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SYFY WIRE Bad Astronomy

A Ceres of Weird Events

By Phil Plait

Ceres keeps getting weirder.

Those white spots on the surface we’ve been seeing for months are still mystifying, and we can now add another bizarro surface feature to the list: A huge 5 kilometer tall mountain sitting in the middle of an otherwise relatively flat part of the asteroid.

Um. Why is that there?

On Earth, mountains can form for several reasons. Continents crash together, creating wrinkles in the surface. That’s what the Himalayas are. Of course, Ceres doesn’t have plate tectonics! That wouldn’t form a solitary mountain anyway.

Volcanoes? Well, we do see that happening on Earth. But we don't see any other features like this at all nearby, making it unlikely to be from a weak spot in the crust. Devil’s Tower in Wyoming is similar to this feature, though; that tower may have been created by upwelling magma seeping into prehistoric sedimentary layers. But clearly that’s not going to happen on an asteroid! Sedimentary rocks would be, I expect, rather difficult to produce. 

Mountains on airless bodies like asteroids (or our Moon) can be made in several ways as well. Giant impacts have mountain ranges around their rim, created by rocks lifted up at the edge of the crater. But this mountain on Ceres is alone.

Smaller craters can get central peaks, where the rock rebounds upward after the initial impact (similar to the drop that splashes up in the center of a glass when you pour milk). But there’s no obvious crater around this mountain. Maybe other forces filled it in, or subsequent impacts eroded it away. There's evidence of landslides on the surface as well, which could eventually erase the features of a crater. This seems most likely to me. We've seen other craters on Ceres with central peaks, but I don't think any yet this size. Given all the evidence, though, this is the way I'd lean.

But I’m simply guessing. We’re just now seeing this strange feature, and it’ll be a while, I suspect, before planetary scientists can get enough data to understand it better. Note that Dawn, the spacecraft now orbiting Ceres that took this picture, is still in a relatively high surveying orbit, 4,400 km above the surface. It’ll be dropping down to get much higher resolution images in the coming months.

Hopefully then we’ll get some definitive answers to these mysteries. Ceres is odd. We know there’s ice under the surface, and there’s evidence it also has geysers, eruptions of water, from its surface. That might explain the white spots, too, but there’s still a long way to go to figure all this out.

Ceres is the largest asteroid in the asteroid belt (some call it a dwarf planet; I find the term not terribly useful). It’s unique in that sense, and big enough to have geological processes on it and in it we haven’t fully grasped yet. It’s not Earth, for sure, but it’s far more than a simple monolithic rock in space.

It’s a world. And with a surface area of nearly 3 million square kilometers, there’s a lot of it to explore.

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