Those bright spots on Ceres just won’t go away, will they? While New Horizons and the dwarf planet Pluto might have been hogging the limelight recently, the Dawn spacecraft deserves its fair share of attention too – and it may now be close to solving the mystery of the bright spots on fellow dwarf planet Ceres.
Ever since Dawn entered orbit around Ceres earlier this year, scientists have been left baffled by the appearance of bright spots seemingly reflecting sunlight in craters on the surface. Theories for their origin have ranged from ice – exposed by impacts on the surface – to salt flats or even cryovolcanoes.
Now scientists might be closer to solving the mystery by spotting a "haze" above one group of spots, suggesting their origin is ice. The latest findings were revealed by Christopher Russell, the principal investigator on the mission, at an exploration meeting at NASA’s Ames Research Center yesterday.
If confirmed, this would be the first such haze ever found in the asteroid belt, and could indicate the presence of ice turning into gas – known as sublimation – on Ceres. The haze was found confined to the Occator crater, which contains the most famous spots on the surface, labelled Spot 5.
“At noontime, if you look at a glancing angle, you can see what seems to be haze,” said Russell to Nature. “It comes back in a regular pattern.”
NASA's Dawn spacecraft (artist's impression shown) entered orbit around Ceres on March 6, 2015. NASA/JPL-Caltech.
More than a quarter of Ceres’ mass is thought to be composed of water (the other three-quarters is rock), much more than is thought to be present on asteroids. Whether these spots are made of water-ice, though, or something else entirely has been up for debate. Now, this discovery of haze lends strong evidence to the ice theory.
Andrew Rivkin, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, writing for The Planetary Society, notes that the team had been favoring “a non-ice composition for the bright spots in recent weeks,” so there may yet be another explanation for the haze.
Dawn is continuing to spiral closer and closer to Ceres as it lowers its orbit, and by August it will be 1,500 kilometers (900 miles) above the surface, compared to less than 4,000 kilometers (2,500 miles) now. It will also soon use its infrared spectrometer, which should be able to work out if the spots are made of ice or salt.
By August, then, we can expect to have a much better understanding of the bright spots. Whatever they turn out to be, the answer is sure to provide a fascinating insight into some of the processes taking place on Ceres.