Mars Global Surveyor Orbiter's Long Life Helps Scientists Track Changes On Mars

That's just one of the surprising discoveries that have resultedfrom the extended life of NASA's Mars Global Surveyor, which this monthbegan its ninth year in orbit around Mars. Boulders tumbling down aMartian slope left tracks that weren't there two years ago. New impactcraters formed since the 1970s suggest changes to age-estimatingmodels. And for three Mars summers in a row, deposits of frozen carbondioxide near Mars' south pole have shrunk from the previous year'ssize, suggesting a climate change in progress.

"Our prime mission ended in early 2001, but many of the mostimportant findings have come since then, and even bigger ones might lieahead," said Tom Thorpe, project manager for Mars Global Surveyor atNASA's Jet Propulsion Laboratory, Pasadena, Calif. The orbiter ishealthy and may be able to continue studying Mars for five to 10 moreyears, he said.

Mars years are nearly twice as long as Earth years. The orbiter'slongevity has enabled monitoring of year-to-year patterns on Mars, suchas seasonal dust storms and changes in the polar caps. "Mars is anactive planet, and over a range of timescales changes occur, even inthe surface," said Dr. Michael Malin of Malin Space Science Systems,San Diego, principal investigator for the Mars Orbiter Camera on MarsGlobal Surveyor.

"To see new gullies and other changes in Mars surface features on atime span of a few years presents us with a more active, dynamic planetthan many suspected before Mars Global Surveyor got there," saidMichael Meyer, Mars Exploration Program chief scientist, NASAHeadquarters, Washington.

Two gullies appear in an April 2005 image of a sand-dune slope wherethey did not exist in July 2002. The Mars Orbiter Camera team has foundmany sites on Mars with fresh-looking gullies, and checked back at morethan 100 gullied sites for possible changes between imaging dates, butthis is the first such find. Some gullies, on slopes of large sanddunes, might have formed when frozen carbon dioxide, trapped bywindblown sand during winter, vaporized rapidly in spring, releasinggas that made the sand flow as a gully-carving fluid.

At another site, more than a dozen boulders left tracks when theyrolled down a hill sometime between the taking of images in November2003 and December 2004. It is possible that they were set in motion bystrong wind or by a "marsquake," Malin said.

Some changes are slower than expected. Studies suggest new impactcraters might appear at only about one-fifth the pace assumedpreviously, Malin said. That pace is important because crater countsare used to estimate the ages of Mars surfaces.

The camera has recorded seasonal patterns of clouds and dust withinthe atmosphere over the entire planet. In addition, other instrumentson Mars Global Surveyor have provided information about atmosphericchanges and year-to-year patterns on Mars as the mission has persisted.Daily mapping of dust abundance in Mars' atmosphere by the ThermalEmission Spectrometer has shown dust over large areas during three Marssouthern hemisphere summers in a row. However, the extent and durationof dust storms varied from year to year.

Mars Global Surveyor was launched Nov. 7, 1996; entered orbit aroundMarsSept. 12, 1997; and returned the first Mars data from its scienceinstruments Sept. 15, 1997. Beyond its own investigations, the orbiterprovides support for other Mars missions, such as landing-siteevaluations, atmospheric monitoring, communication relay and imaging ofhardware on the surface. JPL, a division of the California Institute ofTechnology in Pasadena, manages the mission for NASA's Science MissionDirectorate, Washington. JPL's industrial partner is Lockheed MartinSpace Systems, Denver, which built and operates the spacecraft.

For newly released images on the Internet, visit: http://www.nasa.gov/vision/universe/solarsystem/mgs-092005-images.html and http://www.msss.com/mars_images/moc/2005/09/20/ .

For more information about NASA and agency programs on the Internet, visit: http://www.nasa.gov/home