In June NASA launched two spacecraft in its new Mars Exploration Rover program. Both contain instruments designed by ASU scientist Philip Christensen and are set to land on the Martian surface in 2004.

"The keystone experiment on the Mars Exploration Rover mission, our most bold return to the surface of Mars since the Viking mission of a generation ago, is the device that ASU, under Phil Christensen, is running,"said Jim Garvin, the lead scientist for Mars exploration at the National Aeronautics and Space Administration (NASA) headquarters in Washington, D.C.

Christensen's instruments identify the composition of the Martian surface and atmosphere by measuring the thermal infrared energy, or heat, given off by the planet. His thermal emissions spectrometer (TES) on board the Mars Global Surveyor and his thermal emission imaging system (THEMIS) on board the Odyssey are both currently orbiting Mars, beaming back invaluable images. The rovers will each contain a "mini-TES"that will conduct mineral mapping directly on the Red Planet's surface -- the first time such research has ever been conducted on another world. Christensen is the principal investigator for all three flight instruments.

"It's as if we put on binoculars or night vision scopes and can then see into the rocks and how they were assembled,"marveled Garvin. "In my view, that's the best way to really attack our questions regarding the history of water on Mars."

Some of those questions have recently been answered by Christensen's research. For example, he proposed that images from Odyssey and Global Surveyor suggest melting snow is the likely cause of the numerous eroded gullies on Mars.

Looking at an image of an impact crater on Mars, Christensen noted eroded gullies on the crater's cold, pole-facing northern wall and immediately next to them a section of what he calls "pasted-on terrain."Such unique terrain represents a smooth deposit of material that Mars researchers have concluded is "volatile"(composed of materials that evaporate in the thin Mars atmosphere), because it characteristically occurs only in the coldest, most sheltered areas. The most likely composition of this slowly evaporating material is snow, according to Christensen. In a paper published earlier this year by Nature online, Christensen wrote that the gullies are carved by water melting and flowing beneath snow packs, where it is sheltered from rapid evaporation in the planet's thin atmosphere.

"The Odyssey image shows a crater on the pole-facing side has this 'pasted-on' terrain, and as you come around to the west there are all these gullies,"said Christensen. "I saw it and said 'Ah-ha!' It looks for all the world like these gullies are being exposed as this terrain is being removed through melting and evaporation."

Only time will tell what sort of "ah-ha"discoveries the rovers will uncover, but Garvin is sure of one thing.

"When we get Phil's instrument on the surface of Mars, it's going to make the Rover mission hit a home run,"he enthused. "It will find something. Whether it's what we expect, or whether Mars throws another curve at us, I don't care. It will be neat."

James Hathaway contributed to this article.

A working model of the Mars Rover is on display in the lobby of the Moeur Building.

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Lines on the Martian surface indicate material flowed along the valley.