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Styczinski MJ, Cooper ZS, Glaser DM, Lehmer O, Mierzejewski V, Tarnas J. Chapter 7: Assessing Habitability Beyond Earth. ASTROBIOLOGY 2024; 24:S143-S163. [PMID: 38498826 DOI: 10.1089/ast.2021.0097] [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: 03/20/2024]
Abstract
All known life on Earth inhabits environments that maintain conditions between certain extremes of temperature, chemical composition, energy availability, and so on (Chapter 6). Life may have emerged in similar environments elsewhere in the Solar System and beyond. The ongoing search for life elsewhere mainly focuses on those environments most likely to support life, now or in the past-that is, potentially habitable environments. Discussion of habitability is necessarily based on what we know about life on Earth, as it is our only example. This chapter gives an overview of the known and presumed requirements for life on Earth and discusses how these requirements can be used to assess the potential habitability of planetary bodies across the Solar System and beyond. We first consider the chemical requirements of life and potential feedback effects that the presence of life can have on habitable conditions, and then the planetary, stellar, and temporal requirements for habitability. We then review the state of knowledge on the potential habitability of bodies across the Solar System and exoplanets, with a particular focus on Mars, Venus, Europa, and Enceladus. While reviewing the case for the potential habitability of each body, we summarize the most prominent and impactful studies that have informed the perspective on where habitable environments are likely to be found.
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Affiliation(s)
- M J Styczinski
- University of Washington, Seattle, Washington, USA
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | - Z S Cooper
- University of Washington, Seattle, Washington, USA
| | - D M Glaser
- School of Molecular Sciences, Arizona State University, Tempe, Arizona, USA
| | - O Lehmer
- NASA Ames Research Center, Moffett Field, California, USA
| | - V Mierzejewski
- School of Earth and Space Exploration, Arizona State University, Arizona, USA
| | - J Tarnas
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
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2
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Ćuk M, Rhoden AR. Mimas's surprise ocean prompts an update of the rule book for moons. Nature 2024; 626:263-264. [PMID: 38326598 DOI: 10.1038/d41586-024-00194-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2024]
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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: 1] [Impact Index Per Article: 1.0] [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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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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Kempf S, Altobelli N, Schmidt J, Cuzzi JN, Estrada PR, Srama R. Micrometeoroid infall onto Saturn's rings constrains their age to no more than a few hundred million years. SCIENCE ADVANCES 2023; 9:eadf8537. [PMID: 37172091 PMCID: PMC10181170 DOI: 10.1126/sciadv.adf8537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
There is ongoing debate as to whether Saturn's main rings are relatively young or ancient- having been formed shortly after Saturn or during the Late Heavy Bombardment. The rings are mostly water-ice but are polluted by non-icy material with a volume fraction ranging from ∼0.1 to 2%. Continuous bombardment by micrometeoroids exogenic to the Saturnian system is a source of this non-icy material. Knowledge of the incoming mass flux of these pollutants allows estimation of the rings' exposure time, providing a limit on their age. Here we report the final measurements by Cassini's Cosmic Dust Analyzer of the micrometeoroid flux into the Saturnian system. Several populations are present, but the flux is dominated by low-relative velocity objects such as from the Kuiper belt. We find a mass flux between 6.9 · 10-17 and 2.7 · 10-16 kg m-2s-1 from which we infer a ring exposure time ≲100 to 400 million years in support of recent ring formation scenarios.
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Affiliation(s)
- Sascha Kempf
- Department of Physics, University of Colorado, Boulder, CO 80309, USA
- Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA
| | | | - Jürgen Schmidt
- Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
- Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland
| | - Jeffrey N Cuzzi
- Space Science Division, NASA Ames Research Center, Moffett Field, CA 94035, USA
| | - Paul R Estrada
- Space Science Division, NASA Ames Research Center, Moffett Field, CA 94035, USA
| | - Ralf Srama
- Institut für Raumfahrtsysteme, Universität Stuttgart, Stuttgart, Germany
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6
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El Moutamid M. How Saturn got its tilt and its rings. Science 2022; 377:1264-1265. [DOI: 10.1126/science.abq3184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The destruction of a hypothetical moon may help explain the origin of both
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Affiliation(s)
- Maryame El Moutamid
- Cornell Center of Astrophysics and Planetary Sciences, Cornell University, Ithaca, NY, USA
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7
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Wisdom J, Dbouk R, Militzer B, Hubbard WB, Nimmo F, Downey BG, French RG. Loss of a satellite could explain Saturn’s obliquity and young rings. Science 2022; 377:1285-1289. [DOI: 10.1126/science.abn1234] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The origin of Saturn’s ~26.7° obliquity and ~100-million-year-old rings is unknown. The observed rapid outward migration of Saturn’s largest satellite, Titan, could have raised Saturn’s obliquity through a spin-orbit precession resonance with Neptune. We use Cassini data to refine estimates of Saturn’s moment of inertia, finding that it is just outside the range required for the resonance. We propose that Saturn previously had an additional satellite, which we name Chrysalis, that caused Saturn’s obliquity to increase through the Neptune resonance. Destabilization of Chrysalis’s orbit ~100 million years ago can then explain the proximity of the system to the resonance and the formation of the rings through a grazing encounter with Saturn.
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Affiliation(s)
- Jack Wisdom
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Rola Dbouk
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Burkhard Militzer
- Department of Astronomy, University of California, Berkeley, CA 94720, USA
- Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA
| | - William B. Hubbard
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721-0092, USA
| | - Francis Nimmo
- Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA
| | - Brynna G. Downey
- Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA
| | - Richard G. French
- Department of Astronomy, Wellesley College, Wellesley, MA 02481, USA
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8
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Durante D, Guillot T, Iess L, Stevenson DJ, Mankovich CR, Markham S, Galanti E, Kaspi Y, Zannoni M, Gomez Casajus L, Lari G, Parisi M, Buccino DR, Park RS, Bolton SJ. Juno spacecraft gravity measurements provide evidence for normal modes of Jupiter. Nat Commun 2022; 13:4632. [PMID: 36042221 PMCID: PMC9427753 DOI: 10.1038/s41467-022-32299-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Accepted: 07/21/2022] [Indexed: 11/25/2022] Open
Abstract
The Juno spacecraft has been collecting data to shed light on the planet’s origin and characterize its interior structure. The onboard gravity science experiment based on X-band and Ka-band dual-frequency Doppler tracking precisely measured Jupiter’s zonal gravitational field. Here, we analyze 22 Juno’s gravity passes to investigate the gravity field. Our analysis provides evidence of new gravity field features, which perturb its otherwise axially symmetric structure with a time-variable component. We show that normal modes of the planet could explain the anomalous signatures present in the Doppler data better than other alternative explanations, such as localized density anomalies and non-axisymmetric components of the static gravity field. We explain Juno data by p-modes having an amplitude spectrum with a peak radial velocity of 10–50 cm/s at 900–1200 μHz (compatible with ground-based observations) and provide upper bounds on lower frequency f-modes (radial velocity smaller than 1 cm/s). The new Juno results could open the possibility of exploring the interior structure of the gas giants through measurements of the time-variable gravity or with onboard instrumentation devoted to the observation of normal modes, which could drive spacecraft operations of future missions. Juno spacecraft experienced unknown accelerations near the closest approach to Jupiter. Here, the authors show that Jupiter’s axially symmetric, north-south asymmetric gravity field measured by Juno is perturbed by a time-variable component, associated to internal oscillations.
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Affiliation(s)
- Daniele Durante
- Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, Rome, Italy.
| | - Tristan Guillot
- Observatoire de la Côte d'Azur, Université Côte d'Azur, CNRS, Nice, France
| | - Luciano Iess
- Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, Rome, Italy
| | - David J Stevenson
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
| | - Christopher R Mankovich
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
| | - Steve Markham
- Observatoire de la Côte d'Azur, Université Côte d'Azur, CNRS, Nice, France
| | - Eli Galanti
- Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Yohai Kaspi
- Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Marco Zannoni
- Department of Industrial Engineering, University of Bologna, Forlì, Italy
| | - Luis Gomez Casajus
- Department of Industrial Engineering, University of Bologna, Forlì, Italy
| | - Giacomo Lari
- Department of Mathematics, University of Pisa, Pisa, Italy
| | - Marzia Parisi
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Dustin R Buccino
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Ryan S Park
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
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Parisi M, Kaspi Y, Galanti E, Durante D, Bolton SJ, Levin SM, Buccino DR, Fletcher LN, Folkner WM, Guillot T, Helled R, Iess L, Li C, Oudrhiri K, Wong MH. The depth of Jupiter's Great Red Spot constrained by Juno gravity overflights. Science 2021; 374:964-968. [PMID: 34709940 DOI: 10.1126/science.abf1396] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
[Figure: see text].
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Affiliation(s)
- Marzia Parisi
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Yohai Kaspi
- Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Eli Galanti
- Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Daniele Durante
- Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, 00184 Rome Italy
| | - Scott J Bolton
- Southwest Research Institute, San Antonio, TX 78238, USA
| | - Steven M Levin
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Dustin R Buccino
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Leigh N Fletcher
- School of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
| | - William M Folkner
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Tristan Guillot
- Université Côte d'Azur, Observatoire de la Côte d'Azur, Laboratoire Lagrange, Centre National de la Recherche Scientifique, 06304 Nice, France
| | - Ravit Helled
- Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich, 8057 Zurich, Switzerland
| | - Luciano Iess
- Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, 00184 Rome Italy
| | - Cheng Li
- Department of Astronomy, University of California, Berkeley, CA 94720, USA
| | - Kamal Oudrhiri
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Michael H Wong
- Department of Astronomy, University of California, Berkeley, CA 94720, USA.,Carl Sagan Center for Research, SETI Institute, Mountain View, CA 94043, USA
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10
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Wakeford HR, Dalba PA. The exoplanet perspective on future ice giant exploration. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20200054. [PMID: 33161853 DOI: 10.1098/rsta.2020.0054] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 07/06/2020] [Indexed: 05/20/2023]
Abstract
Exoplanets number in their thousands, and the number is ever increasing with the advent of new surveys and improved instrumentation. One of the most surprising things we have learnt from these discoveries is not that small-rocky planets in their stars habitable zones are likely to be common, but that the most typical size of exoplanets is that not seen in our solar system-radii between that of Neptune and the Earth dubbed mini-Neptunes and super-Earths. In fact, a transiting exoplanet is four times as likely to be in this size regime than that of any giant planet in our solar system. Investigations into the atmospheres of giant hydrogen/helium dominated exoplanets has pushed down to Neptune and mini-Neptune-sized worlds revealing molecular absorption from water, scattering and opacity from clouds, and measurements of atmospheric abundances. However, unlike measurements of Jupiter, or even Saturn sized worlds, the smaller giants lack a ground truth on what to expect or interpret from their measurements. How did these sized worlds form and evolve and was it different from their larger counterparts? What is their internal composition and how does that impact their atmosphere? What informs the energy budget of these distant worlds? In this we discuss what characteristics we can measure for exoplanets, and why a mission to the ice giants in our solar system is the logical next step for understanding exoplanets. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.
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Affiliation(s)
- H R Wakeford
- School of Physics, University of Bristol, HH Wills Laboratory, Tyndall Avenue, Bristol BS8 1TL, UK
| | - P A Dalba
- Department of Earth and Planetary Sciences, University of California Riverside, 900 University Avenue, Riverside CA 92521, USA
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11
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Helled R, Fortney JJ. The interiors of Uranus and Neptune: current understanding and open questions. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20190474. [PMID: 33161856 DOI: 10.1098/rsta.2019.0474] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Uranus and Neptune form a distinct class of planets in our Solar System. Given this fact, and ubiquity of similar-mass planets in other planetary systems, it is essential to understand their interior structure and composition. However, there are more open questions regarding these planets than answers. In this review, we concentrate on the things we do not know about the interiors of Uranus and Neptune with a focus on why the planets may be different, rather than the same. We next summarize the knowledge about the planets' internal structure and evolution. Finally, we identify the topics that should be investigated further on the theoretical front as well as required observations from space missions. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.
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Affiliation(s)
- Ravit Helled
- Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich, Zurich, Switzerland
| | - Jonathan J Fortney
- Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
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12
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Friedson AJ. Ice giant seismology: prospecting for normal modes. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20190475. [PMID: 33161861 DOI: 10.1098/rsta.2019.0475] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The properties of ice giant normal mode oscillations, including their periods, spatial structure, stratospheric amplitudes and relative influence on the external gravity field, are surveyed for the purpose of formulating the best strategy for their eventual detection. Measurement requirements for detecting a normal mode's periodic pressure and temperature variations, including a possible stratospheric signal, and its effect on the external gravity field, are discussed in terms of its radial velocity amplitude at the 1 bar pressure level. It is found that for reasonable amplitudes, detection of the pressure and temperature variations of ice giant normal modes presents an extraordinary technical challenge. The prospects for detecting their gravitational influence on an orbiting spacecraft are more promising, with requirements that lie within the range of current technology. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.
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Affiliation(s)
- A James Friedson
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
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13
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Saturn's near-equatorial ionospheric conductivities from in situ measurements. Sci Rep 2020; 10:7932. [PMID: 32404966 PMCID: PMC7220909 DOI: 10.1038/s41598-020-64787-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Accepted: 04/21/2020] [Indexed: 11/08/2022] Open
Abstract
Cassini's Grand Finale orbits provided for the first time in-situ measurements of Saturn's topside ionosphere. We present the Pedersen and Hall conductivities of the top near-equatorial dayside ionosphere, derived from the in-situ measurements by the Cassini Radio and Wave Plasma Science Langmuir Probe, the Ion and Neutral Mass Spectrometer and the fluxgate magnetometer. The Pedersen and Hall conductivities are constrained to at least 10-5-10-4 S/m at (or close to) the ionospheric peak, a factor 10-100 higher than estimated previously. We show that this is due to the presence of dusty plasma in the near-equatorial ionosphere. We also show the conductive ionospheric region to be extensive, with thickness of 300-800 km. Furthermore, our results suggest a temporal variation (decrease) of the plasma densities, mean ion masses and consequently the conductivities from orbit 288 to 292.
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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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15
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Guillot T, Fletcher LN. Revealing giant planet interiors beneath the cloudy veil. Nat Commun 2020; 11:1555. [PMID: 32214104 PMCID: PMC7096516 DOI: 10.1038/s41467-020-15431-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Accepted: 02/28/2020] [Indexed: 11/16/2022] Open
Abstract
Observations from the Juno and Cassini missions provide essential constraints on the internal structures and compositions of Jupiter and Saturn, resulting in profound revisions of our understanding of the interior and atmospheres of Gas Giant planets. The next step to understand planetary origins in our Solar System requires a mission to their Ice Giant siblings, Uranus and Neptune.
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Affiliation(s)
- Tristan Guillot
- Université Côte d'Azur, OCA, Lagrange CNRS, 06304, Nice, France.
| | - Leigh N Fletcher
- School of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
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16
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Fletcher LN, Kaspi Y, Guillot T, Showman AP. How Well Do We Understand the Belt/Zone Circulation of Giant Planet Atmospheres? SPACE SCIENCE REVIEWS 2020; 216:30. [PMID: 32214508 PMCID: PMC7067733 DOI: 10.1007/s11214-019-0631-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 12/24/2019] [Indexed: 05/20/2023]
Abstract
The atmospheres of the four giant planets of our Solar System share a common and well-observed characteristic: they each display patterns of planetary banding, with regions of different temperatures, composition, aerosol properties and dynamics separated by strong meridional and vertical gradients in the zonal (i.e., east-west) winds. Remote sensing observations, from both visiting spacecraft and Earth-based astronomical facilities, have revealed the significant variation in environmental conditions from one band to the next. On Jupiter, the reflective white bands of low temperatures, elevated aerosol opacities, and enhancements of quasi-conserved chemical tracers are referred to as 'zones.' Conversely, the darker bands of warmer temperatures, depleted aerosols, and reductions of chemical tracers are known as 'belts.' On Saturn, we define cyclonic belts and anticyclonic zones via their temperature and wind characteristics, although their relation to Saturn's albedo is not as clear as on Jupiter. On distant Uranus and Neptune, the exact relationships between the banded albedo contrasts and the environmental properties is a topic of active study. This review is an attempt to reconcile the observed properties of belts and zones with (i) the meridional overturning inferred from the convergence of eddy angular momentum into the eastward zonal jets at the cloud level on Jupiter and Saturn and the prevalence of moist convective activity in belts; and (ii) the opposing meridional motions inferred from the upper tropospheric temperature structure, which implies decay and dissipation of the zonal jets with altitude above the clouds. These two scenarios suggest meridional circulations in opposing directions, the former suggesting upwelling in belts, the latter suggesting upwelling in zones. Numerical simulations successfully reproduce the former, whereas there is a wealth of observational evidence in support of the latter. This presents an unresolved paradox for our current understanding of the banded structure of giant planet atmospheres, that could be addressed via a multi-tiered vertical structure of "stacked circulation cells," with a natural transition from zonal jet pumping to dissipation as we move from the convectively-unstable mid-troposphere into the stably-stratified upper troposphere.
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Affiliation(s)
- Leigh N. Fletcher
- School of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH UK
| | - Yohai Kaspi
- Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, 76100 Israel
| | - Tristan Guillot
- Université Côte d’Azur, OCA, Lagrange CNRS, 06304 Nice, France
| | - Adam P. Showman
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721-0092 USA
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17
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Saturn’s Probable Interior: An Exploration of Saturn’s Potential Interior Density Structures. ACTA ACUST UNITED AC 2020. [DOI: 10.3847/1538-4357/ab71ff] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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18
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Vance SD, Melwani Daswani M. Serpentinite and the search for life beyond Earth. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20180421. [PMID: 31902342 DOI: 10.1098/rsta.2018.0421] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 11/27/2019] [Indexed: 06/10/2023]
Abstract
Hydrogen from serpentinization is a source of chemical energy for some life forms on Earth. It is a potential fuel for life in the subsurface of Mars and in the icy ocean worlds in the outer solar system. Serpentinization is also implicated in life's origin. Planetary exploration offers a way to investigate such theories by characterizing and ultimately searching for life in geochemical settings that no longer exist on Earth. At present, much of the current context of serpentinization on other worlds relies on inference from modelling and studies on Earth. While there is evidence from orbital spectral imaging and martian meteorites that serpentinization has occurred on Mars, the extent and duration of that activity has not been constrained. Similarly, ongoing serpentinization might explain hydrogen found in the ocean of Saturn's tiny moon Enceladus, but this raises questions about how long such activity has persisted. Titan's hydrocarbon-rich atmosphere may derive from ancient or present-day serpentinization at the bottom of its ocean. In Europa, volcanism or serpentinization may provide hydrogen as a redox couple to oxygen generated at the moon's surface. We assess the potential extent of serpentinization in the solar system's wet and rocky worlds, assuming that microfracturing from thermal expansion anisotropy sets an upper limit on the percolation depth of surface water into the rocky interiors. In this bulk geophysical model, planetary cooling from radiogenic decay implies the infiltration of water to greater depths through time, continuing to the present. The serpentinization of this newly exposed rock is assessed as a significant source of global hydrogen. Comparing the computed hydrogen and surface-generated oxygen delivered to Europa's ocean reveals redox fluxes similar to Earth's. Planned robotic exploration missions to other worlds can aid in understanding the planetary context of serpentinization, testing the predictions herein. This article is part of a discussion meeting issue 'Serpentinite in the Earth System'.
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Affiliation(s)
- S D Vance
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8001, USA
| | - M Melwani Daswani
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8001, USA
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19
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Models of Saturn's Interior Constructed with an Accelerated Concentric Maclaurin Spheroid Method. ACTA ACUST UNITED AC 2019. [DOI: 10.3847/1538-4357/ab23f0] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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20
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Tiscareno MS, Nicholson PD, Cuzzi JN, Spilker LJ, Murray CD, Hedman MM, Colwell JE, Burns JA, Brooks SM, Clark RN, Cooper NJ, Deau E, Ferrari C, Filacchione G, Jerousek RG, Le Mouélic S, Morishima R, Pilorz S, Rodriguez S, Showalter MR, Badman SV, Baker EJ, Buratti BJ, Baines KH, Sotin C. Close-range remote sensing of Saturn's rings during Cassini's ring-grazing orbits and Grand Finale. Science 2019; 364:364/6445/eaau1017. [PMID: 31196983 DOI: 10.1126/science.aau1017] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2018] [Accepted: 05/07/2019] [Indexed: 11/02/2022]
Abstract
Saturn's rings are an accessible exemplar of an astrophysical disk, tracing the Saturn system's dynamical processes and history. We present close-range remote-sensing observations of the main rings from the Cassini spacecraft. We find detailed sculpting of the rings by embedded masses, and banded texture belts throughout the rings. Saturn-orbiting streams of material impact the F ring. There are fine-scaled correlations among optical depth, spectral properties, and temperature in the B ring, but anticorrelations within strong density waves in the A ring. There is no spectral distinction between plateaux and the rest of the C ring, whereas the region outward of the Keeler gap is spectrally distinct from nearby regions. These results likely indicate that radial stratification of particle physical properties, rather than compositional differences, is responsible for producing these ring structures.
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Affiliation(s)
- Matthew S Tiscareno
- Carl Sagan Center for the Study of Life in the Universe, SETI Institute, Mountain View, CA 94043, USA.
| | | | | | - Linda J Spilker
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Carl D Murray
- Astronomy Unit, Queen Mary University of London, London E1 4NS, UK
| | - Matthew M Hedman
- Department of Physics, University of Idaho, Moscow, ID 83844, USA
| | - Joshua E Colwell
- Department of Physics, University of Central Florida, Orlando, FL 32816, USA
| | - Joseph A Burns
- Department of Astronomy, Cornell University, Ithaca, NY 14853, USA.,College of Engineering, Cornell University, Ithaca, NY 14853, USA
| | - Shawn M Brooks
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | | | | | - Estelle Deau
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.,Department of Earth, Planetary, and Space Sciences, University of California at Los Angeles, Los Angeles, CA 90095, USA
| | - Cecile Ferrari
- Institut de Physique du Globe de Paris, Centre National de la Recherche Scientifique (CNRS)-Unité Mixte de Recherche (UMR) 7154, Université Paris-Diderot, Université Sorbonne-Paris-Cité (USPC), Paris, France
| | - Gianrico Filacchione
- INAF-IAPS (Istituto Nazionale di AstroFisica-Istituto di Astrofisica e Planetologia Spaziali), Rome, Italy
| | - Richard G Jerousek
- Department of Physics, University of Central Florida, Orlando, FL 32816, USA
| | - Stéphane Le Mouélic
- Laboratoire de Planetologie et Geodynamique, CNRS-UMR 6112, Université de Nantes, 44322 Nantes, France
| | - Ryuji Morishima
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.,Department of Earth, Planetary, and Space Sciences, University of California at Los Angeles, Los Angeles, CA 90095, USA
| | - Stu Pilorz
- Carl Sagan Center for the Study of Life in the Universe, SETI Institute, Mountain View, CA 94043, USA
| | - Sébastien Rodriguez
- Institut de Physique du Globe de Paris, Centre National de la Recherche Scientifique (CNRS)-Unité Mixte de Recherche (UMR) 7154, Université Paris-Diderot, Université Sorbonne-Paris-Cité (USPC), Paris, France
| | - Mark R Showalter
- Carl Sagan Center for the Study of Life in the Universe, SETI Institute, Mountain View, CA 94043, USA
| | - Sarah V Badman
- Physics Department, Lancaster University, Lancaster LA1 4YB, UK
| | | | - Bonnie J Buratti
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Kevin H Baines
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Christophe Sotin
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
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21
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Abstract
Cassini data constrain the age and history of the giant planet's rings
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Affiliation(s)
- Shigeru Ida
- Earth-Life Science Institute, Tokyo Institute of Technology, 152-8550 Tokyo, Japan.
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