TY - JOUR
T1 - Fully Coupled Photochemistry of the Deuterated Ionosphere of Mars and Its Effects on Escape of H and D
AU - Cangi, Eryn
AU - Chaffin, Michael
AU - Yelle, Roger
AU - Gregory, Bethan
AU - Deighan, Justin
N1 - Funding Information: This work was supported by three separate funding sources. First, this work was supported by Mars Data Analysis Program Grant NNX14AM20G. Second, this material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant DGE 1650115. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. Third, this work was supported by NASA's FINESST Program (Grant 80NSSC22K1326). Publisher Copyright: © 2023. American Geophysical Union. All Rights Reserved.
PY - 2023/7
Y1 - 2023/7
N2 - Although deuterium (D) on Mars has received substantial attention, the deuterated ionosphere remains relatively unstudied. This means that we also know very little about non-thermal D escape from Mars, since it is primarily driven by excess energy imparted to atoms produced in ion-neutral reactions. Most D escape from Mars is expected to be non-thermal, highlighting a gap in our understanding of water loss from Mars. In this work, we set out to fill this knowledge gap. To accomplish our goals, we use an upgraded 1D photochemical model that fully couples ions and neutrals and does not assume photochemical equilibrium. To our knowledge, such a model has not been applied to Mars previously. We model the atmosphere during solar minimum, mean, and maximum, and find that the deuterated ionosphere behaves similarly to the H-bearing ionosphere, but that non-thermal escape on the order of 8,000–9,000 cm−2 s−1 dominates atomic D loss under all solar conditions. The total fractionation factor, f, is f = 0.04–0.07, and integrated water loss is 147–158 m global equivalent layer. This is still less than geomorphological estimates. Deuterated ions at Mars are likely difficult to measure with current techniques due to low densities and mass degeneracies with more abundant H ions. Future missions wishing to measure the deuterated ionosphere in situ will need to develop innovative techniques to do so.
AB - Although deuterium (D) on Mars has received substantial attention, the deuterated ionosphere remains relatively unstudied. This means that we also know very little about non-thermal D escape from Mars, since it is primarily driven by excess energy imparted to atoms produced in ion-neutral reactions. Most D escape from Mars is expected to be non-thermal, highlighting a gap in our understanding of water loss from Mars. In this work, we set out to fill this knowledge gap. To accomplish our goals, we use an upgraded 1D photochemical model that fully couples ions and neutrals and does not assume photochemical equilibrium. To our knowledge, such a model has not been applied to Mars previously. We model the atmosphere during solar minimum, mean, and maximum, and find that the deuterated ionosphere behaves similarly to the H-bearing ionosphere, but that non-thermal escape on the order of 8,000–9,000 cm−2 s−1 dominates atomic D loss under all solar conditions. The total fractionation factor, f, is f = 0.04–0.07, and integrated water loss is 147–158 m global equivalent layer. This is still less than geomorphological estimates. Deuterated ions at Mars are likely difficult to measure with current techniques due to low densities and mass degeneracies with more abundant H ions. Future missions wishing to measure the deuterated ionosphere in situ will need to develop innovative techniques to do so.
KW - Mars
KW - atmospheric escape
KW - ionosphere
KW - non-thermal
KW - photochemistry
KW - water
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U2 - 10.1029/2022JE007713
DO - 10.1029/2022JE007713
M3 - Article
SN - 2169-9097
VL - 128
JO - Journal of Geophysical Research: Planets
JF - Journal of Geophysical Research: Planets
IS - 7
M1 - e2022JE007713
ER -