Energy Distributions for Desorption of Sodium and Potassium from Ice: The Na/K Ratio at Europa
โ Scribed by R.E. Johnson; F. Leblanc; B.V. Yakshinskiy; T.E. Madey
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 170 KB
- Volume
- 156
- Category
- Article
- ISSN
- 0019-1035
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โฆ Synopsis
The sputtering and decomposition of the surface of Europa by fast ions and electrons lead to the production of an atomosphere containing sodium and potassium atoms. Here time-of-flight energy distributions are measured for Na and K sputtered from a vapordeposited ice by 200-eV electrons. These data are then used in a Monte Carlo simulation for alkalis in Europa's atmosphere. Na/K ratios versus distance from Europa are calculated and compared to the recent observations in the range 6 to 18 Europan radii from the surface. Normalizing to the observations, the Na/K ratio for the loss rates is โผ27 and the ratio for the average surface source rates is โผ20. These ratios are very different from the Na/K ratio at Io and are larger than the Na/K ratio suggested for Europa's putative subsurface ocean, consistent with fractionation on freezing and upwelling of ocean material.
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