Space scientists have chosen two sites on Mars where twin robot vehicles will look for evidence that a warmer, wetter red planet might once have harbored life. Two spacecraft carrying the rovers will be launched on May 30 and June 25, and both should reach Mars 18 days apart next January, NASA officials said Friday. One site is a giant crater where images from the orbiting Mars Global Surveyor spacecraft indicate that a lake might once have existed, fed by a deep and sinuous river that has left only a dry trace now.
The other landing area is on a broad plain containing outcroppings of a mineral called hematite -- a form of iron oxide that on Earth is known to accumulate in standing water. Hematite could be a signal not only of some ancient lake but also even of a spot where microbes and plants could have flourished 2 billion or 3 billion years ago -- long before the planet became the cold, dry and virtually airless rock-strewn desert that it is today. The first of the two six-wheeled Mars Exploration Rovers is tentatively scheduled to land with its mother spacecraft at a large impact crater named Gusev, about 15 degrees south of the Martian equator. The second robot will be directed toward an area called Meridani Planum, about 2 degrees south of the equator and halfway around the planet from Gusev.
"Meridani and Gusev both show powerful evidence of past liquid water, but in very different ways," said Steven W. Squyres, a Cornell University astronomer and the science chief for the rovers' tasks. "Meridani has a chemical signature for past water and at Gusev you've got a big hole in the ground with a dry riverbed going right into it. They are fabulous sites, and they complement each other because they're so different." Landing the rovers near the Martian equator increases the time that both vehicles are able to do their jobs in sunlight, for both will be powered by solar panels.
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