SPACEPHOTOS

This high resolution picture of a moderately small impact crater on Mars was taken by the Mars Global Surveyor Orbiter Camera (MOC) on October 17, 1997 at 4:11:07 PM PST, during MGS orbit 22. The image covers an area 2.9 by 48.4 kilometers (1.8 by 30 miles) at 9.6 m (31.5 feet) per picture element, and is centered at 21.3°N, 179.8°W, near Orcus Patera. The MOC image is a factor of 15 better than pervious Viking views of this particular crater (shown in A, above, Viking image 545A49). The unnamed crater is one of three closely adjacent impact features that display the ejecta pattern characteristic of one type of 'flow-ejecta' crater. Such patterns are considered evidence of fluidized movement of the materials ejected during the cratering event, and are believed to indicate the presence of subsurface ice or liquid water. Long, linear features of different brightness values can be seen on the on the steep slopes inside and outside the crater rim. This type of feature, first identified in Viking Orbiter images acquried over 20 years ago, are more clearly seen in this new view (about 3 times better than the best previous observations). Their most likely eplanation is that small land- or dirt slides, initiated by seismic or wind action, have flowed down the steep slopes. Initially dark because of the nature of the surface disturbance, these features get lighter with time as the ubiquitous fine, bright dust settles onto them from the martian atmosphere. Based on estimates of the dust fall-out rate, many of these features are probably only a few tens to hundreds of years old. Thus, they are evidence of a process that is active on Mars today