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Poor Astronomy | Ahuna Mons: A muddy, icy volcano on Ceres



Ceres is the largest object in the asteroid belt, the rubble band that orbits the sun between Mars and Jupiter. At a width of almost 1,000 kilometers, it's technically a protoplanet – something that was on the way to becoming a full-fledged planet before it runs out of food for food and growth. That was over 4 billion years ago, so you could now expect that it is a dead, frozen world, on the geologically nothing new happens, except possibly one or the other asteroid impact.

But the one thing that does the universe well, is perverted our expectations. When the space probe Dawn arrived in Ceres in 2015, she actually saw a world marked by impacts. But there were also two very, very strange things. One was a series of bright reflective patches that were usually scattered across the surface in craters and were easily seen, unlike the generally very dark gray surface.

The other was Ahuna Mons.

This is an elongated mountain that protrudes from the side of the Protoplaneten, 1

7 km wide and over 4 km high in the airless sky. It's flat, like a mesa, with long, angled flanks that surround it like a rock. There is nothing like it on Ceres, and with the exception of a single adjacent crater, the terrain around it is relatively flat and free of any structures. Ahuna Mons is literally alone.

And that's weird. Ceres has no tectonic activity, so it can not grow mountains this way. This usually forms mountain ranges (like the continental plate collisions on Earth that spawned the Rocky Mountains and the Himalayas).

That leaves only one other explanation: ascend. In the truest sense of the word something below the surface that tries its best to come out.

This is not a new idea, and indeed it was proposed directly after Ahuna Mons was first discovered. It was thought to be a kind of cryovolcan – literally a volcano operated with water (yes, water) instead of molten rock – but the details were unclear. However, new research has refined the idea a bit and has even been able to explore the material that causes it to swell: Not just water, but also many stone particles suspended in it.

So: mud. [19659002] How is this possible?

Ceres is not like other asteroids. It was large enough when it first formed to partially differentiate, which meant that heavy material such as stone and some metals fell in the middle while it was still hot, while lighter material like water, aluminum-rich ones Material and some rock with lower density continued to stay out. Finally, it cooled and formed a crust with an average thickness of 40 km on an approximately 400 km deep ice shell. Measurements from Dawn showed that the mantle is about twice as dense as the crust (1.3 grams per cubic centimeter versus 2.4, with water having a density of 1). Not only that, but also the decay of the small amount of radioactive material in Ceres can heat it so much that the water deep below the surface can still be liquid after all this time.

Much of the water in the mantle is liquid. and things near the bottom of the coat become warmer than things near the top. That is, the water will convect, with warmer material rising and cooler material falling. With sufficient pressure from below, the water penetrates through cracks upwards and through the surface.

Many stones and the like dissolve in the water and make it briny. When it hits the surface, it freezes and sunlight eventually turns it into a gas. It evaporates (technically sublimates) and leaves the brine: that makes the bright spots that we see everywhere on Ceres.

Sometimes, however, the water rises in a cloud, like the one that makes up the Canary Islands and the Hawaiian Islands. In fact, this fits better with the data, and the authors believe this could be done below the surface to create Ahuna Mons.

In itself this could not penetrate the surface. However, if it has found a stain in the crust that is thinner and there is a channel in the crust with a diameter of only 10 meters, this could explain what is being seen. The water that comes to the surface freezes, but more water comes out of the cloud and pushes the ice up. It eventually forms a mountain, essentially a slow volcano. It does not have much structural strength, so it collapses on the sides and forms the skirt.

The new work uses a clever method to find out what material is in Ahuna Mons. The orbit of the dawn depended on the total mass of Ceres (that's how gravity works), but as dawn swept over a region of higher density, it became faster. By carefully measuring the Doppler shift of radio signals sent back to Earth, scientists can accurately measure the spacecraft's orbit, and thus the density of the material beneath it at a given time.

Measuring the gravity of Ceres, they found an anomaly directly at the position of Ahuna Mons. Using some physics to adapt computer models to gravity, they found that the best fit was achieved with a lump of material about 80 x 40 km in size and 30 km deep. The density of the material was about 2.4 g / cc, which corresponds to the coat density. This suggests that it is a stain from the mantle that drills through the surface (probably where the fire was less thick, as it averages 40 km deep).

Examining the morphology of Ahuna Mons, the physics of how material moves around Ceres and on cooling, they find that the material is 55-70 vol% of water and about 30-45 vol% consisted of "insoluble solid particles, essentially a slurry".

in other words, mud.

This could explain why Ahuna Mons is also the only mountain of its kind; Feathers are not common, especially near places where the crust is thinner. And if someone else had formed, they would probably have collapsed and collapsed over a few tens or hundreds of millions of years. This also means that Ahuna Mons is geologically young. It is quite possible that the cloud is still active. However, it may take a while to know if there are landslides now when material is pushed up.

Unfortunately, Dawn ran out of fuel at the end of 2018, and scientific observations have ceased. We hope to send another probe into this weird little world to see what's wrong. and what has changed since Dawn? I like how we are always surprised by our solar system, which escapes expectations at every turn. But it is said that if we knew what we would find out there, it would not be exploration.


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