Backstory: Don't swat that fly. It's a spacecraft!

Picture this: Swarms of one-legged robots hopping across Mars like malformed chicks. They dart in and out of caves and crevices, grabbing soil samples and searching for signs of ancient microbes - and thus life.

Or this: A flying wing that gently flaps across the cloud tops of Venus, sniffing the atmosphere for organic molecules. Elsewhere in the solar system, robots that buzz and flit like insects will hover over planets, hunting for hot spots formed by lava or exploring crater walls.

Welcome to the space exploration of tomorrow. While NASA struggles to return humans to the moon, scientists and engineers in labs across the country are letting their imaginations run free in designing hardware for far more distant exploration of the solar system.

For the moment, the only disciplinarians are the laws of physics and the folks who write the checks. So far, at least the laws of physics present no showstoppers.

At first glance, many of these concepts seem like refugees from "A Hitchhiker's Guide to the Galaxy." But advances in exotic materials, increasingly "intelligent" software, and shrinking electronics are bringing once-fanciful ideas closer to the drafting table.

Individually, these celestial machines could help revolutionize planetary exploration. But their true potential may lie in using them with traditional orbiters, landers, and rovers. The resulting research would come about as close to human exploration as you can get without putting actual bootprints on Mars or the moon. The robots and rovers would essentially set their own exploration agenda. They may not make missions cheaper, but they could squeeze more science out of each voyage.

These days, a typical mission to Mars begins with an orbiter scouting for landing sites. Some 16 months later, NASA launches a rover or lander mission. While today's rovers can take key measurements, they are restricted to relatively smooth terrain, which can limit discovery. The results lead to planning yet more missions, over many years. "You get a global picture, and a very local picture of Mars" with this approach, says Wolfgang Fink, a physicist at the California Institute of Technology in Pasadena.

But in the not-too-distant future, Dr. Fink, along with hydrologist James Dohm of the University of Arizona and two other colleagues, envision layer-cake exploration. As described in the journal Planetary and Space Science, it would use a multitude of smaller, less expensive sensors to scour a planet and coordinate with the rover. Different sensors would probe different terrain. All would "talk" to each other and react to conditions without waiting for instructions from scientists a solar system away.

Many of the pieces needed to adopt this exploration strategy already are emerging in labs and studies funded by NASA's Institute for Advanced Concepts in Atlanta. Take the "chick" robots of Steven Dubowsky and Penny Boston. Dr. Boston, who directs the cave and karst studies program at the New Mexico Institute of Mining and Technology in Socorro, is interested in finding evidence of life on other planets by identifying the mineral signals that microbes leave behind.

This would mean exploring caves, cracks, and natural tunnels in old lava floes - places sheltered from the radiation and erosion that can kill off tiny organisms. They are also places that today's rovers would "quake in their wheels" to explore, says Boston.

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