A third act will be denied to the Dawn spacecraft, which has explored Vesta and Ceres, the two largest bodies in the asteroid belt. On 1 July, NASA headquarters said that the spacecraft should remain in orbit around Ceres, rather than using its ion propulsion engine to visit 145 Adeona, a 150-kilometer-wide asteroid, in 2019, as its mission leaders had wanted.
Learning of the decision, the Dawn team was surprised and disappointed. “We thought that everyone we had talked to about this plan was enthusiastic about it,” says Chris Russell, the mission principal investigator at the University of California, Los Angeles. “I had no negative vibes until this particular moment.”
The decision was based on the recommendations of a senior review panel, which evaluated all the agency’s ongoing planetary missions, NASA planetary division director Jim Green, who is based in Washington, D.C., said in a statement. “The long-term monitoring of Ceres, particularly as it gets closer to perihelion—the part of its orbit with the shortest distance to the sun—has the potential to provide more significant science discoveries than a flyby of Adeona,” Green said.