| Autor: |
Verkercke, S., Leblanc, F., Chaufray, J.‐Y., Morrissey, L., Sarantos, M., Prem, P. |
| Předmět: |
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| Zdroj: |
Geophysical Research Letters; 11/16/2024, Vol. 51 Issue 21, p1-11, 11p |
| Abstrakt: |
Mercury's surface undergoes large temperature gradients between day and night, which repeats periodically over the same longitudes due to its 3:2 spin‐orbit resonance. This effect combined with the orbit's eccentricity, creates hot and cold geographic longitudes. The planet is covered with a highly porous regolith, allowing exospheric atoms to diffuse in depth. By using a 1‐D diffusion model, we studied the subsurface precipitation of gas over the cold and hot longitudes to understand gas retention. This work identifies the cold longitudes as favorable regions to form subsurface reservoirs closer to the surface. Moreover, subsurface reservoirs of adsorbates increase two to three times faster over cold longitudes than over hot longitudes, depending on the surface binding energy distribution of the atoms. We suggest that this result may be related to the observation that Mercury's sodium exosphere persists at later local times over the cold pole. Plain Language Summary: The surface of Mercury experience large temperature differences between day and night, and this repeatedly occurs over the same geographic positions as an orbit of the planet around the Sun lasts exactly one and half Mercury day. Additionally, Mercury's orbit is highly elliptic, causing the planet‐Sun distance to vary. This creates cold and hot geographic longitudes on the planet surface. Mercury's surface is porous and covered with very fine grains which allows gas to diffuse through it. By using a one dimensional model, we study how gases can penetrate Mercury's surface depending on the geographic position. We identify that colder regions are favorable to the formation of shallow gas reservoirs, which grow two to three times faster than over the hottest regions, depending on the gas‐surface interactions. This result may be related to the higher measurements of sodium over the cold geographic longitudes of Mercury, which last through each local afternoon. Key Points: Subsurface diffusion of sodium forms shallow reservoir in the first meter of regolith, which is denser at the cold longitudesGreater surface binding energies increase the amount of sodium retained in the regolith per synodic cycleConvergence of the sodium accumulation should happen on timescales of billions of years, which could lead to the saturation of the regolith [ABSTRACT FROM AUTHOR] |
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