After months of research, scientists say they’ve cracked the mystery of the bright spots seen by NASA’s Dawn spacecraft on the surface of dwarf planet Ceres. The glowing spots are likely salt deposits, say researchers in a paper published yesterday (December 9, 2015) in Nature.

Ceres has more than 130 bright areas, and most of them are associated with impact craters, say the study authors. Images from Dawn’s framing camera suggest the bright material is consistent with a type of magnesium sulfate called hexahydrite. A different type of magnesium sulfate is familiar on Earth as Epsom salt.

Lucille Le Corre of the Max Planck Institute for Solar System Researchis a study co-authors. She said:

We reviewed three possible analogs for the bright spots (ice, clays and salts). Salts seem to fit the bill and are the best possible explanation of what we see on the surface of Ceres.

The researchers say that these salt-rich areas were likely left behind when water-ice sunk into Ceres surface sometime in the past. Impacts from asteroids would have unearthed the mixture of ice and salt, they say.

Study co-author Vishnu Reddy is a PSI Research Scientist at the Planetary Science Institute. Reddy said:

The location of some bright spots also coincide with places where water vapor was detected by other spacecraft. This gives us confidence that the bright spots are likely salt deposits left over by sublimating salty water.

Andreas Nathues at Max Planck Institute for Solar System Research is the study’s lead author. Natheus said:

The global nature of Ceres’ bright spots suggests that this world has a subsurface layer that contains briny water-ice.

Dawn is continuing to descend toward its final orbit at Ceres, which will be around 240 miles (385 kilometers) from the surface of Ceres. In mid-December, Dawn will begin taking observations from this orbit, including images at a resolution of 120 feet (35 meters) per pixel, gamma ray and neutron spectra, and high-resolution gravity data.

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Bottom line: According to a paper published December 9, 2015, in Nature, the bright spots seen by NASA’s Dawn spacecraft on the surface of dwarf planet Ceres are likely salt deposits.

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