https://doi.org/10.1016/j.icarus.2021.114404

 

Michael D. Smith, Frank Daerden, Lori Neary, Alain S.J. Khayat, James A. Holmes, Manish R. Patel, Geronimo Villanueva, Giuliano Liuzzi, Ian R. Thomas, Bojan Ristic, Giancarlo Bellucci, Jose Juan Lopez-Moreno, Ann Carine Vandaele.

 

More than a full Martian year of observations have now been made by the Nadir Occultation for MArs Discovery (NOMAD) instrument suite on-board the ExoMars Trace Gas Orbiter. Radiative transfer modeling of NOMAD observations taken in the nadir geometry enable the seasonal and global-scale variations of carbon monoxide gas in the Martian atmosphere to be characterized. These retrievals show the column-averaged volume mixing ratio of carbon monoxide to be about 800 ppmv, with significant variations at high latitudes caused by the condensation and sublimation of the background CO2 gas. Near summer solstice in each hemisphere, the CO volume mixing ratio falls to 400 ppmv in the south and 600 ppmv in the north. At low latitudes, carbon monoxide volume mixing ratio inversely follows the annual cycle of surface pressure. Comparison of our retrieved CO volume mixing ratio against that computed by the GEM-Mars general circulation model reveals a good match in their respective seasonal and spatial trends, and can provide insight into the physical processes that control the distribution of CO gas in the current Martian atmosphere.

 

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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.

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Science Advance 10 Feb 2021, https://doi.org/10.1126/sciadv.abe4386

Oleg Korablev,Kevin S. Olsen,Alexander Trokhimovskiy,Franck Lefèvre,Franck Montmessin,Anna A. Fedorova,Michael J. Toplis,Juan Alday,Denis A. Belyaev,Andrey Patrakeev,Nikolay I. Ignatiev,Alexey V. Shakun,Alexey V. Grigoriev,Lucio Baggio,Irbah Abdenour,Gaetan Lacombe, Yury S. Ivanov,Shohei Aoki,Ian R. Thomas,Frank Daerden,Bojan Ristic,Justin T. Erwin,Manish Patel,Giancarlo Bellucci,Jose-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.

 

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Science Advances 10 Feb 2021, https://doi.org/10.1126/sciadv.abc8843

Geronimo L. Villanueva,Giuliano Liuzzi,Matteo M. J. Crismani,Shohei Aoki,Ann Carine Vandaele,Frank Daerden,Michael D. Smith, Michael J. Mumma,Elise W. Knutsen,Lori Neary,Sebastien Viscardy,Ian R. Thomas,Miguel Angel Lopez-Valverde,Bojan Ristic,Manish R. Patel,James A. Holmes,Giancarlo Bellucci,Jose 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.

 

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Icarus (2020) https://doi.org/10.1016/j.icarus.2020.114266

Elise W. Knutsen, Geronimo L. Villanueva, Giuliano Liuzzi, Matteo M.J. Crismani, Michael J. Mumma, Michael D. Smith, Ann Carine Vandaele, Shohei Aoki, Ian R. Thomas, Frank Daerden, Sébastien Viscardy, Justin T. Erwin, Loic Trompet, Lori Neary, Bojan Ristic, Miguel Angel Lopez-Valverde, Jose Juan Lopez-Moreno, Manish 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.

 

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