"Faraway Planets Collided, Study Suggests"
Space.com (January 9, 2009)
"An extrasolar planet about one-fourth the heft of Jupiter might have formed from the collision and merger of two planets, astronomers announced today.
"Known as 2M1207B, the object orbits a brown-dwarf star called 2M1207A located 170 light-years from Earth and seen in the direction of the constellation Centaurus.
"Astronomers have long puzzled over the mysterious object, which seems to fall outside the spectrum of physical possibility. Its temperature, age and brightness don't match up with what astrophysical theory would predict...."
2M1207B was too hot for its age, about 8,000,000 years, and mass. On the other hand, researchers ran the numbers and found: "...A smashup between a Saturn-sized gas giant and a planet about three times the size of Earth could explain the extra heat...."
That sort of collision isn't at all uncommon, if the current models of planet formation are at all accurate. Right now, the solar system seems fairly stable, with most of the planets in nice, circular orbits.
But, the article points out, it doesn't look like it was always that way. One of the less unlikely explanations for how Earth as we know it and our moon came to be is that something about the size of Mars hit this planet, early in the life of the Solar system. (More at "24 Hours of Chaos: The Day The Moon Was Made," Space.com (August 15, 2001) - And it wasn't really that "chaotic." I wouldn't have wanted to be around, but there's pretty straightforward physics involved.)
And, there's a quite remote chance that Mercury's orbit will get more eccentric, resulting in serious collisions in the inner Solar system. (More at "Long Shot: Planet Could Hit Earth in Distant Future," Space.com (June 10, 2009). Not to worry: the odds are very low, and it wouldn't happen for a few billion years - if ever.)
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