Mars Global Surveyor
Mars Orbiter Camera

South Melea Planum, By The Dawn's Early Light

MGS MOC Release No. MOC2-126, 11 May 1999



MOC "sees" by the dawn's early light! These two pictures were taken over the high southern polar latitudes during the first week of May 1999. The areas shown are currently in southern winter darkness. Because sunlight is scattered over the horizon by aerosols--dust and ice particles--suspended in the atmosphere, sufficient light reaches regions within a few degrees of the terminator (the line dividing night and day) to be visible to the Mars Global Surveyor Mars Orbiter Camera (MOC) when the maximum exposure settings are used.

The picture on the left (MOC2-126a) shows a polygonally-patterned surface on southern Malea Planum. At the time the picture was taken, the sun was more than 4.5° below the northern horizon. The scene covers an area 3 kilometers (1.9 miles) wide, with the illumination from the top of the picture.

The image on the right (MOC2-126b) shows a bright, wispy cloud hanging over southern Malea Planum. This cloud would not normally be visible, since it is currently in darkness. At the time this picture was taken, the sun was more than 5.7° below the northern horizon. The scene covers an area 3 kilometers (1.9 miles) wide. Again, the illumination is from the top.

In both frames, the surface appears a relatively uniform gray. At the time the pictures were acquired, the surfaces were covered with south polar wintertime frost. The highly reflective frost, in fact, may have contributed to the increased visibility of these surfaces.

This "twilight imaging" technique for viewing Mars can only work near the terminator; thus in early May only regions between about 67°S and 74°S were visible in twilight images in the southern hemisphere, and a similar narrow latitude range could be imaged in the northern hemisphere. MOC cannot "see" in the total darkness of full-borne night.


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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