Most of our solar system is downright unfriendly for life. Close to the Sun, it's too hot. And far away from the Sun, it's too cold. The only region where conditions are just right for life is right where Earth is -- in a narrow band known as the habitable zone. It's the distance from the Sun where temperatures are just right for liquid water -- a critical ingredient for life as we know it.
It's not surprising, then, that scientists hope to find planets in other star systems that are inside their own habitable zones -- especially small, rocky planets like Earth.
So far, the census of known planets that fit that description is exactly zero.
But that should change over the next few years. Several searches are underway to find those kinds of planets. And the most ambitious to date is just about to get started. It's a space-based telescope called Kepler, and it's scheduled for launch as early as this week.
Kepler will stare at about a hundred thousand stars in Cygnus and Lyra, out to distances of up to 3,000 light-years. It'll look for a tiny, brief drop in the light from these stars. Such a drop could be caused by a planet passing in front of the star, blocking a little bit of its light. If the dimming is just the right amount, and repeats at just the right times, then the planet is about the same size as Earth, and about the same distance out from the star -- in the habitable zone.
We'll have more about Kepler tomorrow.
Script by Damond Benningfield, Copyright 2009
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