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Communication Dans Un Congrès Année : 2019

MAVEN/IUVS Measurements of the D/H Ratio in the Martian Upper Atmosphere

Résumé

Observations of H and D Lyman-alpha emissions in the upper atmosphere of Mars have been made with the MAVEN IUVS echelle channel since 2014 and with the HST/STIS since 1990. Both instruments detect H throughout the martian year, while HST can detect D at all times and IUVS can detect D near perihelion. Observations with IUVS and HST close in time in summer 2018 have established consistent calibrations for the emission brightnesses between the two instruments, anchored to stellar calibrations by HST. Following a determination of the global scale patterns in temperature and atomic number density, and the application of a new spherically asymmetric radiative transfer code, it is now possible to quote accurate values for the densities of H and D and the D/H ratio in the martian upper atmosphere over the course of the martian year. The densities and escape fluxes of both atoms show a strong seasonal variation with a large increase during southern summer /perihelion. Around aphelion the thermospheric D/H ratio at Mars is consistent with the value in lower atmospheric water. By contrast, near perihelion both the H and D densities increase sharply, and the D/H ratio is enhanced by a factor of 5-10 over the value at aphelion. Initial thoughts on the processes responsible for these variations will be presented.
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Dates et versions

insu-04410775 , version 1 (22-01-2024)

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J. T. Clarke, M. Mayyasi, D. Bhattacharyya, Jean-Yves Chaufray, Jean-Loup Bertaux, et al.. MAVEN/IUVS Measurements of the D/H Ratio in the Martian Upper Atmosphere. American Geophysical Union, Fall Meeting 2019, Dec 2019, San Francisco, United States. pp.abstract #P41B-3439. ⟨insu-04410775⟩
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