Jupiter moon could host life, Purdue researchers find

Europa, one of Jupiter’s 95 moons, has a thicker ice shell than previously thought, according to a study recently published in the Scientific Advances journal.

Published by Purdue associate professor Brandon Johnson and research scientist Shigeru Wakita, the findings suggest an important thing: Europa might be able to sustain life.

The study is centered on the formation of multi-ring basins, a type of crater seen on Jupiter’s moon Europa, to determine the thickness of its surface ice shell.

“The surfaces of all the solid planetary bodies are covered in craters,” Johnson, a professor in the Department of Earth, Atmospheric and Planetary Sciences, said, “so there’s always some new interesting thing to find out about craters and what they can tell us about the bodies they form on.”

Johnson also teaches a course called Impacts, which is about impact cratering and processes.

Among scientists, there is a broad consensus that Europa has a subsurface ocean under its ice shell, Johnson said, making it only one of a few planetary bodies in our solar system that could sustain life.

“Whether it has a thick or a thin ice shell really changes the way we think about what is happening in the ice shell,” Johnson said. “It also changes how you think about how materials might be transported from the ocean to the surface and from the surface down to the ocean, which means that kind of exchange can be really important for whether Europa’s subsurface ocean might be habitable.”

Johnson said the researchers used data from satellite imagery from the Galileo mission to estimate the thickness of the ice shell. From there, they looked at the tectonic features of basins, then plotted how much extension happened as a function of the distance of the crater.

“So if the ice shell is too thin, we see tectonic features that are in compression rather than extension. If the ice shells are thick, then that collapse is accommodated by warm ice at depth,” he said. “And then during this collapse of the central uplift, we don’t get that compression happening. And so we only see the extension from that initial collapse.”

The team created simulations using iSALE-2D, a physics software that is used to study the impact of craters.

“We can plot up the extension we have in the models and and compare that to the observed extension, and we see that we get a really good fit when the ice shell is thicker than about 20 kilometers, and if it’s thinner than 15 kilometers, then we start to see that compression, and we know that’s not a good simulation,” he said.

Johnson said the recent Europa findings were the “longest time scale I’ve had for any paper, between being excited about some idea, and wanting to work on it and actually getting a paper out about it.

“But sometimes these things take a long time.”

He began studying and simulating the formation of basins and shell properties more than 10 years ago, and found exciting results, but he “wasn’t quite there.” He later attended a conference where another attendee was presented work about mapping the tectonics and basins of Europa.

Later this year, in October, NASA will launch its Europa Clipper, a mission that will “conduct a detailed reconnaissance of Jupiter’s moon Europa and investigate whether the icy moon could harbor conditions suitable for life,” according to NASA’s Jet Propulsion Laboratory website.

“One of the things I’m really excited about is one of these craters that we simulated, Tyre, is a target of one of their flybys, and the radar should be able to see liquid water within the ice shell,” Johnson said.