mpl_siteimages_991115The varied terrain of the Mars Polar Lander's chosen
target region poses several dangers for a small craft attempting to gingerly plop down in the midst of its rolling hills. Overall, though, mission controllers say they couldn't hope for a better site."I've looked at the images that have come in over the past month or so, and there is very little in the way of hazards" said Joseph Boyce, the project scientist for the Mars Polar Lander and NASA's Mars Exploration Program. "You see some cracks, but the rolling hills that you see, they seem to roll at just about the right angle for you to land anything you want on it."
A team of scientists and engineers is continually analyzing landing site images as they arrive from the camera aboard the Mars Global Surveyor, Boyce said. After a review last week of the latest intelligence data from the target landing site, Boyce asked several members of that team to imaging the best-possible site, he said.
"I asked them, 'If you were to build a landing site that you wanted in the polar regions, what would it look like? What you would hope for?' And every last one of them said, 'Actually, I think we've got it,' " Boyce said.
This image of an area in Mars's southern polar region shows the rolling roughness of the terrain. Inset at the top right is an image of Qualcomm (formerly Jack Murphy) Stadium in San Diego, Calif. at the same scale. The bar at the lower left represents 400 meters -- about one quarter mile. Image courtesy of NASA, JPL and Malin Space Sciences Systems.
The reason the polar lander's target touchdown site is so welcoming is that it appears to be relatively free of the large boulders that would easily wreck any small spacecraft attempting to set down on top of them. The lander has no ability to distinguish a safe landing spot from a dangerous one, and will come down just as confidently on a treacherous obstacle as on a flat plain.
For this reason, mission operators believe the polar landing site is more forgiving than any of the sites where craft have landed in the past.
The landing site where the Mars Pathfinder touched down in 1997 would be much more risky for a tripod-footed craft like the polar lander, Boyce said. Even though no pictures showed the Pathfinder site at a scale that could show boulder-size features, scientists knew that big rocks would cover the landscape.
The image on the left shows the area around the site where the airbag-protected Mars Pathfinder bounced to the surface in 1997. The image on the right shows an area from the Mars Polar Lander's target landing site. The white bar at the bottom represents 800 meters, which is about half a mile. Image courtesy of NASA, JPL and Malin Space Sciences Systems.
The site was near large impact craters and in the middle of an ancient flood channel. It would certainly be strewn with rocks deposited by flood waters and thrown out of the craters.
Boyce, who was program scientist for the Viking 1 mission and a member of the landing-site selection team for Viking 2, is familiar with landing on other planets. The Viking 1 and Viking 2 landers reached Mars in 1976.
The apparently smooth hillocks of the polar ground make this site much safer than the areas where the Viking landers set down, Boyce said.
"I think we're ten times better off here. We may have a rolling landing site, but we see there are almost nothing in the way of rocks," he said.
"This is the kind of landing site that you'd like to see a rock because it tells you that you're not landing in fluffy stuff. So seeing a few rocks is good news, and there are a few things we think are rocks, but there are not many."
The hazards at the pole are not rocks but cracks, Boyce said, but any cracks appear to be shallow and smooth, and less hazardous, at any rate, than the Viking sites.
But not all scientists involved in the mission are entirely so optimistic.
Peter Smith, who built the camera for the Mars Pathfinder and two cameras on the polar lander, has seen many of the recent images of the polar landing site. He cautions that many unanticipated hazards may lie on the martian ground.Almost every reconnaissance picture that comes back from the Mars Global Surveyor is different from the previous one, Smith said. "Some (of the areas) are layered, some are sloped, some are pitted, some are hillock-y, some are spotted. Every kind of fractal dimension that you can imagine is represented on this polar layered terrain." Such terrain just beckons to be explored, Smith said, despite the potential risks.
"I don't want to understate the hazards," Boyce said. "This is not an easy thing to do, Mars is not an easy nut to crack when it comes to landing."
If the mission succeeds it will be due to a small measure of luck that the spacecraft missed any hazards on the way down, but mostly thanks to the hard work of everyone on the team, Boyce said. During the landing though, everyone involved will just have to wait as the polar lander drops through the atmosphere and executes the automatic landing sequence that sets it down on whatever happens to be there.
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