As the search for extraterrestrials continues, astronomers have tried to narrow down the best places to look for Earth like planets and human life. To do this they've defined a region in space called the habitable zone.
The habitable zone is defined as the distance from a star at which an Earth like planet can harvest liquid water (and potentially life). It's often referred to as the Goldilocks Region, because it's "not too hot and not too cold". Lucky for us, Earth is at just the right distance from the sun to form life. The other planets in our solar system are too hot or too cold to have liquid water, so it's not such a big surprise that we haven't found life elsewhere in our solar system.
You can define a habitable zone around size of star. Stars bigger and hotter than the sun have a habitable zone farther away from it, while small cooler stars have a closer habitable zone (blue shading on the graph). Astronomers have actually found a few planets that are in the habitable zone around other stars in our galaxy! The problem with most of them is that they are big and gaseous, like Jupiter, and therefore don't have a solid surface for life to live on. There is high hope, though, that the Kepler Space Telescope (launched last year I believe) will discover Earth like planets in the habitable zone in the next few years!
Next Topic: Halley's Comet
