Early Mercurian atmospheric mystery

Mercury is the smallest planet in the solar system, and also the closest to the sun. It experiences extreme temperature fluctuations, with temperatures reaching 430 degrees Celsius during the day, and night temperatures as low as -170 degrees Celsius. Despite its proximity to the sun, why is the surface of Mercury rich in volatile elements like sodium and sulphur? Noah JΓ€ggi, a graduate student at the University of Bern, and colleagues have addressed this question.

In its early days, Mercury had a magma ocean caused due to impacts of accretion and bombardments, which were highly energetic, along with the heat generated by radioactive decay. Models suggest these processes caused the temperature of the surface to rise to about 2,400 Kelvin.

JΓ€ggi and his team started by considering both volatile (carbon dioxide/monoxide, hydrogen) and relatively non-volatile (silicon, sodium, iron) species, which remain gaseous only at the high temperatures thought to have existed there, to be present in the early magma ocean. The team was interested in modelling the effects of evaporation from the magma ocean into the atmosphere and the consequent β€˜mass loss’ from the atmosphere – either into space or back to the surface, by accounting for the various physical and chemical processes. Molecules can escape from the atmosphere through various mechanisms.

They found the total mass loss from the atmosphere to be similar for volatile and non-volatile elements. However, the mass loss and evaporation did not account for much of the composition of Mercury. Quantitatively, the atmospheric escape processes could only account for a loss of around 0.3 percent of Mercury’s initial mass, or around 2.3 kilometers of crust.

Therefore, the results suggest that the overall mass loss did not significantly alter most of Mercury’s mantle composition, during the early magma ocean stage. “It tells us that there must be more to the high sodium measurements on Mercury’s surface, as they cannot be accumulated nor lost in any significant amount given our modelled loss rates and magma ocean lifetimes”, JΓ€ggi said.

Source:Β https://phys.org/news/2021-12-earliest-atmosphere-mercury.html

By Gaurav Pundir

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