Fluorescent Hydroxyl Emissions from Saturn's Ring Atmosphere

Abstract

Just before Earth passed through Saturn's ring plane on 10 August 1995, the Hubble Space Telescope Faint Object Spectrograph detected ultraviolet fluorescent emissions from a tenuous atmosphere of OH molecules enveloping the rings. Brightnesses decrease with increasing distance above the rings, implying a scale height of about 0.45 Saturn radii (R_S). A spatial scan 0.28R_S above the A and B rings indicates OH column densities of about 10¹³ cm^-2 and number densities of up to 700 cm^-3. Saturn's rings must produce roughly 10²⁵ to 10²⁹ OH molecules per second to maintain the observed OH distribution.