Creative destruction is central to economic growth. It is also believed by many researchers to be central to the growth of solar systems. Planets, the theory goes, evolve by colliding with each other. Sometimes such collisions result in the protagonists sticking together and making a bigger planet. Sometimes, by contrast, they knock lumps off one another, as is thought to have happened when the Earth's moon formed. Then, it appears, the proto-Earth was hit by something the size of Mars. When the dust had settled, the result was what is, in effect, a double planet. Looking back across the 4.5 billion years since that occurred is obviously an exercise fraught with guesswork. But telescopes have now reached the point where they should be able to see evidence of similar collisions in other, younger solar systems. And two of those telescopes, the Gemini Observatory telescope in Chile, and the Spitzer Space Telescope, in orbit around Earth, have recently come up with the goods.
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