Baltimore ? Astronomers are trying to find places in the solar system and beyond where conditions are right for life. Thus far, more than 80 planets have been discovered orbiting distant stars, but all are forbidding and unlike Earth.

What the experts want to find are planets where the temperature is right and the orbit is not too far or too close to the central star. There needs to be liquid water and oxygen. It also has to be in a reasonably quiet neighborhood without frequent asteroids or comet collisions.

A place, in other words, kind of like Earth.

“The questions are how many stars have planets and how many of those planets are habitable,” said Charles Beichman, a scientist at the Jet Propulsion Laboratory in Pasadena, Calif. “Within the next decade, we’ll get some very good answers.”

Researchers have found extrasolar planets by using a technique that measures the very, very slight wobble motion that an orbiting planet causes in its central star. But all of the discovered planets are large, most many times the size of Jupiter which is 318 times more massive than Earth and unfriendly to life.

Beichman said Wednesday at a symposium at the Space Telescope Science Institute that in 2007, the National Aeronautics and Space Administration hopes to start launching specialized spacecraft to conduct a systematic search for Earthlike planets, and then to probe those planets for the chemical evidence of life.

The first step is the launch of a spacecraft called Kepler. Beichman said the craft will spend two years to three years observing light from stars and will be looking for a slight dimming, evidence of a shadow cast by an orbiting planet.

Kepler’s instruments will be keen enough to detect Earth-sized objects orbiting stars up to 4,000 light years away. It will take measurements every 10 minutes and could study up to 100,000 stars.

“This will give us a statistical sample” of how common Earth-sized planets are, Beichman said.

In 2009, another spacecraft, the Space Interferometer Mission, will be launched to analyze stars out to about 50 light years. This craft will analyze the wobble of a central star and should be able to detect planets the size of Earth orbiting within a distance of 0.5 to 10 astronomical units. An astronomical unit is the distance between the Earth and sun, about 93 million miles.

Beichman said the Kepler and SIM spacecraft will locate targets for the third spacecraft, the Terrestrial Planet Finder, scheduled for launch about 2015.

This craft, he said, will analyze the atmospheres of the candidate planets, searching for the chemical signature of life.