TY - JOUR
T1 - Study of the hydrogen escape rate at Mars during martian years 28 and 29 from comparisons between SPICAM/Mars express observations and GCM-LMD simulations
AU - Chaufray, J. Y.
AU - Gonzalez-Galindo, F.
AU - Lopez-Valverde, M. A.
AU - Forget, F.
AU - Quémerais, E.
AU - Bertaux, J. L.
AU - Montmessin, F.
AU - Chaffin, M.
AU - Schneider, N.
AU - Clarke, J. T.
AU - Leblanc, F.
AU - Modolo, R.
AU - Yelle, R. V.
N1 - Funding Information:
This project was partially funded by the Programme National de Planetologie and Programme National Soleil Terre and by the Centre National d'Etudes Spatiales. This work has been partially funded by the European Union Horizon 2020 Programme (H2020 Compet -08-2014) under grant agreement UPWARDS-633127. FGG has been partly funded by the Spanish Ministerio de Ciencia e Innovación, the Agencia Estatal de Investigacion and EC FEDER funds under projects ESP2017-87143-R and RTI2018-100920-J-I00. We would like to thank G. Lacombe and L. Baggio for their support on the calibration. We thank Allyson Leffler for her careful review of grammatical aspects of this paper. The SPICAM/MEX data used in this study are available through the ESA Planetary Science Archive (PSA, https://archives.esac.esa.int/psa/). The monthly average 3D simulated hydrogen exosphere can be found on: https://owncloud.latmos.ipsl.fr/index.php/s/AdUgv9PdipA2rim
Funding Information:
This project was partially funded by the Programme National de Planetologie and Programme National Soleil Terre and by the Centre National d'Etudes Spatiales. This work has been partially funded by the European Union Horizon 2020 Programme (H2020 Compet -08-2014) under grant agreement UPWARDS-633127. FGG has been partly funded by the Spanish Ministerio de Ciencia e Innovación , the Agencia Estatal de Investigacion and EC FEDER funds under projects ESP2017-87143-R and RTI2018-100920-J-I00 . We would like to thank G. Lacombe and L. Baggio for their support on the calibration. We thank Allyson Leffler for her careful review of grammatical aspects of this paper. The SPICAM/MEX data used in this study are available through the ESA Planetary Science Archive (PSA, https://archives.esac.esa.int/psa/ ). The monthly average 3D simulated hydrogen exosphere can be found on: https://owncloud.latmos.ipsl.fr/index.php/s/AdUgv9PdipA2rim
Publisher Copyright:
© 2019 Elsevier Inc.
PY - 2021/1/1
Y1 - 2021/1/1
N2 - We have simulated the 3D atomic hydrogen density in the Martian upper atmosphere and associated Jeans escape rate during Martian years 28 and 29. The coronal Lyman-α brightness is computed using a 3D radiative transfer model which accounts for the monthly average hydrogen density for these two years and is compared to a large set of observations by Mars Express/SPICAM. The simulated brightness is generally in good agreement with the observations for Ls <230° and Ls >330° for Martian year 28 and Ls < 270°, Ls > 340° for Martian year 29, but the model strongly underestimated the brightness for 230 < Ls < 330° for Martian year 28 and 270 < Ls < 340° for Martian year 29. In these simulations the transport of water vapor contributes to the production of hydrogen at high altitudes during southern summer. A possible explanation for the model discrepancy is an underestimate of this water transport, associated with an underestimate of the hygropause altitude and/or an underestimate of the supersaturation of the mesosphere. Considering this discrepancy, we estimate the hydrogen escape rate during these two Martian years to vary by almost two orders of magnitude, between ~1025 to 6 × 1026 s−1 (equivalent to a global layer of water ~33 to 2000 mm deep every billion years), in agreement with the seasonal variations estimated directly from the fit of the SPICAM observations during the Martian year 28 by Chaffin et al. (2014). Our analysis suggests that episodic dust storms and associated enhancements at high altitude near perihelion are a major factor in the H escape estimates averaged over one martian year or longer periods, but the accumulated water lost at this rate for 4 billion years is much lower than the amount of water needed to form the flow channels observed on Mars.
AB - We have simulated the 3D atomic hydrogen density in the Martian upper atmosphere and associated Jeans escape rate during Martian years 28 and 29. The coronal Lyman-α brightness is computed using a 3D radiative transfer model which accounts for the monthly average hydrogen density for these two years and is compared to a large set of observations by Mars Express/SPICAM. The simulated brightness is generally in good agreement with the observations for Ls <230° and Ls >330° for Martian year 28 and Ls < 270°, Ls > 340° for Martian year 29, but the model strongly underestimated the brightness for 230 < Ls < 330° for Martian year 28 and 270 < Ls < 340° for Martian year 29. In these simulations the transport of water vapor contributes to the production of hydrogen at high altitudes during southern summer. A possible explanation for the model discrepancy is an underestimate of this water transport, associated with an underestimate of the hygropause altitude and/or an underestimate of the supersaturation of the mesosphere. Considering this discrepancy, we estimate the hydrogen escape rate during these two Martian years to vary by almost two orders of magnitude, between ~1025 to 6 × 1026 s−1 (equivalent to a global layer of water ~33 to 2000 mm deep every billion years), in agreement with the seasonal variations estimated directly from the fit of the SPICAM observations during the Martian year 28 by Chaffin et al. (2014). Our analysis suggests that episodic dust storms and associated enhancements at high altitude near perihelion are a major factor in the H escape estimates averaged over one martian year or longer periods, but the accumulated water lost at this rate for 4 billion years is much lower than the amount of water needed to form the flow channels observed on Mars.
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U2 - 10.1016/j.icarus.2019.113498
DO - 10.1016/j.icarus.2019.113498
M3 - Article
AN - SCOPUS:85075360357
VL - 353
JO - Icarus
JF - Icarus
SN - 0019-1035
M1 - 113498
ER -