Space Science Reviews, 08 February 2021, https://doi.org/10.1007/s11214-020-00788-2
C. E. Newman, M. de la Torre Juárez, J. Pla-García, R. J. Wilson, S. R. Lewis, L. Neary, M. A. Kahre, F. Forget, A. Spiga, M. I. Richardson, F. Daerden, T. Bertrand, D. Viúdez-Moreiras, R. Sullivan, A. Sánchez-Lavega, B. Chide & J. A. Rodriguez-Manfredi
Nine simulations are used to predict the meteorology and aeolian activity of the Mars 2020 landing site region. Predicted seasonal variations of pressure and surface and atmospheric temperature generally agree. Minimum and maximum pressure is predicted at Ls∼145∘ and 250∘, respectively. Maximum and minimum surface and atmospheric temperature are predicted at Ls∼180∘ and 270∘, respectively; i.e., are warmest at northern fall equinox not summer solstice. Daily pressure cycles vary more between simulations, possibly due to differences in atmospheric dust distributions. Jezero crater sits inside and close to the NW rim of the huge Isidis basin, whose daytime upslope (∼east-southeasterly) and nighttime downslope (∼northwesterly) winds are predicted to dominate except around summer solstice, when the global circulation produces more southerly wind directions. Wind predictions vary hugely, with annual maximum speeds varying from 11 to 19 ms−1 and daily mean wind speeds peaking in the first half of summer for most simulations but in the second half of the year for two. Most simulations predict net annual sand transport toward the WNW, which is generally consistent with aeolian observations, and peak sand fluxes in the first half of summer, with the weakest fluxes around winter solstice due to opposition between the global circulation and daytime upslope winds. However, one simulation predicts transport toward the NW, while another predicts fluxes peaking later and transport toward the WSW. Vortex activity is predicted to peak in summer and dip around winter solstice, and to be greater than at InSight and much greater than in Gale crater.
Science Advances 10 Feb 2021, https://doi.org/10.1126/sciadv.abc8843
View ORCID ProfileGeronimo L. Villanueva, View ORCID ProfileGiuliano Liuzzi, View ORCID ProfileMatteo M. J. Crismani, View ORCID ProfileShohei Aoki, View ORCID ProfileAnn Carine Vandaele, View ORCID ProfileFrank Daerden, View ORCID ProfileMichael D. Smith, Michael J. Mumma, View ORCID ProfileElise W. Knutsen, View ORCID ProfileLori Neary, View ORCID ProfileSebastien Viscardy, View ORCID ProfileIan R. Thomas, View ORCID ProfileMiguel Angel Lopez-Valverde, View ORCID ProfileBojan Ristic, View ORCID ProfileManish R. Patel, View ORCID ProfileJames A. Holmes, View ORCID ProfileGiancarlo Bellucci, View ORCID ProfileJose Juan Lopez-Moreno, and the NOMAD team
Isotopic ratios and, in particular, the water D/H ratio are powerful tracers of the evolution and transport of water on Mars. From measurements performed with ExoMars/NOMAD, we observe marked and rapid variability of the D/H along altitude on Mars and across the whole planet. The observations (from April 2018 to April 2019) sample a broad range of events on Mars, including a global dust storm, the evolution of water released from the southern polar cap during southern summer, the equinox phases, and a short but intense regional dust storm. In three instances, we observe water at very high altitudes (>80 km), the prime region where water is photodissociated and starts its escape to space. Rayleigh distillation appears the be the driving force affecting the D/H in many cases, yet in some instances, the exchange of water reservoirs with distinctive D/H could be responsible.
Icarus (2020) https://doi.org/10.1016/j.icarus.2020.114266
Elise W. Knutsen, Geronimo L. Villanueva,Giuliano Liuzzi,Matteo M.J. CrismaniMichael J. MummaMichael D. SmithAnn Carine VandaeleShohei AokiIan R. ThomasFrank DaerdenSébastien ViscardyJustin T. ErwinLoic TrompetLori NearyBojan RisticMiguel Angel Lopez-ValverdeJose Juan Lopez-MorenoManish R. Patel, Giancarlo Bellucci
Methane (CH4) on Mars has attracted a great deal of attention since it was first detected in January 2003. As methane is considered a potential marker for past/present biological or geological activity, any possible detection would require evidence with strong statistical significance. Ethane (C2H6) and ethylene (C2H4) are also relevant chemical species as their shorter lifetimes in the Martian atmosphere make them excellent tracers for recent and ongoing releases. If detected, a CH4/C2Hn ratio could aid in constraining the potential source of organic production. Here we present the results of an extensive search for hydrocarbons in the Martian atmosphere in 240,000 solar occultation measurements performed by the ExoMars Trace Gas Orbiter/NOMAD instrument from April 2018 to April 2019. The observations are global, covering all longitudes and latitudes from 85°N to 85°S, and sampled from 6 to 100 km altitude with a typical vertical resolution of 2 km. There were no statistically significant detections of organics and new stringent upper limits for global ethane and ethylene were set at 0.1 ppbv and 0.7 ppbv, respectively. No global background level of methane was observed, obtaining an upper limit of 0.06 ppbv, in agreement with early results from ExoMars (Korablev et al., 2019). Dedicated searches for localized plumes at more than 2000 locations provided no positive detections, implying that if methane were released in strong and rapid events, the process would have to be sporadic.
Science Advance 10 Feb 2021, https://doi.org/10.1126/sciadv.abe4386
Oleg Korablev, View ORCID ProfileKevin S. Olsen, View ORCID ProfileAlexander Trokhimovskiy, View ORCID ProfileFranck Lefèvre, View ORCID ProfileFranck Montmessin, View ORCID ProfileAnna A. Fedorova,Michael J. Toplis, View ORCID ProfileJuan Alday, View ORCID ProfileDenis A. Belyaev, View ORCID ProfileAndrey Patrakeev, View ORCID ProfileNikolay I. Ignatiev, View ORCID ProfileAlexey V. Shakun, View ORCID ProfileAlexey V. Grigoriev, View ORCID ProfileLucio Baggio, View ORCID ProfileIrbah Abdenour, View ORCID roGaetan Lacombe, Yury S. Ivanov, View ORCID ProfileShohei Aoki,View ORCID ProfileIan R. Thomas, View ORCID ProfileFrank Daerden, View ORCID ProfileBojan Ristic, View ORCID ProfileJustin T. Erwin, View ORCID ProfileManish Patel, View ORCID ProfileGiancarlo Bellucci, View ORCID ProfileJose-Juan Lopez-Moreno, Ann C. Vandaele
A major quest in Mars’ exploration has been the hunt for atmospheric gases, potentially unveiling ongoing activity of geophysical or biological origin. Here, we report the first detection of a halogen gas, HCl, which could, in theory, originate from contemporary volcanic degassing or chlorine released from gas-solid reactions. Our detections made at ~3.2 to 3.8 μm with the Atmospheric Chemistry Suite and confirmed with Nadir and Occultation for Mars Discovery instruments onboard the ExoMars Trace Gas Orbiter, reveal widely distributed HCl in the 1- to 4-ppbv range, 20 times greater than previously reported upper limits. HCl increased during the 2018 global dust storm and declined soon after its end, pointing to the exchange between the dust and the atmosphere. Understanding the origin and variability of HCl shall constitute a major advance in our appraisal of martian geo- and photochemistry.
JQSRT (2021), https://doi.org/10.1016/j.jqsrt.2020.107361.
Frédéric Schmidt, Guillaume Cruz Mermy, Justin Erwin, Séverine Robert, Lori Neary, Ian R. Thomas, Frank Daerden, Bojan Ristic, Manish R. Patel, Giancarlo Bellucci, Jose-Juan Lopez-Moreno, Ann-Carine Vandaele
One of the main difficulties to analyze modern spectroscopic datasets is due to the large amount of data. For example, in atmospheric transmittance spectroscopy, the solar occultation channel (SO) of the NOMAD instrument onboard the ESA ExoMars2016 satellite called Trace Gas Orbiter (TGO) had produced ~ 10 millions of spectra in ~ 20000 acquisition sequences since the beginning of the mission in April 2018 until 15 January 2020. Other datasets are even larger with ~ billions of spectra for OMEGA onboard Mars Express or CRISM onboard Mars Reconnaissance Orbiter. Usually, new lines are discovered after a long iterative process of model fitting and manual residual analysis. Here we propose a new method based on unsupervised machine learning, to automatically detect new minor species. Although precise quantification is out of scope, this tool can also be used to quickly summarize the dataset, by giving few endmembers (”source”) and their abundances.
The methodology is the following: we proposed a way to approximate the dataset non-linearity by a linear mixture of abundance and source spectra (endmembers). We used unsupervised source separation in form of non-negative matrix factorization to estimate those quantities. Several methods are tested on synthetic and simulation data. Our approach is dedicated to detect minor species spectra rather than precisely quantifying them. On synthetic example, this approach is able to detect chemical compounds present in form of 100 hidden spectra out of 104, at 1.5 times the noise level. Results on simulated spectra of NOMAD-SO targeting CH4 show that detection limits goes in the range of 100–500 ppt in favorable conditions. Results on real martian data from NOMAD-SO show that CO2 and H2O are present, as expected, but CH4 is absent. Nevertheless, we confirm a set of new unexpected lines in the database, attributed by ACS instrument Team to the CO2 magnetic dipole.
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