Ceres takes life from an ice volcano at a time

According to a new study by the University of Arizona, ice volcanoes on the dwarf planet Ceres generate, on average, enough material to fill a cinema every year during its 4.5 billion years of life.

The study, conducted by global researcher Michael Sori, marks the first time that a cryovolcanic activity rate has been calculated from observations and its results help solve a mystery concerning the missing mountains of Ceres.

Discovered in 2015 by NASA's Dawn spacecraft, the 3-mile-high Ahuna Mons ice volcano stands lonely on the surface of Ceres. Still geologically young, the mountain is at most 200 million years old, which means it is no longer erupting but has been active in the recent past.

The youth and loneliness of Ahuna Mons have presented a mystery. It seemed unlikely that Ceres had slept for centuries and suddenly burst at one place. But if other ice volcanoes had emerged from the surface of Cereal in the past, where are these volcanoes now? Why is Ahuna Mons so lonely?

Sori and his co-authors, including researcher Ali Bramson, and Shane Byrne, professor of global science, sought to answer these questions.

In an article published last year, they theorized that evidence of older volcanoes on the dwarf planet had been erased over time by a natural process called "viscous relaxation." Viscous materials, such as honey or putty, can start as thick droplets, but the weight of the drop causes a flatter shape over time.

"The rocks do not do that in normal temperatures and time scales, but the ice does," Sori said.

Since Ceres is made up of rocks and ice, Sori continued the theory that the formations on the dwarf planet move and move under their own weight, as glaciers do on the Earth. The composition and temperature of formations would influence the speed with which they relax in the surrounding landscape. The more ice in a formation, the faster it flows; The lower the temperature, the lower the flow rate.

Although Ceres is never warmer than -30 degrees Fahrenheit, the temperature varies over its entire surface.

"The Ceres posts are cold enough so that if you start with a mountain of ice, it does not relax," said Sori. "But the equator is hot enough for a mountain of ice to relax on geologic time scales."

Computer simulations have shown that Sori's theory is viable. Model cryovolcanoes at the Ceres poles remained frozen on the spot for eternity. At other latitudes of the dwarf planet, model volcanoes began to grow and become stiff, but they became shorter, wider and more rounded over time.

To prove that the computer simulations went well, Sori scrutinized the topographical observations of the Dawn spacecraft, which has orbited around Ceres since 2015, to find reliefs corresponding to the models.

Sori and his team discovered 22 mountains, including Ahuna Mons, that looked exactly like the simulation's predictions.

"The really exciting part that made us think that this might be real is that we found only one mountain at the pole," said Sori.

Although it is old and battered by the impacts, the polar mountain, nicknamed Yamor Mons, has the same general shape as Ahuna Mons. It is five times wider than tall, giving it an aspect ratio of 0.2. The mountains found elsewhere on Ceres have smaller proportions, as predicted by the models: they are much larger than they are large.

By matching the real mountains to the model mountains, Sori was able to determine the age of many of them. The volume of volcanoes was estimated by studying their topography and, by combining age and volume, the Sori team was able to calculate the rate of cryovolcano formation on Ceres.

"We have discovered that a volcano is forming every 50 million years," Sori said.

That's an average of more than 13,000 cubic yards of cryovolcanic material a year – enough to fill a movie theater or four Olympic-sized pools. This activity is much less volcanic than that observed on Earth, where rock volcanoes generate more than one billion cubic meters of material per year.

In addition to being less productive, volcanic eruptions on Ceres are rarer than those on Earth. Instead of explosive eruptions, cryovolcans create the iced equivalent of a lava dome: the cryomagma – a salty mixture of rocks, ice and other volatile substances such as l & # 39; Ammonia – escapes the volcano and freezes on the surface. Most cryovolcanoes once powerful on Ceres probably formed this way before relaxing.

The causes of cryovolcanic eruptions on Ceres remain a mystery, but future research could provide answers, as signs of ice volcanoes were observed on other bodies of the solar system as the probes flew. . Ceres is the first cryovolcanic body that the mission put into orbit, but Europa and Enceladus, the moons of Jupiter and Saturn, are likely candidates for cryovolcanism, as is Pluto and its moon Charon. Europa is of particular interest because it is thought that liquid oceans are trapped under a thick layer of ice, which some scientists believe to be dotted with ice volcanoes. "There could be similarities between Europa and Ceres, but we have to send the next mission there before we can say for sure," said Sori.

As scientists explore other potentially cryovolcanic bodies in the solar system, it will be fun, said Sori, to see how Ceres compares itself.

The study entitled "Cryovolcanic Rates on Ceres Revealed by Topography" was recently published in Astronomy of nature.

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More information:
Cryovolcanic rates on Ceres revealed by the topography, Astronomy of nature (2018). DOI: 10.1038 / s41550-018-0574-1, https://www.nature.com/articles/s41550-018-0574-1