Ceres: The tiny world where volcanoes erupt ice

September 1, 2016, Arizona State University
Volcanic dome Ahuna Mons rises above a foreground impact crater, as seen by NASA's Dawn spacecraft with no vertical exaggeration. Eruptions of salty, muddy water built the mountain by repeated eruptions, flows, and freezing. Streaks from falls of rocks and debris run down its flanks, while overhead views show fracturing across its summit. Credit: Dawn Science Team and NASA/JPL-Caltech/GSFC

Ahuna Mons is a volcano that rises 13,000 feet high and spreads 11 miles wide at its base. This would be impressive for a volcano on Earth. But Ahuna Mons stands on Ceres, a dwarf planet less than 600 miles wide that orbits the Sun between Mars and Jupiter. Even stranger, Ahuna Mons isn't built from lava the way terrestrial volcanoes are—it's built from ice.

"Ahuna is the one true 'mountain' on Ceres," said David Williams, associate research professor in Arizona State University's School of Earth and Space Exploration. "After studying it closely, we interpret it as a dome raised by cryovolcanism."

This is a form of low-temperature volcanic activity, where molten ice—water, usually mixed with salts or ammonia—replaces the molten silicate rock erupted by terrestrial volcanoes. Giant mountain Ahuna is a volcanic dome built from repeated eruptions of freezing salty water.

Williams is part of a team of scientists working with NASA's Dawn mission who have published papers in the journal Science this week. His specialty is volcanism, and that drew him to the puzzle of Ahuna Mons.

"Ahuna is truly unique, being the only mountain of its kind on Ceres," he said. "It shows nothing to indicate a tectonic formation, so that led us to consider cryovolcanism as a method for its origin."

Dawn scientist Ottaviano Ruesch, of NASA's Goddard Space Flight Center, Greenbelt, Maryland, is the lead author on the Science paper about Ceres volcanism. He says, "This is the only known example of a cryovolcano that potentially formed from a salty mud mix, and which formed in the geologically recent past."

Dawn's Framing Camera looks down on the fractured summit of Ahuna Mons, tallest mountain on dwarf planet Ceres. The cracks on top suggest Ahuna grew by inflation: icy freezing water pushed up inside the mountain, making a dome. (This image and the following one have the same scale and orientation, and are taken from the Science paper.) Credit: Dawn Science Team and NASA/JPL-Caltech/GSFC

Williams explained that "Ahuna has only a few craters on its surface, which points to an age of just couple hundred million years at most."

According to the Dawn team, the implications of Ahuna Mons being volcanic in origin are enormous. It confirms that although Ceres' surface temperature averages almost -40° (Celsius or Fahrenheit; the scales converge at this temperature), its interior has kept warm enough for liquid water or brines to exist for a relatively long period. And this has allowed volcanic activity at the surface in recent geological time.

Ahuna Mons is not the only place where icy volcanism happens on Ceres. Dawn's instruments have spotted features that point to cryovolcanic activity that resurfaces areas rather than building tall structures. Numerous craters, for example, show floors that appear flatter than impacts by meteorites would leave them, so perhaps they have been flooded from below. In addition, such flat-floored craters often show cracks suggesting that icy "magma" has pushed them upward, then subsided.

A few places on Ceres exhibit a geo-museum of features. "Occator Crater has several bright spots on its floor," said Williams. "The central spot contains what looks like a cryovolcanic dome, rich in sodium carbonates." Other bright spots, he says, occur over fractures that suggest venting of water vapor mixed with bright salts.

"As the vapor has boiled away," he explained, "it leaves the bright 1salts and carbonate minerals behind. "

Researchers draped a digital terrain model over a shaded image of Ahuna, placing contour lines at 100 meter (330 foot) elevation intervals. Key spot elevations are shown in meters. Credit: Dawn Science Team and NASA/JPL-Caltech/GSFC
Looking inside

Although volcanic-related features appear across the surface of Ceres, for scientists perhaps the most interesting aspect is what these features say about the interior of the dwarf world. Dawn observations suggest that Ceres has an outer shell that's not purely ice or rock, but rather a mixture of both.

Recently, Williams was involved in research that discovered that large impact craters are missing, presumably erased by internal heat, but smaller craters are preserved. "This shows that Ceres' crust has a variable composition—it's weak at large scales but strong at smaller scales," he said. "It has also evolved geologically."

In the big picture, said Williams, "Ceres appears differentiated internally, with a core and a complex crust made of 30 to 40 percent water ice mixed with silicate rock and salts." And perhaps pockets of brine still exist in its interior.

"We need to continue studying the data to better understand the interior structure of Ceres," said Williams.

The geological map of the major units at Ahuna Mons will be filled in with more details as scientists continue to study this small world shaped by icy volcanism. Credit: f Dawn Science Team and NASA/JPL-Caltech/GSFC

Ceres is the second port of call for the Dawn mission, which was launched in 2007 and visited another asteroid, Vesta, from 2011 to 2012. The spacecraft arrived at Ceres in March 2015. It carries a suite of cameras, spectrometers, and gamma-ray and neutron detectors. These were built to image, map, and measure the shape and surface materials of Ceres, and they collect information to help scientists understand the history of these small worlds and what they can tell us of the solar system's birth.

NASA plans for Dawn to continue orbiting Ceres and collecting data for another year or so. The is slowly moving toward its closest approach to the Sun, called perihelion, which will come in April 2018. Scientists expect that the growing solar warmth will produce some detectable changes in Ceres' surface or maybe even trigger .

"We hope that by observing Ceres as it approaches perihelion, we might see some active venting. This would be an ideal way to end the mission," said Williams.

Explore further: New studies provide unexpected insights into dwarf planet Ceres

More information: "Cratering on Ceres: Implications for its crust and evolution," Science science.sciencemag.org/cgi/doi … 1126/science.aaf4759

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16 comments

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Tuxford
1 / 5 (7) Sep 01, 2016
Notice they said nothing about the immediately adjacent crater that is shaped exactly the same outline as the mountain. Come on guys, really think we are that stupid.

OK if the mountain is volcanic, how about the crater? You can't explain one without explaining the other!
chordorganblues
5 / 5 (9) Sep 01, 2016
Notice they said nothing about the immediately adjacent crater that is shaped exactly the same outline as the mountain. Come on guys, really think we are that stupid.

OK if the mountain is volcanic, how about the crater? You can't explain one without explaining the other!


I'm gonna feel like a dummy if I'm just taking a joke post seriously... but, just in case...

That's a normal impact crater. It's rather roundish, like most craters are. Ahuna Mons is roundish like most volcanos are. They are indeed about the same size, which is neat, considering their proximity (here's a cool gif that really shows off how dramatic this specific bit of terrain is: http://i.imgur.com/Kk1Y3vv.gif ) Still, I don't think there's a very likely explanation out there that would tie their geological history together. As it is, it's already pretty freakin' cool! Itty bitty Ceres has a cryovolcano!
tinitus
Sep 01, 2016
This comment has been removed by a moderator.
RNP
3 / 5 (4) Sep 02, 2016
@chordorganblues

Thanks for linking the picture, it is really cool. It also clearly shows that the two features, although similar in size, do not have the same overall shape as claimed by some.
Tuxford
1 / 5 (6) Sep 02, 2016
So you guys are really going to argue that the mountain and the crater are unrelated??

http://phys.org/n...res.html

http://phys.org/n...ges.html
JongDan
5 / 5 (4) Sep 02, 2016
Still, I don't think there's a very likely explanation out there that would tie their geological history together.

Maybe the impact opened a crack in the crust somehow? Just trying to make connections. What's the estimated geological age of the crater though?
Jonseer
5 / 5 (6) Sep 02, 2016
Notice they said nothing about the immediately adjacent crater that is shaped exactly the same outline as the mountain. Come on guys, really think we are that stupid.

OK if the mountain is volcanic, how about the crater? You can't explain one without explaining the other!


You need your vision checked. They are NOT EXACTLY the same shape, and the pictures you linked to are extremely clear on that point. You are seeing what you want to see, not what is really there. That is why no one will seriously discuss your point. You have no point. You're very obviously wrong, and there is nothing to discuss. Ahuna is a rounded triangle. The crater is circular like a crater. If you can't see that, it's because you don't want to.
RNP
3.7 / 5 (6) Sep 02, 2016
So you guys are really going to argue that the mountain and the crater are unrelated??

http://phys.org/n...res.html


Yep. Although JongDan may have a point.
Guy_Underbridge
4.3 / 5 (6) Sep 02, 2016
You can't explain one without explaining the other!
So you're saying you know, as fact, the mountain wasn't there before the crater was formed?
antialias_physorg
5 / 5 (9) Sep 02, 2016
So you guys are really going to argue that the mountain and the crater are unrelated??

http://phys.org/n...res.html


Even in the image of the articel you linked there is a very similar looking crater below and to the right of the crater/mountain formation.

If you think they are unrelated then why do you think the two close to each other are related? Just because they are close to each other?

I grabbed a screenshot and did a quick measurement. The shape factor (ratio of east/west axist to north south) for the mountain is 1.3, whereas that of the crater is 0.9. Not all that similar.
Tuxford
1 / 5 (8) Sep 02, 2016
You guys are again seeing what you want to see, just like in the Huge Bang Fantasy. I am merely pointing out again, that there is another way to look at data.

The shape of the mountain and the crater outline are very similar. The walls of each are also very similar. What are the odds that the these two formations happen to be so close together if they are not related?? Just like the merger fantasy, it has got to be very remote.

So why not think that sometime in the distant past aliens mined for the buried treasure. They burned the conical mountain from ground, somehow hardening the surface layer of each in order to hold the mountain together, while they removed it, flipped it, and set it down next to the resulting crater. Then they lopped off the top to get the buried good stuff and dumped the remains in the bottom of the crater. The hardened sides are then impact resistant.

Just a different interpretation that seems to fit the observation.
Speleo
1 / 5 (6) Sep 02, 2016
I think that Tuxford's suggestion of related ice mountain and adjacent crater makes sense.

Could the mountain be a diapir instead of a volcano and the crater be a collapse structure?

They have different shapes, but mountain and crater appear to have similar volumes. If the mountain is the upper portion of a large ice mass surrounded by denser rock/ice material, then lithostatic pressure will push the less-dense ice block upwards. This is sort of how salt domes work here on Earth. If the ice mountain were thus formed, a similar volume would have to be made up from somewhere nearby ... maybe from under that crater through process of subsurface rock/ice flow and collapse.

Consider ... the talus slopes on both mountain and crater seem equally fresh and clear of craters, suggesting similar age and youth. The mountain summit and crater floor look similar to the adjacent undisturbed surface, which is consistent with an gradual uplift here and collapse there.
MaxwellSmith
1 / 5 (5) Sep 02, 2016
Did Nasa release a digital terrain model of the crater along with the tailings pile (er, I mean ice volcano)? That is what you need to compare volume of the two features. Taking 2 dimensional measurements doesn't disprove anything.
It really does look like an open pit mining operation with a tailings pile. Regardless, without any direct proof, I guess we have an ice volcano!
Homebrook
4.2 / 5 (5) Sep 05, 2016
There is absolutely no reason to think the two geologic structures have anything to do with one another.

Perhaps Mr. Tuxford needs to read about Occams Razor.
jonesdave
3.4 / 5 (5) Sep 06, 2016
Perhaps Mr. Tuxford needs to read about Occams Razor.


Or pareidolia!

Protoplasmix
5 / 5 (2) Sep 06, 2016
Post totals for this thread ...

Tuxford: posts=3; 1 / 5 (18)
chordorganblues: posts=1; 5 / 5 (9)
tinitus: posts=1; 1 / 5 (1)
RNP: posts=2; 5 / 5 (6)
Phys1: posts=1; 5 / 5 (2)
JongDan: posts=1; 5 / 5 (4)
Jonseer: posts=1; 5 / 5 (6)
Guy_Underbridge: posts=1; 5 / 5 (5)
antialias_physorg: posts=1; 5 / 5 (9)
Speleo: posts=1; 1 / 5 (6)
MaxwellSmith: posts=1; 1 / 5 (5)
Homebrook: posts=1; 5 / 5 (1)
jonesdave: posts=1; 5 / 5 (1)

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