Planets appear to be tough little buggers. They can form from the debris around exploded stars. They can survive the heat when they're close to a parent star. And they can even survive collisions -- perhaps merging to form bigger planets.
From studying our own solar system, scientists know that collisions are common. The young Earth probably was hit by an object as big as Mars -- an impact that created the Moon. The giant planet Uranus was flipped on its side by an impact, and Venus may have been flipped head over heels.
And earlier this year, astronomers reported that an object in another system might be a planet that not only survived an impact, but grew bigger in the process.
The system is known as 2M1207. It's about 170 light-years away. It consists of two objects, which are only about eight million years old. One is a brown dwarf -- an object that's more massive than a planet, but not massive enough to shine as a true star. It shines because of the lingering heat of its birth.
The second object is smaller, but it's much hotter than expected.
Astronomers who studied the system suggest that this object survived a collision between a planet about the mass of Saturn, and another a few times the mass of Earth. Despite the force of the impact, the two objects merged, forming a bigger planet. It's still hot from the collision -- a powerful blast that couldn't crack a tough planet.
More about extrasolar planets tomorrow.
Script by Damond Benningfield, Copyright 2008
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