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Nimmo F, Neveu M, Howett C. Origin and Evolution of Enceladus's Tidal Dissipation. Space Sci Rev 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] [What about the content of this article? (0)] [Affiliation(s)] [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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2
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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 Sci Rev 2023; 219:46. [PMID: 37636325 PMCID: PMC10457249 DOI: 10.1007/s11214-023-00990-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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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] [What about the content of this article? (0)] [Affiliation(s)] [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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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? Sci Adv 2022; 8:eabm4665. [PMID: 35857831 PMCID: PMC9299536 DOI: 10.1126/sciadv.abm4665] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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Rovira‐Navarro M, Katz RF, Liao Y, van der Wal W, Nimmo F. The Tides of Enceladus' Porous Core. J Geophys Res Planets 2022; 127:e2021JE007117. [PMID: 35865509 PMCID: PMC9285949 DOI: 10.1029/2021je007117] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/05/2021] [Revised: 04/01/2022] [Accepted: 04/27/2022] [Indexed: 06/15/2023]
Abstract
The inferred density of Enceladus' core, together with evidence of hydrothermal activity within the moon, suggests that the core is porous. Tidal dissipation in an unconsolidated core has been proposed as the main source of Enceladus' geological activity. However, the tidal response of its core has generally been modeled assuming it behaves viscoelastically rather than poroviscoelastically. In this work, we analyze the poroviscoelastic response to better constrain the distribution of tidal dissipation within Enceladus. A poroviscoelastic body has a different tidal response than a viscoelastic one; pressure within the pores alters the stress field and induces a Darcian porous flow. This flow represents an additional pathway for energy dissipation. Using Biot's theory of poroviscoelasticity, we develop a new framework to obtain the tidal response of a spherically symmetric, self-gravitating moon with porous layers and apply it to Enceladus. We show that the boundary conditions at the interface of the core and overlying ocean play a key role in the tidal response. The ocean hinders the development of a large-amplitude Darcian flow, making negligible the Darcian contribution to the dissipation budget. We therefore infer that Enceladus' core can be the source of its geological activity only if it has a low rigidity and a very low viscosity. A future mission to Enceladus could test this hypothesis by measuring the phase lags of tidally induced changes of gravitational potential and surface displacements.
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Affiliation(s)
- Marc Rovira‐Navarro
- Department of Ocean SystemsNIOZ Royal Netherlands Institute for Sea ResearchYersekeThe Netherlands
- Faculty of Aerospace EngineeringTU DelftDelftThe Netherlands
- Lunar and Planetary LaboratoryUniversity of ArizonaTucsonAZUSA
| | | | - Yang Liao
- Department of Geology and GeophysicsWoods Hole Oceanographic InstitutionWoods HoleMAUSA
| | | | - Francis Nimmo
- Department of Earth and Planetary SciencesUniversity of CaliforniaSanta CruzCAUSA
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6
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Dalle Ore CM, Long CJ, Nichols-Fleming F, Scipioni F, Rivera Valentín EG, Lopez Oquendo AJ, Cruikshank DP. Dione's Wispy Terrain: A Cryovolcanic Story? Planet Sci J 2021; 2:83. [PMID: 35005622 PMCID: PMC8740528 DOI: 10.3847/psj/abe7ec] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
We examine the H2O ice phase on the surface of Dione, one of Saturn's icy satellites, to investigate whether it might harbor cryovolcanic activity induced by a subcrustal body of water. Several studies have searched for such a signature, as summarized in Buratti et al.; however, none has yet produced sufficient evidence to dissipate doubts. In the radiation environment characteristic of Saturn's icy moons, the presence of crystalline H2O ice has been used as a marker of a high-temperature region. Because ion bombardment will, over time, drive crystalline ice toward an increasingly amorphous state, the current phase of the H2O ice can be used to gauge the temporal temperature evolution of the surface. We adopt a technique described by Dalle Ore et al. to map the fraction of amorphous to crystalline H2O ice on Dione's surface, observed by the Cassini Visible and Infrared Mapping Spectrometer, and provide an ice exposure age. We focus on a region observed at high spatial resolution and centered on one of the faults of the Wispy Terrain, which is measured to be fully crystalline. By assuming an amorphous to crystalline ice fraction of 5% (i.e., 95% crystallinity), significantly higher than the actual measurement, we obtain an upper limit for the age of the fault of 152 Ma. This implies that the studied fault has been active in the last ~100 Ma, supporting the hypothesis that Dione might still be active or was active a very short time ago, and similarly to Enceladus, might still be harboring a body of liquid water under its crust.
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Affiliation(s)
- Cristina M Dalle Ore
- SETI Institute, 183 Bernardo Avenue, Ste 200, Mountain View, CA 94043, USA
- NASA Ames Research Center, Moffett Field, CA 94035, USA
| | | | - Fiona Nichols-Fleming
- Department of Earth, Environmental and Planetary Sciences, Brown University, 324 Brook Street, Providence, RI 02912, USA
| | - Francesca Scipioni
- SETI Institute, 183 Bernardo Avenue, Ste 200, Mountain View, CA 94043, USA
| | - Edgard G Rivera Valentín
- Lunar and Planetary Institute, Universities Space Research Association, 3600 Bay Area Boulevard, Houston, TX 77058, USA
| | - Andy J Lopez Oquendo
- Lunar and Planetary Institute, Universities Space Research Association, 3600 Bay Area Boulevard, Houston, TX 77058, USA
- Department of Astronomy and Planetary Science, Northern Arizona University, 527 S. Beaver Street, Flagstaff, AZ 86011, USA
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7
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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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8
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9
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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: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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10
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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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11
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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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12
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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13
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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14
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Abstract
We review various laboratory strategies and methods that can be utilized to simulate prebiotic processes and origin of life in hydrothermal vent systems on icy/ocean worlds. Crucial steps that could be simulated in the laboratory include simulations of water-rock chemistry (e.g., serpentinization) to produce hydrothermal fluids, the types of mineral catalysts and energy gradients produced in vent interfaces where hydrothermal fluids interface with the surrounding seawater, and simulations of biologically relevant chemistry in flow-through gradient systems (i.e., far-from-equilibrium experiments). We describe some examples of experimental designs in detail, which are adaptable and could be used to test particular hypotheses about ocean world energetics or mineral/organic chemistry. Enceladus among the ocean worlds provides an ideal test case, since the pressure at the ocean floor is more easily simulated in the lab. Results for Enceladus could be extrapolated with further experiments and modeling to understand other ocean worlds. Key Words: Enceladus-Ocean worlds-Icy worlds-Hydrothermal vent-Iron sulfide-Gradient. Astrobiology 17, 820-833.
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Affiliation(s)
- Laura M Barge
- NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California
| | - Lauren M White
- NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California
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15
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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: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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16
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Jennings DE, Flasar FM, Kunde VG, Nixon CA, Segura ME, Romani PN, Gorius N, Albright S, Brasunas JC, Carlson RC, Mamoutkine AA, Guandique E, Kaelberer MS, Aslam S, Achterberg RK, Bjoraker GL, Anderson CM, Cottini V, Pearl JC, Smith MD, Hesman BE, Barney RD, Calcutt S, Vellacott TJ, Spilker LJ, Edgington SG, Brooks SM, Ade P, Schinder PJ, Coustenis A, Courtin R, Michel G, Fettig R, Pilorz S, Ferrari C. Composite infrared spectrometer (CIRS) on Cassini. Appl Opt 2017; 56:5274-5294. [PMID: 29047582 DOI: 10.1364/ao.56.005274] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Accepted: 05/25/2017] [Indexed: 06/07/2023]
Abstract
The Cassini spacecraft orbiting Saturn carries the composite infrared spectrometer (CIRS) designed to study thermal emission from Saturn and its rings and moons. CIRS, a Fourier transform spectrometer, is an indispensable part of the payload providing unique measurements and important synergies with the other instruments. It takes full advantage of Cassini's 13-year-long mission and surpasses the capabilities of previous spectrometers on Voyager 1 and 2. The instrument, consisting of two interferometers sharing a telescope and a scan mechanism, covers over a factor of 100 in wavelength in the mid and far infrared. It is used to study temperature, composition, structure, and dynamics of the atmospheres of Jupiter, Saturn, and Titan, the rings of Saturn, and surfaces of the icy moons. CIRS has returned a large volume of scientific results, the culmination of over 30 years of instrument development, operation, data calibration, and analysis. As Cassini and CIRS reach the end of their mission in 2017, we expect that archived spectra will be used by scientists for many years to come.
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17
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Maynard-Casely HE. ‘Peaks in space’ – crystallography in planetary science: past impacts and future opportunities. CRYSTALLOGR REV 2016. [DOI: 10.1080/0889311x.2016.1242127] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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18
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19
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Taubner RS, Schleper C, Firneis MG, Rittmann SKMR. Assessing the Ecophysiology of Methanogens in the Context of Recent Astrobiological and Planetological Studies. Life (Basel) 2015; 5:1652-86. [PMID: 26703739 PMCID: PMC4695842 DOI: 10.3390/life5041652] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Revised: 10/15/2015] [Accepted: 11/10/2015] [Indexed: 12/31/2022] Open
Abstract
Among all known microbes capable of thriving under extreme and, therefore, potentially extraterrestrial environmental conditions, methanogens from the domain Archaea are intriguing organisms. This is due to their broad metabolic versatility, enormous diversity, and ability to grow under extreme environmental conditions. Several studies revealed that growth conditions of methanogens are compatible with environmental conditions on extraterrestrial bodies throughout the Solar System. Hence, life in the Solar System might not be limited to the classical habitable zone. In this contribution we assess the main ecophysiological characteristics of methanogens and compare these to the environmental conditions of putative habitats in the Solar System, in particular Mars and icy moons. Eventually, we give an outlook on the feasibility and the necessity of future astrobiological studies concerning methanogens.
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Affiliation(s)
- Ruth-Sophie Taubner
- Research Platform: ExoLife, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria.
- Institute of Astrophysics, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria.
| | - Christa Schleper
- Archaea Biology and Ecogenomics Division, Department of Ecogenomics and Systems Biology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria.
| | - Maria G Firneis
- Research Platform: ExoLife, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria.
- Institute of Astrophysics, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria.
| | - Simon K-M R Rittmann
- Archaea Biology and Ecogenomics Division, Department of Ecogenomics and Systems Biology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria.
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20
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Spitale JN, Hurford TA, Rhoden AR, Berkson EE, Platts SS. Curtain eruptions from Enceladus’ south-polar terrain. Nature 2015; 521:57-60. [DOI: 10.1038/nature14368] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Accepted: 02/27/2015] [Indexed: 11/09/2022]
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21
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Andrews-Hanna JC, Besserer J, Head JW, Howett CJA, Kiefer WS, Lucey PJ, McGovern PJ, Melosh HJ, Neumann GA, Phillips RJ, Schenk PM, Smith DE, Solomon SC, Zuber MT. Structure and evolution of the lunar Procellarum region as revealed by GRAIL gravity data. Nature 2014; 514:68-71. [PMID: 25279919 DOI: 10.1038/nature13697] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2014] [Accepted: 07/16/2014] [Indexed: 11/09/2022]
Abstract
The Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations, thin crust, and high surface concentrations of the heat-producing elements uranium, thorium, and potassium. The region has been interpreted as an ancient impact basin approximately 3,200 kilometres in diameter, although supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features. Here we use data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to examine the subsurface structure of Procellarum. The Bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border Procellarum and are interpreted to be the frozen remnants of lava-filled rifts and the underlying feeder dykes that served as the magma plumbing system for much of the nearside mare volcanism. The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of border structures in a quasi-rectangular pattern with angular intersections, contrary to the expected circular or elliptical shape of an impact basin. The spatial pattern of magmatic-tectonic structures bounding Procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings, coupled with magmatic activity driven by the greater-than-average heat flux in the region.
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Affiliation(s)
- Jeffrey C Andrews-Hanna
- Department of Geophysics and Center for Space Resources, Colorado School of Mines, Golden, Colorado 80401, USA
| | - Jonathan Besserer
- Department of Earth and Planetary Sciences, University of California, Santa Cruz, California 95064, USA
| | - James W Head
- Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, Rhode Island 02912, USA
| | - Carly J A Howett
- Planetary Science Directorate, Southwest Research Institute, Boulder, Colorado 80302, USA
| | | | - Paul J Lucey
- Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, Hawaii 96822, USA
| | | | - H Jay Melosh
- Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana 47907, USA
| | - Gregory A Neumann
- Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
| | - Roger J Phillips
- Planetary Science Directorate, Southwest Research Institute, Boulder, Colorado 80302, USA
| | - Paul M Schenk
- Lunar and Planetary Institute, Houston, Texas 77058, USA
| | - David E Smith
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA
| | - Sean C Solomon
- 1] Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington DC 20015, USA [2] Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA
| | - Maria T Zuber
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA
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22
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Iess L, Stevenson DJ, Parisi M, Hemingway D, Jacobson RA, Lunine JI, Nimmo F, Armstrong JW, Asmar SW, Ducci M, Tortora P. The Gravity Field and Interior Structure of Enceladus. Science 2014; 344:78-80. [DOI: 10.1126/science.1250551] [Citation(s) in RCA: 269] [Impact Index Per Article: 26.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The small and active Saturnian moon Enceladus is one of the primary targets of the Cassini mission. We determined the quadrupole gravity field of Enceladus and its hemispherical asymmetry using Doppler data from three spacecraft flybys. Our results indicate the presence of a negative mass anomaly in the south-polar region, largely compensated by a positive subsurface anomaly compatible with the presence of a regional subsurface sea at depths of 30 to 40 kilometers and extending up to south latitudes of about 50°. The estimated values for the largest quadrupole harmonic coefficients (106J2= 5435.2 ± 34.9, 106C22= 1549.8 ± 15.6, 1σ) and their ratio (J2/C22= 3.51 ± 0.05) indicate that the body deviates mildly from hydrostatic equilibrium. The moment of inertia is around 0.335MR2, whereMis the mass andRis the radius, suggesting a differentiated body with a low-density core.
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23
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Küppers M, O'Rourke L, Bockelée-Morvan D, Zakharov V, Lee S, von Allmen P, Carry B, Teyssier D, Marston A, Müller T, Crovisier J, Barucci MA, Moreno R. Localized sources of water vapour on the dwarf planet (1) Ceres. Nature 2014; 505:525-7. [PMID: 24451541 DOI: 10.1038/nature12918] [Citation(s) in RCA: 229] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Accepted: 11/26/2013] [Indexed: 11/08/2022]
Abstract
The 'snowline' conventionally divides Solar System objects into dry bodies, ranging out to the main asteroid belt, and icy bodies beyond the belt. Models suggest that some of the icy bodies may have migrated into the asteroid belt. Recent observations indicate the presence of water ice on the surface of some asteroids, with sublimation a potential reason for the dust activity observed on others. Hydrated minerals have been found on the surface of the largest object in the asteroid belt, the dwarf planet (1) Ceres, which is thought to be differentiated into a silicate core with an icy mantle. The presence of water vapour around Ceres was suggested by a marginal detection of the photodissociation product of water, hydroxyl (ref. 12), but could not be confirmed by later, more sensitive observations. Here we report the detection of water vapour around Ceres, with at least 10(26) molecules being produced per second, originating from localized sources that seem to be linked to mid-latitude regions on the surface. The water evaporation could be due to comet-like sublimation or to cryo-volcanism, in which volcanoes erupt volatiles such as water instead of molten rocks.
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24
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Walker CC, Bassis JN, Liemohn MW. On the application of simple rift basin models to the south polar region of Enceladus. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012je004084] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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