The team behind NASA's Dawn mission has confirmed that Dawn has ended its mission to explore the asteroid belt. More accurately, Dawn has run out of the hydrazine fuel it uses to stay oriented so that it can keep its antenna pointed at Earth and recharge its batteries with its solar panels.
The spacecraft missed its scheduled communications with the Deep Space Network on October 31 and November 1, not that it surprised the team very much. The fuel has actually lasted a little longer than expected.
“We’ve known for months that it would most likely run out of fuel between the middle of September and the middle of October,” said Dawn chief engineer Marc Raymond.
Dawn launched in 2007 to explore Vesta and Ceres, the two largest objects in the asteroid belt between Mars and Jupiter. On the surface, Vesta looks like a normal, if large, asteroid at 325 miles in diameter. Based on data from Dawn, scientists now believe that Vesta actually has an iron core. It also contains water-rich minerals that were likely delivered by collisions with comets and other asteroids.
“The same process has been invoked as an explanation for how Earth has so much water, so that is a really nice discovery to make,” Raymond said.
Exploration of Ceres, a dwarf planet with a diameter of 588 miles, turned up even more interesting discoveries. Scientists have found evidence of volcanic activity at some point in the past. The data from Dawn suggests that Ceres may have had a briny ocean under its surface and might still have pockets of underground liquid water. Dawn also detected signs of organic molecules on the surface. The dwarf planet may have also formed in the outer solar system and migrated to the asteroid belt.
Engineers have determined that the Dawn spacecraft did not require as dramatic a demise as Galileo's famous plunge into Jupiter's atmosphere because it is in a stable orbit and unlikely to contaminate any habitable worlds. Dawn simply turned its antenna off when it ran out of fuel. NASA engineers and scientists have expressed an interest in sending future missions to the asteroid belt.
“There is so much more we want to learn,” Raymond said. “We didn’t go and find this inert object with a record of stuff that used to happen. It was almost like, ‘It’s alive.’”
 

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