The mysterious bright spots on Ceres may no longer be so mysterious.
The bright spots captured the public imagination when they were first spotted by NASA's unmanned Dawn spacecraft as it approached the dwarf planet in March. There are more than 130 bright spots, usually at the scene of impact craters.
Speculation has centered around ice or salt, although some scientists have said geysers, volcanoes or other activity were also possible.
Now, a new study in the journal Nature says it's likely just one of these answers: salt.
NASA's Jet Propulsion Laboratory said that it's specifically a type of magnesium sulfate called hexahydrite. A different type of magnesium sulfate is quite familiar here on Earth, where it's more commonly known as Epsom salt.
This week, NASA also released a rendering that uses images from Dawn to create a flyover effect. The footage was rendered in false color to highlight the differences in surface materials -- including those in the bright spots:
The biggest of the bright spots, above, rests in what's known as the Occator crater. It's about 60 miles in diameter, with the bright material in a central pit about 6 miles wide and 0.3 miles deep.
Here's the planet from a little further away, showing how widespread the bright spots are:
"The global nature of Ceres' bright spots suggests that this world has a subsurface layer that contains briny water-ice," Andreas Nathues at Max Planck Institute for Solar System Research, who led the study, said in a news release.
A second study, also in Nature, finds ammonia-rich clays on the planet.
NASA said that while ammonia by itself would evaporate on Ceres, the molecules could bind to other minerals.
"The presence of ammonia-bearing species suggests that Ceres is composed of material accreted in an environment where ammonia and nitrogen were abundant," lead author Maria Cristina De Sanctis of the National Institute of Astrophysics said in the news release. "Consequently, we think that this material originated in the outer cold solar system."
That means Ceres may have formed in the outer solar system long ago -- or that it formed near its current position, but with materials that drifted in from the outer solar system, according to NASA.
The Dawn spacecraft is now 240 miles above Ceres, its final orbit altitude, where it will gather infrared, gamma ray and neutron spectra, and high-resolution gravity data.
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