D. P. Cruikshank, O. M. Umurhan, R. A. Beyer, B. Schmitt, J. T. Keane, K. D. Runyon, D. Atri, O. L. White, I. Matsuyama, J. M. Moore, W. B. McKinnon, S. A. Sandford, K. N. Singer, W. M. Grundy, C. M. Dalle Ore, J. C. Cook, T. Bertrand, S. A. Stern, C. B. Olkin, H. A. Weaver, L. A. Young, J. R. Spencer, C. M. Lisse, R. P. Binzel, A. M. Earle, S. J. Robbins, G. R. Gladstone, R. J. Cartwright, and K. Ennico. Recent cryovolcanism in Virgil Fossae on Pluto. Icarus, 330:155-168, 2019. [ bib | DOI | ADS link ]
The Virgil Fossae region on Pluto exhibits three spatially coincident properties that are suggestive of recent cryovolcanic activity over an area approximately 300 by 200 km. Situated in the fossae troughs or channels and in the surrounding terrain are exposures of H2O ice in which there is entrained opaque red-colored matter of unknown composition. The H2O ice is also seen to carry spectral signatures at 1.65 and 2.2 μm of NH3 in some form, possibly as a hydrate, an ammoniated salt, or some other compound. Model calculations of NH3 destruction in H2O ice by galactic cosmic rays suggest that the maximum lifetime of NH3 in the uppermost meter of the exposed surface is 109 years, while considerations of Lyman-α ultraviolet and solar wind charged particles suggest shorter timescales by a factor of 10 or 10000. Thus, 109 y is taken as an upper limit to the age of the emplacement event, and it could be substantially younger.
The red colorant in the ammoniated H2O in Virgil Fossae and surroundings may be a macromolecular organic material (tholin) thought to give color to much of Pluto's surface, but probably different in composition and age. Owing to the limited spectral range of the New Horizons imaging spectrometer and the signal precision of the data, apart from the H2O and NH3 signatures there are no direct spectroscopic clues to the chemistry of the strongly colored deposit on Pluto. We suggest that the colored material was a component of the fluid reservoir from which the material now on the surface in this region was erupted. Although other compositions are possible, if it is indeed a complex organic material it may incorporate organics inherited from the solar nebula, further processed in a warm aqueous environment inside Pluto.
A planet-scale stress pattern in Pluto's lithosphere induced by true polar wander, freezing of a putative interior ocean, and surface loading has caused fracturing in a broad arc west of Sputnik Planitia, consistent with the structure of Virgil Fossae and similar extensional features. This faulting may have facilitated the ascent of fluid in subsurface reservoirs to reach the surface as flows and as fountains of cryoclastic materials, consistent with the appearance of colored, ammoniated H2O ice deposits in and around Virgil Fossae. Models of a cryoflow emerging from sources in Virgil Fossae indicate that the lateral extent of the flow can be several km (Umurhan et al., 2019). The deposit over the full length (200 km) of the main trough in the Virgil Fossae complex and extending through the north rim of Elliot crater and varying in elevation over a range of 2.5 km, suggests that it debouched from multiple sources, probably along the length of the strike direction of the normal faults defining the graben. The source or sources of the ammoniated H2O are one or more subsurface reservoirs that may or may not connect to the global ocean postulated for Pluto's interior. Alternatives to cryovolcanism in producing the observed characteristics of the region around Virgil Fossae are explored in the discussion section of the paper.
T. Bertrand, F. Forget, O. M. Umurhan, J. M. Moore, L. A. Young, S. Protopapa, W. M. Grundy, B. Schmitt, R. D. Dhingra, R. P. Binzel, A. M. Earle, D. P. Cruikshank, S. A. Stern, H. A. Weaver, K. Ennico, C. B. Olkin, and New Horizons Science Team. The CH4 cycles on Pluto over seasonal and astronomical timescales. Icarus, 329:148-165, 2019. [ bib | DOI | arXiv | ADS link ]
Pluto's surface is covered in numerous CH4 ice deposits, that vary in texture and brightness, as revealed by the New Horizons spacecraft as it flew by Pluto in July 2015. These observations suggest that CH4 on Pluto has a complex history, involving reservoirs of different composition, thickness and stability controlled by volatile processes occurring on different timescales. In order to interpret these observations, we use a Pluto volatile transport model able to simulate the cycles of N2 and CH4 ices over millions of years. By assuming fixed solid mixing ratios, we explore how changes in surface albedos, emissivities and thermal inertias impact volatile transport. This work is therefore a direct and natural continuation of the work by Bertrand et al. (2018), which only explored the N2 cycles. Results show that bright CH4 deposits can create cold traps for N2 ice outside Sputnik Planitia, leading to a strong coupling between the N2 and CH4 cycles. Depending on the assumed albedo for CH4 ice, the model predicts CH4 ice accumulation (1) at the same equatorial latitudes where the Bladed Terrain Deposits are observed, supporting the idea that these CH4-rich deposits are massive and perennial, or (2) at mid-latitudes (25deg- 70deg), forming a thick mantle which is consistent with New Horizons observations. In our simulations, both CH4 ice reservoirs are not in an equilibrium state and either one can dominate the other over long timescales, depending on the assumptions made for the CH4 albedo. This suggests that long-term volatile transport exists between the observed reservoirs. The model also reproduces the formation of N2 deposits at mid-latitudes and in the equatorial depressions surrounding the Bladed Terrain Deposits, as observed by New Horizons. At the poles, only seasonal CH4 and N2 deposits are obtained in Pluto's current orbital configuration. Finally, we show that Pluto's atmosphere always contained, over the last astronomical cycles, enough gaseous CH4 to absorb most of the incoming Lyman-α flux.
H. Tran, M. Turbet, S. Hanoufa, X. Landsheere, P. Chelin, Q. Ma, and J.-M. Hartmann. The CO2-broadened H2O continuum in the 100-1500 cm-1 region: Measurements, predictions and empirical model. Journal of Quantitative Spectroscopy and Radiative Transfer, 230:75-80, 2019. [ bib | DOI | arXiv | ADS link ]
Transmission spectra of H2O+CO2 mixtures have been recorded, at 296, 325 and 366 K, for various pressures and mixture compositions using two experimental setups. Their analysis enables to retrieve values of the “continuum” absorption by the CO2-broadened H2O line wings between 100 and 1500 cm-1. The results are in good agreement with those, around 1300 cm-1, of the single previous experimental study available. Comparisons are also made with direct predictions based on line-shape correction factors χ calculated, almost thirty years ago, using a quasistatic approach and an input H2Osbnd CO2 intermolecular potential. They show that this model quite nicely predicts, with slightly overestimated values, the continuum over a spectral range where it varies by more than three orders of magnitude. An empirical correction is proposed, based on the experimental data, which should be useful for radiative transfer and climate studies in CO2 rich planetary atmospheres.
E. Meza, B. Sicardy, M. Assafin, J. L. Ortiz, T. Bertrand, E. Lellouch, J. Desmars, F. Forget, D. Bérard, A. Doressoundiram, J. Lecacheux, J. M. Oliveira, F. Roques, T. Widemann, F. Colas, F. Vachier, S. Renner, R. Leiva, F. Braga-Ribas, G. Benedetti-Rossi, J. I. B. Camargo, A. Dias-Oliveira, B. Morgado, A. R. Gomes-Júnior, R. Vieira-Martins, R. Behrend, A. C. Tirado, R. Duffard, N. Morales, P. Santos-Sanz, M. Jelínek, R. Cunniffe, R. Querel, M. Harnisch, R. Jansen, A. Pennell, S. Todd, V. D. Ivanov, C. Opitom, M. Gillon, E. Jehin, J. Manfroid, J. Pollock, D. E. Reichart, J. B. Haislip, K. M. Ivarsen, A. P. LaCluyze, A. Maury, R. Gil-Hutton, V. Dhillon, S. Littlefair, T. Marsh, C. Veillet, K.-L. Bath, W. Beisker, H.-J. Bode, M. Kretlow, D. Herald, D. Gault, S. Kerr, H. Pavlov, O. Faragó, O. Klös, E. Frappa, M. Lavayssière, A. A. Cole, A. B. Giles, J. G. Greenhill, K. M. Hill, M. W. Buie, C. B. Olkin, E. F. Young, L. A. Young, L. H. Wasserman, M. Devogèle, R. G. French, F. B. Bianco, F. Marchis, N. Brosch, S. Kaspi, D. Polishook, I. Manulis, M. Ait Moulay Larbi, Z. Benkhaldoun, A. Daassou, Y. El Azhari, Y. Moulane, J. Broughton, J. Milner, T. Dobosz, G. Bolt, B. Lade, A. Gilmore, P. Kilmartin, W. H. Allen, P. B. Graham, B. Loader, G. McKay, J. Talbot, S. Parker, L. Abe, P. Bendjoya, J.-P. Rivet, D. Vernet, L. Di Fabrizio, V. Lorenzi, A. Magazzú, E. Molinari, K. Gazeas, L. Tzouganatos, A. Carbognani, G. Bonnoli, A. Marchini, G. Leto, R. Z. Sanchez, L. Mancini, B. Kattentidt, M. Dohrmann, K. Guhl, W. Rothe, K. Walzel, G. Wortmann, A. Eberle, D. Hampf, J. Ohlert, G. Krannich, G. Murawsky, B. Gährken, D. Gloistein, S. Alonso, A. Román, J.-E. Communal, F. Jabet, S. deVisscher, J. Sérot, T. Janik, Z. Moravec, P. Machado, A. Selva, C. Perelló, J. Rovira, M. Conti, R. Papini, F. Salvaggio, A. Noschese, V. Tsamis, K. Tigani, P. Barroy, M. Irzyk, D. Neel, J. P. Godard, D. Lanoiselée, P. Sogorb, D. Vérilhac, M. Bretton, F. Signoret, F. Ciabattari, R. Naves, M. Boutet, J. De Queiroz, P. Lindner, K. Lindner, P. Enskonatus, G. Dangl, T. Tordai, H. Eichler, J. Hattenbach, C. Peterson, L. A. Molnar, and R. R. Howell. Lower atmosphere and pressure evolution on Pluto from ground-based stellar occultations, 1988-2016. Astronomy Astrophysics, 625:A42, 2019. [ bib | DOI | arXiv | ADS link ]
Context. The tenuous nitrogen (N2) atmosphere on Pluto undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has recently (July 2015) been observed by the New Horizons spacecraft. <BR /> Aims: The main goals of this study are (i) to construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and (ii) to constrain the structure of the lower atmosphere using a central flash observed in 2015. <BR /> Methods: Eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between altitude levels of 5 and 380 km (i.e. pressures from 10 μbar to 10 nbar). <BR /> Results: (i) Pressure has suffered a monotonic increase from 1988 to 2016, that is compared to a seasonal volatile transport model, from which tight constraints on a combination of albedo and emissivity of N2 ice are derived. (ii) A central flash observed on 2015 June 29 is consistent with New Horizons REX profiles, provided that (a) large diurnal temperature variations (not expected by current models) occur over Sputnik Planitia; and/or (b) hazes with tangential optical depth of 0.3 are present at 4-7 km altitude levels; and/or (c) the nominal REX density values are overestimated by an implausibly large factor of 20%; and/or (d) higher terrains block part of the flash in the Charon facing hemisphere.
A. C. Vandaele, O. Korablev, F. Daerden, S. Aoki, I. R. Thomas, F. Altieri, M. López-Valverde, G. Villanueva, G. Liuzzi, M. D. Smith, J. T. Erwin, L. Trompet, A. A. Fedorova, F. Montmessin, A. Trokhimovskiy, D. A. Belyaev, N. I. Ignatiev, M. Luginin, K. S. Olsen, L. Baggio, J. Alday, J.-L. Bertaux, D. Betsis, D. Bolsée, R. T. Clancy, E. Cloutis, C. Depiesse, B. Funke, M. Garcia-Comas, J.-C. Gérard, M. Giuranna, F. Gonzalez-Galindo, A. V. Grigoriev, Y. S. Ivanov, J. Kaminski, O. Karatekin, F. Lefèvre, S. Lewis, M. López-Puertas, A. Mahieux, I. Maslov, J. Mason, M. J. Mumma, L. Neary, E. Neefs, A. Patrakeev, D. Patsaev, B. Ristic, S. Robert, F. Schmidt, A. Shakun, N. A. Teanby, S. Viscardy, Y. Willame, J. Whiteway, V. Wilquet, M. J. Wolff, G. Bellucci, M. R. Patel, J.-J. López-Moreno, F. Forget, C. F. Wilson, H. Svedhem, J. L. Vago, D. Rodionov, NOMAD Science Team, and ACS Science Team. Martian dust storm impact on atmospheric H2O and D/H observed by ExoMars Trace Gas Orbiter. Nature, 568:521-525, 2019. [ bib | DOI | ADS link ]
Global dust storms on Mars are rare1,2 but can affect the atmospheric dynamics and inflation of the atmosphere3, primarily owing to solar heating of the dust3. In turn, changes in atmospheric dynamics can affect the distribution of atmospheric water vapour, with potential implications for the atmospheric photochemistry and climate on Mars4. Recent observations of the water vapour abundance in the Martian atmosphere during dust storm conditions revealed a high-altitude increase in atmospheric water vapour that was more pronounced at high northern latitudes5,6, as well as a decrease in the water column at low latitudes7,8. Here we present concurrent, high-resolution measurements of dust, water and semiheavy water (HDO) at the onset of a global dust storm, obtained by the NOMAD and ACS instruments onboard the ExoMars Trace Gas Orbiter. We report the vertical distribution of the HDO/H2O ratio (D/H) from the planetary boundary layer up to an altitude of 80 kilometres. Our findings suggest that before the onset of the dust storm, HDO abundances were reduced to levels below detectability at altitudes above 40 kilometres. This decrease in HDO coincided with the presence of water-ice clouds. During the storm, an increase in the abundance of H2O and HDO was observed at altitudes between 40 and 80 kilometres. We propose that these increased abundances may be the result of warmer temperatures during the dust storm causing stronger atmospheric circulation and preventing ice cloud formation, which may confine water vapour to lower altitudes through gravitational fall and subsequent sublimation of ice crystals3. The observed changes in H2O and HDO abundance occurred within a few days during the development of the dust storm, suggesting a fast impact of dust storms on the Martian atmosphere.
O. Korablev, A. C. Vandaele, F. Montmessin, A. A. Fedorova, A. Trokhimovskiy, F. Forget, F. Lefèvre, F. Daerden, I. R. Thomas, L. Trompet, J. T. Erwin, S. Aoki, S. Robert, L. Neary, S. Viscardy, A. V. Grigoriev, N. I. Ignatiev, A. Shakun, A. Patrakeev, D. A. Belyaev, J.-L. Bertaux, K. S. Olsen, L. Baggio, J. Alday, Y. S. Ivanov, B. Ristic, J. Mason, Y. Willame, C. Depiesse, L. Hetey, S. Berkenbosch, R. Clairquin, C. Queirolo, B. Beeckman, E. Neefs, M. R. Patel, G. Bellucci, J.-J. López-Moreno, C. F. Wilson, G. Etiope, L. Zelenyi, H. Svedhem, J. L. Vago, Acs, and NOMAD Science Teams. No detection of methane on Mars from early ExoMars Trace Gas Orbiter observations. Nature, 568:517-520, 2019. [ bib | DOI | ADS link ]
The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today1. A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations2-5. These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere6,7, whichgiven methane's lifetime of several centuriespredicts an even, well mixed distribution of methane1,6,8. Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections2,4. We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater4 would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally.
J. Yang, J. Leconte, E. T. Wolf, T. Merlis, D. D. B. Koll, F. Forget, and D. S. Abbot. Simulations of Water Vapor and Clouds on Rapidly Rotating and Tidally Locked Planets: A 3D Model Intercomparison. Astrophysical Journal, 875:46, 2019. [ bib | DOI | ADS link ]
Robustly modeling the inner edge of the habitable zone is essential for determining the most promising potentially habitable exoplanets for atmospheric characterization. Global climate models (GCMs) have become the standard tool for calculating this boundary, but divergent results have emerged among the various GCMs. In this study, we perform an intercomparison of standard GCMs used in the field on a rapidly rotating planet receiving a G-star spectral energy distribution and on a tidally locked planet receiving an M-star spectral energy distribution. Experiments both with and without clouds are examined. We find relatively small difference (within 8 K) in global-mean surface temperature simulation among the models in the G-star case with clouds. In contrast, the global-mean surface temperature simulation in the M-star case is highly divergent (2030 K). Moreover, even differences in the simulated surface temperature when clouds are turned off are significant. These differences are caused by differences in cloud simulation and/or radiative transfer, as well as complex interactions between atmospheric dynamics and these two processes. For example we find that an increase in atmospheric absorption of shortwave radiation can lead to higher relative humidity at high altitudes globally and, therefore, a significant decrease in planetary radiation emitted to space. This study emphasizes the importance of basing conclusions about planetary climate on simulations from a variety of GCMs and motivates the eventual comparison of GCM results with terrestrial exoplanet observations to improve their performance.
M. Turbet, H. Tran, O. Pirali, F. Forget, C. Boulet, and J.-M. Hartmann. Far infrared measurements of absorptions by CH4 + CO2 and H2 + CO2 mixtures and implications for greenhouse warming on early Mars. Icarus, 321:189-199, 2019. [ bib | DOI | arXiv | ADS link ]
We present an experimental study of the absorption, between 40 and 640 cm-1, by CO2, CH4 and H2 gases as well as by H2 + CO2 and CH4 + CO2 mixtures at room temperature. A Fourier transform spectrometer associated to a multi-pass cell, whose optics were adjusted to obtain a 152 m path length, were used to record transmission spectra at total pressures up to about 0.98 bar. These measurements provide information concerning the collision-induced absorption (CIA) bands as well as about the wing of the CO2 15 μm band. Our results for the CIAs of pure gases are, within uncertainties, in agreement with previous determinations, validating our experimental and data analysis procedures. We then consider the CIAs by H2 + CO2 and CH4 + CO2 and the low frequency wing of the pure CO2 15 μm band, for which there are, to our knowledge, no previous measurements. We confirm experimentally the theoretical prediction of Wordsworth et al. (2017) that the H2 + CO2 and CH4 + CO2 CIAs are significantly stronger in the 50-550 cm-1 region than those of H2 + N2 and CH4 + N2, respectively. However, we find that the shape and the strength of these recorded CIAs differ from the aforementioned predictions. For the pure CO2 line-wings, we show that both the χ-factor deduced from measurements near 4 μm and a line-mixing model very well describe the observed strongly sub-Lorentzian behavior in the 500-600 cm-1 region. These experimental results open renewed perspectives for studies of the past climate of Mars and extrasolar analogues.
T. Encrenaz, T. K. Greathouse, E. Marcq, H. Sagawa, T. Widemann, B. Bézard, T. Fouchet, F. Lefèvre, S. Lebonnois, S. K. Atreya, Y. J. Lee, R. Giles, and S. Watanabe. HDO and SO2 thermal mapping on Venus. IV. Statistical analysis of the SO2 plumes. Astronomy Astrophysics, 623:A70, 2019. [ bib | DOI | ADS link ]
Since January 2012 we have been monitoring the behavior of sulfur dioxide and water on Venus, using the Texas Echelon Cross-Echelle Spectrograph (TEXES) imaging spectrometer at the NASA InfraRed Telescope Facility (IRTF, Mauna Kea Observatory). We present here the observations obtained between January 2016 and September 2018. As in the case of our previous runs, data were recorded around 1345 cm-1 (7.4 μm). The molecules SO2, CO2, and HDO (used as a proxy for H2O) were observed, and the cloudtop of Venus was probed at an altitude of about 64 km. The volume mixing ratio of SO2 was estimated using the SO2/CO2 line depth ratios of weak transitions; the H2O volume mixing ratio was derived from the HDO/CO2 line depth ratio, assuming a D/H ratio of 200 times the Vienna Standard Mean Ocean Water (VSMOW). As reported in our previous analyses, the SO2 mixing ratio shows strong variations with time and also over the disk, showing evidence of the formation of SO2 plumes with a lifetime of a few hours; in contrast, the H2O abundance is remarkably uniform over the disk and shows moderate variations as a function of time. We performed a statistical analysis of the behavior of the SO2 plumes, using all TEXES data between 2012 and 2018. They appear mostly located around the equator. Their distribution as a function of local time seems to show a depletion around noon; we do not have enough data to confirm this feature definitely. The distribution of SO2 plumes as a function of longitude shows no clear feature, apart from a possible depletion around 100E-150E and around 300E-360E. There seems to be a tendency for the H2O volume mixing ratio to decrease after 2016, and for the SO2 mixing ratio to increase after 2014. However, we see no clear anti-correlation between the SO2 and H2O abundances at the cloudtop, neither on the individual maps nor over the long term. Finally, there is a good agreement between the TEXES results and those obtained in the UV range (SPICAV/Venus Express and UVI/Akatsuki) at a slightly higher altitude. This agreement shows that SO2 observations obtained in the thermal infrared can be used to extend the local time coverage of the SO2 measurements obtained in the UV range.
Y. Nishikawa, P. Lognonné, T. Kawamura, A. Spiga, E. Stutzmann, M. Schimmel, T. Bertrand, F. Forget, and K. Kurita. Mars' Background Free Oscillations. Space Science Reviews, 215:13, 2019. [ bib | DOI | ADS link ]
Observations and inversion of the eigenfrequencies of free oscillations constitute powerful tools to investigate the internal structure of a planet. On Mars, such free oscillations can be excited by atmospheric pressure and wind stresses from the Martian atmosphere, analogous to what occurs on Earth. Over long periods and on a global scale, this phenomenon may continuously excite Mars' background free oscillations (MBFs), which constitute the so-called Martian hum. However, the source exciting MBFs is related both to the global-scale atmospheric circulation on Mars and to the variations in pressure and wind at the planetary boundary layer, for which no data are available.
To overcome this drawback, we focus herein on a global-scale source and use results of simulations based on General Circular Models (GCMs). GCMs can predict and reproduce long-term, global-scale Martian pressure and wind variations and suggest that, contrary to what happens on Earth, daily correlations in the Martian hum might be generated by the solar-driven GCM. After recalling the excitation terms, we calculate MBFs by using GCM computations and estimate the contribution to the hum made by the global atmospheric circulation. Although we work at the lower limit of MBF signals, the results indicate that the signal is likely to be periodic, which would allow us to use more efficient stacking theories than can be applied to Earth's hum. We conclude by discussing the perspectives for the InSight SEIS instrument to detect the Martian hum. The amplitude of the MBF signal is on the order of nanogals and is therefore hidden by instrumental and thermal noise, which implies that, provided the predicted daily coherence in hum excitation is present, the InSight SEIS seismometer should be capable of
F. Ferri, Ö. Karatekin, S. R. Lewis, F. Forget, A. Aboudan, G. Colombatti, C. Bettanini, S. Debei, B. Van Hove, V. Dehant, A.-M. Harri, M. Leese, T. Mäkinen, E. Millour, I. Muller-Wodarg, G. G. Ori, A. Pacifici, S. Paris, M. Patel, M. Schoenenberger, J. Herath, T. Siili, A. Spiga, T. Tokano, M. Towner, P. Withers, S. Asmar, and D. Plettemeier. ExoMars Atmospheric Mars Entry and Landing Investigations and Analysis (AMELIA). Space Science Reviews, 215:8, 2019. [ bib | DOI | ADS link ]
The entry, descent and landing of Schiaparelli, the ExoMars Entry, descent and landing Demonstrator Module (EDM), offered a rare (once-per-mission) opportunity for in situ investigations of the martian environment over a wide altitude range. The aim of the ExoMars AMELIA experiment was to exploit the Entry, Descent and Landing System (EDLS) engineering measurements for scientific investigations of Mars' atmosphere and surface. Here we present the simulations, modelling and the planned investigations prior to the Entry, Descent and Landing (EDL) event that took place on 19th October 2016. Despite the unfortunate conclusion of the Schiaparelli mission, flight data recorded during the entry and the descent until the loss of signal, have been recovered. These flight data, although limited and affected by transmission interruptions and malfunctions, are essential for investigating the anomaly and validating the EDL operation, but can also contribute towards the partial achievement of AMELIA science objectives.
O. L. White, J. M. Moore, A. D. Howard, W. B. McKinnon, J. T. Keane, K. N. Singer, T. Bertrand, S. J. Robbins, P. M. Schenk, B. Schmitt, B. J. Buratti, S. A. Stern, K. Ennico, C. B. Olkin, H. A. Weaver, L. A. Young, G. New Horizons Geology, and Imaging Theme Team. Washboard and fluted terrains on Pluto as evidence for ancient glaciation. Nature Astronomy, 3:62-68, 2019. [ bib | DOI | ADS link ]
Distinctive landscapes termed `washboard' and `fluted' terrains1,2, which border the N2 ice plains of Sputnik Planitia along its northwest margin, are among the most enigmatic landforms yet seen on Pluto. These terrains consist of parallel to sub-parallel ridges that display a remarkably consistent east-northeast-west-southwest orientationa configuration that does not readily point to a simple analogous terrestrial or planetary process or landform. Here, we report on mapping and analysis of their morphometry and distribution as a means to determine their origin. Based on their occurrence in generally low-elevation, low-relief settings adjacent to Sputnik Planitia that coincide with a major tectonic system, and through comparison with fields of sublimation pits seen in southern Sputnik Planitia, we conclude that washboard and fluted terrains represent crustal debris that were buoyant in pitted glacial N2 ice that formerly covered this area, and which were deposited after the N2 ice receded via sublimation. Crater surface age estimates indicate that this N2 ice glaciation formed and disappeared early in Pluto's history, soon after formation of the Sputnik Planitia basin. These terrains constitute an entirely new category of glacial landform.
I. Ordonez-Etxeberria, R. Hueso, A. Sánchez-Lavega, E. Millour, and F. Forget. Meteorological pressure at Gale crater from a comparison of REMS/MSL data and MCD modelling: Effect of dust storms. Icarus, 317:591-609, 2019. [ bib | DOI | ADS link ]
We examine the record of atmospheric pressure in Gale crater measured in-situ by the Rover Environmental Monitoring Station (REMS) instrument (Gómez-Elvira et al., 2012) on the Mars Science Laboratory (MSL) rover over two Martian years. We compare the data with pressure predictions from the Mars Climate Database (MCD) (Forget et al., 1999; Millour et al., 2015) version 5.2, which is a climatological database derived from numerical simulations of the Martian atmosphere produced by a General Circulation Model run over several Martian years. Seasonal and daily trends in pressure data from REMS are well reproduced by the standard climatology of the MCD using its high resolution mode. This high-resolution mode extrapolates pressure values from the nominal model into the altitude of each location using a high-resolution topography model and a fine tuning of the vertical scale height that was chosen to mimic effects of slope winds not directly accounted for in the General Circulation Model on which the MCD is based. Differences between the synthetic MCD pressure data and the REMS measurements are produced by meteorological features that are identified on particular groups of sols and quantified in intensity. We show that regional dust storms outside Gale crater and dust abundance at the crater are important factors in the behaviour of the pressure exciting larger amplitudes on the daily pressure variations and causing most of the largest REMS-MCD differences. We compare the pressure signals with published data of the dust optical depth obtained by the REMS ultraviolet photodiodes and the Mastcam instrument on MSL, and with orbital images of the planet acquired by the MARCI instrument on the Mars Reconnaissance Orbiter (MRO). We show that in some cases regional dust storms induce a characteristic signature in the surface pressure measured by REMS several sols before the dust arrives to Gale crater. We explore the capability of daily pressure measurements to serve as a fast detector of the development of dust storms in the context of the MSL, Insight and Mars 2020 missions.
W. Pluriel, E. Marcq, and M. Turbet. Modeling the albedo of Earth-like magma ocean planets with H2O-CO2 atmospheres. Icarus, 317:583-590, 2019. [ bib | DOI | arXiv | ADS link ]
During accretion, the young rocky planets are so hot that they become endowed with a magma ocean. From that moment, the mantle convective thermal flux control the cooling of the planet and an atmosphere is created by outgassing. This atmosphere will then play a key role during this cooling phase. Studying this cooling phase in details is a necessary step to explain the great diversity of the observed telluric planets and especially to assess the presence of surface liquid water. We used here a radiative-convective 1D atmospheric model (H2O, CO2) to study the impact of the Bond albedo on the evolution of magma ocean planets. We derived from this model the thermal emission spectrum and the spectral reflectance of these planets, from which we calculated their Bond albedos. Compared to Marcq et al. (2017), the model now includes a new module to compute the Rayleigh scattering, and state of the art CO2 and H2O gaseous opacities data in the visible and infrared spectral ranges. We show that the Bond albedo of these planets depends on their surface temperature and results from a competition between Rayleigh scattering from the gases and Mie scattering from the clouds. The colder the surface temperature is, the thicker the clouds are, and the higher the Bond albedo is. We also evidence that the relative abundances of CO2 and H2O in the atmosphere strongly impact the Bond albedo. The Bond albedo is higher for atmospheres dominated by the CO2, better Rayleigh scatterer than H2O. Finally, we provide the community with an empirical formula for the Bond albedo that could be useful for future studies of magma ocean planets.