Europa’s Hemispheric Color Dichotomy as a Constraint on Non-synchronous Rotation

Ethan Burnett, Paul Hayne

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Mar 20, 2020
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Received Date: 11th March 20

Europa's surface reflectance exhibits a pronounced hemispheric dichotomy, which is hypothesized to form due to enhanced irradiation of the trailing hemisphere by energetic particles entrained in the jovian magnetosphere. We propose that this pattern can only persist if the timescale for discoloration is much shorter than that of Europa's rotation relative to the synchronous state. By decomposing the longitudinal ultraviolet and visible color variations from Voyager data into sine and cosine terms, we demonstrate that the contribution due to non-synchronous rotation is small. The results of this analysis suggest that there is essentially no non-synchronous rotation of Europa on geologic timescales, with the period of non-synchronous rotation > 1 Gyr. This same conclusion is reached with two models of discoloration: one representing an actively discoloring surface, and the other assuming that the present-day exogenic discoloration on the surface is in steady-state. This constraint depends on the age of the crater Pwyll, which is assumed to be ~10^6 yr; an older age would indicate a slower non-synchronous rotation period. This result magnifies the outstanding problem of generating sufficient stress to explain Europa's pervasive tectonic features.

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This is an abstract of a preprint hosted on an independent third party site. It has not been peer reviewed but is currently under consideration at Nature Communications.

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