The Discovery of Oxygen Kα X-Ray Emission from the Rings of Saturn

Using the Advanced CCD Imaging Spectrometer (ACIS), the Chandra X-rayObservatory (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 letterwe report the detection of X-ray emission from the rings of Saturn. The X-rayspectrum 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 0.53keV. 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 energyrange 0.24-2.0 keV. Our analysis also finds a clear detection of X-ray emissionfrom 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 fromoxygen atoms in the H2O icy ring material is the likely source mechanism forring X-rays, consistent with the scenario of solar photo-production of atenuous ring oxygen atmosphere and ionosphere recently discovered by Cassini.Comment: 14 pages, 5 figures Astrophys. J Lett., in pres