What Is 13000 Feet Tall, Millions of Years Old, and Spews Out Ice?

Ice volcanoes sound like something out of a Syfy-channel movie, perhaps produced by the same people behind the Sharknado franchise: a muddy mix of ice, rock, and salts erupting through cracks in the terrain and scattering out onto the landscape, freezing everything in its path. But they are in fact a natural phenomenon that scientists believe occurs across our solar system and beyond.

For several years now, scientists have been puzzling over one such volcano on the dwarf planet Ceres. Ceres orbits more than 200 million miles from the sun, between Mars and Jupiter, where it reigns as the largest object in the asteroid belt. Ceres is made of rock and ice, and formed alongside the planets in our solar system about 4.5 billion years ago. For years, scientists using computer simulations of conditions on Ceres predicted that the dwarf planet could host ice volcanoes, or cryovolcanoes.

Rosaly Lopes, a scientist at NASA’s Jet Propulsion Laboratory, has summed them up this way: “If Mount Vesuvius had been a cryovolcano, its lava would have frozen the residents of Pompeii.”

In 2007, NASA launched a mission on a years-long journey to explore the asteroid belt. When the spacecraft Dawn arrived at Ceres in 2015, it captured high-resolution photographs of the dwarf planet. They revealed a surface covered in craters. But near the equator, a curiosity: a sole mountain peak, jutting out against the sea of deep impressions in the rocky terrain.

For the scientists, the peak, standing about 13,000 feet tall, fit the bill: It was their first ice-volcano discovery on the dwarf planet. They named it Ahuna Mons, and estimated its age was 200 million years—old enough to have ceased erupting, but young enough to suggest it was active in the recent past.

It was an exciting find for scientists, who turned to a new question about ice volcanoes on Ceres: Why was there only one?

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Michael Sori, a scientist at the University of Arizona’s Lunar and Planetary Laboratory, suspected that other ice volcanoes had existed on Ceres but were erased by a natural process over time. In this process, known as viscous relaxation—which sounds more like a new skin-care routine than a geological phenomenon—a blob of a material can collapse under its own weight and ooze outward. “Rocks don’t do that under normal temperatures and timescales, but ice does,” Sori explained in a recent press release. The erupting ice eventually flattens the surrounding terrain. Meteor impacts help out, too, by smashing the peaks.

To test this theory, Sori and his colleagues used computer models to simulate the landscape of Ceres over hundreds of millions of years. They inserted ice volcanoes into the terrain and then ran the clock forward. Volcanoes at the dwarf planet’s poles, where it’s colder, remained frozen. Near the equator, where it’s warmer, volcanoes seemed to deflate, becoming shorter and rounder until they flattened out.

To bolster their hypothesis, the researchers needed real data, and they turned to Dawn, the NASA spacecraft. Sori and his team used topographic observations from the probe to look for bumps in the terrain that matched their models. They found 22 mountains, including Ahuna Mons, that aligned nicely with their simulation’s predictions. They estimate the landforms are each hundreds of millions of years old, and that Ceres produces a new ice volcano about once every 50 million years.

Their results were published earlier this week in Nature Astronomy.

The mechanism that fuels these cryovolcanoes on Ceres remains a mystery. Scientists believe the dwarf planet may have enough primordial heat left over from its formation billions of years ago to churn material beneath its surface.

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Hanna Sizemore, a scientist at the Planetary Science Institute and one of the study’s authors, says the evidence for cryovolcanoes on Ceres and other ice-bearing bodies in the solar system is piling up. Scientists have previously observed evidence of ice volcanoes on Jupiter’s moon Europa, Saturn’s moons Enceladus and Titan, Neptune’s moon Triton, and even Pluto. In the case of Europa and Enceladus, the observations suggest the moons harbor massive oceans beneath their icy exterior that may be capable of sustaining microbial life.

“It’s really been kind of debated hotly whether there really are volcanoes on icy planets, if ice and salt and dirt can together really act like molten rock acts on the Earth, Mars, the moon, and Venus,” Sizemore said. “There’s still uncertainty about exactly how analogous what’s happening is to volcanism [on Earth], though I think the case is growing that there really are cryovolcanoes.”

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