It's time to go back to Mars. Once every two years, the orbits of Earth and Mars are aligned just right, so it's possible to send a spacecraft from here to there. That special time is now.
NASA's latest mission, the Mars Science Laboratory (MSL), launched Saturday morning. It's another six-wheeled rover, but much larger than the rovers Spirit and Opportunity that landed on Mars in 2004. They weighed under 400 pounds. MSL weighs nearly a ton and is about the size of a small compact car.
Another important difference between MSL and its predecessors is it doesn't rely on solar panels for its power. Instead, it's carrying 8 pounds of plutonium that gives off heat that is converted to electricity.
The way MSL lands is also different. Spirit and Opportunity "basically crash landed, softly with airbags," says John Grotzinger, project scientist for MSL. "Mars Science Laboratory is so large that we need an active propulsion system."
The active propulsion system makes use of something NASA has never tried before. It's a sort of a rocket-powered helicopter: When it gets to about 200 feet above the surface, it lowers the rover down on a cable. With the rover dangling below, it descends slowly until rover wheels touch the ground.
"The risks are obvious," says Grotzinger, "but the advantages of this are that the rover lands basically intact, and there's almost no subsequent set-up that has to be done after the rover lands."
The rover has a mast with a camera on it, and a robotic arm. But Grotzinger says MSL is not just about taking pictures and pulverizing rocks.
"It is a laboratory, and so within the belly of the rover are two very important instruments," he says. "One of them is an X-ray diffractometer, which is the instrument that geologists use on Earth to characterize the mineral content of rocks and soils."
The other instrument is called the Sample Analysis at Mars, or SAM. It's actually a suite of instruments enclosed in a box about the size of a microwave oven. There are 74 sample cups inside SAM. The idea is that the rover's robotic arm will drill into rocks, and some of the resulting powder will be delivered to one of the cups.
The cup then goes into an oven, where it's heated to 1,000 degrees. "As the gases are coming off, we measure their composition with a mass spectrometer," says Paul Mahaffy of NASA's Goddard Space Flight Center in Greenbelt, Md. Mahaffy is the principal investigator for SAM.
One of the elements SAM will be able to measure is carbon. Carbon is essential for life, but Mahaffy and everyone else associated with this mission say finding carbon compounds will not be proof that there is or was life on Mars. It will be just another piece of evidence pointing in that direction.
"We fully don't expect we're going to go to Mars and get a definitive answer, 'Yes, there was life,' or 'No, there wasn't life,' unless we absolutely happen to hit a home run and land in exactly the right spot, and conditions were exactly right," says Mahaffy.
If everything had gone according to plan, MSL would already be on Mars. The mission was supposed to launch in 2009. But delays in building hardware forced a two-year postponement.
Mahaffy says the launch can't come too soon for him and his team. "We've been anxiously awaiting the launch for a long time," he says, "and even more anxiously awaiting August 6th of 2012, when we land in Gale crater and start exploring."
Gale crater is MSL's target. It's a giant crater with a mountain in the middle of it. The site was chosen because measurements from Mars' orbit showed there was lots of interesting geology in the crater, and possibly evidence that Mars was once habitable. With luck, MSL will provide confirmation of that.
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