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Secret of Ceres' weird bright spots finally revealed?

NASA's Dawn spacecraft has been inching closer to the dwarf planet's surface for months, and new studies using its data now reveal more about curious sights on the largest object in the asteroid belt.

The bright spots of Ceres' Occator crater in false color.

NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Bad news for those of you hoping Ceres and its odd bright spots might be an alien base or real-life Death Star. The largest object in the asteroid belt between Mars and Jupiter isn't beaming ominous rays of light at NASA's Dawn spacecraft via huge artificial headlights, it turns out.

Since Dawn first spotted a number of bright spots earlier this year as it approached the dwarf planet -- including some particularly large bright areas in the center of a crater 60 miles (90 kilometers) wide near the middle of Ceres -- we've heard all kinds of explanations, both boring (ice or salt) and far-fetched (a hidden alien base!).

Two new studies published in the latest issue of the journal Nature seem to confirm scientists' earlier educated guess that the bright reflective material is a kind of salt, and one of the studies also suggests the presence of ammonia-rich clays, providing additional insights into Ceres' history.

"The presence of ammonia-bearing species suggests that Ceres is composed of material accreted in an environment where ammonia and nitrogen were abundant. Consequently, we think that this material originated in the outer cold solar system," said Maria Cristina De Sanctis, lead author of the study, in a release from NASA Wednesday.

In other words, Ceres might have originally been farther out when it was younger, a kind of solar system drifter for a period, then eventually came to reside in the asteroid belt. It's also possible that Ceres formed near where it is today and pulled in ammonia drifting in from those colder climes where the compound is more stable.

As for the bright spots, we knew NASA already suspected salt as the source, but lead study author Andreas Nathues at the Max Planck Institute for Solar System Research in Germany writes that the bright material looks to be a kind of magnesium sulfate called hexahydrite. Another magnesium sulfate we know on Earth is Epsom salt.

It's not the most exciting explanation, especially for the alien hunters of the universe, but it hints at more interesting things below the surface of Ceres.

"The global nature of Ceres' bright spots suggests that this world has a subsurface layer that contains briny water-ice," Nathues said. This bolsters earlier suggestions that Ceres may hide more water frozen beneath its surface than all the fresh water on Earth.

Dawn isn't done with Ceres just yet. The spacecraft is currently preparing for its closest mapping orbit later this month. Over the next week or two it will begin imaging the surface of the dwarf planet from its closest planned distance of just 240 miles (385 kilometers). So perhaps there's still a miniscule chance we'll find an alien salt mining operation at the edge of those bright spots...but probably not.