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Communication Dans Un Congrès Année : 2023

Magnetospheric processes mediate atmospheric escape at Earth, Mars, and Venus: key open questions demand renewed Venus exploration

Résumé

Earth, Mars, and Venus span a range of magnetosphere configurations, from the global/intrinsic dipole field of Earth, through the hybrid crustal field and induced magnetosphere of Mars, to the wholly induced magnetosphere of Venus. These differences in intrinsic field strength and geometry lead to differences in the processes driving atmospheric escape from each planet to space, which may in turn have led to the different evolutionary trajectories and vastly different habitability of these planets. Multiple missions at Earth and Mars have fostered a detailed understanding of their atmospheric escape mechanisms. While gaps remain, this understanding is more developed than that at Venus, which exhibits several characteristics that make it an ideal laboratory to observe the coupling between magnetosphere processes and escape. First, a combination of high Earth-like gravity and low Mars-like thermosphere temperatures suppresses thermal H escape at Venus, uniquely enabling the investigation of nonthermal ion-driven photochemical escape and direct ion escape processes, which may dominate on Venus-like exoplanets. Second, ion escape processes at Venus are required to remove atmospheric O in order to explain the low atmospheric oxygen abundance, but the existing ion escape measurements by the Pioneer Venus Orbiter and Venus Express leave many details of upward transport and acceleration underexplored. While Venus lacks a global dipole magnetic field, the nightside magnetic field configuration is in some ways similar to the Earth's polar regions and Martian crustal field cusps. Thus, cold light and heavy ion outflow driven by ambipolar electric fields may occur at Venus, in analogy to the "polar wind" hydrogen ion outflow at Earth and heavy ion outflow at Mars. For both ion and neutral escape, variation of solar input on evolutionary timescales and across solar system planets requires a focus on understanding physical processes, so that they can be extrapolated to other times and to exoplanets. As the world’s space agencies turn their eyes toward Venus over the coming decade, the essential role played by the magnetosphere in mediating Venus evolution should not be overlooked: future upper atmosphere measurements at Venus are likely to illuminate magnetosphere-escape coupling processes throughout the cosmos.
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Dates et versions

insu-04333407 , version 1 (09-12-2023)

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  • HAL Id : insu-04333407 , version 1

Citer

Michael Chaffin, Christopher M Fowler, Kathleen Gwen Hanley, Robert J Lillis, Aroh Barjatya, et al.. Magnetospheric processes mediate atmospheric escape at Earth, Mars, and Venus: key open questions demand renewed Venus exploration. AGU Fall Meeting 2023, Dec 2023, San Francisco (Califonia), United States. ⟨insu-04333407⟩
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