Largest Object in Asteroid Belt May Have Come From Elsewhere
Ammonia detected on Ceres’ surface suggests a cold birth beyond Neptune’s orbit.
New and controversial observations from NASA’s Dawn spacecraft, which has orbited the dwarf planet Ceres since March, suggest the 4.6-billion-year-old body may have been knocked into the main asteroid belt from the solar system’s chillier outskirts.
Dawn’s discovery of ammoniated clays on the world’s surface—reported November 9 at the Division for Planetary Sciences annual meeting—points to this intriguing scenario. Their presence indicates that Ceres was born somewhere beyond the orbit of Neptune, where the sun’s weaker glare would not vaporize and scatter the ammonia as the minerals formed. Then, sometime in the following 500 million years, gravitational heave-hos may have thrown the dwarf planet inward, delivering it to the main asteroid belt between Mars and Jupiter.
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