ScienceScientists think they've finally solved the mystery of the strange bright spots on dwarf planet Ceres in the Asteroid Belt.
We got our first glimpse of one of the bright spots back in 2003, and this year the Dawn spacecraft revealed that Ceres is covered in them.
But scientists had no idea what they were. Guesses ranged from volcanoes, to geysers, to patches of ice. Some even joked that maybe Ceres was just the Death Star from "Star Wars" in disguise.
Now researchers think they've solved the mystery once and for all.
A new study in the journal Nature identifies the material as a salt made of magnesium sulfate, called magnesium sulfate hexahydrite. Magnesium sulfate also makes up Epsom salt, which is probably in your bathroom right now - and used as a bath salt, laxative, fertilizer, splinter remover, and more here on Earth.
The close-up image below shows one of the bright spots at the bottom of Occator crater on Ceres.
Ceres is fairly drab and gray in color, so presence of the salt is made a bluish-white for emphasis:
NASA
The Dawn spacecraft captured this image from about 2,700 miles above the dwarf planet.
NASA also released an incredible video animation of its Dawn spacecraft passing over the crater.
The salt appears in over 100 spots on the tiny planet:
Scientists think the salt deposits were left behind long ago when water ice on Ceres quickly melted and sublimated into vapor. Asteroids that pummeled the dwarf planet probably unearthed some of the salt - that's why most of the salt appears at the bottom of craters, the researchers say.
It also means Ceres could be hiding a layer of ice beneath the surface.
"The global nature of Ceres' bright spots suggests that this world has a subsurface layer that contains briny water-ice," Andreas Nathues, lead author on the new study, said in a press release.