The Dawn Spacecraft Is About to Reach Its Next Destination—the Dwarf Planet Ceres

We might just learn what the mysterious bright spots on the dwarf planet are—and much more

Ceres' bright spots
Two spots shine like beacons from the dwarf planet Ceres NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

In 1801, a astronomer peering up at the sky from Sicily was busy assembling a great catalog of stars, when he noted something that did not fit. Observations over the next weeks confirmed his hypothesis—the star was moving. He wrote to fellow astronomers: "I have announced this star as a comet, but since it is not accompanied by any nebulosity and, further, since its movement is so slow and rather uniform, it has occurred to me several times that it might be something better than a comet."

The astronomer lost sight of the star and became ill before it could be found again. But he did offer up a name, writes Michael Hoskin for the Observatory of Palermo—Ceres, for the patron goddess of Sicily. 

Now we know that this maybe-better-than-a-comet light in the sky is a dwarf planet. It’s largely made of ice and rock and is the largest body in the gap between Mars and Jupiter. But many questions about Ceres’ characteristics and origins remain, some of which will hopefully be answered with the arrival of NASA’s Dawn spacecraft on March 6. 

One of the first questions Dawn can answer could be: What are those strange bright spots shining from inside the dwarf planet’s crater? An image captured on February 19 shows two spots that appear to be reflecting sunlight, writes Ian Sample for the Guardian. It’s possible that these are patches of ice exposed by collisions with small objects in the asteroid belt. Still, the brightness surprised researchers.

“We knew from Hubble observations that there was variation in the colouration and reflectivity of the surface. But when we got to Ceres we saw bright spots, and they are really, really bright,” Chris Russell, lead scientist on the Dawn mission at the University of California, Los Angeles, told the Guardian.

At this point, scientists are just speculating, as Dawn draws closer to its destination. The spots could be shiny minerals or ice cones pushed up by volcanic activity. Ceres might even be hiding liquid water under a frozen crust. And jets that emanate from the dwarf planet could be evidence of internal heating. Or they could just be sublimating ice from the surface. Another possibility: the liquid may have only existed in the past. But the possibility that Ceres might harbor life (currently or historically) has researchers excited.

Dawn, launched in 2007, is fresh off its successful 14 month orbit around Vesta, a massive asteroid that takes second place in the asteroid belt after Ceres. Comparing the two objects will help scientists get a clearer idea of the Solar System’s formation.

The image of the bright spots was taken from about 29,000 miles away from Ceres, but the mission plan has Dawn spiraling down to eventually reach a close orbit of 233 miles above the surface, according to NASA’s Jet Propulsion Laboratory. There the spacecraft will map the dwarf planet’s surface by measuring gravity, reading elemental signatures and snapping photos in stereo to create 3-D images.

So stay tuned for findings from the dwarf planet: NASA will hold a briefing on the mission on Monday, and NASA TV and Ustream will carry live coverage of the event. Then we’ll get to know the nearest dwarf planet over the next year.

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