Second Rover to Join Spirit on Mars This Weekend

John Roach
for National Geographic News
January 20, 2004
The golf cart-size Spirit rover is off and rolling around Mars trying to figure out if it landed in a sort of ancient water hazard. Its twin, Opportunity, is on course to plop down Saturday on the opposite side of the planet and do the same. Mission scientists are so giddy you'd think they just shot a hole-in-one.

But the Mars Exploration Rovers Mission, or MER as some call it, has nothing to do with golf. The mission team is excited because they finally get to take a shot at what they've practiced for years: science on the red planet.

In particular, the twin rovers carry a suite of high-tech gadgets designed to image, probe, scratch, and sniff the rocks and soils within about a quarter mile (600 meters) of their landing sites for signs of past—or present—water. The substance was essential to the rise of life on Earth and may have allowed life to exist on Mars.

Images beamed to Earth over the last decade from spacecraft in orbit around Mars offer compelling evidence that Mars was once a water-rich environment, such as water channels and what appear to be ancient lakebeds, including Gusev crater—Spirit's new home.

"The question is not was there ever water here. The real question is did water persist for a long enough time to make life plausible?" said Harry McSween, a MER co-investigator from the University of Tennessee in Knoxville. "A quickly evaporating gully or puddle does not offer a good target for life, but a lake does."

Earth Analog

So, under what conditions and for how long does water have to sit around to make life plausible? In search of the answer, Nathalie Cabrol, a MER mission scientist from NASA Ames Research Center and SETI Institute in Moffett Field, California, has been spending a few months each year high up in the Bolivian Altiplano.

There, tucked into the crater of the 19,734-foot (6,014-meter) Licancabur Volcano, is a lake that Cabrol and her colleagues believe represents the closest any spot on Earth comes to resembling what a Martian lake may have been like when the red planet was a wetter place 3.5 billion years ago.

"As you go up in elevation on Earth, the temperature is decreasing, atmospheric pressure is decreasing, and the UV [ultraviolet] radiation is increasing. So now you have an environment a little bit more like Mars was 3.5 billion years ago," said Cabrol.

Cabrol and her colleague have discovered abundant and diverse life forms thriving in the lakes in and around the flanks of Licancabur, raising the speculation that life could have survived on ancient Mars.

Of keen interest to Cabrol is how the life—mostly microscopic—survives the region's ultraviolet radiation, which is 48 percent more intense than it is at sea level. Mars, which doesn't have a shielding ozone layer as does Earth, is today bombarded by UV radiation.

On ancient Mars, lakes and seas may have been deep enough to allow life forms to escape the UV radiation, but about 3.5 billion years ago scientists believe Mars began to dry out, the bodies of water evaporating into the thin air. As the water evaporated, the bodies of waters would have gotten too shallow for life in them to escape the UV radiation. To survive, the life forms would have to adapt.

Cabrol said this scenario that she imagines occurred on ancient Mars is happening right now to the lakes in and around Licancabur. About 15,000 years ago, the climate there was much wetter and all kinds of life forms lived in the lakes. Then about 11,000 years ago the climate shifted and the environment began to dry out. Now much of the life that lives in the lakes does so in the presence of high UV radiation.

The study of these organisms gives the researchers insight to the extreme limits of life. Knowing these limits, especially in an environment that is considered Mars-like, combined with the data collected by the Mars rovers may allow the researchers to infer whether life could have thrived on the red planet.

Mars Water Search

The rovers were sent to Mars to find out if there was indeed a lot of water on Mars. "This starts with the premise that water is critical for life," said Cabrol. "This is the only model we know that works on Earth, so it's logical to look for that on Mars too."

The suite of instruments on the rovers are designed to look for features in the Martian landscape, rocks, and soil such as channels, fine-scale layering common to lake sediments, rounded rocks, and certain minerals that indicate a liquid past, said McSween.

To get to the point of looking for water on Mars with the rovers, scientists relied on evidence supplied by the Mars Odyssey and Mars Global Surveyor orbiters. If Spirit and Opportunity find more compelling evidence for water, the next step would be sending another lander equipped to detect life.

"These rovers were intended to search for water, not life, and they don't really carry the instruments that would be needed for biology," said McSween.

With Spirit now safely on the ground and sending back images of its surroundings, Robert Bodnar, a geologist at Virginia Polytechnic Institute in Blacksburg who studies Martian meteorites for signs of water, said landing in Gusev may really have been an ace in the search for water.

"When I looked at those images, I said I could convince myself—if I didn't know it was Mars—that that's an old lake, or an inland sea shoreline there," he said. "It certainly looked like that."

Confirmation will come as the rovers hack around the Martian landscape, keeping a detailed scorecard for mission scientists to carefully analyze.

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