January 15, 2004
(PLANETQUEST) -- Is there another Mars out there? Within the next decade or so, 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.
While more than 100 planets have been discovered outside our Solar System, all of them are gaseous giants like Jupiter and Saturn. NASA's search for life beyond our Solar System hinges on eventually detecting smaller, rocky planets. As far as we know, these are the only type of planets that could harbor liquid water on the surface, considered essential to life.
But which are we most likely to find -- another Mars, or another Earth, or perhaps a Venus? That remains an open question, according to Vikki Meadows, an astrobiologist at JPL.
"It may be that Earths are unusual, or common. Terrestrial Planet Finder is an experiment we have to run in order to find out," Meadows said.
One of the goals of the Mars Exploration Rover mission is to determine the past climate history of Mars. Knowing what Mars was like before it became the barren, static world we see today would help scientists recognize a younger version Mars, should it turn up out there among the stars.
The Viking mission, which placed two landers on Mars in the 1970s, told scientists that the planet has undergone massive alterations since its formation. Scientists believe it was once a warm, wet world with plate tectonics, active volcanoes, and a magnetic field that could protect the surface from deadly radiation.
But after about 1 billion years, its chances of becoming another Earth were over. Because of its relatively puny mass (about one-tenth that of Earth), Mars didn't have enough gravity to hang onto to some of the conditions favorable to life. It cooled quickly. It lost much of its atmosphere. It froze solid. Its magnetic field collapsed. Its once-fearsome volcanoes sputtered out.
Over subsequent eons, while the Earth stabilized, formed oceans, and developed a hospitable atmosphere, Mars changed very little. Because of this, scientists believe, Mars is the planetary equivalent of a time capsule. "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.
Getting to know our neighbors
In 2013, NASA will launch Terrestrial Planet Finder, a space telescope with revolutionary optics that will be able to detect and characterize small rocky planets around other stars. We might find another planet like Mars, or a planet like Earth. But finding either at exactly the same point in their evolution as our own Solar System is unlikely.
"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 have to 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 project is managed by JPL for NASA's Office of Space Science.
Written by Randal Jackson/PlanetQuest
