- Astrophysics Group, Lennard-Jones Laboratories, Keele University, Keele, Staffordshire ST5 5BG, United Kingdom
| | - Aneurin Evans
- Astrophysics Group, Lennard-Jones Laboratories, Keele University, Keele, Staffordshire ST5 5BG, United Kingdom
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Quantitative evaluation of the feasibility of sampling the ice plumes at Enceladus for biomarkers of extraterrestrial life. Proc Natl Acad Sci U S A 2021; 118:2106197118. [PMID: 34493668 PMCID: PMC8449353 DOI: 10.1073/pnas.2106197118] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Accepted: 08/02/2021] [Indexed: 11/30/2022] Open
Abstract
The search for organic biosignatures indicative of life elsewhere in our solar system is an exciting quest that, if successful, will have a profound impact on our biological uniqueness. Saturn’s icy moon Enceladus is a promising location for a second occurrence of life due to its salty subsurface ocean. Plumes that jet out through the ice surface vents provide an enticing opportunity to sample the underlying ocean for biomarkers. The experiments reported here provide accurate modeling of our ability to fly through these plumes to efficiently and nondestructively gather ice particles for biomolecular analysis. Our measured efficiencies demonstrate that Saturn and/or Enceladus orbital missions will gather sufficient ice to make meaningful measurement of biosignatures in the Enceladus plumes. Enceladus, an icy moon of Saturn, is a compelling destination for a probe seeking biosignatures of extraterrestrial life because its subsurface ocean exhibits significant organic chemistry that is directly accessible by sampling cryovolcanic plumes. State-of-the-art organic chemical analysis instruments can perform valuable science measurements at Enceladus provided they receive sufficient plume material in a fly-by or orbiter plume transit. To explore the feasibility of plume sampling, we performed light gas gun experiments impacting micrometer-sized ice particles containing a fluorescent dye biosignature simulant into a variety of soft metal capture surfaces at velocities from 800 m ⋅ s−1 up to 3 km ⋅ s−1. Quantitative fluorescence microscopy of the capture surfaces demonstrates organic capture efficiencies of up to 80 to 90% for isolated impact craters and of at least 17% on average on indium and aluminum capture surfaces at velocities up to 2.2 km ⋅ s−1. Our results reveal the relationships between impact velocity, particle size, capture surface, and capture efficiency for a variety of possible plume transit scenarios. Combined with sensitive microfluidic chemical analysis instruments, we predict that our capture system can be used to detect organic molecules in Enceladus plume ice at the 1 nM level—a sensitivity thought to be meaningful and informative for probing habitability and biosignatures.
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Tang JWT, Henriques A, Loh TP. Microbes and space travel - hope and hazards. Future Microbiol 2021; 16:1023-1028. [PMID: 34488427 DOI: 10.2217/fmb-2021-0196] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Affiliation(s)
- Julian Wei-Tze Tang
- C/O Clinical Microbiology, 5/F Sandringham Building, Leicester Royal Infirmary, Infirmary Square, Leicester, LE1 5WW, UK
| | - Andre Henriques
- CERN (European Organisation for Nuclear Research), Geneva, Switzerland
| | - Tze Ping Loh
- Laboratory Medicine, National University Hospital, Singapore
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Method for detecting and quantitating capture of organic molecules in hypervelocity impacts. MethodsX 2021; 8:101239. [PMID: 34434762 PMCID: PMC8374173 DOI: 10.1016/j.mex.2021.101239] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2020] [Accepted: 01/18/2021] [Indexed: 11/26/2022] Open
Abstract
Enceladus is a prime candidate in the solar system for in-depth astrobiological studies searching for habitability and life because it has a liquid water ocean with significant organic content and ongoing cryovolcanic activity. The presence of ice plumes that jet up through fissures in the ice crust covering the sub-surface ocean, enables remote sampling and in-situ analysis via a fly-by mission. However, capture and transport of organic materials to organic analyzers presents distinctive challenges as it is unknown whether, and to what extent, organic molecules imbedded in ice particles can be captured and survive hypervelocity impacts. This manuscript provides a fluorescence microscopic method to parametrically determine the amount of an organic fluorescent tracer dye, Pacific Blue™ (PB) deposited on a metallic surface. This method can be used to measure the capture and survival outcomes of terrestrial hypervelocity impact experiments where an ice projectile labeled with Pacific Blue impacts a soft metal surface. This work is an important step in the advancement of instruments like the Enceladus Organic Analyzer for detecting biosignatures in an Enceladus plume fly-by mission. An apparatus consisting of a substrate humidification shroud coupled with an epifluorescence microscope with CCD detector is developed to measure the intensity of quantitatively deposited Pacific Blue droplets under controlled humidity. Calibration curves are produced that relate the integrated fluorescence intensity of humidified PB droplets on metal foils to the number of PB molecules deposited. To demonstrate the utility of this method, our calibrations are used to analyze and quantitate organic capture and survival (up to 11% capture efficiency) following ice particle impacts at a velocity of 1.7 km/s on an aluminum substrate.
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Rivera-Valentín EG, Filiberto J, Lynch KL, Mamajanov I, Lyons TW, Schulte M, Méndez A. Introduction-First Billion Years: Habitability. ASTROBIOLOGY 2021; 21:893-905. [PMID: 34406807 PMCID: PMC8403211 DOI: 10.1089/ast.2020.2314] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Accepted: 12/22/2020] [Indexed: 06/13/2023]
Abstract
The physical processes active during the first billion years (FBY) of Earth's history, such as accretion, differentiation, and impact cratering, provide constraints on the initial conditions that were conducive to the formation and establishment of life on Earth. This motivated the Lunar and Planetary Institute's FBY topical initiative, which was a four-part conference series intended to look at each of these physical processes to study the basic structure and composition of our Solar System that was set during the FBY. The FBY Habitability conference, held in September 2019, was the last in this series and was intended to synthesize the initiative; specifically, to further our understanding of the origins of life, planetary and environmental habitability, and the search for life beyond Earth. The conference included discussions of planetary habitability and the potential emergence of life on bodies within our Solar System, as well as extrasolar systems by applying our knowledge of the Solar System's FBY, and in particular Earth's early history. To introduce this Special Collection, which resulted from work discussed at the conference, we provide a review of the main themes and a synopsis of the FBY Habitability conference.
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Affiliation(s)
| | - Justin Filiberto
- Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas, USA
| | - Kennda L. Lynch
- Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas, USA
| | - Irena Mamajanov
- Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan
| | - Timothy W. Lyons
- Department of Earth and Planetary Sciences, University of California Riverside, Riverside, California, USA
| | - Mitch Schulte
- Planetary Science Division, NASA Headquarters, Washington, District of Columbia, USA
| | - Abel Méndez
- Planetary Habitability Laboratory, University of Puerto Rico Arecibo, Arecibo, Puerto Rico
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Abstract
This Feature introduces and discusses the findings of key analytical techniques used to study planetary bodies in our solar system in the search for life beyond Earth, future missions planned for high-priority astrobiology targets in our solar system, and the challenges we face in performing these investigations.
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Affiliation(s)
- Kenneth Marshall Seaton
- School of Chemistry & Biochemistry, Georgia Institute of Technology, North Avenue NW, Atlanta, Georgia 30332, United States
| | - Morgan Leigh Cable
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, United States
| | - Amanda Michelle Stockton
- School of Chemistry & Biochemistry, Georgia Institute of Technology, North Avenue NW, Atlanta, Georgia 30332, United States
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Blocks Size Frequency Distribution in the Enceladus Tiger Stripes Area: Implications on Their Formative Processes. UNIVERSE 2021. [DOI: 10.3390/universe7040082] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We study the size frequency distribution of the blocks located in the deeply fractured, geologically active Enceladus South Polar Terrain with the aim to suggest their formative mechanisms. Through the Cassini ISS images, we identify ~17,000 blocks with sizes ranging from ~25 m to 366 m, and located at different distances from the Damascus, Baghdad and Cairo Sulci. On all counts and for both Damascus and Baghdad cases, the power-law fitting curve has an index that is similar to the one obtained on the deeply fractured, actively sublimating Hathor cliff on comet 67P/Churyumov-Gerasimenko, where several non-dislodged blocks are observed. This suggests that as for 67P, sublimation and surface stresses favor similar fractures development in the Enceladus icy matrix, hence resulting in comparable block disaggregation. A steeper power-law index for Cairo counts may suggest a higher degree of fragmentation, which could be the result of localized, stronger tectonic disruption of lithospheric ice. Eventually, we show that the smallest blocks identified are located from tens of m to 20–25 km from the Sulci fissures, while the largest blocks are found closer to the tiger stripes. This result supports the ejection hypothesis mechanism as the possible source of blocks.
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30
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Resonance in Chirogenesis and Photochirogenesis: Colloidal Polymers Meet Chiral Optofluidics. Symmetry (Basel) 2021. [DOI: 10.3390/sym13020199] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Metastable colloids made of crystalline and/or non-crystalline matters render abilities of photonic resonators susceptible to chiral chemical and circularly polarized light sources. By assuming that μm-size colloids and co-colloids consisting of π- and/or σ-conjugated polymers dispersed into an optofluidic medium are artificial models of open-flow, non-equilibrium coacervates, we showcase experimentally resonance effects in chirogenesis and photochirogenesis, revealed by gigantic boosted chiroptical signals as circular dichroism (CD), optical rotation dispersion, circularly polarized luminescence (CPL), and CPL excitation (CPLE) spectral datasets. The resonance in chirogenesis occurs at very specific refractive indices (RIs) of the surrounding medium. The chirogenesis is susceptible to the nature of the optically active optofluidic medium. Moreover, upon an excitation-wavelength-dependent circularly polarized (CP) light source, a fully controlled absolute photochirogenesis, which includes all chiroptical generation, inversion, erase, switching, and short-/long-lived memories, is possible when the colloidal non-photochromic and photochromic polymers are dispersed in an achiral optofluidic medium with a tuned RI. The hand of the CP light source is not a determining factor for the product chirality. These results are associated with my experience concerning amphiphilic polymerizable colloids, in which, four decades ago, allowed proposing a perspective that colloids are connectable to light, polymers, helix, coacervates, and panspermia hypotheses, nuclear physics, biology, radioisotopes, homochirality question, first life, and cosmology.
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31
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Aguzzi J, Flexas MM, Flögel S, Lo Iacono C, Tangherlini M, Costa C, Marini S, Bahamon N, Martini S, Fanelli E, Danovaro R, Stefanni S, Thomsen L, Riccobene G, Hildebrandt M, Masmitja I, Del Rio J, Clark EB, Branch A, Weiss P, Klesh AT, Schodlok MP. Exo-Ocean Exploration with Deep-Sea Sensor and Platform Technologies. ASTROBIOLOGY 2020; 20:897-915. [PMID: 32267735 DOI: 10.1089/ast.2019.2129] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
One of Saturn's largest moons, Enceladus, possesses a vast extraterrestrial ocean (i.e., exo-ocean) that is increasingly becoming the hotspot of future research initiatives dedicated to the exploration of putative life. Here, a new bio-exploration concept design for Enceladus' exo-ocean is proposed, focusing on the potential presence of organisms across a wide range of sizes (i.e., from uni- to multicellular and animal-like), according to state-of-the-art sensor and robotic platform technologies used in terrestrial deep-sea research. In particular, we focus on combined direct and indirect life-detection capabilities, based on optoacoustic imaging and passive acoustics, as well as molecular approaches. Such biologically oriented sampling can be accompanied by concomitant geochemical and oceanographic measurements to provide data relevant to exo-ocean exploration and understanding. Finally, we describe how this multidisciplinary monitoring approach is currently enabled in terrestrial oceans through cabled (fixed) observatories and their related mobile multiparametric platforms (i.e., Autonomous Underwater and Remotely Operated Vehicles, as well as crawlers, rovers, and biomimetic robots) and how their modified design can be used for exo-ocean exploration.
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Affiliation(s)
- J Aguzzi
- Instituto de Ciencias del Mar (ICM-CSIC), Barcelona, Spain
- Stazione Zoologica Anton Dohrn, Naples, Italy
| | - M M Flexas
- California Institute of Technology, Pasadena, California, USA
| | - S Flögel
- GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
| | - C Lo Iacono
- Instituto de Ciencias del Mar (ICM-CSIC), Barcelona, Spain
- National Oceanographic Center (NOC), University of Southampton, Southampton, United Kingdom
| | | | - C Costa
- Consiglio per la ricerca in agricoltura e l'analisi dell'economia agraria (CREA)-Centro di ricerca Ingegneria e Trasformazioni agroalimentari - Monterotondo, Rome, Italy
| | - S Marini
- Stazione Zoologica Anton Dohrn, Naples, Italy
- National Research Council of Italy (CNR), Institute of Marine Sciences, La Spezia, Italy
| | - N Bahamon
- Instituto de Ciencias del Mar (ICM-CSIC), Barcelona, Spain
- Centro de Estudios Avanzados de Blanes (CEAB-CSIC), Blanes, Spain
| | - S Martini
- Sorbonne Université, CNRS, Laboratoire d'Océanographie de Villefranche, Villefranche-sur-mer, France
| | - E Fanelli
- Stazione Zoologica Anton Dohrn, Naples, Italy
- Department of Life and Environmental Sciences, Polytechnic University of Marche, Ancona, Italy
| | - R Danovaro
- Stazione Zoologica Anton Dohrn, Naples, Italy
- Department of Life and Environmental Sciences, Polytechnic University of Marche, Ancona, Italy
| | - S Stefanni
- Stazione Zoologica Anton Dohrn, Naples, Italy
| | | | - G Riccobene
- Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali del Sud, Catania, Italy
| | - M Hildebrandt
- German Research Center for Artificial Intelligence (DFKI), Bremen, Germany
| | - I Masmitja
- SARTI, Universitat Politècnica de Catalunya (UPC), Barcelona, Spain
| | - J Del Rio
- SARTI, Universitat Politècnica de Catalunya (UPC), Barcelona, Spain
| | - E B Clark
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | - A Branch
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | | | - A T Klesh
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | - M P Schodlok
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
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32
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Spontaneous formation of geysers at only one pole on Enceladus's ice shell. Proc Natl Acad Sci U S A 2020; 117:14764-14768. [PMID: 32546519 DOI: 10.1073/pnas.2001648117] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The ice shell on Enceladus, an icy moon of Saturn, exhibits strong asymmetry between the northern and southern hemispheres, with all known geysers concentrated over the south pole, even though the expected pattern of tidal forced deformation should be symmetric between the north and south poles. Using an idealized ice-evolution model, we demonstrate that this asymmetry may form spontaneously, without any noticeable a priori asymmetry (such as a giant impact or a monopole structure of geological activity), in contrast to previous studies. Infinitesimal asymmetry in the ice shell thickness due to random perturbations are found to be able to grow indefinitely, ending up significantly thinning the ice shell at one of the poles, thereby allowing fracture formation there. Necessary conditions to trigger this hemispheric symmetry-breaking mechanism are found analytically. A rule of thumb we find is that, for Galilean and Saturnian icy moons, the ice shell can undergo hemispheric symmetry breaking only if the mean shell thickness is around 10 to 30 km.
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Abstract
The Cassini-Huygens mission to Saturn provided a close-up study of the gas giant planet, as well as its rings, moons, and magnetosphere. The Cassini spacecraft arrived at Saturn in 2004, dropped the Huygens probe to study the atmosphere and surface of Saturn's planet-sized moon Titan, and orbited Saturn for the next 13 years. In 2017, when it was running low on fuel, Cassini was intentionally vaporized in Saturn's atmosphere to protect the ocean moons, Enceladus and Titan, where it had discovered habitats potentially suitable for life. Mission findings include Enceladus' south polar geysers, the source of Saturn's E ring; Titan's methane cycle, including rain that creates hydrocarbon lakes; dynamic rings containing ice, silicates, and organics; and Saturn's differential rotation. This Review discusses highlights of Cassini's investigations, including the mission's final year.
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Affiliation(s)
- Linda Spilker
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
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34
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Castillo-Rogez JC, Neveu M, Scully JEC, House CH, Quick LC, Bouquet A, Miller K, Bland M, De Sanctis MC, Ermakov A, Hendrix AR, Prettyman TH, Raymond CA, Russell CT, Sherwood BE, Young E. Ceres: Astrobiological Target and Possible Ocean World. ASTROBIOLOGY 2020; 20:269-291. [PMID: 31904989 DOI: 10.1089/ast.2018.1999] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Ceres, the most water-rich body in the inner solar system after Earth, has recently been recognized to have astrobiological importance. Chemical and physical measurements obtained by the Dawn mission enabled the quantification of key parameters, which helped to constrain the habitability of the inner solar system's only dwarf planet. The surface chemistry and internal structure of Ceres testify to a protracted history of reactions between liquid water, rock, and likely organic compounds. We review the clues on chemical composition, temperature, and prospects for long-term occurrence of liquid and chemical gradients. Comparisons with giant planet satellites indicate similarities both from a chemical evolution standpoint and in the physical mechanisms driving Ceres' internal evolution.
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Affiliation(s)
| | - Marc Neveu
- Sciences and Exploration Directorate, NASA Goddard Space Flight Center, Greenbelt, Maryland
- University of Maryland College Park, Greenbelt, Maryland
| | - Jennifer E C Scully
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Christopher H House
- Department of Geosciences,Penn State Astrobiology Research Center, The Pennsylvania State University, University Park, Pennsylvania
| | - Lynnae C Quick
- Sciences and Exploration Directorate, NASA Goddard Space Flight Center, Greenbelt, Maryland
| | - Alexis Bouquet
- LAM (Laboratoire d'Astrophysique de Marseille), Aix Marseille Université, CNRS, UMR 7326, Marseille, France
| | - Kelly Miller
- Southwest Research Institute, San Antonio, Texas
| | | | | | - Anton Ermakov
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | | | | | - Carol A Raymond
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Christopher T Russell
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California
| | | | - Edward Young
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California
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Martin KP, MacKenzie SM, Barnes JW, Ytreberg FM. Protein Stability in Titan's Subsurface Water Ocean. ASTROBIOLOGY 2020; 20:190-198. [PMID: 31730377 PMCID: PMC7041334 DOI: 10.1089/ast.2018.1972] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Accepted: 10/08/2019] [Indexed: 06/10/2023]
Abstract
Models of Titan predict that there is a subsurface ocean of water and ammonia under a layer of ice. Such an ocean would be important in the search for extraterrestrial life since it provides a potentially habitable environment. To evaluate how Earth-based proteins would behave in Titan's subsurface ocean environment, we used molecular dynamics simulations to calculate the properties of proteins with the most common secondary structure types (alpha helix and beta sheet) in both Earth and Titan-like conditions. The Titan environment was simulated by using a temperature of 300 K, a pressure of 1000 bar, and a eutectic mixture of water and ammonia. We analyzed protein compactness, flexibility, and backbone dihedral distributions to identify differences between the two environments. Secondary structures in the Titan environment were found to be less long-lasting, less flexible, and had small differences in backbone dihedral preferences (e.g., in one instance a pi helix formed). These environment-driven differences could lead to changes in how these proteins interact with other biomolecules and therefore changes in how evolution would potentially shape proteins to function in subsurface ocean environments.
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Affiliation(s)
- Kyle P. Martin
- Department of Physics, University of Idaho, Moscow, Idaho
- Institute for Modeling Collaboration and Innovation, University of Idaho, Moscow, Idaho
| | | | | | - F. Marty Ytreberg
- Department of Physics, University of Idaho, Moscow, Idaho
- Institute for Modeling Collaboration and Innovation, University of Idaho, Moscow, Idaho
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36
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Taubner RS, Olsson-Francis K, Vance SD, Ramkissoon NK, Postberg F, de Vera JP, Antunes A, Camprubi Casas E, Sekine Y, Noack L, Barge L, Goodman J, Jebbar M, Journaux B, Karatekin Ö, Klenner F, Rabbow E, Rettberg P, Rückriemen-Bez T, Saur J, Shibuya T, Soderlund KM. Experimental and Simulation Efforts in the Astrobiological Exploration of Exooceans. SPACE SCIENCE REVIEWS 2020; 216:9. [PMID: 32025060 PMCID: PMC6977147 DOI: 10.1007/s11214-020-0635-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Accepted: 01/06/2020] [Indexed: 05/05/2023]
Abstract
The icy satellites of Jupiter and Saturn are perhaps the most promising places in the Solar System regarding habitability. However, the potential habitable environments are hidden underneath km-thick ice shells. The discovery of Enceladus' plume by the Cassini mission has provided vital clues in our understanding of the processes occurring within the interior of exooceans. To interpret these data and to help configure instruments for future missions, controlled laboratory experiments and simulations are needed. This review aims to bring together studies and experimental designs from various scientific fields currently investigating the icy moons, including planetary sciences, chemistry, (micro-)biology, geology, glaciology, etc. This chapter provides an overview of successful in situ, in silico, and in vitro experiments, which explore different regions of interest on icy moons, i.e. a potential plume, surface, icy shell, water and brines, hydrothermal vents, and the rocky core.
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Affiliation(s)
- Ruth-Sophie Taubner
- Archaea Biology and Ecogenomics Division, University of Vienna, Vienna, Austria
| | | | | | | | | | | | - André Antunes
- State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau SAR, China
| | | | | | - Lena Noack
- Freie Universität Berlin, Berlin, Germany
| | | | | | | | | | | | | | - Elke Rabbow
- German Aerospace Center (DLR), Cologne, Germany
| | | | | | | | - Takazo Shibuya
- Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
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37
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Rettberg P, Antunes A, Brucato J, Cabezas P, Collins G, Haddaji A, Kminek G, Leuko S, McKenna-Lawlor S, Moissl-Eichinger C, Fellous JL, Olsson-Francis K, Pearce D, Rabbow E, Royle S, Saunders M, Sephton M, Spry A, Walter N, Wimmer Schweingruber R, Treuet JC. Biological Contamination Prevention for Outer Solar System Moons of Astrobiological Interest: What Do We Need to Know? ASTROBIOLOGY 2019; 19:951-974. [PMID: 30762429 PMCID: PMC6767865 DOI: 10.1089/ast.2018.1996] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
To ensure that scientific investments in space exploration are not compromised by terrestrial contamination of celestial bodies, special care needs to be taken to preserve planetary conditions for future astrobiological exploration. Significant effort has been made and is being taken to address planetary protection in the context of inner Solar System exploration. In particular for missions to Mars, detailed internationally accepted guidelines have been established. For missions to the icy moons in the outer Solar System, Europa and Enceladus, the planetary protection requirements are so far based on a probabilistic approach and a conservative estimate of poorly known parameters. One objective of the European Commission-funded project, Planetary Protection of Outer Solar System, was to assess the existing planetary protection approach, to identify inherent knowledge gaps, and to recommend scientific investigations necessary to update the requirements for missions to the icy moons.
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Affiliation(s)
- Petra Rettberg
- Research Group Astrobiology, Radiation Biology Department, German Aerospace Center (DLR), Institute of Aerospace Medicine, Köln, Germany
- Address correspondence to: Petra Rettberg, German Aerospace Center (DLR), Institute of Aerospace Medicine, Radiation Biology Department, Research Group Astrobiology, Linder Höhe, 51147 Köln, Germany
| | - André Antunes
- GEMM—Group for Extreme and Marine Microbiology, Department of Biology, Edge Hill University, Ormskirk, United Kingdom
| | - John Brucato
- Department of Physics and Astronomy, Astrophysical Observatory of Arcetri, National Institute for Astrophysics (INAF), Florence, Italy
| | - Patricia Cabezas
- Science Connect–European Science Foundation (ESF), Strasbourg, France
| | - Geoffrey Collins
- Department of Physics and Astronomy, Wheaton College, Massachusetts, Norton, Massachusetts
| | - Alissa Haddaji
- Committee on Space Research (COSPAR), Montpellier, France
| | - Gerhard Kminek
- Committee on Space Research (COSPAR), Montpellier, France
| | - Stefan Leuko
- Research Group Astrobiology, Radiation Biology Department, German Aerospace Center (DLR), Institute of Aerospace Medicine, Köln, Germany
| | | | | | - Jean-Louis Fellous
- Department of Physics and Astronomy, Wheaton College, Massachusetts, Norton, Massachusetts
| | - Karen Olsson-Francis
- Faculty of Science, Technology, Engineering & Mathematics, School of Environment, Earth & Ecosystem Sciences, The Open University, Milton Keynes, United Kingdom
| | - David Pearce
- Department of Applied Sciences, Northumbria University, Newcastle, United Kingdom
| | - Elke Rabbow
- Research Group Astrobiology, Radiation Biology Department, German Aerospace Center (DLR), Institute of Aerospace Medicine, Köln, Germany
| | - Samuel Royle
- Faculty of Engineering, Department of Earth Science & Engineering, Imperial College, London, United Kingdom
| | - Mark Saunders
- Independent Consultant for the US National Academies of Sciences (NAS), Washington, District of Columbia
| | - Mark Sephton
- Faculty of Engineering, Department of Earth Science & Engineering, Imperial College, London, United Kingdom
| | - Andy Spry
- Carl Sagan Center, SETI, Mountain View, California
| | - Nicolas Walter
- Science Connect–European Science Foundation (ESF), Strasbourg, France
| | - Robert Wimmer Schweingruber
- Institut für Experimentelle und Angewandte Physik, Abteilung Extraterrestrische Physik, Christian-Albrechts-Universität zu Kiel, Kiel, Germany
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Iess L, Militzer B, Kaspi Y, Nicholson P, Durante D, Racioppa P, Anabtawi A, Galanti E, Hubbard W, Mariani MJ, Tortora P, Wahl S, Zannoni M. Measurement and implications of Saturn’s gravity field and ring mass. Science 2019; 364:science.aat2965. [DOI: 10.1126/science.aat2965] [Citation(s) in RCA: 104] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Accepted: 12/19/2018] [Indexed: 11/03/2022]
Abstract
The interior structure of Saturn, the depth of its winds, and the mass and age of its rings constrain its formation and evolution. In the final phase of the Cassini mission, the spacecraft dived between the planet and its innermost ring, at altitudes of 2600 to 3900 kilometers above the cloud tops. During six of these crossings, a radio link with Earth was monitored to determine the gravitational field of the planet and the mass of its rings. We find that Saturn’s gravity deviates from theoretical expectations and requires differential rotation of the atmosphere extending to a depth of at least 9000 kilometers. The total mass of the rings is (1.54 ± 0.49) × 1019 kilograms (0.41 ± 0.13 times that of the moon Mimas), indicating that the rings may have formed 107 to 108 years ago.
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Affiliation(s)
- L. Iess
- Department of Mechanical and Aerospace Engineering, Sapienza Università di Roma, Rome 00184, Italy
| | - B. Militzer
- Department of Astronomy, University of California, Berkeley, Berkeley, CA 94720, USA
- Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Y. Kaspi
- Department of Earth and Planetary Sciences Weizmann Institute of Science, Rehovot 76100, Israel
| | - P. Nicholson
- Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
| | - D. Durante
- Department of Mechanical and Aerospace Engineering, Sapienza Università di Roma, Rome 00184, Italy
| | - P. Racioppa
- Department of Mechanical and Aerospace Engineering, Sapienza Università di Roma, Rome 00184, Italy
| | - A. Anabtawi
- Jet Propulsion Laboratory–Caltech, Pasadena, CA 91109, USA
| | - E. Galanti
- Department of Earth and Planetary Sciences Weizmann Institute of Science, Rehovot 76100, Israel
| | - W. Hubbard
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
| | - M. J. Mariani
- Department of Mechanical and Aerospace Engineering, Sapienza Università di Roma, Rome 00184, Italy
| | - P. Tortora
- Department of Industrial Engineering, Università di Bologna, Forlì 47100, Italy
| | - S. Wahl
- Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720, USA
| | - M. Zannoni
- Department of Industrial Engineering, Università di Bologna, Forlì 47100, Italy
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39
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Hendrix AR, Hurford TA, Barge LM, Bland MT, Bowman JS, Brinckerhoff W, Buratti BJ, Cable ML, Castillo-Rogez J, Collins GC, Diniega S, German CR, Hayes AG, Hoehler T, Hosseini S, Howett CJ, McEwen AS, Neish CD, Neveu M, Nordheim TA, Patterson GW, Patthoff DA, Phillips C, Rhoden A, Schmidt BE, Singer KN, Soderblom JM, Vance SD. The NASA Roadmap to Ocean Worlds. ASTROBIOLOGY 2019; 19:1-27. [PMID: 30346215 PMCID: PMC6338575 DOI: 10.1089/ast.2018.1955] [Citation(s) in RCA: 68] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2018] [Accepted: 09/21/2018] [Indexed: 05/20/2023]
Abstract
In this article, we summarize the work of the NASA Outer Planets Assessment Group (OPAG) Roadmaps to Ocean Worlds (ROW) group. The aim of this group is to assemble the scientific framework that will guide the exploration of ocean worlds, and to identify and prioritize science objectives for ocean worlds over the next several decades. The overarching goal of an Ocean Worlds exploration program as defined by ROW is to "identify ocean worlds, characterize their oceans, evaluate their habitability, search for life, and ultimately understand any life we find." The ROW team supports the creation of an exploration program that studies the full spectrum of ocean worlds, that is, not just the exploration of known ocean worlds such as Europa but candidate ocean worlds such as Triton as well. The ROW team finds that the confirmed ocean worlds Enceladus, Titan, and Europa are the highest priority bodies to target in the near term to address ROW goals. Triton is the highest priority candidate ocean world to target in the near term. A major finding of this study is that, to map out a coherent Ocean Worlds Program, significant input is required from studies here on Earth; rigorous Research and Analysis studies are called for to enable some future ocean worlds missions to be thoughtfully planned and undertaken. A second finding is that progress needs to be made in the area of collaborations between Earth ocean scientists and extraterrestrial ocean scientists.
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Affiliation(s)
- Amanda R. Hendrix
- Planetary Science Institute, Tucson, Arizona
- Address correspondence to: Amanda R. Hendrix, Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719
| | | | - Laura M. Barge
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Michael T. Bland
- Astrogeology Science Center, U.S. Geological Survey, Flagstaff, Arizona
| | - Jeff S. Bowman
- Scripps Institution of Oceanography, La Jolla, California
| | | | - Bonnie J. Buratti
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Morgan L. Cable
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Julie Castillo-Rogez
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | | | - Serina Diniega
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | | | - Alexander G. Hayes
- Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, New York
| | - Tori Hoehler
- NASA Ames Research Center, Mountain View, California
| | - Sona Hosseini
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | | | - Alfred S. McEwen
- Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona
| | - Catherine D. Neish
- Planetary Science Institute, Tucson, Arizona
- Department of Earth Sciences, The University of Western Ontario, London, Ontario, Canada
| | - Marc Neveu
- NASA HQ/Universities Space Association, Washington, District of Columbia
| | - Tom A. Nordheim
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | | | | | - Cynthia Phillips
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | | | - Britney E. Schmidt
- School of Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia
| | | | - Jason M. Soderblom
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts
| | - Steven D. Vance
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
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40
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Neveu M, Rhoden AR. Evolution of Saturn's Mid-Sized Moons. NATURE ASTRONOMY 2019; 3:543-552. [PMID: 31360776 PMCID: PMC6662725 DOI: 10.1038/s41550-019-0726-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Accepted: 02/14/2019] [Indexed: 05/20/2023]
Abstract
The orbits of Saturn's inner mid-sized moons (Mimas, Enceladus, Tethys, Dione, and Rhea) have been notably difficult to reconcile with their geology. Here, we present numerical simulations coupling thermal, geophysical, and simplified orbital evolution for 4.5 billion years that reproduce observed characteristics of their orbits and interiors, provided that the outer four moons are old. Tidal dissipation within Saturn expands the moons' orbits over time. Dissipation within the moons decreases their eccentricities, which are episodically increased by moon-moon interactions, causing past or present oceans in the interior of Enceladus, Dione, and Tethys. In contrast, Mimas' proximity to Saturn's rings generates interactions that cause such rapid orbital expansion that Mimas must have formed only 0.1-1 Gyr ago if it postdates the rings. The resulting lack of radionuclides keeps it geologically inactive. These simulations can explain the Mimas-Enceladus dichotomy, reconcile the moons' orbital properties and geological diversity, and self-consistently produce a recent ocean on Enceladus.
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Affiliation(s)
- Marc Neveu
- Department of Astronomy, University of Maryland, College Park, MD, USA
- CRESST II and Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA
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41
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A Systematic Way to Life Detection: Combining Field, Lab and Space Research in Low Earth Orbit. ACTA ACUST UNITED AC 2018. [DOI: 10.1007/978-3-319-96175-0_5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Jones RM, Goordial JM, Orcutt BN. Low Energy Subsurface Environments as Extraterrestrial Analogs. Front Microbiol 2018; 9:1605. [PMID: 30072971 PMCID: PMC6058055 DOI: 10.3389/fmicb.2018.01605] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Accepted: 06/27/2018] [Indexed: 11/13/2022] Open
Abstract
Earth's subsurface is often isolated from phototrophic energy sources and characterized by chemotrophic modes of life. These environments are often oligotrophic and limited in electron donors or electron acceptors, and include continental crust, subseafloor oceanic crust, and marine sediment as well as subglacial lakes and the subsurface of polar desert soils. These low energy subsurface environments are therefore uniquely positioned for examining minimum energetic requirements and adaptations for chemotrophic life. Current targets for astrobiology investigations of extant life are planetary bodies with largely inhospitable surfaces, such as Mars, Europa, and Enceladus. Subsurface environments on Earth thus serve as analogs to explore possibilities of subsurface life on extraterrestrial bodies. The purpose of this review is to provide an overview of subsurface environments as potential analogs, and the features of microbial communities existing in these low energy environments, with particular emphasis on how they inform the study of energetic limits required for life. The thermodynamic energetic calculations presented here suggest that free energy yields of reactions and energy density of some metabolic redox reactions on Mars, Europa, Enceladus, and Titan could be comparable to analog environments in Earth's low energy subsurface habitats.
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Affiliation(s)
| | | | - Beth N. Orcutt
- Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, United States
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Dougherty MK, Spilker LJ. Review of Saturn's icy moons following the Cassini mission. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:065901. [PMID: 29651989 DOI: 10.1088/1361-6633/aabdfb] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
We review our knowledge of the icy moons of Saturn prior to the Cassini orbital mission, describe the discoveries made by the instrumentation onboard the Cassini spacecraft.
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Affiliation(s)
- Michele K Dougherty
- The Blackett Laboratory, Physics Department, Imperial College London, London, United Kingdom
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44
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Postberg F, Khawaja N, Abel B, Choblet G, Glein CR, Gudipati MS, Henderson BL, Hsu HW, Kempf S, Klenner F, Moragas-Klostermeyer G, Magee B, Nölle L, Perry M, Reviol R, Schmidt J, Srama R, Stolz F, Tobie G, Trieloff M, Waite JH. Macromolecular organic compounds from the depths of Enceladus. Nature 2018; 558:564-568. [PMID: 29950623 PMCID: PMC6027964 DOI: 10.1038/s41586-018-0246-4] [Citation(s) in RCA: 101] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Accepted: 03/23/2018] [Indexed: 11/13/2022]
Abstract
Saturn's moon Enceladus harbours a global water ocean 1 , which lies under an ice crust and above a rocky core 2 . Through warm cracks in the crust 3 a cryo-volcanic plume ejects ice grains and vapour into space4-7 that contain materials originating from the ocean8,9. Hydrothermal activity is suspected to occur deep inside the porous core10-12, powered by tidal dissipation 13 . So far, only simple organic compounds with molecular masses mostly below 50 atomic mass units have been observed in plume material6,14,15. Here we report observations of emitted ice grains containing concentrated and complex macromolecular organic material with molecular masses above 200 atomic mass units. The data constrain the macromolecular structure of organics detected in the ice grains and suggest the presence of a thin organic-rich film on top of the oceanic water table, where organic nucleation cores generated by the bursting of bubbles allow the probing of Enceladus' organic inventory in enhanced concentrations.
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Affiliation(s)
- Frank Postberg
- Institut für Geowissenschaften, Universität Heidelberg, Heidelberg, Germany.
- Klaus-Tschira-Labor für Kosmochemie, Universität Heidelberg, Heidelberg, Germany.
- Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany.
| | - Nozair Khawaja
- Institut für Geowissenschaften, Universität Heidelberg, Heidelberg, Germany
| | - Bernd Abel
- Leibniz-Institute für Oberflächenmodifizierung (IOM), Leipzig, Germany
| | - Gael Choblet
- Laboratoire de Planétologie et Géodynamique, UMR-CNRS 6112, Université de Nantes, Nantes, France
| | - Christopher R Glein
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX, USA
| | - Murthy S Gudipati
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Bryana L Henderson
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Hsiang-Wen Hsu
- Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA
| | - Sascha Kempf
- Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA
| | - Fabian Klenner
- Institut für Geowissenschaften, Universität Heidelberg, Heidelberg, Germany
| | | | - Brian Magee
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX, USA
- Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA
| | - Lenz Nölle
- Institut für Geowissenschaften, Universität Heidelberg, Heidelberg, Germany
| | - Mark Perry
- Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, USA
| | - René Reviol
- Institut für Geowissenschaften, Universität Heidelberg, Heidelberg, Germany
| | - Jürgen Schmidt
- Astronomy Research Unit, University of Oulu, Oulu, Finland
| | - Ralf Srama
- Institut für Raumfahrtsysteme, Universität Stuttgart, Stuttgart, Germany
| | - Ferdinand Stolz
- Leibniz-Institute für Oberflächenmodifizierung (IOM), Leipzig, Germany
- Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, Leipzig, Germany
| | - Gabriel Tobie
- Laboratoire de Planétologie et Géodynamique, UMR-CNRS 6112, Université de Nantes, Nantes, France
| | - Mario Trieloff
- Institut für Geowissenschaften, Universität Heidelberg, Heidelberg, Germany
- Klaus-Tschira-Labor für Kosmochemie, Universität Heidelberg, Heidelberg, Germany
| | - J Hunter Waite
- Laboratoire de Planétologie et Géodynamique, UMR-CNRS 6112, Université de Nantes, Nantes, France
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45
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Serabyn E, Liewer K, Wallace JK. Resolution optimization of an off-axis lensless digital holographic microscope. APPLIED OPTICS 2018; 57:A172-A180. [PMID: 29328143 DOI: 10.1364/ao.57.00a172] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Accepted: 10/28/2017] [Indexed: 06/07/2023]
Abstract
Microscopes aimed at detecting cellular life in extreme environments such as ocean-bearing solar system moons must provide high resolution in a compact, robust instrument. Here, we consider the resolution optimization of a compact off-axis lensless digital holographic microscope (DHM) that consists of a sample placed between an input point-source pair and a detector array. Two optimal high-resolution regimes are identified at opposite extremes-a low-magnification regime with the sample located near a small-pixel detector array, and a high-magnification regime with the sample near the input plane. In the former, resolution improves with smaller pixels, while in the latter, the effect of the finite pixel size is obviated, and the spatial resolution improves with detector array size. Using an off-axis lensless DHM with a 2 k×2 k array of 5.5 μm-pixels in the high-magnification regime, and standard aberration correction software, a resolution of ∼0.95 μm has been demonstrated, a factor of 5.8 smaller than the pixel size. Our analysis further suggests that with yet larger detector arrays, a lensless DHM should be capable of near wavelength-scale resolution.
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Vance SD, Kedar S, Panning MP, Stähler SC, Bills BG, Lorenz RD, Huang HH, Pike WT, Castillo JC, Lognonné P, Tsai VC, Rhoden AR. Vital Signs: Seismology of Icy Ocean Worlds. ASTROBIOLOGY 2018; 18:37-53. [PMID: 29345986 DOI: 10.1089/ast.2016.1612] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Ice-covered ocean worlds possess diverse energy sources and associated mechanisms that are capable of driving significant seismic activity, but to date no measurements of their seismic activity have been obtained. Such investigations could reveal the transport properties and radial structures, with possibilities for locating and characterizing trapped liquids that may host life and yielding critical constraints on redox fluxes and thus on habitability. Modeling efforts have examined seismic sources from tectonic fracturing and impacts. Here, we describe other possible seismic sources, their associations with science questions constraining habitability, and the feasibility of implementing such investigations. We argue, by analogy with the Moon, that detectable seismic activity should occur frequently on tidally flexed ocean worlds. Their ices fracture more easily than rocks and dissipate more tidal energy than the <1 GW of the Moon and Mars. Icy ocean worlds also should create less thermal noise due to their greater distance and consequently smaller diurnal temperature variations. They also lack substantial atmospheres (except in the case of Titan) that would create additional noise. Thus, seismic experiments could be less complex and less susceptible to noise than prior or planned planetary seismology investigations of the Moon or Mars. Key Words: Seismology-Redox-Ocean worlds-Europa-Ice-Hydrothermal. Astrobiology 18, 37-53.
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Affiliation(s)
- Steven D Vance
- 1 Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California, USA
| | - Sharon Kedar
- 1 Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California, USA
| | - Mark P Panning
- 1 Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California, USA
| | - Simon C Stähler
- 2 Institute of Geophysics , ETH Zürich, Zürich, Switzerland
- 3 Leibniz-Institute for Baltic Sea Research (IOW) , Rostock, Germany
| | - Bruce G Bills
- 1 Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California, USA
| | - Ralph D Lorenz
- 4 Johns Hopkins Applied Physics Laboratory , Laurel, Maryland, USA
| | - Hsin-Hua Huang
- 5 Institute of Earth Sciences , Academia Sinica, Taipei, Taiwan
- 6 Seismological Laboratory, California Institute of Technology , Pasadena, California, USA
| | - W T Pike
- 7 Optical and Semiconductor Devices Group, Department of Electrical and Electronic Engineering, Imperial College , London, UK
| | - Julie C Castillo
- 1 Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California, USA
| | - Philippe Lognonné
- 8 Univ Paris Diderot-Sorbonne Paris Cité, Institut de Physique du Globe de Paris , Paris, France
| | - Victor C Tsai
- 6 Seismological Laboratory, California Institute of Technology , Pasadena, California, USA
| | - Alyssa R Rhoden
- 9 School of Earth and Space Exploration, Arizona State University , Tempe, Arizona, USA
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Mathies RA, Razu ME, Kim J, Stockton AM, Turin P, Butterworth A. Feasibility of Detecting Bioorganic Compounds in Enceladus Plumes with the Enceladus Organic Analyzer. ASTROBIOLOGY 2017; 17:902-912. [PMID: 28915087 PMCID: PMC5610425 DOI: 10.1089/ast.2017.1660] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Enceladus presents an excellent opportunity to detect organic molecules that are relevant for habitability as well as bioorganic molecules that provide evidence for extraterrestrial life because Enceladus' plume is composed of material from the subsurface ocean that has a high habitability potential and significant organic content. A primary challenge is to send instruments to Enceladus that can efficiently sample organic molecules in the plume and analyze for the most relevant molecules with the necessary detection limits. To this end, we present the scientific feasibility and engineering design of the Enceladus Organic Analyzer (EOA) that uses a microfluidic capillary electrophoresis system to provide sensitive detection of a wide range of relevant organic molecules, including amines, amino acids, and carboxylic acids, with ppm plume-detection limits (100 pM limits of detection). Importantly, the design of a capture plate that effectively gathers plume ice particles at encounter velocities from 200 m/s to 5 km/s is described, and the ice particle impact is modeled to demonstrate that material will be efficiently captured without organic decomposition. While the EOA can also operate on a landed mission, the relative technical ease of a fly-by mission to Enceladus, the possibility to nondestructively capture pristine samples from deep within the Enceladus ocean, plus the high sensitivity of the EOA instrument for molecules of bioorganic relevance for life detection argue for the inclusion of EOA on Enceladus missions. Key Words: Lab-on-a-chip-Organic biomarkers-Life detection-Planetary exploration. Astrobiology 17, 902-912.
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Affiliation(s)
- Richard A. Mathies
- Department of Chemistry, University of California at Berkeley, Berkeley, California
| | - Md Enayet Razu
- Department of Mechanical Engineering, Texas Tech University, Lubbock, Texas
| | - Jungkyu Kim
- Department of Mechanical Engineering, Texas Tech University, Lubbock, Texas
| | - Amanda M. Stockton
- Department of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia
| | - Paul Turin
- Berkeley Space Sciences Lab, University of California at Berkeley, Berkeley, California
| | - Anna Butterworth
- Berkeley Space Sciences Lab, University of California at Berkeley, Berkeley, California
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48
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Suer TA, Padovan S, Whitten JL, Potter RW, Shkolyar S, Cable M, Walker C, Szalay J, Parker C, Cumbers J, Gentry D, Harrison T, Naidu S, Trammell HJ, Reimuller J, Budney CJ, Lowes LL. FIRE - Flyby of Io with Repeat Encounter: A conceptual design for a New Frontiers mission to Io. ADVANCES IN SPACE RESEARCH : THE OFFICIAL JOURNAL OF THE COMMITTEE ON SPACE RESEARCH (COSPAR) 2017; 60:1080-1100. [PMID: 33162637 PMCID: PMC7646308 DOI: 10.1016/j.asr.2017.05.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
A conceptual design is presented for a low complexity, heritage-based flyby mission to Io, Jupiter's innermost Galilean satellite and the most volcanically active body in the Solar System. The design addresses the 2011 Decadal Surveys recommendation for a New Frontiers class mission to Io and is based upon the result of the June 2012 NASA-JPL Planetary Science Summer School. A science payload is proposed to investigate the link between the structure of Io's interior, it's volcanic activity, it's surface composition, and it's tectonics. A study of Io's atmospheric processes and Io's role in the Jovian magnetosphere is also planned. The instrument suite includes a visible/near IR imager, a magnetic field and plasma suite, a dust analyzer and a gimbaled high gain antenna to perform radio science investigations. Payload activity and spacecraft operations would be powered by three Advanced Stirling Radioisotope Generators (ASRG). The primary mission includes 10 flybys with close-encounter altitudes as low as 100 km. The mission risks are mitigated by ensuring that relevant components are radiation tolerant and by using redundancy and flight-proven parts in the design. The spacecraft would be launched on an Atlas V rocket with a delta-v of 1.3 km/s. Three gravity assists (Venus, Earth, Earth) would be used to reach the Jupiter system in a 6-year cruise. The resulting concept demonstrates the rich scientific return of a flyby mission to Io.
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Affiliation(s)
- Terry-Ann Suer
- Institut de Mineralogie, de Physique des Materiaux, et de Cosmochimie (IMPMC) Sorbonne Universites - UPMC, Univ Paris 06, France
| | - Sebastiano Padovan
- German Aerospace Center (DLR), Department of Planetary Physics, Rutherfordstraße 2, Berlin 12489, Germany
| | - Jennifer L. Whitten
- Center for Earth and Planetary Studies, Smithsonian Institution, MRC 315, PO Box 37012, Washington, DC 20013-7012, United States
| | - Ross W.K. Potter
- Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, United States
| | - Svetlana Shkolyar
- Geophysical Laboratory, Carnegie Institution for Science, Jocelyn St NW, Washington, DC 20015, USA
| | - Morgan Cable
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, United Statess
| | - Catherine Walker
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, United Statess
| | - Jamey Szalay
- Southwest Research Institute, San Antonio, TX, United States
| | - Charles Parker
- John Hopkins Applied Physics Lab, Laurel, MD 20723, United States
| | - John Cumbers
- SynBioBeta LLC, Mountain View, CA 94040, United States
| | | | - Tanya Harrison
- School of Earth and Space Exploration, Arizona State University, AR, United States
| | - Shantanu Naidu
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, United Statess
| | | | | | - Charles J. Budney
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, United Statess
| | - Leslie L. Lowes
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, United Statess
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Běhounková M, Souček O, Hron J, Čadek O. Plume Activity and Tidal Deformation on Enceladus Influenced by Faults and Variable Ice Shell Thickness. ASTROBIOLOGY 2017; 17:941-954. [PMID: 28816521 PMCID: PMC5610426 DOI: 10.1089/ast.2016.1629] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Accepted: 06/20/2017] [Indexed: 05/23/2023]
Abstract
We investigated the effect of variations in ice shell thickness and of the tiger stripe fractures crossing Enceladus' south polar terrain on the moon's tidal deformation by performing finite element calculations in three-dimensional geometry. The combination of thinning in the polar region and the presence of faults has a synergistic effect that leads to an increase of both the displacement and stress in the south polar terrain by an order of magnitude compared to that of the traditional model with a uniform shell thickness and without faults. Assuming a simplified conductive heat transfer and neglecting the heat sources below the ice shell, we computed the global heat budget of the ice shell. For the inelastic properties of the shell described by a Maxwell viscoelastic model, we show that unrealistically low average viscosity of the order of 1013 Pa s is necessary for preserving the volume of the ocean, suggesting the important role of the heat sources in the deep interior. Similarly, low viscosity is required to predict the observed delay of the plume activity, which hints at other delaying mechanisms than just the viscoelasticity of the ice shell. The presence of faults results in large spatial and temporal heterogeneity of geysering activity compared to the traditional models without faults. Our model contributes to understanding the physical mechanisms that control the fault activity, and it provides potentially useful information for future missions that will sample the plume for evidence of life. Key Words: Enceladus-Tidal deformation-Faults-Variable ice shell thickness-Tidal heating-Plume activity and timing. Astrobiology 17, 941-954.
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Affiliation(s)
- Marie Běhounková
- Charles University, Faculty of Mathematics and Physics, Department of Geophysics, Prague, Czech Republic
| | - Ondřej Souček
- Mathematical Institute of Charles University, Prague, Czech Republic
| | - Jaroslav Hron
- Mathematical Institute of Charles University, Prague, Czech Republic
| | - Ondřej Čadek
- Charles University, Faculty of Mathematics and Physics, Department of Geophysics, Prague, Czech Republic
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Teolis BD, Perry ME, Hansen CJ, Waite JH, Porco CC, Spencer JR, Howett CJA. Enceladus Plume Structure and Time Variability: Comparison of Cassini Observations. ASTROBIOLOGY 2017; 17:926-940. [PMID: 28872900 PMCID: PMC5610430 DOI: 10.1089/ast.2017.1647] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Accepted: 07/06/2017] [Indexed: 05/23/2023]
Abstract
During three low-altitude (99, 66, 66 km) flybys through the Enceladus plume in 2010 and 2011, Cassini's ion neutral mass spectrometer (INMS) made its first high spatial resolution measurements of the plume's gas density and distribution, detecting in situ the individual gas jets within the broad plume. Since those flybys, more detailed Imaging Science Subsystem (ISS) imaging observations of the plume's icy component have been reported, which constrain the locations and orientations of the numerous gas/grain jets. In the present study, we used these ISS imaging results, together with ultraviolet imaging spectrograph stellar and solar occultation measurements and modeling of the three-dimensional structure of the vapor cloud, to constrain the magnitudes, velocities, and time variability of the plume gas sources from the INMS data. Our results confirm a mixture of both low and high Mach gas emission from Enceladus' surface tiger stripes, with gas accelerated as fast as Mach 10 before escaping the surface. The vapor source fluxes and jet intensities/densities vary dramatically and stochastically, up to a factor 10, both spatially along the tiger stripes and over time between flyby observations. This complex spatial variability and dynamics may result from time-variable tidal stress fields interacting with subsurface fissure geometry and tortuosity beyond detectability, including changing gas pathways to the surface, and fluid flow and boiling in response evolving lithostatic stress conditions. The total plume gas source has 30% uncertainty depending on the contributions assumed for adiabatic and nonadiabatic gas expansion/acceleration to the high Mach emission. The overall vapor plume source rate exhibits stochastic time variability up to a factor ∼5 between observations, reflecting that found in the individual gas sources/jets. Key Words: Cassini at Saturn-Geysers-Enceladus-Gas dynamics-Icy satellites. Astrobiology 17, 926-940.
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Affiliation(s)
- Ben D. Teolis
- Space Science Division, Southwest Research Institute, San Antonio, Texas
| | - Mark E. Perry
- Johns Hopkins University, Applied Physics Laboratory, Laurel, Maryland
| | | | - J. Hunter Waite
- Space Science Division, Southwest Research Institute, San Antonio, Texas
| | - Carolyn C. Porco
- University of California, Berkeley, California
- CICLOPS, Space Science Institute, Boulder, Colorado
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