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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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Wakita S, Johnson BC, Silber EA, Singer KN. Multiring basin formation constrains Europa's ice shell thickness. SCIENCE ADVANCES 2024; 10:eadj8455. [PMID: 38507497 PMCID: PMC10954210 DOI: 10.1126/sciadv.adj8455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Accepted: 02/14/2024] [Indexed: 03/22/2024]
Abstract
Jupiter's moon Europa hosts a subsurface ocean under an ice shell of uncertain thickness. Europa has two multiring basins that exhibit several concentric rings. The formation of these multiring basins is thought to be sensitive to the thickness and thermal structure of the ice shell. Here, we simulate multiring basin forming impacts on Europa finding that a total ice shell greater than 20 kilometers thick is required to reproduce observed ring structures. Thin ice shells (<15 kilometers thick) result in compressional tectonics inconsistent with observed ring structures. Our simulations are also sensitive to the thermal structure of the ice shell and indicate that Europa's at least 20-kilometer ice shell is composed of a 6- to 8-kilometer-thick conductive lid overlying warm convecting ice. The constraints on Europa's ice shell structure resulting from this work are directly relevant to our understanding of the potential habitability of Europa.
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Affiliation(s)
- Shigeru Wakita
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
- Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA
| | - Brandon C. Johnson
- Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA
- Department of Physics and Astronomy, Purdue University, West Lafayette, IN, USA
| | - Elizabeth A. Silber
- Department of Earth Sciences, Western University, London, ON, Canada
- Institute for Earth and Space Exploration, Western University, London, ON, Canada
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3
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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: 3.0] [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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Bland MT, Elder CM. Silicate Volcanism on Europa's Seafloor and Implications for Habitability. GEOPHYSICAL RESEARCH LETTERS 2022; 49:e2021GL096939. [PMID: 35866068 PMCID: PMC9286870 DOI: 10.1029/2021gl096939] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 01/27/2022] [Accepted: 01/28/2022] [Indexed: 06/15/2023]
Abstract
Habitable ocean environments on Europa require an influx of reactants to maintain chemical disequilibrium. One possible source of reactants is seafloor volcanism. Modeling has shown that dissipation of tidal energy in Europa's asthenosphere can generate melt, but melt formation cannot be equated with volcanism. Melt must also be transported through Europa's cold lithosphere to erupt at the seafloor. Here, we use two models of dike propagation to show that dikes can only traverse the lithosphere if either the fracture toughness of the lithosphere or the flux into the dike is large (>500 MPa m1/2 or ∼1 m2 s-1, respectively). We conclude that cyclic volcanic episodes might provide reactants to Europa's ocean if magma accumulates at the base of the lithosphere for several thousand years. However, if dikes form too frequently, or are too numerous, the magma flux into each will be insufficient, and volcanism cannot support a habitable ocean environment.
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Affiliation(s)
- M. T. Bland
- Astrogeology Science CenterU. S. Geological SurveyFlagstaffAZUSA
| | - C. M. Elder
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
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Mo M, Tang M, Chen Z, Peterson JR, Shen X, Baldwin JK, Frost M, Kozina M, Reid A, Wang Y, E J, Descamps A, Ofori-Okai BK, Li R, Luo SN, Wang X, Glenzer S. Ultrafast visualization of incipient plasticity in dynamically compressed matter. Nat Commun 2022; 13:1055. [PMID: 35217665 PMCID: PMC8881594 DOI: 10.1038/s41467-022-28684-z] [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: 02/15/2021] [Accepted: 01/31/2022] [Indexed: 11/10/2022] Open
Abstract
Plasticity is ubiquitous and plays a critical role in material deformation and damage; it inherently involves the atomistic length scale and picosecond time scale. A fundamental understanding of the elastic-plastic deformation transition, in particular, incipient plasticity, has been a grand challenge in high-pressure and high-strain-rate environments, impeded largely by experimental limitations on spatial and temporal resolution. Here, we report femtosecond MeV electron diffraction measurements visualizing the three-dimensional (3D) response of single-crystal aluminum to the ultrafast laser-induced compression. We capture lattice transitioning from a purely elastic to a plastically relaxed state within 5 ps, after reaching an elastic limit of ~25 GPa. Our results allow the direct determination of dislocation nucleation and transport that constitute the underlying defect kinetics of incipient plasticity. Large-scale molecular dynamics simulations show good agreement with the experiment and provide an atomic-level description of the dislocation-mediated plasticity. Understanding incipient plasticity has been experimentally limited by spatial and temporal resolution. Here the authors report ultra-fast, in situ electron diffraction measurement of dislocation defect dynamics in the early stage of plastic deformation in Al under laser-driven compression.
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Affiliation(s)
- Mianzhen Mo
- SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
| | - Minxue Tang
- School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, Sichuan, 610031, P. R. China
| | - Zhijiang Chen
- SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA
| | - J Ryan Peterson
- SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.,Physics Department, Stanford University, Stanford, CA, 94305, USA
| | - Xiaozhe Shen
- SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA
| | - John Kevin Baldwin
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA
| | - Mungo Frost
- SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA
| | - Mike Kozina
- SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA
| | - Alexander Reid
- SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA
| | - Yongqiang Wang
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.,Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA
| | - Juncheng E
- European XFEL GmbH, 22869, Schenefeld, Germany
| | - Adrien Descamps
- SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.,Aeronautics and Astronautics Department, Stanford University, Stanford, CA, 94305, USA
| | | | - Renkai Li
- SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA
| | - Sheng-Nian Luo
- School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, Sichuan, 610031, P. R. China.
| | - Xijie Wang
- SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
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6
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How Well Do We Know Europa’s Topography? An Evaluation of the Variability in Digital Terrain Models of Europa. REMOTE SENSING 2021. [DOI: 10.3390/rs13245097] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Jupiter’s moon Europa harbors one of the most likely environments for extant extraterrestrial life. Determining whether Europa is truly habitable requires understanding the structure and thickness of its ice shell, including the existence of perched water or brines. Stereo-derived topography from images acquired by NASA Galileo’s Solid State Imager (SSI) of Europa are often used as a constraint on ice shell structure and heat flow, but the uncertainty in such topography has, to date, not been rigorously assessed. To evaluate the current uncertainty in Europa’s topography we generated and compared digital terrain models (DTMs) of Europa from SSI images using both the open-source Ames Stereo Pipeline (ASP) software and the commercial SOCET SET® software. After first describing the criteria for assessing stereo quality in detail, we qualitatively and quantitatively describe both the horizontal resolution and vertical precision of the DTMs. We find that the horizontal resolution of the SOCET SET® DTMs is typically 8–11× the root mean square (RMS) pixel scale of the images, whereas the resolution of the ASP DTMs is 9–13× the maximum pixel scale of the images. We calculate the RMS difference between the ASP and SOCET SET® DTMs as a proxy for the expected vertical precision (EP), which is a function of the matching accuracy and stereo geometry. We consistently find that the matching accuracy is ~0.5 pixels, which is larger than well-established “rules of thumb” that state that the matching accuracy is 0.2–0.3 pixels. The true EP is therefore ~1.7× larger than might otherwise be assumed. In most cases, DTM errors are approximately normally distributed, and errors that are several times the derived EP occur as expected. However, in two DTMs, larger errors (differences) occur and correlate with real topography. These differences primarily result from manual editing of the SOCET SET® DTMs. The product of the DTM error and the resolution is typically 4–8 pixel2 if calculated using the RMS image scale for SOCET SET® DTMs and the maximum images scale for the ASP DTMs, which is consistent with recent work using martian data sets and suggests that the relationship applies more broadly. We evaluate how ASP parameters affect DTM quality and find that using a smaller subpixel refinement kernel results in DTMs with smaller (better) resolution but, in some cases, larger gaps, which are sometimes reduced by increasing the size of the correlation kernel. We conclude that users of ASP should always systematically evaluate the choice of parameters for a given dataset.
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7
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Vandenberghe N, Vermorel R, Villermaux E. Star-shaped crack pattern of broken windows. PHYSICAL REVIEW LETTERS 2013; 110:174302. [PMID: 23679734 DOI: 10.1103/physrevlett.110.174302] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Indexed: 06/02/2023]
Abstract
Broken thin brittle plates like windows and windshields are ubiquitous in our environment. When impacted locally, they typically present a pattern of cracks extending radially outward from the impact point. We study the variation of the pattern of cracks by performing controlled transverse impacts on brittle plates over a broad range of impact speed, plate thickness, and material properties, and we establish from experiments a global scaling law for the number of radial cracks incorporating all these parameters. A model based on Griffith's theory of fracture combining bending elastic energy and fracture energy accounts for our observations. These findings indicate how the postmortem shape of broken samples are related to material properties and impact parameters, a procedure relevant to forensic science, archaeology, or astrophysics.
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8
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He L, Sewell TD, Thompson DL. Molecular dynamics simulations of shock waves in oriented nitromethane single crystals: Plane-specific effects. J Chem Phys 2012; 136:034501. [DOI: 10.1063/1.3676727] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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9
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10
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Greenberg R. Exploration and protection of Europa's biosphere: implications of permeable ice. ASTROBIOLOGY 2011; 11:183-191. [PMID: 21417946 DOI: 10.1089/ast.2011.0608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Europa has become a high-priority objective for exploration because it may harbor life. Strategic planning for its exploration has been predicated on an extreme model in which the expected oceanic biosphere lies under a thick ice crust, buried too deep to be reached in the foreseeable future, which would beg the question of whether other active satellites might be more realistic objectives. However, Europa's ice may in fact be permeable, with very different implications for the possibilities for life and for mission planning. A biosphere may extend up to near the surface, making life far more readily accessible to exploration while at the same time making it vulnerable to contamination. The chances of finding life on Europa are substantially improved while the need for planetary protection becomes essential. The new National Research Council planetary protection study will need to go beyond its current mandate if meaningful standards are to be put in place.
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Affiliation(s)
- Richard Greenberg
- Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85719, USA.
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11
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Kunz C, Murphy C, Singh H, Pontbriand C, Sohn RA, Singh S, Sato T, Roman C, Nakamura KI, Jakuba M, Eustice R, Camilli R, Bailey J. Toward extraplanetary under-ice exploration: Robotic steps in the Arctic. J FIELD ROBOT 2009. [DOI: 10.1002/rob.20288] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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12
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Cammarano F, Lekic V, Manga M, Panning M, Romanowicz B. Long-period seismology on Europa: 1. Physically consistent interior models. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2006je002710] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- F. Cammarano
- Berkeley Seismological Laboratory; University of California, Berkeley; Berkeley California USA
| | - V. Lekic
- Berkeley Seismological Laboratory; University of California, Berkeley; Berkeley California USA
| | - M. Manga
- Department of Earth and Planetary Science; University of California, Berkeley; Berkeley California USA
| | - M. Panning
- Berkeley Seismological Laboratory; University of California, Berkeley; Berkeley California USA
| | - B. Romanowicz
- Berkeley Seismological Laboratory; University of California, Berkeley; Berkeley California USA
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13
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Wahr JM, Zuber MT, Smith DE, Lunine JI. Tides on Europa, and the thickness of Europa's icy shell. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2006je002729] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- J. M. Wahr
- Department of Physics and Cooperative Institute for Research in Environmental Sciences; University of Colorado; Boulder Colorado USA
| | - M. T. Zuber
- Department of Earth, Atmospheric and Planetary Sciences; Massachusetts Institute of Technology; Cambridge Massachusetts USA
| | - D. E. Smith
- Solar System Exploration Division; NASA Goddard Space Flight Center; Greenbelt Maryland USA
| | - J. I. Lunine
- Istituto di Fisica dello Spazio Interplanetario; Rome Italy
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14
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Bringa EM, Rosolankova K, Rudd RE, Remington BA, Wark JS, Duchaineau M, Kalantar DH, Hawreliak J, Belak J. Shock deformation of face-centred-cubic metals on subnanosecond timescales. NATURE MATERIALS 2006; 5:805-9. [PMID: 16980954 DOI: 10.1038/nmat1735] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2006] [Accepted: 08/10/2006] [Indexed: 05/11/2023]
Abstract
Despite its fundamental importance for a broad range of applications, little is understood about the behaviour of metals during the initial phase of shock compression. Here, we present molecular dynamics (MD) simulations of shock-wave propagation through a metal allowing a detailed analysis of the dynamics of high strain-rate plasticity. Previous MD simulations have not seen the evolution of the strain from one- to three-dimensional compression that is observed in diffraction experiments. Our large-scale MD simulations of up to 352 million atoms resolve this important discrepancy through a detailed understanding of dislocation flow at high strain rates. The stress relaxes to an approximately hydrostatic state and the dislocation velocity drops to nearly zero. The dislocation velocity drop leads to a steady state with no further relaxation of the lattice, as revealed by simulated X-ray diffraction.
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Affiliation(s)
- E M Bringa
- Lawrence Livermore National Laboratory, Livermore, California 94551, USA.
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15
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Hand KP, Chyba CF, Carlson RW, Cooper JF. Clathrate hydrates of oxidants in the ice shell of Europa. ASTROBIOLOGY 2006; 6:463-82. [PMID: 16805702 DOI: 10.1089/ast.2006.6.463] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Europa's icy surface is radiolytically modified by high-energy electrons and ions, and photolytically modified by solar ultraviolet photons. Observations from the Galileo Near Infrared Mapping Spectrometer, ground-based telescopes, the International Ultraviolet Explorer, and the Hubble Space Telescope, along with laboratory experiment results, indicate that the production of oxidants, such as H2O2, O2, CO2, and SO2, is a consequence of the surface radiolytic chemistry. Once created, some of the products may be entrained deeper into the ice shell through impact gardening or other resurfacing processes. The temperature and pressure environments of regions within the europan hydrosphere are expected to permit the formation of mixed clathrate compounds. The formation of carbon dioxide and sulfur dioxide clathrates has been examined in some detail. Here we add to this analysis by considering oxidants produced radiolytically on the surface of Europa. Our results indicate that the bulk ice shell could have a approximately 1.7-7.6% by number contamination of oxidants resulting from radiolysis at the surface. Oxidant-hosting clathrates would consequently make up approximately 12-53% of the ice shell by number relative to ice, if oxidants were entrained throughout. We examine, in brief, the consequences of such contamination on bulk ice shell thickness and find that clathrate formation could lead to substantially thinner ice shells on Europa than otherwise expected. Finally, we propose that double occupancy of clathrate cages by O2 molecules could serve as an explanation for the observation of condensed-phase O2 on Europa. Clathrate-sealed, gas-filled bubbles in the near surface ice could also provide an effective trapping mechanism, though they cannot explain the 5771 A (O2)2 absorption.
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Affiliation(s)
- Kevin P Hand
- Department of Geological & Environmental Sciences, Stanford University, Stanford, California 94305, USA.
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16
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Affiliation(s)
- Sarah T. Stewart
- Lindhurst Laboratory of Experimental Geophysics; California Institute of Technology; Pasadena California USA
| | - Thomas J. Ahrens
- Lindhurst Laboratory of Experimental Geophysics; California Institute of Technology; Pasadena California USA
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17
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Zolotov MY. A model for low-temperature biogeochemistry of sulfur, carbon, and iron on Europa. ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2003je002194] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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18
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Sohl F, Hussmann H, Schwentker B, Spohn T, Lorenz RD. Interior structure models and tidal Love numbers of Titan. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/2003je002044] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- F. Sohl
- Institut für Planetologie; Westfälische Wilhelms-Universität; Münster Germany
| | - H. Hussmann
- Institut für Planetologie; Westfälische Wilhelms-Universität; Münster Germany
| | - B. Schwentker
- Institut für Planetologie; Westfälische Wilhelms-Universität; Münster Germany
| | - T. Spohn
- Institut für Planetologie; Westfälische Wilhelms-Universität; Münster Germany
| | - R. D. Lorenz
- Lunar and Planetary Laboratory; University of Arizona; Tucson Arizona USA
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19
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Ice-volcanism due to tidal stress on Europa. CHINESE SCIENCE BULLETIN-CHINESE 2003. [DOI: 10.1007/bf03184185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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20
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Figueredo PH, Greeley R, Neuer S, Irwin L, Schulze-Makuch D. Locating potential biosignatures on Europa from surface geology observations. ASTROBIOLOGY 2003; 3:851-861. [PMID: 14987486 DOI: 10.1089/153110703322736132] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We evaluated the astrobiological potential of the major classes of geologic units on Europa with respect to possible biosignatures preservation on the basis of surface geology observations. These observations are independent of any formational model and therefore provide an objective, though preliminary, evaluation. The assessment criteria include high mobility of material, surface concentration of non-ice components, relative youth, textural roughness, and environmental stability. Our review determined that, as feature classes, low-albedo smooth plains, smooth bands, and chaos hold the highest potential, primarily because of their relative young age, the emplacement of low-viscosity material, and indications of material exchange with the subsurface. Some lineaments and impact craters may be promising sites for closer study despite the comparatively lower astrobiological potential of their classes. This assessment will be expanded by multidisciplinary examination of the potential for habitability of specific features.
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Affiliation(s)
- Patricio H Figueredo
- Department of Geological Sciences, Arizona State University, Tempe, Arizona 85287-1404, USA.
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21
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Schenk PM. Thickness constraints on the icy shells of the galilean satellites from a comparison of crater shapes. Nature 2002; 417:419-21. [PMID: 12024207 DOI: 10.1038/417419a] [Citation(s) in RCA: 188] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A thin outer ice shell on Jupiter's large moon Europa would imply easy exchange between the surface and any organic or biotic material in its putative subsurface ocean. The thickness of the outer ice shell is poorly constrained, however, with model-dependent estimates ranging from a few kilometres to ten or more kilometres. Here I present measurements of depths of impact craters on Europa, Ganymede and Callisto that reveal two anomalous transitions in crater shape with diameter. The first transition is probably related to temperature-dependent ductility of the crust at shallow depths (7 8 km on Europa). The second transition is attributed to the influence of subsurface oceans on all three satellites, which constrains Europa's icy shell to be at least 19 km thick. The icy lithospheres of Ganymede and Callisto are equally ice-rich, but Europa's icy shell has a thermal structure about 0.25 0.5 times the thicknesses of Ganymede's or Callisto's shells, depending on epoch. The appearances of the craters on Europa are inconsistent with thin-ice-shell models and indicate that exchange of oceanic and surface material could be difficult.
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Affiliation(s)
- Paul M Schenk
- Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, USA.
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22
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Schulze-Makuch D, Irwin LN. Energy cycling and hypothetical organisms in Europa's ocean. ASTROBIOLOGY 2002; 2:105-121. [PMID: 12449859 DOI: 10.1089/153110702753621385] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
While Europa has emerged as a leading candidate for harboring extraterrestrial life, the apparent lack of a source of free energy for sustaining living systems has been argued. In this theoretical analysis, we have quantified the amount of energy that could in principle be obtained from chemical cycling, heat, osmotic gradients, kinetic motion, magnetic fields, and gravity in Europa's subsurface ocean. Using reasonable assumptions based on known organisms on Earth, our calculations suggest that chemical oxidation-reduction cycles in Europa's subsurface ocean could support life. Osmotic and thermal gradients, as well as the kinetic energy of convection currents, also represent plausible alternative sources of energy for living systems at Europa. Organisms thriving on these gradients could interact with each other to form the complex energy cycling necessary for establishing a stable ecosystem.
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Affiliation(s)
- Dirk Schulze-Makuch
- Department of Geological Sciences, University of Texas at El Paso, El Paso, TX, USA.
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