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arXiv · 2107.14068

On Charon's Far-Ultraviolet Surface Reflectance

Brian A. Keeney·Joel Wm. Parker·Nathaniel Cunningham·S. Alan Stern·Anne J. Verbiscer·the New Horizons Team
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Abstract

We present the first measurements of Charon's far-ultraviolet surface reflectance, obtained by the Alice spectrograph on New Horizons. We find no measurable flux shortward of 1650 A, and Charon's geometric albedo is $<0.019$ ($3σ$) at 1600 A. From 1650--1725 A Charon's geometric albedo increases to $0.166\pm0.068$, and remains nearly constant until 1850 A. As this spectral shape is characteristic of H$_2$O ice absorption, Charon is the first Kuiper belt object with a H$_2$O ice surface to be detected in the far-ultraviolet. Charon's geometric albedo is $\sim3.7$ times lower than Enceladus' at these wavelengths, but has a very similar spectral shape. We attribute this to similarities in their surface compositions, and the difference in absolute reflectivity to a high concentration or more-absorbing contaminants on Charon's surface. Finally, we find that Charon has different solar phase behavior in the FUV than Enceladus, Mimas, Tethys, and Dione, with a stronger opposition surge than Enceladus and a shallower decline at intermediate solar phase angles than any of these Saturnian satellites.

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Brian A. Keeney, Joel Wm. Parker, Nathaniel Cunningham, S. Alan Stern, Anne J. Verbiscer, the New Horizons Team. 2021-07-29. On Charon's Far-Ultraviolet Surface Reflectance. https://doi.org/10.3847/psj%2Fac16da

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