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Having created a behemoth computer program to track the gravitational attraction between millions of chunks, Quinn, Stadel, and postdoc Derek Richardson wondered if the same code could applied to other astronomy puzzles. They found such a puzzle: the creation of the planets in our solar system. The researchers started with the young solar system. The big planets--Jupiter, Saturn, Uranus, and Neptune--have already formed, but the inner solar system is still a disk of asteroids. Quinn wants to know if the computer simulations will produce Mercury, Venus, and Earth. "The goal is to follow them for a million years so that we can see the development of the Earth," he says. | ||||||||||
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The equations are the same as in the cosmological simulations, but now each particle represents an asteroid a few tens of miles wide rather than a chunk of galaxy. An important difference in the simulations is the behavior of particles when their paths cross. When two particles cross in the galaxy simulation "you want them to pass through each other like a collection of real stars would," Quinn says. That's a realistic assumption because each particle represents a clump of stars with empty space in between. Individual stars almost never collide with each other. |
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The initial conditions for the researchers' simulations of large-scale structure came from measurements of the diffuse infrared and microwave radiation from the early universe as seen by COBE, COsmic Background Explorer satellite. COBE was launched by NASA in 1989. | |
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When each particle represents an asteroid, however, the story is different. "They're chunks of rock and they hit each other," Quinn says. The two rocks can pulverize each other, bounce off each other, or stick together. Quinn's current computer runs assume that any collision between asteroids causes them to stick together. That's unrealistic, but it doesn't diminish the value of the simulations in providing an overview of the evolution of the early solar system. They show how, over the span of a few thousand years, asteroids orbiting in paths that later belong to Venus and Earth clump together into chunks hundreds of miles wide. These chunks will later coalesce into the planets. |
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The simulation also shows why the asteroid belt between Mars and Jupiter never coalesced into a planet. As Jupiter orbits the Sun, its enormous gravity nudges those asteroids into elliptical orbits, which cross paths much less frequently. Fewer collisions means fewer chances for them to form larger asteroids and fewer chances to form a planet. The researchers are currently refining their algorithms to speed up their planetary calculations. When they're done, they'll have a virtual solar system to accompany their virtual universe. | |||||||||
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