Five years ago today — September 27, 2007 — a Delta-II launch vehicle carried the Dawn spacecraft to space from Cape Canaveral, sending it on a roundabout journey to the asteroid belt.
(Artist’s conception of the Dawn spacecraft. The glow represents one of the xenon-ion thrusters operating. NASA image.)
After a gravity-boost flyby of Mars in February 2009, Dawn reached its first asteroid target, 4 Vesta, and entered orbit around it in August 2011. There it began its mission to “characterize the asteroids’ internal structure, density, shape, size, composition and mass and to return data on surface morphology, cratering, and magnetism.” Dawn’s measurements and subsequent analysis should help scientists understand better the conditions in the early solar system.
On the main mission page, you can read about one of Dawn’s most exciting discoveries: hydrated minerals on the surface of 4 Vesta. While not as potentially useful as discovering actual water, it did provide evidence that Vesta once held water, but it long since boiled away.
Dawn left Vesta’s orbit this past September 5th, and is scheduled to rendezvous with 1 Ceres in February 2015. It will study that asteroid until the end of its mission, currently set for July 2015.
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