Detection of Mercury's Potassium Tail

Abstract : Ground-based observations of Mercury's exosphere bridge the gap between the MESSENGER and BepiColombo missions and provide a broad counterpart to their in situ measurements. Here we report the first detection of Mercury's potassium tail in both emission lines of the D doublet. The sodium to potassium abundance ratio at 5 planetary radii down-tail is approximately 95, near the mid-point of a wide range of values that have been quoted over the planet's disk. This is several times the Na/K present in atmospheres of the Galilean satellites and more than an order of magnitude above Mercury's usual analogue, the Moon. The observations confirm that Mercury's anomalously high Na/K ratios cannot be explained by differences in neutral loss rates. The width and structure of the Na and K tails is comparable and both exhibit a persistent enhancement in their northern lobe. We interpret this as a signature of Mercury's offset magnetosphere; the exosphere's source rates are locally enhanced at the southern surface, and sloshing from radiation pressure and gravity guides this population into the northern region of the tail.
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Submitted on : Thursday, December 14, 2017 - 6:14:28 PM
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Carl Schmidt, François Leblanc, Luke Moore, Thomas A. Bida. Detection of Mercury's Potassium Tail. 49th Annual Division for Planetary Sciences Meeting, Oct 2017, Provo, United States. ⟨insu-01664385⟩

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