The elevation measurements were collected by the Mars Orbiter Laser Altimeter (MOLA), an instrument aboard NASA's MarsGlobalSurveyorspacecraft, during the spring and summer of 1998.
Images taken by the orbiting NASA's MarsGlobalSurveyorspacecraft enabled scientists to detect changes in the walls of two craters in the southern hemisphere of Mars, apparently caused by the downhill flow of water in the past few years.