It Looks Like Pluto Has a Liquid Water Ocean

For a frigid little space rock at the ass-
end of the solar system, Pluto is full
surprises. Ice volcanoes, hazy skies ,
vast plains of churning nitrogen,
what’s next? Just maybe, a subsurface
ocean.
Perhaps the most incredible discovery
of the New Horizons Pluto encounter
last summer was that the former
ninth planet is geologically active,
with widespread evidence of tectonic
activity across its icy surface. This
pretty much flies in the face of
everything we’d expect for a world so
small that sits so far from the sun,
and planetary scientists have
struggled to explain it for the better
part of a year.
A modeling paper published this week
in Geophysical Research Letters offers
a simple but fascinating explanation:
partial freezing within a subsurface,
liquid water ocean.
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“Our model shows that recent
geological activity on Pluto can be
driven just from phase changes in the
ice—no tides or exotic materials or
unusual processes are required,” lead
study author Noah Hammond said in
a statement.
The idea of a liquid water ocean on
Pluto isn’t new. We now know that
Pluto’s surface consists of a layer of
so-called volatile ices, including
nitrogen, methane, and CO2. It’s also
widely accepted that these exotic ices
are merely a dusting atop a much
thicker, water-based mantle that
extends all the way to a rocky core.
Most of that mantle is probably frozen
—but it’s possible that a layer hugging
close to the hot core is still liquid.
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What’s significant about the new
study is that it finds evidence for a
liquid water ocean today in the
tectonic scarring seen on Pluto’s
surface. Specifically, the absence of
compressional tectonic features—
which would form if the innermost
layers of water had frozen into a
dense form of ice known as ice II—
suggests that Pluto may not be entirely
solid.
“The formation of ice II would cause
Pluto to experience volume
contraction and compressional
tectonic features to form on the
surface,” Hammond explained. “Since
the tectonic features on Pluto’s surface
are all extensional and there is no
obvious compressional features, it
suggests that ice II has not formed and
that therefore, Pluto’s subsurface
ocean has likely survived to present
day.”
If Hammond’s models turn out to be
correct, they raise the exciting
possibility that subsurface oceans are
a common feature throughout the icy
rocks littering the Kuiper Belt .
Whether any of these exotic oceans
could support life as we know it
remains to be seen—but it’s all the
more reason to keep sending space
probes out there to explore.