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Gravitational forces in protoplanetary disks may push super-Earths close to their stars

The galaxy is littered with planetary systems vastly different from ours. In the solar system, the planet closest to the sun -- Mercury, with an orbit of 88 days -- is also the smallest. But NASA's Kepler spacecraft has discovered thousands of systems full of very large planets -- called super-Earths -- in very small orbits that zip around their host star several times every 10 days. Now, researchers may have a better understanding of how such planets formed. A team of National Science Foundation-funded astronomers found that as planets form out of the chaotic churn of gravitational, hydrodynamic -- or, drag -- and magnetic forces and collisions within the dusty, gaseous protoplanetary disk that surrounds a star as a planetary system starts to form, the orbits of these planets eventually get in synch, causing them to slide -- follow the leader style -- toward the star. The team's computer simulations result in planetary systems with properties that match up with those of actual planetary systems observed by the Kepler space telescope of solar systems.

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