FLUORESCENT HYDROXYL EMISSIONS FROM SATURNS RING ATMOSPHERE

Just before Earth passed through Saturn's ring plane on 10 August 1995 , the Hubble Space Telescope Faint Object Spectrograph detected ultrav iolet fluorescent emissions from a tenuous atmosphere of OH molecules enveloping the rings. Brightnesses decrease with increasing distance a bove 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 colu mn densities of about 10(13) cm(-2) and number densities of up to 700 cm(-3). Saturn's rings must produce roughly 10(25) to 10(29) OH molecu les per second to maintain the observed OH distribution.