Ceres, Now a Dwarf Planet, Is Scheduled for Exploration

Part of the fallout from the “Is-Pluto-a-planet?” debate is that the asteroid Ceres is no longer just a rock among hundreds of thousands of rocks in the asteroid belt between Mars and Jupiter.
Ceres is now also a dwarf planet. At almost 590 miles wide, it is big enough that its gravity has made it round, but not big enough to be considered a planet. Like Pluto, it fails part of the planet definition passed by the International Astronomical Union: it has not “cleared the neighborhood around its orbit.”
Ceres’s new celebrity on the solar system B-list will perhaps bring more prominence to NASA’s Dawn spacecraft, scheduled to be launched on Saturday atop a Delta II rocket. The spacecraft is to visit Vesta, the third largest asteroid, in October 2011, and depart in April 2012 to Ceres It would arrive at Ceres in February 2015.
Asteroids turn out to be a fairly diverse bunch.
By contrast, under Ceres’ outer coating of dust the asteroid appears to have a thick layer of ice, perhaps 60 miles deep, wrapped around a ball of rock. But there is no iron core. It is still by far the largest asteroid, with about a third of all of the mass in the asteroid belt.
But first, the spacecraft needs to get off the launching pad. Some last-minute glitches delayed the take-off date from June 20 to July 7. But if there are any more delays, NASA might have to pull the Dawn off the launching pad to make room for the Mars Phoenix probe, which must launch by Aug. 25 or Mars and Earth will be out of alignment for two years.
The NASA team meets today to decide whether to continue preparations for a Saturday launching of Dawn.
Dawn has its own time and cost constraints. Taking it off the launching pad could cost NASA up to $25 million. And after November, Ceres and Vesta move too far apart so that Dawn would never be able to get from Vesta to Ceres, Dr. Russell said.