Scientists find obstacle at heart of Beagle landing zone
BY JUSTIN RAY
Posted: December 29, 2003
The first clear view of the specific area where the British Beagle 2 lander should have touched down Christmas Day has revealed a one-kilometer crater dead center in the target landing zone, but officials are quick to say the discovery doesn't dash their optimism of finding the missing craft.
"This would be an incredibly unlucky situation," Colin Pillinger, lead scientist for the Beagle 2 project, said this morning.
To date, all attempts using the American Mars Odyssey orbiter and radio telescopes in the U.K. and California have failed to detect a peep from Beagle.
"Meteor Crater out in Arizona is a 1.2-kilometer crater...several hundred meters deep. This crater is comparable in size," Pillinger said.
Although Beagle scientists had examined numerous photographs of the broad Isidis Planitia region near the Martian equator while selecting that area to send the lander, the new Global Surveyor image is the first good view of the ellipse-shaped zone where Beagle was expected to land.
"When we were choosing this site in the first place, we avoided the obvious craters that we could see at relatively low-resolution. You cannot avoid every crater on Mars, you'd never go there," Pillinger said.
"We'd chosen the area that we were landing because we believed it was the right sort of area to risk a landing -- no slopes, low altitude, rock abundance less than 15 percent. It was repeatedly said 'enough to keep the geologists happy but not so many (rocks) that it frightens the engineers to death.'"
Global Surveyor's camera is operated by Malin Space Science Systems.
"Something which came out of Mike Malin taking pictures of the actual area in which we believe we were targeted to land is right at the center, right at the center of the ellipse that we were aiming at, is a one-kilometer-across crater," Pillinger said.
"When we started to plan the mission, the estimate of the landing ellipse was 480 by 300 (kilometers), which is a very large area. As Mars Express has flown out to Mars, navigation has gotten better and better," mission manager Mark Sims said.
Following Beagle's deployment from the Mars Express orbiter on December 19, mission officials were able to narrow the landing zone to an ellipse-shaped swath 70 kilometers long and 10 kilometers wide.
"There is absolutely no way you could target to avoid a one-kilometer crater. The target got smaller the better we knew the trajectory of Mars Express. The best, the absolute best that could be done, was we were targeting 70 by 10 kilometers. There are an awful lot of one-kilometer craters that you can put into an ellipse that size," Pillinger said.
Despite this new revelation, officials say the chances of Beagle reaching the crater are slim.
"We must stress this a low probability, it is only one of a number of possibilities," Sims said of why Beagle has yet to phone home.
"We would have to be incredibly accurate and also incredibly unlucky that we went down this crater, which would not be good news -- one would not want to go into a crater, one would not want bounce on the edge and bounce into it," Pillinger added.
The highly ambitious Beagle lander used parachutes to slow its descent and then three balloon-like airbags around the craft to cushion multiple bounces on the surface before coming to rest. Designers said the landing system needed to avoid bouncing on slopes and rocky terrain. Also, landing in a crater could cause shadows on the craft's power-generating solar panels that would create more trouble.
The Martian landscape is covered by impact craters. Such places have their certain risks to robotic spacecraft but also rewards for scientists.
"There are two ways of looking at craters -- you don't want to land right by them but you want to land near enough to them so you can take advantage. The impact excavates rocks and gives you a nice, diverse suite of rocks that you can analyze," Pillinger said.
Over the coming days, further tries are planned to receive a signal from Beagle with the Odyssey spacecraft and the Stanford University radio telescope. The European Mars Express orbiter will begin searching in early January using a communications link previously tested with the lander.
"We are working under the assumption that Beagle 2 is on the surface of Mars and for some reason cannot communicate to us. In particular, we're looking at two major issues. One is communications, and there are also related timing and software issues," Sims said.
"We've got a few more Odyssey contacts, the last one being on December 31. Then we have four contacts with Mars Express already pre-programmed into Beagle, assuming the software is running, on (January) 6, 12, 13 and 17. The 6th and 12th are when Mars Express is maneuvering into its final orbit, so they are not optimum for Beagle 2 communications. The 13th and 17th are very good opportunities for Mars Express."
Attempts using the Jodrell Bank radio telescope concluded last night since the side of Mars where the landing site is located is no longer visible to the observatory when Beagle should be transmitting its call.
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