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Mars Missions Offer Clues in Hunt for New Worlds
This image shows the Spirit rover probing its first target rock on Mars, Adirondack.Is there another Mars out there?

Within the next decade, NASA plans to develop space telescopes with super-sharp vision that can detect planets like Mars or Earth around other stars. In the meantime, learning as much as we can about our terrestrial next-door neighbors will help us understand what to look for, according to scientists at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

This image shows the Spirit rover probing its first target rock on Mars, Adirondack. Each mission to the red planet teaches us more about our terrestrial neighbor.

More than 100 planets have been discovered outside our Solar System, but they all are gaseous giants like Jupiter and Saturn. NASA's search for life beyond our Solar System hinges on finding smaller, rocky planets. As far as we know, only this type of planet could harbor liquid water on the surface, a feature considered essential to life.

But which are we most likely to find -- another Mars, a planet like Earth, or perhaps one similar to Venus?

"It may be that Earths are unusual, or common. Terrestrial Planet Finder is an experiment we have to run in order to find out," said Vikki Meadows, an astrobiologist at JPL.

The Mars Exploration Rover mission may determine the past climate history of Mars. The discovery would help scientists recognize a younger version of Mars, should one turn up out there among the stars.

The Viking mission of the 1970s told scientists that the planet has undergone massive changes since it formed. Scientists believe Mars once was a warm, wet world.

But since it has only one-tenth of Earth's mass, Mars didn't have enough gravity to hang onto some of the conditions favorable to life. While the Earth stabilized, formed oceans, and developed a hospitable atmosphere, Mars changed very little.

"Mars is a snapshot that shows us what terrestrial planets look like at an early age," said David Crisp, a senior research scientist at JPL.

An artist concept of Terrestrial Planet Finder.An artist's concept of Terrestrial Planet Finder. The mission will hunt for terrestrial planets outside our Solar System.

In 2013, NASA will launch Terrestrial Planet Finder, a space telescope with revolutionary optics that will be able to find and characterize terrestrial planets. But we're unlikely to find one at the same point in its evolution as our own Solar System.

"With Terrestrial Planet Finder, you don't get to pick the age of the solar system you look at," Crisp said. "You only get to look at solar systems in various stages of their evolution. We may find planets that look like early Earth or early Mars. So it would be nice to understand them."

For the time being, the best way scientists can prepare is by understanding the history of our own terrestrial neighbors.

"Terrestrial planets in our Solar System are remarkably diverse," Meadows said, "and I don't think they span the range of what you might see (in other solar systems). If you don't understand your nearest neighbors, there's no point in studying the distant ones."

The Terrestrial Planet Finder mission is managed by JPL as part of NASA's Origins program.
The Mars Exploration Rover mission is managed by JPL for NASA's Office of Space Science.
NASA's PlanetQuest and Kennedy Space Center