Astronomers believe they've found evidence of a massive collision between two planets in a mature solar system, shaking theories that such pileups only occur in young systems where planetary orbits aren't yet stabilized. Says lead researcher Benjamin Zuckerman:
"It's as if Earth and Venus collided with each other.... Astronomers have never seen anything like this before; apparently major, catastrophic, collisions can take place in a fully mature planetary system" [Reuters].
Researchers base their theory on observations of vast clouds of dust and debris in a binary star system 300 light years away in the Aries constellation. Initially, they had a different idea about why the system contains 1 million times more dust that our own solar system: They had
assumed it was a young star, just a few hundred million years old, and the debris was leftovers from planet formation. But earlier this year, another study showed the star was actually a binary pair, and that the stars were billions of years old [SPACE.com].
That finding forced astronomers to rethink what could have caused the dust; in older systems, most debris has either been consolidated into planets or pushed away by solar winds. Zuckerman's team then came up with a new hypothesis, which will be described in the December issue of the Astrophysical Journal: A recent collision between rocky planets, whose orbits could have been destabilized by the pull of double stars, could have created the dust.
Zuckerman believes the collision that produced the dust must have been massive. "The collision of earth with an asteroid 65 million years ago, which apparently finished off the dinosaurs, would have been miniscule by comparison," says Zuckerman [ABC Science].
Researchers were quick to set minds at ease by announcing that the odds of such a collision happening in our own solar system are very low.
Zuckerman noted, however, that collisions have occurred in our solar system's past. "Many astronomers believe our moon was formed from the grazing collision of two planetary embryos, the young Earth and a body about the size of Mars, a crash that created tremendous debris, some of which condensed to form the moon and some of which went into orbit around the young sun," he said [AFP].
For the whole story of how the moon may have been formed by an impact sometimes called "the big whack," turn to the DISCOVER article "Where Did the Moon Come From?" Image: UCLA/Lynette R. Cook
