Parallel Ice Ridges Increase the Odds That Jupiter’s Moon Europa Harbors Alien Life

Europa Double Ridges

This artist’s conception shows how double ridges on the surface of Jupiter’s moon Europa may form over shallow, refreezing water pockets within the ice shell. This mechanism is based on the study of an analogous double ridge feature found on Earth’s Greenland Ice Sheet. Credit: Justice Blaine Wainwright

Parallel ice ridges, a common feature on Jupiter’s moon Europa, are found on Greenland’s ice sheet – and could bode well for Europa’s potential habitability.

Europa’s icy shell could be riddled with pockets of water because of the striking resemblance parallel ice ridges in Greenland bear to ridges on Jupiter’s ice-encased moon.

This resemblance might considerably boost the chances of NASA’s Europa Clipper mission detecting potentially habitable environments on the Jovian moon. The ice-penetrating radar sensor REASON (short for Radar for Europa Assessment and Sounding: Ocean to Near-surface) aboard the spacecraft will be ideally suited for performing such a search.

“If there are pockets of water under the ridges, we have the right instruments to see them,” said Dustin Schroeder, a Stanford University associate professor and coauthor of a new study published in the journal Nature Communications that compares Greenland’s “double ridges” with those of Europa.

According to evidence gathered this far, scientists believe that Europa has a deep liquid ocean concealed behind an ice shell that might be 10 to 15 miles (15 to 25 kilometers) thick. Because the ice on the moon is so thick, one great mystery is whether anything from the deep ocean makes contact with the surface — or whether contact occurs the other way around, with surface stuff filtering down to the ocean water.

Watery Plumes Jupiter's Moon Europa

The surface geology of Jupiter’s icy moon Europa is on display in this view made from images taken by NASA’s Galileo spacecraft in the late 1990s. Credit: NASA/JPL-Caltech/SETI Institute

“It’s exciting, what it would mean if you have plenty of water within the ice shell,” said coauthor Gregor Steinbru¨gge, a former Stanford researcher who is now a planetary scientist at NASA’s Jet Propulsion Laboratory in Southern California. “It would mean the ice shell on Europa is extremely dynamic. It could facilitate exchange processes between the surface and the subsurface ocean. It could go in both directions.”

Potential life-sustaining nutrients on Europa’s surface – perhaps deposited there by another Jupiter moon, volcanic Io – might find their way to the subsurface ocean, he said. And chemicals or other material from the subsurface indicating a habitable ocean environment could end up on the surface.

How Ridges May Have Formed

During a presentation on Europa’s ridges, the study’s lead author, Stanford graduate student Riley Culberg, said he noticed similar landforms in Greenland. Ice-penetrating radar data collected from 2015 to 2017 by NASA’s Operation IceBridge, an aerial observation campaign, showed not only the existence of a double ridge in northwestern Greenland, but also details of how it evolved.

The double ridges observed on the surface of the Greenland Ice Sheet formed when water from nearby surface lakes drained into a layer of impermeable ice within the ice sheet. Once there, the water pocket refroze and fractured the overlying ice, forcing peaks to rise on either side.

Double Ridge Cutting Across the Surface of Europa

A double ridge cutting across the surface of Europa is seen in this mosaic of two images taken by NASA’s Galileo during the spacecraft’s close flyby on February 20, 1997. Analysis of a similar feature in Greenland suggests shallow liquid water may be ubiquitous across the Jovian moon’s icy shell. Credit: NASA/JPL/ASU

Something similar could be happening on Europa, but instead with water forced up toward the surface from the subsurface ocean. The ridge features on Europa, while similar to the Greenland ridges, are much larger and with taller peaks, perhaps due in part to lower gravity on Europa.

Europa Clipper’s REASON instrument is designed to make the same kind of measurements at Europa that the IceBridge radar made in Greenland. Both use radio waves that can penetrate deeply into ice. The same waves, however, cannot penetrate liquid water and are instead reflected back to the radar instrument. Water shows up as a bright patch in the radar images. These radargrams can therefore provide a vertical profile of water and ice deep below the surface.

“You get reflections that are a thousand times brighter for water as opposed to ice,” Schroeder said.

Schroeder, a co-investigator on REASON and part of a group that studies Europa’s interior, said the new study could help the Europa Clipper team design observations to determine whether the ridges on the moon and in Greenland arose from the same underlying causes – and whether water pockets are common within Europa’s icy shell.

The study also highlights the growing synergy between scientists who study our planetary neighbors in the solar system and those who focus on Earth.

“This research will help us either use Earth to understand what we will see on Europa or, when we get to Europa, help us interpret what we see when we get there,” Schroeder said.

For more on this research, see Breaking News in Search for Extraterrestrial Life: Evidence of Water Near Europa’s Surface.

Reference: “Double ridge formation over shallow water sills on Jupiter’s moon Europa” by Riley Culberg, Dustin M. Schroeder and Gregor Steinbrügge, 19 April 2022, Nature Communications.
DOI: 10.1038/s41467-022-29458-3

More About the Mission

Missions such as Europa Clipper contribute to the field of astrobiology, the interdisciplinary research on the variables and conditions of distant worlds that could harbor life as we know it. While Europa Clipper is not a life-detection mission, it will conduct detailed reconnaissance of Europa and investigate whether the icy moon, with its subsurface ocean, has the capability to support life. Understanding Europa’s habitability will help scientists better understand how life developed on Earth and the potential for finding life beyond our planet.

Managed by Caltech in Pasadena, California, JPL leads the development of the Europa Clipper mission in partnership with APL for NASA’s Science Mission Directorate in Washington. The Planetary Missions Program Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama, executes program management of the Europa Clipper mission.

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