Beneath the surface of Jupiter's icy moon, there is an ocean up to 100 km deep that is two to three times the volume of every ocean on Earth combined. The ocean may have all the necessary ingredients for life because of the activity that occurs in it. One of the most likely places for extraterrestrial life is Europa. Mission planners are eager to send a mission there to study it.
It is difficult to sample this ocean because of the icy surface. The ice sheet could be several dozen kilometers thick according to the two models. Thanks to new research by a team from the University of California, Berkeley, it has been shown that the icy shell of Europa may have an abundance of water pockets inside.
Riley Culberg is a PhD candidate in the School of Earth, Energy and Environmental Sciences at Standford. He was joined by two other people, one of whom was a planetary scientist at the NASA Jet Propulsion Laboratory. The paper about their research was published in the journal Nature Communications.
The research was motivated by a similarity the team noticed during a presentation at Standford. Culberg noticed how similar the landforms were to features they had studied in northern Greenland. NASA collected ground-penetrating radar data of the region between 2015 and 2017, as part of an aerial observation campaign that studies the growth and retreat of ice sheets.
The double ridge was confirmed by this investigation and provided details of how it evolved. The features are formed when water from nearby surface lakes drain into an impermeable layer within the ice sheet. The double ridge feature on the surface is caused by the refreezes and fractured ice above.
The similarities came as a surprise to the team because of how different Earth's land-based subsurface is compared to the ocean of liquid water on the other side of the world.
They found that the M-shaped feature could be a miniature version of the most prominent surface feature. Double ridges appear as gashes that cut across the surface, with crests reaching nearly 300 m (1,000 ft) tall, separated by valleys about 800 meters (2,625 ft) wide. The first detailed surface maps were created after the Galileo spacecraft took images of the Galilean Moons.
Scientists have not been able to explain how these features formed. The team could come up with an answer by comparing the radar data collected by IceBridge with the data they had for Europa. Culberg explained that.
“In Greenland, this double ridge formed in a place where water from surface lakes and streams frequently drains into the near-surface and refreezes. One way that similar shallow water pockets could form on Europa might be through water from the subsurface ocean being forced up into the ice shell through fractures – and that would suggest there could be a reasonable amount of exchange happening inside of the ice shell.”
The findings suggest that the ice shell may be more dynamic than previously thought. This is supported by other recent findings, such as Hubble's discovery of plume activity on the surface in 2012 and a new analysis of Galileo data. A dynamic ice shell model is consistent with the exchange of water and minerals on the moon.
Steinbrügge started working on the project as part of his research at the university.
“People have been studying these double ridges for over 20 years now, but this is the first time we were actually able to watch something similar on Earth and see nature work out its magic. We are making a much bigger step into the direction of understanding what processes actually dominate the physics and the dynamics of Europa’s ice shell.”
The existence of these pockets is good news for the mission, in which both Steinbrügge and Schroeder will be involved. In October of 2024, the robot will launch, reach the Jovian system in April of 2020 and spend the next four years examining the surface of Europa. In addition to analyzing the surface ice and plume activity, it will select landing sites for a possible mission. As explained by Schroeder.
“Because it’s closer to the surface, where you get interesting chemicals from space, other moons, and the volcanoes of Io, there’s a possibility that life has a shot if there are pockets of water in the shell. If the mechanism we see in Greenland is how these things happen on Europa, it suggests there’s water everywhere.”
The Europa Clipper will use an ice-penetrating radar to study the interior of the ice sheet. The Radar for Europa Assessment and Sounding: Ocean to Near-Surface (REASON) is overseen by a team that includes Schroeder. The way in which water reflects is one thousand times brighter than ice.
The REASON team will be able to create a vertical profile that maps the distribution of water pockets.
It's possible to find potentially habitable enclaves within the ice sheets, which will make it easier to look for signs of life in the ocean. Increasing accessibility and exploring these pockets decreases the chances of contaminating potential biospheres in the moon's interior ocean. Ensuring the safety of any extraterrestrial life we encounter will be paramount as the missions progress.
It would mean the ice shell on Europa has a lot of water. Exchange processes between the surface and the ocean could be helped by it. It could go either way.
The study shows how connected the study of Earth and the other Solar planets are. It will lead to applications that could have significant impacts here at home.
Further reading: NASA, Nature.
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