Astronomy Journal Entry

NASA Launches Exoplanet Hunter (March 16, 2009)

This month, NASA kicked the search for habitable exoplanets (planets beyond the solar system) into the next gear with the launch of the Kepler spacecraft from Cape Canaveral in Florida. Kepler's mission will take it deep into outer space over the next three and a half years. The spacecraft will look for signs of exoplanets with orbits within the habitable zone of their parent stars.

A habitable zone is a solar system region that's neither too hot nor too cold to have liquid water. If water exists on these planets, there's a chance living organisms might also exist on them.

Kepler will scan the skies with a powerful telescope and state-of-the-art cameras. The cameras are sensitive enough to detect the dimming of a parent star's light that occurs when a planet passes in front of it. Such an event is called a transit.

Astronomers discovered the first exoplanet in 1995. Since then, they've found more than 300 others. A handful of exoplanets found so far have been within the habitable zone but there's no evidence any of them can support life. The others have all been scorchingly hot or icy cold. Most are gas giants more massive than Jupiter. Others, known as ice giants, orbit so far from their parent stars that everything is frozen solid. "Super Earths" are rocky planets with at least ten times the mass of Earth. On these planets, the crush of intense gravity makes life unimaginable.

Kepler will survey more than 100,000 stars on its voyage. The stars are at distances between 30 and 1,000 light-years from our home planet. NASA scientists are optimistic the spacecraft will discover hundreds of exoplanets. The more it finds, the more likely some will lie within the habitable zone.