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Recall of an asteroid. Doesn't affair which asteroid. Odds are skillful you thought of something that looks like a lumpy, craterous potato. Astronomers agree with you — most of the rocks in our asteroid belt look pretty careworn. Then they expected that when NASA's Dawn spacecraft got to Ceres, they would see similarly many large bear on craters marring the dwarf planet'southward surface, just like every other rocky thing in our unabridged solar system. But that'southward not what they constitute. While the planet's surface does prove the expected collage of small bear on craters, at that place are fewer than we expect above threescore miles in diameter, and none in a higher place 175 miles in diameter. Ceres is strangely polish.

Scientists working on the trouble have just published some ideas about why this is so. Ane hypothesis is that Ceres' own internal structure is responsible. Recent studies, including several detailed analyses of the dwarf planet'southward bright spots, points to a layer of ice and salt simply beneath the surface. Over geologic time, a process known as "pasty relaxation" could have smudged out the details of the surface. Information technology'southward not unlike how the freeze-thaw process breaks downwardly rocks over time. Co-author Michael Bland of the USGS said viscous relaxation flattens out big craters faster than small craters.

The other major hypothesis is cryovolcanism. "Nosotros have these bright spots all over the surface – conspicuously, that's stuff that came out of the interior," said Simone Marchi, some other co-author. It'southward possible that an early menstruum of intense cryovolcanic eruptions dramatically altered the planet'due south surface, changing a much unlike early surface into what we see today. Pearlescent, sparkling cryolavas consisting of phyllosilicated ammonia slush could have obliterated craters, filling them in or abrading them away.

Dawn's trajectory through the solar system, starting when it departed from Earth in 2007. Dawn's orbit around the sun is shown in blue. When the spacecraft is in orbit around Vesta or Ceres, its trajectory is the same color as their heliocentric orbits, which are bold when Dawn is accompanying them around the sun. Dawn is carrying out its extended mission in Ceres' permanent gravitational embrace. Image credit: NASA/JPL-Caltech

NASA/JPL-Caltech

Data from Dawn could offer the states answers. The spacecraft is currently in a low-altitude orbit, snapping high-res photos that NASA puts online in an enormous, daily updated gallery. "With this high-resolution information, we can look more specifically at sites on the surface that may have evidence of big-scale cryolavas," Marchi said.

Dawn has loftier-res imaging capabilities in both the visible and the IR bands. It also has instrumentation collecting data on the gravity field surrounding Ceres, and that will give usa a clearer understanding of Ceres' interior.

Speaking of what the spacecraft can do: Dawn's original goal was to orbit Ceres and Vesta, ii protoplanets in the asteroid belt between Mars and Jupiter. This latest barrage of data marks the successful determination of its mission. Only, looking at the stalwart little spacecraft's persistent good health, NASA decided to extend the mission and continue Dawn in orbit around Ceres. The extended mission will continue to extract information from the icy protoplanet, doing scientific discipline from the asteroid chugalug until 2019.