Mars Or Bust
NASA picked landing sites Friday for twin rovers targeted for a January arrival at Mars to prospect for geological evidence that the Red Planet was once a warmer, wetter place hospitable to life.
The sites were selected after extensive analysis to maximize the chances for safe landings while ensuring a good scientific result from the mission.
Data gathered from NASA satellites orbiting the planet suggest both sites once abounded in water.
One is a crater into which a now-dry river apparently once emptied, perhaps filling the basin with a brimming lake. The other is a plain rich in hematite, an iron mineral that typically forms in standing water.
The sites, both near the equator in the southern hemisphere of Mars, are halfway around the planet from each other.
"They aren't the safest sites, they aren't the riskiest sites, they are the best sites," said Steve Squyres, principal investigator for the package of instruments the rovers carry and a Cornell University geologist.
Scientists are confident the scientific tools carried by the elaborate $800 million pair of rovers will enable them to operate as robotic field geologists in the hunt for evidence of past water activity on Mars. The landing sites, Gusev crater and Meridiani Planum, have been studied more closely than any other spots on Mars.
More than 100 scientists and engineers took more than two years to pick the sites, winnowing down a field of 155 prospects.
The sites represent a balance struck between the wishes of the scientists, who crave rocky landscapes for the burly rovers to examine, and the engineers, who abhor such terrain for the dangers it poses to the robots on landing.
The compromise produced two sites that appear flat and safe, but scientifically interesting.
Each of the rovers will land at about 40 mph, swaddled in its own cocoon of airbags, as did 1997's Pathfinder mission with its much smaller Sojourner rover. Engineers fear rocks taller than about knee-height could puncture the airbags.
In selecting where to land, scientists relied on satellite images acquired by NASA's Mars Global Surveyor and Odyssey spacecraft, as well as older Viking data from the 1970s.
Sites too steep, windy, dusty or rocky were off limits. The locations had to be at fairly low altitudes to provide enough atmosphere to fill the parachutes that will help slow the rovers as they plummet to the surface.
The landing sites also needed to be within a narrow band of the planet's equator to ensure the rovers' solar panels receive enough sunlight to meet their power needs. (Each rover also carries eight, 0.1-ounce pellets of radioactive plutonium dioxide that generate 1 watt of heat apiece to keep the six-wheeled robots warm at night.)
Each rover weighs 400 pounds and can move at a top speed of roughly 2 inches a second - about the same as a Galapagos tortoise.
During the 92-day missions, each rover is expected to travel about 2,000 feet and make close-up observations of at least a half-dozen rocks.
The landing sites are actually elongated ellipses, each 60 miles to 120 miles long and roughly 12 miles wide.
Which rover will land where is still tentative: NASA can change the order as late as a month after the launch of the first spacecraft, slated for May 30.
The British Beagle 2 spacecraft is targeting a third location on Mars, Isidis Planitia, for its December landing. That area is thought to contain sediments washed down from highlands to the south.