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Ice Volcanoes on Ceres?

If a terrestrial volcano erupts in molten rock, an ice volcano in the outer Solar System would presumably erupt with volatiles like water or ammonia. We have evidence of such things in places like Pluto and Triton, far beyond the snowline where water is abundant. Some scientists think Quaoar may have had cryovolcanic activity, and other candidates include Titan, Europa and Miranda. Which brings us to Ahuna Mons on the dwarf planet Ceres.

Discovered by the Dawn spacecraft in 2015, Ahuna Mons is unusual in many respects. Its sides are steep, its features well-defined, which suggests it is geologically young. If it is a cryovolcano, it seems to exist in splendid isolation, half the height of Mt. Everest on a surface otherwise bereft of similar features. Moreover, the orbit of Ceres between Mars and Jupiter gives us potential cryovolcanism closer to the Sun than has ever been observed before.

PIA20915-Ceres-DwarfPlanet-AhunaMons-2xHighSimulation

Image: Ahuna Mons seen in a simulated perspective view. The elevation has been exaggerated by a factor of two. The view was made using enhanced-color images from NASA’s Dawn mission. Credit: NASA.

Michael Sori (Lunar and Planetary Laboratory, University of Arizona) has a theory that just may explain Ahuna Mons’ peculiarities. As lead author of a new paper on the dwarf planet, Sori and colleagues have investigated the possibility that Ahuna Mons is simply the most recent of many cryovolcanoes that have formed on Ceres over millions of years, a young example of its type left alone as older ice volcanoes have gradually become deformed.

The heart of the hypothesis is viscous relaxation, the gradual flow of solids over time. We don’t see this with volcanoes on Earth because they are made of rock, but a high ice content could make a gradual flattening of a cryovolcano on Ceres possible. Given enough time, features like Ahuna Mons would effectively disappear from view, leaving no sign of their blocky structure. Ceres’ location relatively close to the Sun could accelerate the process.

PIA20348_crop_-_Ceres_Ahuna_Mons_top_view

Image: Ceres’ mysterious mountain Ahuna Mons is seen in this mosaic of images from NASA’s Dawn spacecraft. Dawn took these images from 385 kilometers above the surface, in December 2015. The resolution of the image is 35 meters per pixel. Credit: NASA.

We know that viscous relaxation occurs on Earth — we see the process in the flow of glaciers. On Ceres, we would have to presume a structure that is ice rich, which is not true over the entire surface. In fact, Dawn has revealed a high population of craters in many areas that show the crust of the dwarf planet is not sufficiently ice-rich to smooth out the topography uniformly. But some areas of Ceres present a different picture. From the paper:

This observation is consistent with Dawn geophysical observations [Ermakov et al., 2016a; Fu et al. 2016; Park et al. 2016], which reveal that Ceres (whose bulk density suggests an ice-rock mixture) is only partially differentiated [Zolotov, 2009] into icy and rocky layers in contrast to some pre-Dawn predictions of complete differentiation [McCord and Sotin, 2005; Thomas et al., 2005; Castillo-Rogez and McCord, 2010; Castillo-Rogez, 2011]. However, while the crust on average must be <30% ice by volume to support topography [Fu et al., 2016], variation in crater morphology [Bland et al., 2016] and spectroscopic detection of localized H2O [Combe et al., 2016] indicate ice content is laterally heterogeneous. Localized regions or individual landforms may be sufficiently ice-rich for flow to occur [Schmidt et al., 2016] even if the crust as a whole is not.

Is Ahuna Mons one such place? Sori and team modeled the flow of the feature assuming different proportions of water in the constituent materials of the mountain. The modeling demonstrates that if Ahuna Mons is composed of more than 40 percent water ice, viscous relaxation could indeed be in play. This would allow a flattening of between 10 to 50 meters per million years, enough to render cryovolcanoes unrecognizable over geologic time.

There could, in other words, have been other features like Ahuna Mons, with the latter, no more than 200 million years old, still in the gradual process of flattening. To firm up the idea, it will be necessary to study the surface for evidence of the remnants of other cryovolcanoes. Testable predictions flow from the modeling:

Based on our results, we predict older cryovolcanoes have shallower slopes, and that cryovolcanoes at mid-latitudes have asymmetries between poleward and equatorward facing slopes. We do not expect extensive viscous relaxation of polar features. The detection of this distribution of features would add strong support to the hypothesis that Ceres undergoes ice-rich cryovolcanism, and flow models would constrain Cerean cryovolcanic history.

The idea seems reasonable, especially given the alternative, that Ahuna Mons is the only ice volcano that formed on a world otherwise without such activity. “Ahuna Mons is at most 200 million years old. It just hasn’t had time to deform,” says Sori. It will take painstaking scrutiny of the Cerean surface to see whether other dome-like features fit into this picture. Also fascinating: The comparison between putative cryovolcanoes here and on other small worlds.

The paper is Sori et al., “The vanishing cryovolcanoes of Ceres,” accepted for publication at Geophysical Research Letters.

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Comments on this entry are closed.

  • Harry R Ray February 7, 2017, 10:38

    There ARE features on Earth that DO disappear due to viscous relaxation. They are called pingoes. Although considerably smaller than Ahuna Mons, they do look strikingly similar. Unlike cryovolcanoes, which require deep underground water “magma chambers” to form, pingoes use available water NEAR OR ON THE SURFACE to form via freeze-thsw” cycles. Although Ahuna Mons is much more likely to be a bona-fide extinct cryovolcano, instead of a “MEGApingo”, the jury is still out on that question. A possible hint is that Ahuna Mons stands RIGHT NEXT TO A LARGE CRATER. The impact that formed the crater could have melted water deep underground, CREATING the magma chamber if the angle of impact was just slightly OFF PERPENDICULAR! Another reason tor the apparent rarity of these features is that it might REQUIRE a perpendicular or near-perpendicular asteroid entry angle to form a magma chamber. If the entry angle of the asteroid responsible for Occator Crater were EXACTLY perpendicular, we may be seeing a cryovolcano in the process of formation, with water from the recently CONFIRMED “haze” freezing out and falling back to the surface. In that case, Ahuna Mons would consist MOSTLY of salts, with JUST ENOUGH WATER to cause the viscous relaxation.

    • galacsi February 7, 2017, 14:17

      Or maybe the crater is all is left from an other montain like Ahuna mons.

  • Mark T. February 7, 2017, 11:56

    While “viscous relaxation” may play some role, sublimation would work a lot faster at most latitudes on Ceres. The low surface gravity on Ceres (about 3% Earth sea level) would limit “viscous relaxation” but would not effect the sublimation of the ices directly. The maximum temperature of Ceres is listed as −36 °F, the average temperature below −100 °F, so the ice would be pretty darn stiff, but still able to sublimate in a vacuum. Given that Ahuna Mons is at 10.46°S, it must be relatively young. Compare with Figure 1 in this paper:

    http://www.hou.usra.edu/meetings/lpsc2016/pdf/2736.pdf

    Impacts are another factor mentioned in the paper.

  • Sanford Zane Meschkow February 7, 2017, 12:11

    Would it be worth drilling into this feature or into the ice near this feature and lowering a sensor package to collect data on activity in the interior of Ceres? I think some strange things might be going on at the interface between large volumes of ice and adjacent large volumes of rock.

  • Michael February 7, 2017, 12:23

    I still think it is a gas build up, it would not take much to lift that mountain.

    • RAS February 7, 2017, 13:48

      Even in the reduced gravity of Ceres it would probably take considerable more than a gas build up to produce Ahuna Mons.

      • Michael February 8, 2017, 10:39

        It only requires around 14 bar to support the weight or a little less due to the shape of it.

  • Bruce Mayfield February 7, 2017, 15:30

    This reminds me of the subsidence of deep ocean volcanic seamounts here on Earth. See the Hawaiian island chain for example. Over enough time, even mountains as tall as the Big Island will subside beneath sea level. Isn’t this also an earthly example of viscous relaxation of ocean basin rocks?

    • Adam February 7, 2017, 17:04

      Different process Bruce. Oceanic crust is moving around thanks to plate tectonics – cold slabs being subducted and new crust being created, pull and push oceanic crust around. As it moves away from a mid-oceanic ridge, the crust subsides, thanks largely to cooling in the hot crust beneath. The Hawaiian island sequence itself is being created by a mantle hot-spot deep below causing a continued up-welling, which breaks out anew for each active island as the oceanic crust moves over it.

      • Bruce Mayfield February 7, 2017, 19:49

        Knew about tectonics & the Hawaiian hot spot, and I wasn’t suggesting these as causes for this mountain on Ceres. I merely point out that when a great deal of mass is added to an area of a planet’s surface it can depress the crust beneath it. Solid rock at deapth often does distort over time.

  • Michael February 8, 2017, 15:06

    I wonder if it’s not an ancient mountain/glacier of ice that was shaken up by the next door impact which caused the regolith on the surface to fall away giving the sharp relief.

  • Harry Ray February 17, 2017, 10:42

    IT’S OFFICIAL! The Dawn spacecraft has just detected organic minerals VERY SIMILAR TO ASPHAULT on Ceres! Go to http://www.phys.org for details.

    • Alex Tolley February 17, 2017, 12:28

      Aliens building roads on Ceres. I just knew there had to be evidence if we just LOOKED CAREFULLY enough. ;)

      • Harry R Ray February 19, 2017, 15:11

        lol. But seriously, a few questions need to be asked here. First, and most important, did Dawn detect these “tars” ON the surface or UNDERNEATH it(like SOFIA detected carbon BENEATH the silicate meteorite dust cover)? Second, If(AND ONLY IF) the FORMER(which I STRONGLY SUSPECT to be TRUE)since the solar wind should break down organic chemicals exposed to the vacuum at the surface RATHER QUICKLY, how do these “tars” get REPLENISHED? The logical answer to this question is that the “tar” on the slopes of the crater is carried via avalanch to the OTHER areas. But, for this to happen, it has to be dry and dusty. “Tars” are ANYTHING BUT DRY AND DUSTY! Third, if the “tars” are NOT transported via avalanche, what other mechanism is there? On Earth, tar bubbles up from the SUBSURFACE, a la La Brea Tar Pits! Fourth, if THIS is what, going on at Ceres, there must be very small, very HOT vents similar to the vents on Enceledus! If Dawn’s orbit could be changed to an eccentric orbit that would bring it within a few kilometers of the crater, would its IR instrument be able to detect these hot spots. Finally, and MOST IMPORTANT, chemicals called mercaptains are found in the atmosphere ABOVE the La Brea Tar Pits. They can ONLY be formed by either industrial processes, OR by the DECAY of BIOLOGICAL ORGANISMS! The SIMPLIST mercaptan is Methyl Mercaptan(CH3SH)of which I have made MANY MANY COMMENTS on this website over the past few years! If Dawn can detect tar-like substances, it can CERTAINLY detect THIS compound! If it EVER DOES it would be MOST CERTAINLY of MAJOR HISTORIC IMPORTANCE!!!

  • ljk February 19, 2017, 23:13
  • ljk March 6, 2017, 10:40

    Cryovolcanism on Dwarf Planet Ceres

    Highly resolved images of Occator crater show evidence for long-lasting geologic activity.

    March 06, 2017

    Among the most striking features on the surface of Ceres are the bright spots in the center of Occator crater which stood out already as NASA’s space probe Dawn approached the dwarf planet. Scientists under the leadership of the Max Planck Institute for Solar System Research (MPS) have now for the first time determined the age of this bright material, which consists mainly of deposits of special mineral salts. With about four million years only, these deposits are about 30 million years younger than the crater itself. This, as well as the distribution and nature of the bright material within the crater, suggests that Occator crater has been the scene of eruptive outbursts of subsurface brine over a long period and until almost recently. Ceres is thus the body closest to the Sun that shows cryovolcanic activity.

    Full article here:

    http://www.mps.mpg.de/Cryovolcanism-on-Dwarf-Planet-Ceres

    The latest Dawn Journal on The Planetary Society blog here:

    http://www.planetary.org/blogs/guest-blogs/marc-rayman/0302-dawn-journal-intricate-maneuvers.html

  • Harry R Ray March 6, 2017, 19:13

    Seems to me we have TWO DISTINCTIVELY DIFFERENT KINDS of active solid worlds beyond the snow line: WILDLY active worlds(Io and Enceledus), and SUBTLEY active worlds(Europa and Ceres). I think the appropriate analogy MAY turn out to be: WILDLY active worlds(the hares)are for show, the SUBBTLEY active worlds(the tortoises) are for DOUGH! Cryovolcanoes MAY turn out to be the BEST place to look for life off Earth in our solar system. There appears to be no cryovolcanic activity on Enceladus at all if you DIFFERENTIATE geysers from volcanoes. Io’s volcanic activity is certainly NOT of the volcanic kind. In the end though, Ceres, the MOST subtle, may turn out to be the most EXCITING by far! ONLY Ceres has localized ALIPHATIC organic compounds, that should break apart MUCH MORE QUICKLY fro radiation than their AROMATIC counterparts! And yet they are there IN GREAT ABUNDANCE around Ernutat crater. What process REPLENISHES them? Present day life anyone?

  • Harry R Ray March 7, 2017, 10:14

    Sorry, I meant “…Io’s volcanic activity is certainly NOT of the cryovolcanic kind…”