Mars Global Surveyor Mars Orbiter Camera Release: MOC2-74 Mars Global Surveyor Mars Orbiter Camera Image ID: 567897575.7707 P077-07
CAPTIONLiquid water on the surface of Mars? Today, Mars is a cold, arid world. The driest deserts of Earth have many factors of ten more water than the surface environment of Mars. However, Mariner 9 and Viking in the 1970s showed abundant evidence that Mars once had channels and valleys carved by liquid water. These earlier missions, however, found only equivocal evidence of places where liquid water might have ponded to form lakes, seas, or even oceans.
MOC image 7707 (above) shows a portion of the wall and floor of an ancient impact crater in the southern cratered terrain of Noachis Terra. The MOC image reveals v-shaped depressions on the crater wall that are characteristic of water seepage from an underground layer that is exposed in the crater walls. The image also shows a smooth, dark surface on the crater floor that might be interpreted as the remains of a pond or lake. There are two types of dark surfaces on the floor of this 50 kilometer (31 miles) diameter crater, located at 65°S, 15°W. One dark surface shows a rippled texture and is known from Viking images to be a field of windblown dunes. The other is a relatively smooth surface with "islands" of bright material within it. The boundary between the dark floor materials and the lighter materials of the crater wall suggests, by the formation of bays and peninsulas, a "ponding" relationship.
There are four general hypotheses that might explain the "pond":
(1) Water seeped out of a layer in the crater wall, ran downslope, and ponded on the crater floor. This water would have eventually dried up, leaving a dark surface of sand similar to the material that comprises the dunes.
(2) The meteorite impact that formed the crater created cracks in the martian crust beneath the crater. Eventually, dark (basaltic) lava came up through these cracks and "ponded" on the crater floor (this kind of process is not unusual and is known to have created the "mare" on the Moon). Heat from the magma and lava melted ground ice which then seeped as liquid water from a layer high in the crater wall.
(3) The seepage features are not related to the "ponding" feature. The "ponding" feature is actually coarse sand and/or gravel related to deflation of the crater floor and creation of the large field of dark sand dunes.
(4) None of the above are correct, and the features cannot be explained without additional information.
To test these hypotheses and help determine the role of water in the formation of the "seepage" and "ponding" features, additional images of this crater will be targeted during Mars Global Surveyor's Mapping Phase, which is planned to run from March 1999 to March 2001.
MOC image 7707 was taken during Mars Global Surveyor's Aerobrake-1 Phase on December 29, 1997. This image was also the subject of an earlier MGS MOC release on May 27, 1998. The picture is available here at full resolution (840 KByte GIF) (about 30 meters (98 feet) per pixel) and half resolution (225 KByte GIF) (about 60 meters (196 feet) per pixel). Also available is a version of this image with various features labeled (90 KByte GIF). The scene is approximately 29.5 km (18.3 miles) wide and 37.8 km (23.5 miles) long. (CLICK HERE for a context image).
Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.
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