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Abstract The asteroid belt contains less than a thousandth of Earth's mass and is radially segregated, with S-types dominating the inner belt and C-types the outer belt. It is generally assumed that the belt formed with far more mass and was later strongly depleted. We show that the present-day asteroid belt is consistent with having formed empty, without any planetesimals between Mars and Jupiter's present-day orbits. This is consistent with models in which drifting dust is concentrated into an isolated annulus of terrestrial planetesimals. Gravitational scattering during terrestrial planet formation causes radial spreading, transporting planetesimals from inside 1 to 1.5...

CAPE CANAVERAL, Fla. - NASA is about to embark on an unprecedented asteroid-belt mission with a spacecraft aptly named Dawn. The 3 billion-mile, eight-year journey to probe the earliest stages of the solar system will begin with liftoff, planned for just after sunrise Thursday. Rain is forecast, however, and could force a delay. Scientists have been waiting for Dawn to rise since July, when the mission was put off because of the more pressing need to launch NASA's latest Mars lander, the Phoenix. Once Phoenix rocketed away in August, that cleared the way for Dawn. "For the people in the...