J.‐C. Gérard, S. Aoki, L. Gkouvelis, L. Soret, Y. Willame, I. R. Thomas, C. Depiesse, B. Ristic, A. C. Vandaele, B. Hubert, F. Daerden, M. R. Patel, J.‐J. López‐Moreno, G. Bellucci, J. P. Mason, M. A. López‐Valverde
Following the recent detection of the oxygen green line airglow on Mars, we have improved the statistical analysis of the data recorded by the NOMAD/UVIS instrument on board the ExoMars Trace Gas Orbiter mission by summing up hundreds of spectra to increase the signal‐to‐noise ratio. This led to the observation of the OI 630 nm emission, the first detection in a planetary atmosphere outside the Earth. The average limb profile shows a broad peak intensity of 4.8 kR near 150 km. Comparison with a photochemical model indicates that it is well predicted by current photochemistry, considering the sources of uncertainty. The red/green line intensity ratio decreases dramatically with altitude as a consequence of the efficient quenching of O(1D) by CO2. Simultaneous observations of the green and red dayglow will provide information on variations in the thermosphere in response to seasonal changes and the effects of solar events.
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.
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.
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.
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