Mars Global Surveyor enters phase two

Parts of Mars are better known than areas of the Earth

By BBC News Online science editor Dr David Whitehouse

Nasa's Mars Global Surveyor (MGS) spacecraft has completed its primary mission of studying the Red Planet for a Martian year and is now entering a new phase of observations.

"By any conceivable measure, the scientific impact of MGS has been extraordinary," said Dr Arden Albee, of the California Institute of Technology. "In many ways we now know Mars to be a different planet than when the spacecraft arrived in 1997.

"In some aspects, we now have better maps of Mars than we do of Earth," he said.

During its primary science mission, MGS has studied the Martian climate, surface topography, and may have found evidence for running water on the planet's surface.

Problems at first

MGS arrived at Mars on 12 September, 1997, but immediately ran into technical problems. It was only in March 1999 that it began its first mapping phase.

Evidence of recent running water?

What MGS's cameras have revealed is a Mars we barely imagined before it got there.

Some of the most significant achievements of the mission include:

• Evidence for recent liquid water on the surface;
• Evidence for layering of rocks indicating widespread ponding of water or lakes when Mars was young;
• The first good estimate of the quantity of water trapped in both Martian polar caps, about one and a half times the amount of ice in Greenland;
• Recognition of the flat Northern Hemisphere, a region that has been proposed as the site of an ancient ocean;
• The surprising detection of highly magnetised crust, indicating the rapid cooling of Mars when it was young;
• Identification of the mineral haematite, indicating former wet areas in which to search for evidence of early life.

As of 31 January, 2001, the spacecraft will have made 8,505 orbits of the planet, taking more than 58,000 images. It has also carried out 490 million laser-altimeter shots to measure surface topography and performed 97 million spectral measurements.

Its new mission will be to scout for future landing sites for several upcoming missions.