Two-dimensional model for the martian exosphere: Applications to hydrogen and deuterium Lyman α observations

Abstract

The analysis of Lyman α observations in the exosphere of Mars has become limited by the assumption of spherical symmetry in the modeling process, as the models are being used to analyze increasingly detailed measurements. In order to overcome this limitation, a two-dimensional density model is presented, which better emulates the density distribution of deuterium and hydrogen atoms in the exosphere of Mars. A two-dimensional radiative transfer model developed in order to simulate multiple scattering of solar Lyman α photons by an asymmetric, nonisothermal hydrogen exosphere, is also presented here. The models incorporate changes in density and temperature structure of the martian atmosphere with radial distance and solar zenith angle.The 2-D models were applied to the MAVEN-IUVS echelle observations of deuterium and hydrogen Lyman α as well as HST Lyman α observations of hydrogen at Mars. The asymmetric 2-D model provided better fits to the data and smaller thermal escape rates in comparison to the symmetric 1-D model for the exosphere of Mars. However, intensity differences between both models became small above ~2.5 martian radii indicating that the exosphere of Mars approaches spherical symmetry at higher altitudes, in agreement with earlier studies. In addition, a new cross calibration of the absolute sensitivities of two instruments on the Hubble Space Telescope and the MAVEN-IUVS echelle mode is presented based on near-simultaneous observations of the geocorona and Mars.

Variability of Upstream Proton Cyclotron Wave Properties and Occurrence at Mars Observed by MAVEN

“…Moreover, dust activity and atmospheric upwelling can have a significant role in varying lower atmospheric water vapor concentration, influencing H exosphere variability. This has been suggested by several studies, including work based on MAVEN, MEX, and Hubble Space Telescope scattered Lyman α brightness observations (e.g., Bhattacharyya et al, 2015Bhattacharyya et al, , 2017Bhattacharyya et al, , 2020Chaffin et al, 2014;Clarke et al, 2014Clarke et al, , 2017). Martian regional dust storms have been observed to increase the near-surface atmospheric temperature at 0.5 mbar by 15-20 K, whereas planet-encircling dust storms can raise the temperature by 30-40 K, due to an increased opacity of the lower atmosphere (Smith, 2009).…”

Estimate of the D/H Ratio in the Martian Upper Atmosphere from the Low Spectral Resolution Mode of MAVEN/IUVS

“…Specifically, 1) the exospheric temperature, 2) the density profile below 120 km, and 3) absolute calibration used for the retrieval, can lead to systematic error in D/H at 80 km of a factor of ∼10. This is currently the main limitation of our method however the two first assumptions could be improved in the future, (e.g., by using improved 2D or 3D empirical/numerical temperature model distributions for different seasons, as done by Bhattacharyya et al., 2020). For the first two periods studied, near simultaneous observations were performed with the IUVS high‐resolution mode and low‐resolution mode making it possible to provide an estimate of the exospheric temperatures based on the best fit.…”

“…Subsequent MAVEN observations showed consistently low deuterium emission brightnesses near aphelion (Mayyasi et al., 2017). Analysis of D and H high resolution profiles, obtained below 300 km, showed significant seasonal variations of deuterium abundance at 200 km (Bhattacharyya et al., 2020; Mayyasi et al., 2019). D densities were found to increase from 1,000 ± 200 cm −3 near Ls = 220°, to a peak density of 3,000 ± 1,000 near Ls = 290°, then to decrease once more, down to 1,600 ± 1,000 cm −3 toward the end of the dusty season (Ls = 330°).…”

Upgrades to the MAVEN Echelle Data Reduction Pipeline: New Calibration Standard and Improved Faint Emission Detection Algorithm at Lyman‐α

“…In the NASA Planetary Data System (PDS), archived MAVEN/Echelle data products include 1‐σ uncertainties for both H and D brightness derivations. In several scientific applications of the data that utilized the old data reduction pipeline, conservative 3‐σ values have been used to depict the measurement uncertainties to account for any detector effects not captured in the data reduction (e.g., Bhattacharyya et al., 2020; Clarke et al., 2017; Mayyasi et al., 2018, 2019, 2020; Mayyasi, Clarke, Bhattacharyya, et al., 2017; Mayyasi, Clarke, Quémerais, et al., 2017).…”