Through analyses of surface elevation data and ice-penetrating radar collected from 2015 to 2017 by NASA’s Operation IceBridge, the researchers revealed how the double ridge on northwest Greenland was produced when the ice fractured around a pocket of pressurized liquid water that was refreezing inside of the ice sheet, causing two peaks to rise into the distinct shape.

“In Greenland, this double ridge formed in a place where water from surface lakes and streams frequently drains into the near-surface and refreezes,” said lead study author Riley Culberg, a PhD student in electrical engineering at Stanford. “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.”

Snowballing complexity

Rather than behaving like a block of inert ice, the shell of Europa seems to undergo a variety of geological and hydrological processes – an idea supported by this study and others, including evidence of water plumes that erupt to the surface. A dynamic ice shell supports habitability since it facilitates the exchange between the subsurface ocean and nutrients from neighboring celestial bodies accumulated on the surface.

“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,” said study co-author Gregor Steinbrügge, a planetary scientist at NASA’s Jet Propulsion Laboratory (JPL) who started working on the project as a postdoctoral researcher at Stanford. “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 co-authors said their explanation for how the double ridges form is so complex, they couldn’t have conceived it without the analog on Earth.

“The mechanism we put forward in this paper would have been almost too audacious and complicated to propose without seeing it happen in Greenland,” Schroeder said.

The findings equip researchers with a radar signature for quickly detecting this process of double ridge formation using ice-penetrating radar, which is among the instruments currently planned for exploring Europa from space.

“We are another hypothesis on top of many – we just have the advantage that our hypothesis has some observations from the formation of a similar feature on Earth to back it up,” Culberg said. “It’s opening up all these new possibilities for a very exciting discovery.”

To read all stories about Stanford science, subscribe to the biweekly Stanford Science Digest.

Schroeder is also a faculty affiliate with the Institute for Human-Centered Artificial Intelligence (HAI), an associate professor, by courtesy, of electrical engineering and a center fellow, by courtesy, at the Stanford Woods Institute for the Environment.

This research was supported by a National Defense Science and Engineering Graduate Fellowship and, in part, by NASA Grant NNX16AJ95G and NSF Grant 1745137.

Media Contacts

Riley Culberg, School of Engineering:

Dustin Schroeder, School of Earth, Energy & Environmental Sciences: (650) 725-7861, (440) 567-8343 (cell);

Danielle Torrent Tucker, School of Earth, Energy & Environmental Sciences: (650) 497-9541;