  Using the Advanced CCD Imaging Spectrometer (ACIS), the Chandra X-ray
Observatory (CXO) observed the Saturnian system for one rotation of the planet
(~37 ks) on 20 January, 2004, and again on 26-27 January, 2004. In this letter
we report the detection of X-ray emission from the rings of Saturn. The X-ray
spectrum from the rings is dominated by emission in a narrow (~130 eV wide)
energy band centered on the atomic oxygen K-alpha fluorescence line at 0.53
keV. The X-ray power emitted from the rings in the 0.49-0.62 keV band is 84 MW,
which is about one-third of that emitted from Saturn disk in the photon energy
range 0.24-2.0 keV. Our analysis also finds a clear detection of X-ray emission
from the rings in the 0.49-0.62 keV band in an earlier (14-15 April, 2003)
Chandra ACIS observation of Saturn. Fluorescent scattering of solar X-rays from
oxygen atoms in the H2O icy ring material is the likely source mechanism for
ring X-rays, consistent with the scenario of solar photo-production of a
tenuous ring oxygen atmosphere and ionosphere recently discovered by Cassini.
