Ice Volcanoes in Outer Space
We are all familiar with the terrestrial or rocky planets in our solar system—Mercury, Venus, Earth, Mars, as well as a number of terrestrial satellites such as our moon or Jupiter’s moon, Io, but far less is known about the icy water worlds that populate our solar system. Since the late 1980s, spacecraft such as Voyager 2, Galileo, Cassini, Dawn, and New Horizons have revealed images of many of these water worlds, including Jupiter’s moon Europa, Saturn’s moons Enceladus and Titan, and Neptune’s moon Triton. Surface features on these bodies often resemble features on Earth associated with lava flows or calderas, and a number of these bodies have been observed erupting water or other volatile compounds that would be frozen solid at the surface temperature of the body, a process called cryovolcanism. So, who better to study these ice volcanoes or geysers than MU’s own lava expert, Professor Alan Whittington, chair of the Department of Geological Sciences?
“The Cassini satellite managed to fly through one of these plumes on Enceladus and measured what it was composed of, so the geysers are made of whatever the ocean is made up of under the ice,” Whittington says. “Somewhere in the interior there’s probably going to be something similar to Earth’s sea floor. We have mid-ocean ridges with volcanoes, which are great places for life such as tubeworms. On these bodies, we don’t think there are plate tectonics, but there should be warmth from hydrothermal circulations, and these are perhaps the most likely places in the solar system to find current life. The bodies that have a layer of water are most likely to harbor life.”
NASA Green Lights the MU Proposal
Whittington and geology doctoral student Aaron Morrison recently received word that NASA agreed to fund their research proposal, “Rheological Investigation of Cryovolcanic Lavas.” Rheology is the study of the properties and behavior of matter as it flows or deforms. The grant funding will pay for a new rheometer (a device to measure viscosity, or stress required to deform a material) for the geology department, and Morrison eventually will go the Jet Propulsion Lab (JPL) at the California Institute of Technology in Pasadena to expand upon the experiments he will begin at MU. Morrison says he first heard of the concept of cryovolcanism while taking a course Whittington and his wife, astronomy Professor Angela Speck, co-teach on the science of our solar system. But Morrison says when the class finally broached the topic, Whittington admitted that scientists don’t know much about the phenomenon at this point.
“I’d never heard of this before, and I wanted to learn more,” Morrison says. Then Morrison accompanied Whittington to a Geological Society of America conference, where NASA scientists presented data from the New Horizons probe at Pluto.
“At the end of one of their talks they said, ‘What we really need right now is some rheological data on these findings,’ and I thought, ‘Well, that’s what I do—why don’t I contact these folks and see if we can do something cool?’” Morrison says. He says they can determine the composition of the surface ices/geysers from spectral analyses conducted by the probes and then synthesize those materials in the lab. Morrison will use the new rheometer to determine the viscosity of the briny liquids he will be testing.
The Search for Answers, and Life
Whittington says the goal of the research is to characterize and understand the chemical, mineralogical, and physical features of these planetary surfaces and the fluids that interact with the surface, and to understand the process of cryovolcanism and interpret the physical features it produces. He says he thought about looking at the rheology of cryolavas a decade ago, but that was before the probes had reached these outer bodies, and there was no funding available for the research. Whittington says the recent success of the Cassini probe plus plans to send a probe to Europa made it a good time to request funding.
“One of the nice things Aaron did in the proposal is to make the link clearly between making some basic measurements that need to be made and tying that to how we can improve our understanding of what the interior ocean might be made of,” he says. Whittington says probes to Europa and other water worlds will likely land near cryovolcanoes to sample bits of the interior oceans belched up to the surface. Those frozen chucks of ocean are the most likely to harbor life since life cannot exist on the surface, where temperatures range from -256˚F at the equator to -364˚ at the poles.