1
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Murdoch N, Stott AE, Gillier M, Hueso R, Lemmon M, Martinez G, Apéstigue V, Toledo D, Lorenz RD, Chide B, Munguira A, Sánchez-Lavega A, Vicente-Retortillo A, Newman CE, Maurice S, de la Torre Juárez M, Bertrand T, Banfield D, Navarro S, Marin M, Torres J, Gomez-Elvira J, Jacob X, Cadu A, Sournac A, Rodriguez-Manfredi JA, Wiens RC, Mimoun D. The sound of a Martian dust devil. Nat Commun 2022; 13:7505. [PMID: 36513637 PMCID: PMC9747922 DOI: 10.1038/s41467-022-35100-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Accepted: 11/18/2022] [Indexed: 12/15/2022] Open
Abstract
Dust devils (convective vortices loaded with dust) are common at the surface of Mars, particularly at Jezero crater, the landing site of the Perseverance rover. They are indicators of atmospheric turbulence and are an important lifting mechanism for the Martian dust cycle. Improving our understanding of dust lifting and atmospheric transport is key for accurate simulation of the dust cycle and for the prediction of dust storms, in addition to being important for future space exploration as grain impacts are implicated in the degradation of hardware on the surface of Mars. Here we describe the sound of a Martian dust devil as recorded by the SuperCam instrument on the Perseverance rover. The dust devil encounter was also simultaneously imaged by the Perseverance rover's Navigation Camera and observed by several sensors in the Mars Environmental Dynamics Analyzer instrument. Combining these unique multi-sensorial data with modelling, we show that the dust devil was around 25 m large, at least 118 m tall, and passed directly over the rover travelling at approximately 5 m s-1. Acoustic signals of grain impacts recorded during the vortex encounter provide quantitative information about the number density of particles in the vortex. The sound of a Martian dust devil was inaccessible until SuperCam microphone recordings. This chance dust devil encounter demonstrates the potential of acoustic data for resolving the rapid wind structure of the Martian atmosphere and for directly quantifying wind-blown grain fluxes on Mars.
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Affiliation(s)
- N. Murdoch
- grid.508721.9Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | - A. E. Stott
- grid.508721.9Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | - M. Gillier
- grid.508721.9Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | - R. Hueso
- grid.11480.3c0000000121671098Física Aplicada, Escuela de Ingeniería de Bilbao, Universidad del País Vasco (UPV/EHU), Bilbao, Spain
| | - M. Lemmon
- grid.296797.40000 0004 6023 5450Space Science Institute, Boulder, CO 80301 USA
| | - G. Martinez
- grid.410493.b0000 0000 8634 1877Lunar and Planetary Institute, Universities Space Research Association, Houston, TX USA ,grid.214458.e0000000086837370Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI USA
| | - V. Apéstigue
- grid.15312.340000 0004 1794 1528Instituto Nacional de Técnica Aeroespacial, Madrid, Spain
| | - D. Toledo
- grid.15312.340000 0004 1794 1528Instituto Nacional de Técnica Aeroespacial, Madrid, Spain
| | - R. D. Lorenz
- grid.474430.00000 0004 0630 1170Space Exploration Sector, Johns Hopkins Applied Physics Laboratory, Laurel, MD USA
| | - B. Chide
- grid.148313.c0000 0004 0428 3079Space and Planetary Exploration Team, Los Alamos National Laboratory, Los Alamos, NM USA
| | - A. Munguira
- grid.11480.3c0000000121671098Física Aplicada, Escuela de Ingeniería de Bilbao, Universidad del País Vasco (UPV/EHU), Bilbao, Spain
| | - A. Sánchez-Lavega
- grid.11480.3c0000000121671098Física Aplicada, Escuela de Ingeniería de Bilbao, Universidad del País Vasco (UPV/EHU), Bilbao, Spain
| | | | | | - S. Maurice
- grid.15781.3a0000 0001 0723 035XInstitut de Recherche en Astrophysique et Planétologie, Université de Toulouse 3 Paul Sabatier, CNRS, CNES, Toulouse, France
| | - M. de la Torre Juárez
- grid.20861.3d0000000107068890Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA USA
| | - T. Bertrand
- grid.482824.00000 0004 0370 8434Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique (LESIA), Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
| | - D. Banfield
- grid.5386.8000000041936877XCornell University, Ithaca, NY USA ,grid.419075.e0000 0001 1955 7990NASA AMES Research Center, Moffett Field, CA USA
| | - S. Navarro
- grid.462011.00000 0001 2199 0769Centro de Astrobiología (INTA-CSIC), Madrid, Spain
| | - M. Marin
- grid.462011.00000 0001 2199 0769Centro de Astrobiología (INTA-CSIC), Madrid, Spain
| | - J. Torres
- grid.462011.00000 0001 2199 0769Centro de Astrobiología (INTA-CSIC), Madrid, Spain
| | - J. Gomez-Elvira
- grid.15312.340000 0004 1794 1528Instituto Nacional de Técnica Aeroespacial, Madrid, Spain
| | - X. Jacob
- grid.15781.3a0000 0001 0723 035XInstitut de Mécanique des Fluides, Université de Toulouse III Paul Sabatier, INP, CNRS, Toulouse, France
| | - A. Cadu
- grid.508721.9Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | - A. Sournac
- grid.508721.9Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | | | - R. C. Wiens
- grid.169077.e0000 0004 1937 2197Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN USA
| | - D. Mimoun
- grid.508721.9Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
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2
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Viúdez‐Moreiras D, de la Torre M, Gómez‐Elvira J, Lorenz RD, Apéstigue V, Guzewich S, Mischna M, Sullivan R, Herkenhoff K, Toledo D, Lemmon M, Smith M, Newman CE, Sánchez‐Lavega A, Rodríguez‐Manfredi JA, Richardson M, Hueso R, Harri AM, Tamppari L, Arruego I, Bell J. Winds at the Mars 2020 Landing Site. 2. Wind Variability and Turbulence. J Geophys Res Planets 2022; 127:e2022JE007523. [PMID: 37033152 PMCID: PMC10078282 DOI: 10.1029/2022je007523] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/06/2022] [Revised: 11/18/2022] [Accepted: 11/29/2022] [Indexed: 06/19/2023]
Abstract
Wind speeds measured by the Mars 2020 Perseverance rover in Jezero crater were fitted as a Weibull distribution. InSight wind data acquired in Elysium Planitia were also used to contextualize observations. Jezero winds were found to be much calmer on average than in previous landing sites, despite the intense aeolian activity observed. However, a great influence of turbulence and wave activity was observed in the wind speed variations, thus driving the probability of reaching the highest wind speeds at Jezero, instead of sustained winds driven by local, regional, or large-scale circulation. The power spectral density of wind speed fluctuations follows a power-law, whose slope deviates depending on the time of day from that predicted considering homogeneous and isotropic turbulence. Daytime wave activity is related to convection cells and smaller eddies in the boundary layer, advected over the crater. The signature of convection cells was also found during dust storm conditions, when prevailing winds were consistent with a tidal drive. Nighttime fluctuations were also intense, suggesting strong mechanical turbulence. Convective vortices were usually involved in rapid wind fluctuations and extreme winds, with variations peaking at 9.2 times the background winds. Transient high wind events by vortex-passages, turbulence, and wave activity could be driving aeolian activity at Jezero. We report the detection of a strong dust cloud of 0.75-1.5 km in length passing over the rover. The observed aeolian activity had major implications for instrumentation, with the wind sensor suffering damage throughout the mission, probably due to flying debris advected by winds.
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Affiliation(s)
- D. Viúdez‐Moreiras
- Centro de Astrobiología (CAB, CSIC‐INTA) and National Institute for Aerospace Technology (INTA)MadridSpain
| | - M. de la Torre
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | - J. Gómez‐Elvira
- National Institute for Aerospace Technology (INTA)MadridSpain
| | | | - V. Apéstigue
- National Institute for Aerospace Technology (INTA)MadridSpain
| | - S. Guzewich
- NASA Goddard Spaceflight CenterGreenbeltMDUSA
| | - M. Mischna
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | | | | | - D. Toledo
- National Institute for Aerospace Technology (INTA)MadridSpain
| | - M. Lemmon
- Space Science InstituteCollege StationTXUSA
| | - M. Smith
- NASA Goddard Spaceflight CenterGreenbeltMDUSA
| | | | | | - J. A. Rodríguez‐Manfredi
- Centro de Astrobiología (CAB, CSIC‐INTA) and National Institute for Aerospace Technology (INTA)MadridSpain
| | | | - R. Hueso
- Universidad del País Vasco (UPV/EHU)BilbaoSpain
| | - A. M. Harri
- Finnish Meteorological InstituteHelsinkiFinland
| | - L. Tamppari
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | - I. Arruego
- National Institute for Aerospace Technology (INTA)MadridSpain
| | - J. Bell
- School of Earth and Space ExplorationArizona State UniversityTempeAZUSA
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3
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Lemmon MT, Lorenz RD, Rabinovitch J, Newman CE, Williams NR, Sullivan R, Golombek MP, Bell JF, Maki JN, Vicente‐Retortillo A. Lifting and Transport of Martian Dust by the Ingenuity Helicopter Rotor Downwash as Observed by High-Speed Imaging From the Perseverance Rover. J Geophys Res Planets 2022; 127:e2022JE007605. [PMID: 37033154 PMCID: PMC10078181 DOI: 10.1029/2022je007605] [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: 09/30/2022] [Revised: 11/19/2022] [Accepted: 11/29/2022] [Indexed: 06/19/2023]
Abstract
Martian atmospheric dust is a major driver of weather, with feedback between atmospheric dust distribution, circulation changes from radiative heating and cooling driven by this dust, and winds that mobilize surface dust and distribute it in the atmosphere. Wind-driven mobilization of surface dust is a poorly understood process due to significant uncertainty about minimum wind stress and whether the saltation of sand particles is required. This study utilizes video of six Ingenuity helicopter flights to measure dust lifting during helicopter ascents, traverses, and descents. Dust mobilization persisted on takeoff until the helicopter exceeded 3 m altitude, with dust advecting at 4-6 m/s. During landing, dust mobilization initiated at 2.3-3.6 m altitude. Extensive dust mobilization occurred during traverses at 5.1-5.7 m altitude. Dust mobilization threshold friction velocity of rotor-induced winds during landing is modeled at 0.4-0.6 m/s (factor of two uncertainty in this estimate), with higher winds required when the helicopter was over undisturbed terrain. Modeling dust mobilization from >5 m cruising altitude indicates mobilization by 0.3 m/s winds, suggesting nonsaltation mechanisms such as mobilization and destruction of dust aggregates. No dependence on background winds was seen for the initiation of dust lifting but one case of takeoff in 7 m/s winds created a track of darkened terrain downwind of the helicopter, which may have been a saltation cluster. When the helicopter was cruising at 5-6 m altitude, recirculation was seen in the dust clouds.
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Affiliation(s)
| | | | | | | | - N. R. Williams
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | | | - M. P. Golombek
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | | | - J. N. Maki
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
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4
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Turtle EP, Perry JE, Hayes AG, Lorenz RD, Barnes JW, McEwen AS, West RA, Del Genio AD, Barbara JM, Lunine JI, Schaller EL, Ray TL, Lopes RMC, Stofan ER. Rapid and Extensive Surface Changes Near Titan’s Equator: Evidence of April Showers. Science 2011; 331:1414-7. [DOI: 10.1126/science.1201063] [Citation(s) in RCA: 167] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- E. P. Turtle
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
| | - J. E. Perry
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
| | - A. G. Hayes
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
| | - R. D. Lorenz
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
| | - J. W. Barnes
- Department of Physics, University of Idaho, Moscow, ID 83844, USA
| | - A. S. McEwen
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
| | - R. A. West
- Jet Propulsion Laboratory, Pasadena, CA 91109, USA
| | - A. D. Del Genio
- NASA Goddard Institute for Space Studies, New York, NY 10025, USA
| | - J. M. Barbara
- NASA Goddard Institute for Space Studies, New York, NY 10025, USA
| | - J. I. Lunine
- Dipartimento di Fisica, Università degli Studi di Roma “Tor Vergata,” 00133 Rome, Italy
| | - E. L. Schaller
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
| | - T. L. Ray
- Jet Propulsion Laboratory, Pasadena, CA 91109, USA
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5
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Stofan ER, Elachi C, Lunine JI, Lorenz RD, Stiles B, Mitchell KL, Ostro S, Soderblom L, Wood C, Zebker H, Wall S, Janssen M, Kirk R, Lopes R, Paganelli F, Radebaugh J, Wye L, Anderson Y, Allison M, Boehmer R, Callahan P, Encrenaz P, Flamini E, Francescetti G, Gim Y, Hamilton G, Hensley S, Johnson WTK, Kelleher K, Muhleman D, Paillou P, Picardi G, Posa F, Roth L, Seu R, Shaffer S, Vetrella S, West R. The lakes of Titan. Nature 2007; 445:61-4. [PMID: 17203056 DOI: 10.1038/nature05438] [Citation(s) in RCA: 440] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2006] [Accepted: 11/09/2006] [Indexed: 11/09/2022]
Abstract
The surface of Saturn's haze-shrouded moon Titan has long been proposed to have oceans or lakes, on the basis of the stability of liquid methane at the surface. Initial visible and radar imaging failed to find any evidence of an ocean, although abundant evidence was found that flowing liquids have existed on the surface. Here we provide definitive evidence for the presence of lakes on the surface of Titan, obtained during the Cassini Radar flyby of Titan on 22 July 2006 (T16). The radar imaging polewards of 70 degrees north shows more than 75 circular to irregular radar-dark patches, in a region where liquid methane and ethane are expected to be abundant and stable on the surface. The radar-dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes, including associated channels and location in topographic depressions. Some of the lakes do not completely fill the depressions in which they lie, and apparently dry depressions are present. We interpret this to indicate that lakes are present in a number of states, including partly dry and liquid-filled. These northern-hemisphere lakes constitute the strongest evidence yet that a condensable-liquid hydrological cycle is active in Titan's surface and atmosphere, in which the lakes are filled through rainfall and/or intersection with the subsurface 'liquid methane' table.
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Affiliation(s)
- E R Stofan
- Proxemy Research, Rectortown, Virginia 20140, USA.
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6
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Lorenz RD, Wall S, Radebaugh J, Boubin G, Reffet E, Janssen M, Stofan E, Lopes R, Kirk R, Elachi C, Lunine J, Mitchell K, Paganelli F, Soderblom L, Wood C, Wye L, Zebker H, Anderson Y, Ostro S, Allison M, Boehmer R, Callahan P, Encrenaz P, Ori GG, Francescetti G, Gim Y, Hamilton G, Hensley S, Johnson W, Kelleher K, Muhleman D, Picardi G, Posa F, Roth L, Seu R, Shaffer S, Stiles B, Vetrella S, Flamini E, West R. The Sand Seas of Titan: Cassini RADAR Observations of Longitudinal Dunes. Science 2006; 312:724-7. [PMID: 16675695 DOI: 10.1126/science.1123257] [Citation(s) in RCA: 304] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show approximately 100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of approximately 0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.
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Affiliation(s)
- R D Lorenz
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.
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7
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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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8
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Lorenz RD, Lunine JI, McKay CP. Geologic settings for aqueous organic synthesis on Titan revisited. Enantiomer 2001; 6:83-96. [PMID: 11570428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Abstract
The photochemistry in Titan's cold reducing atmosphere is an evolutionary dead end. However, the hydrocarbons and nitriles deposited from the atmosphere can undergo aqueous synthesis into prebiotic molecules in ephemeral settings such as impact melt sheets. We re-examine the longevity of aqueous solutions on Titan, noting that recent measurements of the thermal conductivity of ammonia-rich ices suggest that the melt pockets may be longer-lived than previously thought. We propose an important role in surface organic reactions for ultraviolet sunlight transported to the surface as chemical energy stored in acetylene and released by polymerization at Titan's surface.
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Affiliation(s)
- R D Lorenz
- Lunar and Planetary Lab, University of Arizona, Tucson 85721-0092, USA
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9
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Abstract
When the Voyager 1 spacecraft returned images in 1980, the dense atmosphere of Saturn's moon Titan was assumed to be bland and featureless. As Lorenz discusses in his Perspective, recent ground-based spectroscopy, and images from the Hubble Space Telescope, are changing this perception. Observations such as the short-lived clouds in Titan's atmosphere reported by Griffith et al. suggest that although average precipitation is likely to be low, individual precipitation events may be heavy enough to cause deep valleys on Titan's surface.
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Affiliation(s)
- R D Lorenz
- Lunar and Planetary Laboratory, University of Arizona, Tucson, 85721, USA.
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10
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Abstract
We develop a semiempirical grey radiative model to quantify Titan's surface temperature as a function of pressure and composition of a nitrogen-methane-hydrogen atmosphere, solar flux and atmospheric haze. We then use this model, together with non-ideal gas-liquid equilibrium theory to investigate the behavior of the coupled surface-atmosphere system on Titan. We find that a volatile-rich Titan is unstable with respect to a runaway greenhouse-small increases in solar luminosity from the present value can lead to massive increases in surface temperature. If methane has been photolyzed throughout Titan's history, then this runaway can only be avoided if the photolytic ethane is removed from the surface-atmosphere system.
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Affiliation(s)
- R D Lorenz
- Lunar and Planetary Laboratory, University of Arizona, Tucson 85721-0092, USA.
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11
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Abstract
We analyze recently published nitrogen and hydrogen isotopic data to constrain the initial volatile abundances on Saturn's giant moon Titan. The nitrogen data are interpreted in terms of a model of non-thermal escape processes that lead to enhancement in the heavier isotope. We show that these data do not, in fact, strongly constrain the abundance of nitrogen present in Titan's early atmosphere, and that a wide range of initial atmospheric masses (all larger than the present value) can yield the measured enhancement. The enrichment in deuterated methane is now much better determined than it was when Pinto et al. (1986. Nature 319, 388-390) first proposed a photochemical mechanism to preferentially retain the deuterium. We develop a simple linear theory to provide a more reliable estimate of the relative dissociation rates of normal and deuterated methane. We utilize the improved data and models to compute initial methane reservoirs consistent with the observed enhancement. The result of this analysis agrees with an independent estimate for the initial methane abundance based solely on the present-day rate of photolysis and an assumption of steady state. This consistency in reservoir size is necessary but not sufficient to infer that methane photolysis has proceeded steadily over the age of the solar system to produce large quantities of less volatile organics. Our analysis indicates an epoch of early atmospheric escape of nitrogen, followed by a later addition of methane by outgassing from the interior. The results also suggest that Titan's volatile inventory came in part or largely from a circum-Saturnian disk of material more reducing than the surrounding solar nebula. Many of the ambiguities inherent in the present analysis can be resolved through Cassini-Huygens data and a program of laboratory studies on isotopic and molecular exchange processes. The value of, and interest in, the Cassini-Huygens data can be greatly enhanced if such a program were undertaken prior to the prime phase of the mission.
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Affiliation(s)
- J I Lunine
- Reparto di Planetologia, CNR-Istituto di Astrofisica Spaziale, Rome, Italy.
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12
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Abstract
We explore the response of Titan's surface and massive atmosphere to the change in solar spectrum and intensity as the sun evolves into a red giant. Titan's surface temperature is insensitive to insolation increases as the haze-laden atmosphere "puffs up" and blocks more sunlight. However, we find a window of several hundred Myr exists, roughly 6 Gyr from now, when liquid water-ammonia can form oceans on the surface and react with the abundant organic compounds there. The window opens due to a drop in haze production as the ultraviolet flux from the reddening sun plummets. The duration of such a window exceeds the time necessary for life to have begun on Earth. Similar environments, with approximately 200K water-ammonia oceans warmed by methane greenhouses under red stars, are an alternative to the approximately 30OK water-CO2 environments considered the classic "habitable" planet.
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Affiliation(s)
- R D Lorenz
- Department of Planetary Sciences, University of Arizona, Tucson 85721-0092, USA.
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13
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Abstract
Saturn's giant moon Titan has a thick (1.5 bar) nitrogen atmosphere, which has a temperature structure that is controlled by the absorption of solar and thermal radiation by methane, hydrogen, and organic aerosols into which methane is irreversibly converted by photolysis. Previous studies of Titan's climate evolution have been done with the assumption that the methane abundance was maintained against photolytic depletion throughout Titan's history, either by continuous supply from the interior or by buffering by a surface or near surface reservoir. Radiative-convective and radiative-saturated equilibrium models of Titan's atmosphere show that methane depletion may have allowed Titan's atmosphere to cool so that nitrogen, its main constituent, condenses onto the surface, collapsing Titan into a Triton-like frozen state with a thin atmosphere.
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Affiliation(s)
- R D Lorenz
- Department of Planetary Sciences, Lunar and Planetary Laboratory, University of Arizona, Tucson 85721,
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14
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Abstract
We compute the input of meteoric materials expected on Titan, and integrate this dust model with an ablation model and a comprehensive chemical model, investigating the effects on the atmosphere and surface. We find that a water deposition of approximately 10-100 times the expected interplanetary dust flux, or a recent large impact, is required to produce the observed CO2 abundance. Ionisation due to meteoric activity is not likely to be higher than that due to other sources.
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Affiliation(s)
- M A English
- Unit for Space Sciences, University of Kent at Canterbury, UK
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15
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Abstract
Some of the aspects of methane precipitation on Titan are considered. In particular, descent velocities are computed. It is found that raindrops fall much slower than on Earth. Additionally, the maximum size of raindrops on Titan is over 9 mm, compared with under 6 mm on Earth. The composition of drops will vary with altitude. Implications of these properties for Titan and the Huygens mission are considered.
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Affiliation(s)
- R D Lorenz
- Unit for Space Sciences, University of Kent, Canterbury, UK
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16
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Lorenz RD, Lunine JI, Grier JA, Fisher MA. Prediction of aeolian features on planets: Application to Titan paleoclimatology. ACTA ACUST UNITED AC 1995. [DOI: 10.1029/95je02708] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.9] [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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