There's History in Them Thar Hills

Although it will be several more days, perhaps as much as a week, before Spirit engineers certify that the rover is ready to leave the safety of its landing platform and go exploring, scientists have already begun to make a list of places they’d like to visit. A cluster of distant hills to the east are high on their list.

“We certainly want to characterize the deposits in the immediate vicinity of the lander as soon as we’re off and roving,” says Ray Arvidson, deputy principal investigator for the MER missions. The next step will be to examine some of the interesting formations – the “mud-like” material near the lander petal is one favorite; ‘Sleepy Hollow’ is another – that can be reached with one or two days of driving.

The distant hills to the east is the current favorite among potential long-range driving targets. According to current estimates, they are about 50 to 100 meters (about 165 to 330 feet) high and between 1 and 2 kilometers (about half a mile to a mile) away.

What makes the hills an interesting target is that they may be much older than the rocks and soil in the vicinity of the landing site – perhaps billions of years older. If they are, they would tell a story about a completely different time in the history of Gusev Crater than the nearby rocks and soil.

The closer material, for the most part, will tell scientists what geologic processes have taken place in Gusev in the recent past, the last few hundred thousand years. But the material in the hills may be able to tell them what Gusev was like early in Mars’s history, back when Gusev may have been filled with water.

Will Spirit ever head for the hills? It’s too early to tell.

It certainly won’t happen any time soon. At full speed, the rover can clock a maximum of about 50 meters per sol. So even if the hills turn out to be only 1 kilometer away, it will take Spirit about 20 days to get there. And that’s assuming that the robotic geologist doesn’t stop to study any interesting rocks it finds along the way.

For now, says Arvidson, “We want to get off the lander. We want to make some measurements. And some more measurements.” But after that, he adds eagerly, the science team will “probably convince the project manager do to a long drive.”

Even if Spirit doesn’t make it all the way to the hills, the journey might be worthwhile. The closer it gets, the more scientists will learn.

“To get the mineralogy of a relief like that, we don’t necessarily need to be right up against it,” says Nathalie Cabrol, a geologist on the MER science team. As the rover gets closer, it will be able to take increasingly detailed images, giving scientists a better and better shot at figuring out what they’re made of. ‘ Mini-TES and Pancam can do wonders,’ says Cabrol, “even from a kilometer away.”