Hydrogen and helium escape on Venus via energy transfer from hot oxygen atoms
| Autor: | Jun Cui, D.-D. Niu, Jiang Yu, H. Gu |
|---|---|
| Rok vydání: | 2020 |
| Předmět: |
Physics
010504 meteorology & atmospheric sciences biology Hydrogen Energy transfer chemistry.chemical_element Astronomy and Astrophysics Venus biology.organism_classification 01 natural sciences Oxygen atom chemistry Space and Planetary Science 0103 physical sciences Astrophysics::Earth and Planetary Astrophysics Atomic physics 010303 astronomy & astrophysics Helium 0105 earth and related environmental sciences |
| Zdroj: | Monthly Notices of the Royal Astronomical Society. 501:2394-2402 |
| ISSN: | 1365-2966 0035-8711 |
| DOI: | 10.1093/mnras/staa3744 |
| Popis: | Due to the relatively strong gravity on Venus, heavy atmospheric neutrals are difficult to accelerate to the escape velocity. However, a variety of processes, such as the dissociative recombination of ionospheric O$_2^+$, are able to produce hot atoms which could deliver a significant amount of energy to light neutrals and drive their escape. In this study, we construct a Monte Carlo model to simulate atmospheric escape of three light species, H, H2, and He, on Venus via such a knock-on process. Two Venusian background atmosphere models are adopted, appropriate for solar minimum and maximum conditions. Various energy-dependent and species-dependent cross-sections, along with a common strongly forward scattering angle distribution, are used in our calculations. Our model results suggest that knock-on by hot O likely plays the dominant role in driving total atmospheric hydrogen and helium escape on Venus at the present epoch, with a significant portion contributed from regions below the exobase. Substantial variations are also revealed by our calculations. Of special interest is the modelled reduction in escape flux at high solar activities for all species, mainly associated with the enhancement in thermal O concentration near the exobase at high solar activities which hinders escape. Finally, model uncertainties due to several controlling factors, including the distribution of relevant light species in the background atmosphere, the plane-parallel approximation, and the finite O energy distribution, are evaluated. |
| Databáze: | OpenAIRE |
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