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A two-stage mechanism for escape of Na and K from Io

Summers, Michael E. and Yung, Yuk L. and Haff, Peter K. (1983) A two-stage mechanism for escape of Na and K from Io. Nature, 304 (5928). pp. 710-712. ISSN 0028-0836. doi:10.1038/304710a0.

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It is generally accepted that Io is the source of S, O, Na and K which, after ionization, form the constituents of the Io plasma torus. The escape of S and O from Io can be understood in terms of the photochemistry of a predominantly SO_2 atmosphere created by the high vapour pressure of SO_2 (refs 1, 15). However, the vapour pressures of Na_2S, K_2S and other common compounds containing Na and K are negligible at the surface temperatures of Io. This has given rise to the suggestion that over part of Io's surface (the nightside) the atmosphere is thin enough so that surface sputtering by co-rotating ions can eject Na and K directly into the Io torus. The main objection to this idea is that it implies a ‘Sun-locked’ source for Na and K, while observations of the Na and K clouds around Io indicate a ‘Jupiter-locked‘ ejection mechanism. We propose here that Na and K escape from Io in two stages. Atoms of Na and K are first sputtered into the atmosphere from the surface by high-energy magnetospheric ions. Atmospheric sputtering by low-energy co-rotating ions then removes these constituents (along with others present) out of Io's gravitational field. We suggest that the observed Na and K ejection asymmetry is due to preferential sputtering of atmospheric particles on the hemisphere of Io facing Jupiter. The estimated injection rates are sufficiently large to maintain the observed K, Na, and O clouds observed around Io.

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Yung, Yuk L.0000-0002-4263-2562
Additional Information:© 1983 Macmillan Journals Ltd. Received 11 May; accepted 28 June 1983. We thank J. Trauger, A. Dessler, and A. Summers for helpful discussions; and K. Cherrey for calculations. This research was supported by NASA grants NAGW-202 and NAGW-313. Contribution no. 3873 from the Division of Geological and Planetary Sciences, California Institute of Technology.
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Caltech Division of Geological and Planetary Sciences3873
Issue or Number:5928
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49354
Deposited By: Tony Diaz
Deposited On:08 Sep 2014 23:42
Last Modified:10 Nov 2021 18:42

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