Science & Technology

Tiny Ceres Has a Great Big Ice Volcano

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Do you think a dwarf planet is too small to host volcanoes? Think again. Atop a little world called Ceres is a mountain called Ahuna Mons that towers more than 13,000 feet (4,000 meters) high — that's almost half the altitude of Mount Everest here on Earth. Scientists were initially baffled by this huge structure, but a new study suggests a special bubble could have built Ahuna Mons.

Bubbly Past

Ceres is a dwarf planet, meaning that it's smaller than a planet but still big enough to have a rounded shape. (Pluto is also a dwarf planet, by the way.) And even for a dwarf planet, Ceres is rather small. Imagine taking a road trip along the entire U.S. East Coast. If you did the equivalent mileage loop on Ceres, you'd nearly circle the whole dwarf planet in that one trip.

Ceres - Global view (left) and gravitational field view (right). A positive gravity anomaly is clearly visible in the area of Ahuna Mons (white).

Despite its diminutive circumference of just 1,859 miles (2,992 kilometers), Ceres is the largest object in a crowd of asteroids orbiting between the planets Mars and Jupiter. Ceres even hosted a NASA spacecraft called Dawn, which observed the dwarf planet between 2015 and 2018.

Dawn made some neat discoveries on Ceres, including finding bright white "snow" that we now know originated from icy volcanoes. The leftovers from these eruptions were hydrogenated sodium carbonate or ammonium-containing clays, which freeze immediately after they eject. And this process also helps us better understand the origin story of Ahuna Mons.

Early in Ceres' history, a bubble formed in its insides — not the soap bubbles that we're used to seeing on Earth, but rather an interesting combination of salt water, mud, and rock. As you can imagine, this bubble created a pressure point at the surface. Eventually, this gritty substance pushed through and began building up layers in space — a huge, icy mud volcano that today we know as Ahuna Mons.

Perspective view of Ahuna Mons.
Image mosaic of Ahuna Mons taken by NASA's Dawn spacecraft.

Icy Anomaly

So how did scientists find this bubble? It was through Dawn's movements in space, actually. As the spacecraft orbited around and around Ceres, scientists precisely tracked Dawn's path. They noticed that the gravitational pull on the spacecraft was a little stronger in one area; when Dawn moved over this spot, there was a slightly larger effect on the time it took for communications to reach Earth.

An oblique view of Ahuna Mons with elevation coding.

"We took a closer look at this anomaly, and further modeling revealed that it had to be a bulge in Ceres's mantle," said study lead author Ottaviano Ruesch (a research fellow at the European Space Agency) in a statement from the German Space Agency. "The conclusion was obvious: the mixture of fluid substances and rocks had come up to the surface and piled up into Ahuna Mons."

Cryovolcanoes, by the way, are not unique to Ceres. Several moons of Jupiter and Saturn also have these icy eruptions, and it appears that another dwarf planet — Pluto — probably had some structures formed in this way as well. It goes to show that you can't take anything for granted when exploring space. It just keeps on surprising us.

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You can display little Ceres in a place of honor with this 3D Ceres replica, which comes with a sleek acrylic riser and an informative flyer full of fun facts. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Elizabeth Howell June 28, 2019

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