Possible Liquid Water Ponds on the Martian Surface

Recent Mars exploration rover (MER) images have features that appear to be ponds of liquid water. This paper examines this possibility by building a three-dimensional terrain model around one such possible pond. Stereo images from the PanCam system are used to examine the "shoreline" of the "pond" to see if the shoreline is flat (lies in a plane) and whether the terrain around the shoreline is everywhere higher than the shoreline. Our analysis shows the shoreline of the pond to be remarkably flat, down to the few millimeters of vertical resolution provided by the stereo images. The surface of the pond is so smooth and featureless that no correlation can be found between the left and right images. Caused by the complete absence of sand, pebbles, or detritus on the pond, this lack of correlation strongly suggests a liquid surface. Furthermore, the pond appears to be transparent, allowing detection (by stereo triangulation) of submerged objects. Everything that can be determined from the three-dimensional stereo reconstruction is indicative of, and compatible with, the surface of a liquid pond at a constant geopotential altitude. We suggest on-site confirmation of this strong evidence for current liquid water on Mars by having opportunity's rock abrasion tool (RAT) drill a hole in the planar feature.