Now dry and dusty, Mars may have been marbled with vast oceans and seas billions of years ago.
An artist's rendition of an ancient sea on Mars.
An illustration of NASA's new Mars Exploration Rover, on the surface of Mars. NASA and the European Space Agency are both sending new missions to Mars to find clues about the planet's possible watery past.
Missions to Mars
By early 2004, a fleet of spacecraft are expected to be in orbit around the Red Planet. Get the details on the latest missions
Every two years or so, Mars and the Earth are in just the right positions to make it possible to send a spacecraft from here to there. As NPR's Joe Palca reports, now is that golden time.
The first of two NASA Mars missions blasted off Tuesday from the Kennedy Space Center in Florida. The second mission is scheduled for liftoff in late June. If all goes well, the two spacecraft will land on the surface of Mars next January.
The Mars Exploration Rover A, or MER-A as it's known, and its twin, MER-B, both have the same task once they arrive: to figure out what happened to the water on Mars. Although Mars is now an arid planet, Catherine Weitz, a NASA Mars program scientist, says that geologic features on Mars appear to have been formed by water. Scientists believe that Mars' Gusev Crater -- MER-A's target landing site -- once held a giant lake.
"The question we want to know when we go into this crater is how big was that lake, how long was that lake, and could it have supported life in the past," Weitz says.
The MER-A rover will use a mounted stereo camera to image the planet, while a robotic arm will drill away the outer grunge covering rocks and then use a microscope and other tools to see what's underneath.
"We're going to use all these instruments to try and understand what was the water activity at the landing sights," Weitz says. "Was it persistent? Could it have been warmer and wetter, which would have made it more habitable for life in the past?'"
MER-B is going to a place near the Martian equator called Meridiani Planum, where a satellite in orbit around Mars detected crystalline hematite -- a mineral that on Earth is associated with liquid water processes. Weitz says the MER-B mission will study the mineral composition of the area in search of evidence that water once flowed there.
The $800 million NASA missions are part of an international fleet of spacecraft all heading for Mars this summer.
Earlier this week, the European Space Agency launched a mission called Mars Express that will also look for signs of water on the Red Planet. Computer models estimate that some of the water on Mars simply evaporated and was carried into space by the solar wind. Instruments aboard the Mars Express will measure the remnants of water coming from the Martian atmosphere today. The data will be used to estimate the fraction of the Martian atmosphere and water that's been lost to space over time.
But getting to Mars isn't easy. Three of the last six missions to the Red Planet have failed. A Japanese Mars probe called Nozomi, which was launched in 1998, went off course. Engineers got it going in the right direction, but a solar flare knocked out some key electrical systems, and while it may make it to Mars later this year, it may not work once it arrives.