Explanation for formation of abundant features on Europa bodes well for
search for extraterrestrial life
Date:
April 19, 2022
Source:
Stanford University
Summary:
Ice-penetrating radar data from Greenland suggests that shallow
water pockets may be common within Europa's ice shell, increasing
the potential habitability of the Jovian moon's ice shell.
FULL STORY ========================================================================== Europa is a prime candidate for life in our solar system, and its
deep saltwater ocean has captivated scientists for decades. But it's
enclosed by an icy shell that could be miles to tens of miles thick,
making sampling it a daunting prospect. Now, increasing evidence reveals
the ice shell may be less of a barrier and more of a dynamic system --
and site of potential habitability in its own right.
========================================================================== Ice-penetrating radar observations that captured the formation of a
"double ridge" feature in Greenland suggest the ice shell of Europa
may have an abundance of water pockets beneath similar features
that are common on the surface. The findings, which appear in Nature Communications April 19, may be compelling for detecting potentially
habitable environments within the exterior of the Jovian moon.
"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," said
study senior author Dustin Schroeder, an associate professor of geophysics
at Stanford University's School of Earth, Energy & Environmental
Sciences (Stanford Earth). "If the mechanism we see in Greenland is how
these things happen on Europa, it suggests there's water everywhere."
A terrestrial analog On Earth, researchers analyze polar regions using
airborne geophysical instruments to understand how the growth and retreat
of ice sheets might impact sea-level rise. Much of that study area occurs
on land, where the flow of ice sheets is subject to complex hydrology --
such as dynamic subglacial lakes, surface melt ponds and seasonal drainage conduits -- that contributes to uncertainty in sea-level predictions.
Because a land-based subsurface is so different from Europa's subsurface
ocean of liquid water, the study co-authors were surprised when, during
a lab group presentation about Europa, they noticed that formations that
streak the icy moon looked extremely similar to a minor feature on the
surface of the Greenland ice sheet -- an ice sheet that the group has
studied in detail.
==========================================================================
"We were working on something totally different related to climate change
and its impact on the surface of Greenland when we saw these tiny double
ridges - - and we were able to see the ridges go from 'not formed' to 'formed,'?" Schroeder said.
Upon further examination, they found that the "M"-shaped crest in
Greenland known as a double ridge could be a miniature version of the
most prominent feature on Europa.
Prominent and prevalent Double ridges on Europa appear as dramatic gashes across the moon's icy surface, with crests reaching nearly 1000 feet,
separated by valleys about a half-mile wide. Scientists have known about
the features since the moon's surface was photographed by the Galileo spacecraft in the 1990s but have not been able to conceive a definitive explanation of how they were formed.
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 Steinbru"gge, 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." Schroeder is
also a faculty affiliate with theInstitute for Human-Centered Artificial Intelligence (HAI), an associate professor, by courtesy, of electrical engineering and a center fellow, by courtesy, at theStanford 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.
Video:
https://youtu.be/8YOmER50epo
========================================================================== Story Source: Materials provided by Stanford_University. Original
written by Danielle Torrent Tucker. Note: Content may be edited for
style and length.
========================================================================== Related Multimedia:
* An_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.
========================================================================== Journal Reference:
1. Culberg, R., Schroeder, D.M. & Steinbru"gge, G. Double ridge
formation
over shallow water sills on Jupiter's moon Europa. Nat Commun,
2022 DOI: 10.1038/s41467-022-29458-3 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/04/220419112347.htm
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