MGS MOC Release No. MOC2-489, 20 September 2003

This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture shows the pitted floor of the caldera of the martian volcano, Ceraunius Tholus. A caldera is a large collapse pit at the summit of a volcano. For reference, a wide angle MOC view of Ceraunius Tholus was presented on 18 April 2002, "Volcanoes Ceraunius Tholus and Uranius Tholus." Today's picture shows a close-up view of the volcano's caldera floor. The floor exhibits many pits and holes, but it is uncertain whether these were formed by meteor impact, volcanic eruptions, or collapse. Most of them do not have raised rims and ejecta-two features characteristic of meteor impact craters (although a few shown here have raised rims); and none have lava flows or volcanic cones associated with them-characteristics of volcanic eruption. Thus, these pits might have formed by collapse, although it is more likely that they were formed by meteor impact, but the ejecta and rims have been buried by dust or eroded away. This picture is located near 24.3°N, 97.4°W, and covers an area 3 km (1.9 mi) across. Sunlight illuminates the scene from the lower left.