Much of the water that once flowed on the surface of Mars was lost to space long ago, and the total amount lost remains unknown. Clues to the amount lost can be found by studying hydrogen (H) and its isotope deuterium (D), which are produced when atmospheric water molecules H$_2$O and HDO dissociate. The difference in escape efficiencies of H and D (which leads to} an enhanced D/H ratio) is referred to as the fractionation factor $f$. Both the D/H ratio and $f$ are necessary to estimate water loss; thus, if we can constrain the range of $f$ and understand what controls it, we will be able to estimate water loss more accurately. In this study, we use a 1D photochemical model of the neutral Martian atmosphere to determine how $f$ depends on assumed temperature and water vapor profiles. We find that the exobase temperature most strongly controls the value of $f$ for thermal escape processes. When we include estimates of non-thermal escape from other studies, we find that the tropopause temperature is also important. Overall, for the standard Martian atmosphere, $f=0.002$ for thermal escape, and $f=0.06$ for thermal + non-thermal escape. We estimate that Mars has lost at minimum 66-122 m GEL of water. Importantly, our results demonstrate that the value of $f$ depends critically on non-thermal escape of D, and that modeling studies that include D/H fractionation must model both neutral and ion processes throughout the atmosphere.
Oxygen isotope fractionation in the Martian atmosphere induced by CO$_2$ photolysis and O$_3$ formation
Earth-Life Science Institute, Institute of Science Tokyo（地球生命研究所，东京科学大学）；Department of Earth and Space Sciences, University of Washington（华盛顿大学地球与空间科学系）；Department of Geophysics, Graduate School of Science, Tohoku University（东北大学理学研究科地球物理学科）；Department of Complexity Science and Engineering, Graduate School of Frontier Sciences, The University of Tokyo（东京大学前沿科学研究生院复杂科学与工程系）；Instituto de Astrofísica de Andalucía, CSIC（安达卢西亚天体物理研究所，西班牙国家科学研究委员会）；Research Center for Advanced Science and Technology, The University of Tokyo（东京大学先进科学技术研究中心）；Department of Earth and Planetary Sciences, School of Science, Institute of Science Tokyo（东京科学大学理学院地球行星科学系）；Faculty of Environment and Information Studies, Keio University（庆应义塾大学环境信息学部）
Impacting the dayside Martian ionosphere from above and below: Effects of the impact of CIRs and ICMEs close to aphelion (April 2021) and during dust storms (June-July 2022) seen with MAVEN ROSE
Diurnal temperature variations and migrating thermal tides in the Martian lower atmosphere observed by the Emirates Mars InfraRed Spectrometer
Southern University of Science and Technology（南方科技大学）；LMD/IPSL, Sorbonne Université, PSL Research Université, École Normale Supérieure, École Polytechnique, CNRS（巴黎文理研究大学）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；NASA Ames Research Center（美国国家航空航天局艾姆斯研究中心）；Mohammed Bin Rashid Space Centre（穆罕默德·本·拉希德航天中心）；University of Maryland Baltimore County（马里兰大学巴尔的摩县分校）；University of Aberdeen（阿伯丁大学）；United Arab Emirates University（阿联酋大学）；Northern Arizona University（北亚利桑那大学）；Arizona State University（亚利桑那州立大学）；University of Colorado Boulder（科罗拉多大学博尔德分校）
Impact of gravity waves on the middle atmosphere of Mars: a non-orographic gravity wave parameterization based on Global Climate modeling and MCS observations
