  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
$0.166\pm0.068$, 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.
