Saturn's 'Death Star' moon may have a secret ocean, revealing a new
category of worlds that could host alien life
Morgan McFall-Johnsen 20 hours ago
mimas moon round grey rock with large crater
NASA's Cassini spacecraft took the most detailed photo to date of Mimas
on its closest flyby of the Saturn moon in 2010. NASA/JPL-Caltech/Space
Saturn's small moon Mimas could have an ocean of liquid water deep
beneath its surface.
NASA's Cassini spacecraft detected swaying in the icy moon's spin that
could lead to internal heat.
Mimas appears inactive on the surface, so an ocean there could mean a
new class of "stealth" ocean worlds.
NASA is studying several moons of Saturn and Jupiter that carry oceans
of liquid water deep beneath their surfaces, where alien life could
thrive. Another moon, previously assumed to be a barren ice rock, might
join their ranks.
Mimas is a small moon of Saturn, often compared to the Death Star from
Star Wars, thanks to its large, distinct crater. Scientists have long
believed that Mimas is an inert ball of ice because of its heavily
cratered surface. Icy worlds with oceans are usually smooth, since
changes in their surface ice pave over craters, or cracked. Tidal forces
stretch and relax these moons, which both cracks the surface ice and
heats the moons' insides, sustaining internal oceans.
But NASA's Cassini mission, which orbited and studied Saturn for over a
decade, detected an unexpected oscillation in Mimas's rotation. As it
spins on its axis, Mimas wobbles slightly. Such oscillations may point
to an ocean deep beneath the moon's ice, according to a new analysis.
saturn rings up close with distant moon mimas in the background
Mimas orbiting Saturn beyond the planet's rings, pictured by NASA's
Cassini spacecraft in 2008. NASA/JPL/Space Science Institute
"If Mimas has an ocean, it represents a new class of small, 'stealth'
ocean worlds with surfaces that do not betray the ocean's existence,"
Alyssa Rhoden, a geophysicist who led the analysis at the Southwest
Research Institute, said in a press release.
Rhoden's finding was published online in the journal Icarus this week,
in a paper co-authored with Matthew Walker of the Planetary Science
Institute in Arizona.
It's still no guarantee of a secret Mimas ocean. Researchers need to
investigate the moon for further evidence.
"The work doesn't prove that there is a subsurface ocean on Mimas, but
it does show that an ocean is perfectly consistent with the available
data and our understanding of the physics, and the authors are
appropriately cautious about this," Michael Bland, a space scientist who
studies icy worlds at the US Geological Survey, and previously spoke
with Rhoden about the research, told Insider in an email. "I think the
study also opens as many questions as it answers."
Underground oceans on distant moons could mean alien life in our solar
illustration underwater robot studying deep-sea vents in alien ocean
An illustration of a submersible robot exploring the subsurface ocean of
an icy moon. NASA/JPL-Caltech
Mimas's oscillation could indicate that Saturn's gravity stretches and
relaxes the planet as it spins — similar to the moon's gravity pulling
Earth's water back and forth during tides. This process could build up
energy deep inside Mimas, which is released as heat, warming its
internal ice and creating an underground ocean of liquid water.
Rhoden and Walker developed computer models to simulate that stretching
process for Mimas, including how it would affect the stability of the
moon's ice shell, and how that stretching fits in with Cassini's
measurements of Mimas's oscillation. The model indicated that Saturn's
tidal pull could maintain an ocean lying beneath 14 to 20 miles of ice
"This result is really intriguing because it implies that we can't tell
which moons in the outer solar system may have subsurface oceans just
from their surface geology," Bland said.
Some moons — like Jupiter's Europa and Saturn's Enceladus — have plumes
of water shooting up from their internal oceans, through their surface
ice, and into space. In 2020, scientists also discovered evidence of an
underground ocean on a dwarf planet called Ceres, which orbits the sun
between Mars and Jupiter. Salt deposits on Ceres's surface appear to
have percolated up from liquid water below.
These ocean worlds could have deep-sea hydrothermal vents that produce
energy for living organisms. Such vents serve as an energy source for
life at the bottom Earth's oceans, where there is no sunlight. If Mimas
has an ocean, it might be able to host such ecosystems, too.
hydrothermal vent noaa oar nurp
A hydrothermal vent on Earth. OAR/National Undersea Research Program
But the study isn't enough evidence to prove that. If the researchers'
models are off — if Mimas's ice cools faster than they assumed, for
example — there may be no Mimas ocean at all.
"If the Cassini spacecraft had been able to fly closer to Mimas, it
might have sensed a magnetic field generated by the Mimas ocean, which
would be a direct confirmation that an ocean is present today," Steve
Vance, who studies icy worlds at NASA's Jet Propulsion Laboratory, told
Insider in an email. "Hopefully a future mission will be able to look
for an ocean in Mimas."
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