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What We Can't Wait to Learn About Ceres

This morning, NASA's Dawn spacecraft was pulled into orbit around the dwarf planet Ceres, where it will stay until June 2016.

by Ben Richmond
Mar 6 2015, 10:35pm

The view of Ceres from Dawn. Image: ​NASA

This morning, NASA's Dawn spacecraft was pulled into orbit around the dwarf planet Ceres, where it will stay until June 2016, coming as close as 230 miles to its surface. This is uncharted territory—it's the first time that a spacecraft has visited a dwarf planet—and there's a lot to be excited about here.

Now that we've got something actually orbiting Ceres, it's time to get back to demanding that NASA figure out what those weird-ass shiny things they saw on its surface were. But given that it's take over seven years and $473 million to send Dawn on a billion mile trip, that's not all we hope to learn.

"We have much to do over the next year and a half, but we are now on station with ample reserves, and a robust plan to obtain our science objectives," Chris Russell, principal investigator of the Dawn mission at the University of California, Los Angeles, said in a press release.

Like Pluto, Ceres was once called a full-fledged planet after a short stint being known as a comet following its discovery in 1801. It was downgraded to an "asteroid" in the 1860s, when it became clear that Ceres wasn't alone between Jupiter and Mars. Then in 2006, Ceres was redesignated a "dwarf planet" which can be either an upgrade or a downgrade, depending on how you look at it, because at least when it was an asteroid it was the biggest one—comprising 25 percent of the asteroid belt's mass. Now it's the smallest dwarf planet—Pluto is 14 times more massive, and also people have heard of it.

But hey, planets don't have feelings, so who cares what it gets called, right? The guy who found it thought it was probably a comet, which foreshadows one of the most compelling mysteries of Ceres: does it have water, and if so, where and how much?

Last year the Herschel telescope detected plumes of water vapor coming up from the dwarf planet's surface. It was the first time that evidence of ice has been spotted on an object in the asteroid belt. Scientists think that there may be a frozen ocean under Ceres's surface. It may even have ice caps. And if Ceres is 25 percent ice, as scientists estimate it may be, it has more freshwater than all of Earth, despite being only Texas-sized.

Researchers talk about the asteroid belt being leftovers from the first few million years that our solar system existed, disrupted from planethood by Jupiter's mass. Vesta, another asteroid that Dawn visited previously, was dated via meteorite to have come together in just 5-15 million years. We don't have a meteorite record for Ceres, which is all the more reason to send Dawn to check it out. Ceres is sort of a snapshot of the early solar system, but we don't yet know from when.

As Dawn is still 38,000 miles above Ceres, its first month in orbit will be spent drawing closer to the first survey altitude of 2,730 miles. We'll start getting pictures in April, NASA estimates, at which point we can all resume demanding to know what those damn shiny things were, and also ask the other questions that launched Dawn in the first place.