PIA02339: Autumn Frost, North Polar Sand Dunes
 Target Name:  Mars
 Is a satellite of:  Sol (our sun)
 Mission:  Mars Global Surveyor (MGS)
 Spacecraft:  Mars Global Surveyor Orbiter
 Instrument:  Mars Orbiter Camera (MOC)
 Product Size:  418 x 802 pixels (w x h)
 Produced By:  Malin Space Science Systems
 Producer ID:  MOC2-184 MRPS95343 P50602
 Addition Date:  2000-05-13
 Primary Data Set:  MGS EDRs
 Full-Res TIFF:  PIA02339.tif (267.1 kB)
 Full-Res JPEG:  PIA02339.jpg (70.98 kB)

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Original Caption Released with Image:

Autumn in the martian northern hemisphere began around August 1, 1999. Almost as soon as northern fall began, the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) started documenting the arrival of autumn frost--a precursor to the cold winter that will arrive in late December 1999. The first features to become covered by frost were the sand dunes that surround the north polar ice cap. The dunes seen here would normally appear very dark--almost black--except when covered by frost. Why the dunes begin to frost sooner than the surrounding surfaces is a mystery: perhaps the dunes contain water vapor that emerges from the sand during the day and condenses again at night. This picture shows dunes near 74.7N, 61.4W at a resolution of about 7.3 meters (24 feet) per pixel. The area covered is about 3 km (1.9 mi) across and is illuminated from the upper right. The picture appears to be somewhat fuzzy and grainy because the dunes here are seen through the thin haze of the gathering north polar winter hood (i.e., clouds).

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