Spirit Scientists Plot a Course
Pasadena, Spirit Mission Sol 10
|This zoomed-in overhead view of the Mars Exploration Rover Spirit’s estimated landing site and surrounding area shows the rover’s potential "itinerary." Scientists and engineers plan to drive the rover approximately 250 meters (820 feet) from the green point to the rim of a nearby crater measuring 192 meters (630 feet) in diameter. They then plan to drive toward the east hills, the tops of which measure 2-3 kilometers (1-2 miles) away from the rover’s estimated landing site. This image is a composite of images taken by the camera on Mars Global Surveyor and the descent image motion estimation system camera located on the bottom of the rover’s lander.|
"We know where we are now," announced MER Principal Investigator Steve Squyres Tuesday. "And we also know where we’re going."
Mission engineers expect the rover to roll down off its landing platform onto the martian surface late Wednesday night.
The first thing Spirit will do after getting all six wheels on the ground is sample the soil in the immediate vicinity of the landing platform. Once that task is complete, Spirit will head out toward a nearby crater.
The crater, about 200 meters (about 650 feet) across, offers the Spirit team what they believe is their best opportunity to examine older materials from below the surface that may reveal Gusev‘s history.
"As we go closer" to the crater, said Squyres, "we will go deeper and deeper into what geologists call the ejecta blanket, the stuff that was thrown out of the crater. We will see stuff that was excavated from 10, 20, 30 meters down beneath the surface. It will provide a window into the subsurface of Mars."
The crater, as yet unnamed, is about 250 meters (about 800 feet) away. It will take Spirit many days, perhaps weeks, to get there. Even if it made a beeline for the crater, Spirit would need at least 5 or 6 days to reach the its rim. But scientists don’t plan to rush things. The rover will probably stop many times along the way to examine interesting rocks.
Moreover, as Spirit approaches the crater, the very thing that makes it a compelling target of investigation – the fact that rocks have been thrown up to the surface by the impact that created the crater – may slow the rover’s progress. The closer Spirit gets to the crater rim, the more hazardous the terrain may become, and Spirit may need to approach cautiously.
It’s too early to tell whether Spirit will be able to get right up to the crater rim – or perhaps, even to sample material inside the crater. From a distance, scientists can see that the rim is about 5 meters (about 16 feet) high most of the way around. One segment of the rim, which, fortunately, is on the side of the crater from which Spirit will approach, has collapsed. But when the rover gets closer, scientists may decide that it is too risky to make a close approach.
After exploring the crater, Spirit will head for the hills. A cluster of hills, some 100 meters (300 feet) high, lies to the east. They are one of the most prominent features of the landing site. Now that scientists know where Spirit is, they have been able to determine that the nearest of these hills is just under 3 kilometers (less than 2 miles) away.
|In the distance stand the east hills, which are closest to the Mars Exploration Rover Spirit in comparison to other hill ranges seen on the martian horizon. The top of the east hills are approximately 2 to 3 kilometers (1 to 2 miles) away from the rover’s approximate location. This image was taken on Mars by the rover’s panoramic camera.|
What the hills are made and what processes formed them are still unknowns.
One possibility, said Squyres is that the hills represent material that has been sticking up above the crater since before it was filled in. "You can think of them as islands sticking out of a sea of debris that fills the crater."
The other possibility, he said, is that the crater was once filled in to the height of the top of the hills, and that much of it has since been stripped away by water or wind, "leaving these hills as remnants."
Spirit may never reach the hills. Its mission design calls for the rover to traverse a minimum total of 600 meters (about 1/3 of a mile). Spirit will cover nearly half that distance getting to the crater. The hills are nearly 5 times as far away.
Nevertheless, the closer the rover gets, the more it will be able to learn. Spirit’s Pancam will be able to take increasingly detailed images of the hills; and Mini-TES will be able to target smaller and smaller areas in an effort to tease out their mineral composition.
As it approaches, Spirit may also find material on the surface that originated in the hills. "There are a variety of processes that could transport stuff down from the hills," said Squyres. "Impact cratering on the hills could throw stuff out towards where we are." Wind or water erosion could also have deposited material from the hills onto the plain below.
But, Squyres said, the only way to figure out which theories are correct is "to get as close as we can and try to find out."