On Charon's Far-Ultraviolet Surface Reflectance

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 $<0.019$ ($3\sigma$) at 1600 A. From 1650--1725 A Charon's geometric albedo increases to $0.166\pm 0.068$, 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 $\sim 3.7$ 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.

Accepted for publication in the Planetary Science Journal; 9 pages, 7 figures, 2 tables

References in corpus (2)

• ALICE: The Ultraviolet Imaging Spectrograph aboard the New Horizons Pluto-Kuiper Belt Mission
• Pluto's Ultraviolet Spectrum, Surface Reflectance, and Airglow Emissions