‘Chaos terrains’ may get oxygen into Europa’s hidden ocean

Set to launch in 2024, NASA’s Europa Clipper will travel to Jupiter’s moon Europa to investigate whether the moon has conditions necessary to support life. The spacecraft’s instruments will help researchers learn more about the availability and accessibility of the ingredients for life on the moon. (Credit: NASA/JPL-Caltech)

Salt water within the icy shell of Jupiter’s moon Europa could be transporting oxygen into an ice-covered ocean of liquid water where it could potentially help sustain alien life, according to a new study.

Others have proposed this theory, but researchers put it to the test by building the world’s first physics-based computer simulation of the process, with oxygen hitching a ride on salt water under the moon’s “chaos terrains,” landscapes made up of cracks, ridges, and ice blocks that cover a quarter of the icy world.

The results show that not only is the transport possible, but that the amount of oxygen brought into Europa’s ocean could be on a par with the quantity of oxygen in Earth’s oceans today.

The illustration shows rocky chaos terrains with liquid water beneath them connected to the ocean under the Europa's surface
An artist’s interpretation of liquid water on the surface of the Europa pooling beneath chaos terrain. (Credit: : NASA/JPL-Caltech)

“Our research puts this process into the realm of the possible,” says lead researcher Marc Hesse, a professor at the University of Texas Jackson School of Geosciences geological sciences department. “It provides a solution to what is considered one of the outstanding problems of the habitability of the Europa subsurface ocean.”

The study appears in the journal Geophysical Research Letters.

Europa is a top spot to look for alien life because scientists have detected signs of oxygen and water, along with chemicals that could serve as nutrients. However, the moon’s ice shell—which is estimated to be about 15 miles thick—serves as a barrier between water and oxygen, which is generated by sunlight and charged particles from Jupiter striking the icy surface.

“It’s enticing to think of some kind of aerobic organisms living just under the ice.”

If life as we know it exists in the ocean, there needs to be a way for oxygen to get to it. The most plausible scenario based on the available evidence is for the oxygen to be carried by salt water, or brine, Hesse says.

Scientists think that chaos terrains form above regions where Europa’s ice shell partially melts to form brine, which can mix with oxygen from the surface. The computer model the researchers created shows what happens to the brine after the formation of the chaos terrain.

The model shows the brine draining in a distinct manner, taking the form of a “porosity wave” that causes pores in the ice to momentarily widen—allowing the brine to pass through before sealing back up. Hesse compares the process to the classic cartoon gag of a bulge of water making its way down a garden hose.

This mode of transport appears to be an effective way to bring oxygen through the ice, with 86% of the oxygen taken up at the surface riding the wave all the way to the ocean. But the available data allows for a wide range of oxygen levels delivered to Europa’s ocean over its history—with estimates ranging by a factor of 10,000.

The highest estimate would make the oxygen levels in Europa’s ocean similar to those in Earth’s oceans—which raises hope about the potential for that oxygen to support life in the hidden sea, according to coauthor Steven Vance, a research scientist at NASA’s Jet Propulsion Laboratory (JPL) and the supervisor of its Planetary Interiors and Geophysics Group. “It’s enticing to think of some kind of aerobic organisms living just under the ice,” he says.

Vance says that NASA’s upcoming 2024 Europa Clipper mission may help improve estimates for oxygen and other ingredients for life on the icy moon.

Kevin Hand, a scientist focused on Europa research at NASA JPL who was not part of the study, says that the study presents a compelling explanation for oxygen transport on Europa.

“We know that Europa has useful compounds like oxygen on its surface, but do those make it down into the ocean below, where life can use them?” he says. “In the work by Hesse and his collaborators, the answer seems to be yes.”

NASA, the National Science Foundation, and the American Chemical Society Petroleum Research Fund funded the work.

Source: UT Austin