Origin and character of the lunar and mercurian atmospheres

This article presents a description of the lunar and mercurian atmospheres and the outstanding, unanswered questions. In that spirit we will not repeat the information found in the reviews of the lunar (Morgan and Stern, 1991) and mercurian (Hunten et al., 1988) atmospheres, which provide a historical context of the discoveries and initial measurements. These atmospheres are tenuous and transient; different components have lifetimes of hours to weeks. The sources that maintain them are of considerable interest, but direct information on sources is difficult to obtain. We therefore begin by describing the atmospheres and their behavior, and go on to consider the loss processes. This information is then used in the discussion of the most likely sources. (C) 1997 COSPAR. Published by Elsevier Science Ltd.