Ice-Spewing Volcanoes on 2 of Uranus’ Moons Tantalize Scientists

Two small moons orbiting the planet Uranus once had volcanoes unlike anything seen anywhere else in the solar system, two scientists at Cornell University have concluded.

Unlike the molten lava that spews from the Earth’s volcanoes, the volcanoes on Uranus’ moons--Ariel and Miranda--belched forth frozen ice, geophysicist David G. Jankowski said.

“The ice would actually flow up like a volcano and squirt out like toothpaste,” Jankowski said in a telephone interview. It all happened in the distant past, perhaps as long as 4 billion years ago, but it offers new clues about the interior of the satellites today, and the phenomena has not been seen anywhere else, he added.

Tantalize Scientists

The satellites, particularly Miranda, have tantalized geologists and physicists ever since the close-up images taken by the Voyager spacecraft were transmitted back to the Jet Propulsion Laboratory more than two years ago. Both moons, and especially Miranda, appear to have been subjected to the kind of geological forces that would not be expected to be at work on bodies that small.

Miranda, for instance, has deep crevices that appear to have been twisted back and forth, although the moon, which is only about 300 miles in diameter, is much too small to be subjected to the kind of geological activity that has formed similar features on Earth. Scientists throughout the country have studied the images from Voyager in an effort to explain the dynamics of the tiny moon, but no firm consensus has emerged.

Jankowski and Steven W. Squyres of Cornell’s Center for Radiophysics and Space Research, like many other scientists, have been examining the data from Voyager for the last two years, and they discovered something rather odd in the contours on Ariel’s and Miranda’s surfaces. The features most likely resulted from ice flowing to the surface of the moons, but water ice at that great distance from the sun would be frozen so hard it could not possibly flow, Jankowski said.

The scientists, who presented their conclusions in a report in today’s issue of the journal Science, believe that something other than water ice must be buried beneath the surface of the moons. To have low enough viscosity to flow, the ice must have contained other elements, such as ammonia.

“That hints very strongly that there are materials other than water ice inside the satellite,” Jankowski said.

‘Extremely Cold’

“It’s very cold out there, extremely cold,” he added. “How did you get the ice to flow? If you mix in other materials with water ice, you get lower viscosity,” and the ice could be flexible enough to flow to the surface through narrow cracks.

The ice volcanoes examined by the scientists are so subtle that someone standing on the surface of either moon “would have a hard time telling that he was standing on anything in particular,” Jankowski said.

The forces that powered the volcanoes so many years ago are not clearly understood, he added. To have been pushed to the surface, the ice must have been more buoyant than the surrounding material, which itself is curious because it is not clear why less-dense material, including ice, should have been buried just beneath the surface, Jankowski said.