You've got the tent tied to the roof of the van, the kids strapped into the backseat, and you've hit the highway. Where's the campsite? You know it's somewhere in the state of Wyoming, but all you have to go on is a highway map and a beautiful photograph. Let's see—there's a campfire pit, some pine trees, and a nondescript mountain in the distance. Any minute now, the kids will start screaming.
The NASA scientists charged with planning Mars outings face a similar lack of information. Three orbiters have mapped the planet, and three rovers have inched over tiny patches of terrain. Yet scientists still don't have enough data to pick the ideal destinations for tomorrow's robotic or human explorers. Mars is a big place—its surface area is the same as Earth's, minus the oceans. Where are the best spots to find evidence of Martian life? Where might water be lurking just below the surface? More pragmatically, how can the next lander avoid crashing into a giant boulder? To answer such urgent questions, scientists need exponentially more data than they have collected so far.
Gathering that data is the mission of the Mars Reconnaissance Orbiter, or MRO, a 4,800-pound probe now in elliptical orbit around the Red Planet. "We want the ability to get context and zoom in," says Richard Zurek, MRO project scientist at the Jet Propulsion Laboratory in Pasadena, California. The first step is to reach a tight, circular path around the planet. The spacecraft is using an innovative technique called aerobraking, plowing through the thin upper atmosphere and using aerodynamic drag to fine-tune its orbit. Provided the MRO doesn't fry in the process, by the end of this month it will begin gathering images of the Martian surface in unprecedented detail (the images shown here are part of a sneak preview released by NASA when MRO first arrived at Mars). It will capture features as small as a foot across, peer yards below the surface to uncover hidden sediments, fathom the atmosphere, and gather images in a wide range of colors, from visible to infrared light, to reveal the nature of the surface minerals. "All this is to better understand the planet scientifically," Zurek says, "but also to identify those places where the next set of missions going to the surface can be used in the best possible ways."
The centerpiece of MRO is the 150-pound High Resolution Imaging Science Experiment, or HiRISE, the largest and most capable camera ever sent beyond Earth orbit. Whizzing 200 miles above the Martian surface at 2.2 miles per second, it will pick out finer surface details on Mars than commercial satellites can show us on Earth, where cameras have to ride twice as far above the ground to avoid our planet's thicker atmosphere. HiRISE will focus in on only 1 percent of the surface—a breadth similar to other high-resolution orbiting cameras—but will zoom in at five times the resolution of the next-best Mars camera. One mission of HiRISE is to scour seven potential landing zones for a preponderance of rocks larger than about three feet wide, which can wreck a craft upon landing. With HiRISE providing the zoom, the Context Imager (CTX) camera will provide the big picture. CTX will photograph a 20-mile-wide swath of surface at a resolution of 20 feet per pixel, higher than any other orbiting mapper that has visited the Red Planet.
The big prize is evidence of life, past or present. In seeking it, MRO will search out areas where water has played a role in the surface geology or may still remain hidden, perhaps as dirty snow. A good high-resolution camera can find canyons, channels, and other features that may have been formed by water. But determining how such features came to be—were they formed by jets of carbon dioxide or by a gentle spring of water?—requires the ability to analyze the minerals left behind. That's the job of the Complex Reconnaissance Imaging Spectrometer for Mars, or CRISM. CRISM will capture images in 545 different wavelengths, the full spectrum of reflected light, to reveal the chemical fingerprints of surface minerals.