On Jupiter’s moon Io, lava creeping under frost can give rise to towering dune fields.
That finding, described April 19 in nature communicationssuggests that the dunes may be more common on other worlds than previously thoughtalthough the lumps can form in strange ways.
“In a sense, these [other worlds] they look more familiar,” says George McDonald, a planetary scientist at Rutgers University in Piscataway, New Jersey. “But the more you think about it, they feel more and more exotic.”
Io is a world full of erupting volcanoescreated when the gravitational forces of Jupiter and some of its other moons attract Io and generate heat (Serial number: 6/8/14). About 20 years ago, scientists reported another type of feature on Io’s dynamic surface: mountain ridges. The features resemble dunes, but that might not be the case, the scientists reasoned, because Io’s atmosphere is too thin for winds to form a dunescape.
But in recent years, dune-like features have been discovered in comet 67p (Serial number: 09/21/20) Y Pluto (Serial number: 8/24/21), planetary bodies that also lack thick atmospheres. Inspired by these alien dune landscapes, McDonald and his colleagues took another look at the issue of Io’s mysterious lumps. All they needed was some kind of airborne force to carve out the dunes on the moon.
On Earth, powerful steam explosions occur when flows of molten rock meet bodies of water. While no water is found on Io, sulfur dioxide frost is ubiquitous. So scientists hypothesize that when lava flows slowly into and just below a layer of frost, jets of sulfur dioxide gas could erupt from the frost. Those jets could send grains of rock and other material flying and forming dunes.
The researchers calculate that an advancing lava flow, buried under at least 10 centimeters of frost, could sublimate some of the frost into pockets of hot steam. When enough steam builds up and the pressure becomes high enough to equal or exceed the weight of the frost covering it, the steam could burst at speeds of more than 70 kilometers per hour. These bursts could propel grains with diameters from 20 micrometers to 1 centimeter in size, the team estimates.
Analysis of images of Io’s surface, collected by NASA’s now-defunct Galileo spacecraft, revealed highly reflective streaks of material radiating outward over dunes in front of lava flows, possibly material newly deposited at the time by steam jets.
Furthermore, using the images to measure the features of the mounds showed that their dimensions align with those of dunes on other planetary bodies. Some of the Ionian dunes are more than 30 meters high, the team estimates.
“I think a lot about [scientists] I looked at them and thought, hey, they really could be dunes,” says Jani Radebaugh, a planetary scientist at Brigham Young University in Provo, Utah, who was not involved in the study. “But what’s exciting about this is that they’ve come up with a nice physical mechanism to explain how it’s possible.”
Io is usually thought of as a world of volcanoes. The possibility of dunes suggests there could be more going on there than scientists thought, says McDonald. “It certainly adds a layer of complexity.”