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| Double ridges on the surface of Jupiter's frozen moon Europa may form over shallow, refreezing water pockets within the ice shell, as depicted in this artist's idea. The study of an equivalent double ridge phenomenon found on Earth's Greenland Ice Sheet inspired this mechanism. Justice Blaine Wainwright is the author of this piece. |
The discovery of a plausible explanation for the
creation of numerous characteristics on Europa is encouraging for the search
for extraterrestrial life.
Europa, Jupiter's moon, is a great contender for life
in our solar system, and its deep saltwater ocean has captivated scientists for
decades. It is, however, covered in an icy shell that could be hundreds of
miles thick, making sampling difficult. According to mounting data, the ice
shell is more of a dynamic system than a barrier – and an astrobiology location
with potential habitability in and of itself.
Ice-penetrating radar investigations of the creation
of a "double ridge" characteristic in Greenland suggest that Europa's
ice shell may have a plethora of water pockets beneath comparable features
found on the surface. The findings, which will be published on April 19,
2022 in the journal Nature Communications, could be useful in discovering
possibly livable situations on the Jovian moon's surface.
"Because it's closer to the surface, where you get fascinating compounds from space, other moons, and the volcanoes of Io," said research senior author Dustin Schroeder, an associate professor of geophysics at Stanford University's School of Earth, Energy & Environmental Sciences (Stanford Earth). "If the process we see in Greenland is how these things happen on Europa, that means there's water all around."
A terrestrial analog
On Earth, researchers use aerial geophysical
instruments to study polar regions in order to better understand how ice sheet
expansion and retreat affect sea-level rise. Much of the research area is on
land, where ice sheet movement is influenced by complicated hydrology – such as
dynamic subglacial lakes, surface melt ponds, and seasonal drainage conduits –
which adds to the uncertainty in sea-level projections.
Because a land-based subsurface is so different from
Europa's subsurface ocean of liquid water, the study co-authors were taken
aback when they noticed that formations that streak the icy moon looked
strikingly similar to a minor feature on the surface of the Greenland ice
sheet, which the group has studied extensively.
"We were working on something completely
unrelated about climate change and its impact on Greenland's surface when we
noticed these little double ridges – and we were able to witness the ridges
progress from 'not formed' to 'formed,'" Schroeder explained.
They discovered that the "M"-shaped crest
known as a double ridge in Greenland could be a tiny replica of Europa's most
noticeable feature after additional investigation.
Prominent and prevalent
On Europa, double ridges appear as dramatic gashes
across the frozen surface, with crests reaching about 1000 feet and valleys a
half-mile wide. Scientists have known about the features since the Galileo
spacecraft imaged the moon's surface in the 1990s, but they have yet to come up
with a solid explanation for how they evolved.
The researchers discovered how the double ridge on
northwest Greenland was formed when the ice fractured around a pocket of
pressurised liquid water that was refreezing inside the ice sheet, causing two
peaks to rise into the distinct shape, using surface elevation data and
ice-penetrating radar collected by NASA's Operation IceBridge from 2015 to
2017.
"This double ridge evolved in Greenland in a
place where water from surface lakes and streams routinely drains into the
near-surface and refreezes," said Riley Culberg, a Stanford PhD student in
electrical engineering. "Water from the underlying ocean may be driven up
into the ice shell through fractures, forming similar shallow water pockets on
Europa – and that would suggest there could be a considerable amount of
exchange going on inside the ice shell."
Snowballing complexity
Rather than acting like a block of inert ice, Europa's
shell appears to be subjected to a range of geological and hydrological
processes, as evidenced by these and other studies, as well as evidence of
water plumes erupting to the surface. A dynamic ice shell aids habitability by
facilitating the flow of nutrients from nearby celestial bodies deposited on
the top with the deep ocean.
"People have been studying these double ridges
for over 20 years, but this is the first time we've been able to see something
similar on Earth and see nature at work," said study co-author Gregor
Steinbrügge, a planetary scientist at NASA's Jet Propulsion Laboratory (JPL)
who began working on the project as a postdoctoral researcher at Stanford.
"We're taking a major step forward in terms of figuring out what processes
actually control the physics and dynamics of Europa's ice shell."
The co-authors claim that their theory for how the
double ridges form is so complicated that they couldn't have imagined it
without the Earth analogue.
"Without seeing it happen in Greenland, the
technique we propose in this work would have been almost too ambitious and hard
to propose," Schroeder said.
The findings provide researchers with a radar signal
that can be used to swiftly detect the emergence of double ridges using
ice-penetrating radar, which is one of the equipment currently being developed
for space exploration of Europa.
"We're just another idea on top of a lot of
others - we only have the advantage that our hypothesis is backed up by some
observations from the genesis of a similar feature on Earth," Culberg
explained. "It opens up a whole new world of possibilities for a really
interesting discovery."
Reference: Journal Nature
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