8 possible explanations for those bright spots on dwarf planet Ceres

It's a real-life mystery cliffhanger. We've come up with a list of possible reasons a large crater on the biggest object in the asteroid belt looks lit up like a Christmas tree.

Eric Mack Contributing Editor
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Eric Mack
5 min read

An artist's rendering of Dawn heading for Ceres. NASA/JPL-Caltech

We could be approaching the cliffhanger ending of the first installment of a great sci-fi trilogy in which we discover something mysterious on a nearby dwarf planet. We have some clues as to what it might be, but no one knows for sure, except that it could be something big. Then the screen fades to black and we have to wait for the next chapter to learn the secret.

But this isn't science fiction, it's a pair of real, inexplicable bright spots seen by NASA's Dawn spacecraft on its approach to Ceres, the largest object in the asteroid belt. This Friday, Dawn will enter into orbit around Ceres for a mission surveying its surface and investigating the dwarf planet, which is believed to harbor a large frozen ocean under its rocky shell, not to mention whatever appears to be reflecting the sun's rays with an intensity that Dawn's deputy principal investigator, Carol Raymond, described this week as "off the charts."

And that's the cliffhanger ending to this first installment of the story. Now the waiting begins, as Dawn spends the next several weeks making its way down to its "science orbit," where the real investigation starts. The next chapter may not really begin until the end of April, when that data begins to make its way back to Earth.

In the meantime, we can speculate about the most likely explanations for those strange bright spots, which Raymond became visibly excited about when she mentioned them during NASA's Dawn press conference on Monday.

"The team is really, really excited about this feature because it is unique in the solar system," she said. "The mystery will be solved, but it's one that's really got us on the edge of our seats."

OK, now the suspense is too much. What are those mysterious spots? Let's review the possibilities, starting with the boring and building up to the awesome/crazy.

1. A salt flat. It's not exciting, but one of the possibilities mentioned by NASA and others is that those bright spots are simply the reflection of large mineral deposits on the surface of Ceres left by some sort of impact, or from earlier days when it may have been covered by water. In other words, we might not be seeing anything more interesting than a big pile of salt or talc.

2. Shiny metals. NASA's Raymond says the brightness of the spots is consistent with a highly reflective material. On Earth, polished silver and aluminum are among the most reflective surfaces you can find, which is why they're used in large telescopes. While it's not clear if anyone would be available on Ceres to be doing the polishing, there's reason to believe both metals could exist there. Plenty of precious metals have been found in meteorites, and aluminum is actually the most abundant metallic element in the Earth's crust. It wouldn't be too far-fetched to imagine that nearby rocky dwarf planets also harbor some as well.

Also, how do we really know that all our aluminum cans are really recycled? Who's to say they aren't being launched toward the asteroid belt?

3. Exposed ice. Ice can be another highly reflective material, and scientists think Ceres has plenty of the stuff below its surface. So what if an asteroid or comet collided with Ceres, puncturing a hole in that rocky shell and exposing the icy layer below to the sun?

4. Water vapor. Perhaps there are geologic processes happening on Ceres that caused some of its ice core to melt and then get shot out into space via a geyser of sorts. In 2014, the European Herschel telescope detected plumes of water vapor emanating from Ceres, and guess what? One of the plumes was located in the same area as the bright spots we're seeing now. Even if the spots aren't actually plumes, they could be involved in the explanation.

An artist's rendering of Ceres with plumes of water in the asteroid belt ESA/ATG medialab

5. Ice volcanoes. This explanation kicks off the second, more out-there half of our list. Cryovolcanoes, or volcanoes that spew water or ice rather than lava, are believed to exist in the colder reaches of the solar system, and it would make sense to see them on Ceres given what's suspected about its water and ice content. However, the observations of the area around the bright spot give no indication that there are raised sections consistent with a volcano or piles of whatever type of debris it might fling about.

6. Aliens' solar concentrators. In a 2008 TED talk, physicist and futurist Freeman Dyson suggested that the dwarf planets of the outer solar system, near Pluto and the Kuiper Belt, would be a good place to look for life. Dyson thought that although finding it might be unlikely, it might not be that hard to search if we simply looked for the reflection of the mirrors and lenses that any life forms would surely need to concentrate sunlight to survive on places like Europa and beyond. It sounds far out, but could it be that we've just found some ancient, abandoned solar concentrators even closer to home than Dyson imagined?

7. Genetically engineered colonists from another civilization. In the same talk, Dyson also suggested that if we don't find life forms hanging out in the cold reaches of the outer solar system, we should genetically engineer our own life forms to go check it out. Obviously, we haven't reached that point yet, and we tend to favor sending robots rather than clones of ourselves with frost and radiation resistance, but what if another distant civilization beat us to the punch and has sent mutant, genetically enhanced images of themselves to start poking around in our asteroid belt?

8. It's a spacecraft. Finally, as many of you devoted CNET readers have suggested, the bright spots on Ceres seem to resemble headlights.

So, sure, why not allow for the possibility that Ceres itself is a spacecraft in disguise? And yes, I recognize its aesthetic similarity to the Death Star. If that's the case, I guess it's a good thing SpaceX is already working on its "X-wing" designs as we wait for the next chapter in our real-life space mystery.

Updated at 11:37 a.m. -- An earlier version of the story stated that aluminum is the most abundant element in the Earth's crust rather than the most abundant metallic element. This error has been corrected.