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 Scientists said on Friday that Jupiter's moon Ganymede may possess
ice and liquid oceans stacked up in several layers much like the
popular multilayered sandwich. They added that this arrangement may
raise the chances that this distant icy world harbors life.
NASA's Galileo spacecraft flew by Ganymede in the 1990s and
confirmed the presence of an interior ocean, also finding evidence
for salty water perhaps from the salt known as magnesium sulfate.
Ganymede, which with its diameter of about 3,300 miles (5,300 km),
is the largest moon in the solar system and is bigger than the
planet Mercury.
A team of scientists performed computer modeling of Ganymede's
ocean, taking into account for the first time how salt increases the
density of liquids under the type of extreme conditions present
inside Ganymede. Their work followed experiments in the laboratory
that simulated such salty seas.
While earlier research suggested a routine "sandwich" arrangement in
which there is ice at the surface, then a layer of liquid water and
another layer of ice on the bottom, this new study indicated there
might be more layers than that.
Steve Vance, an astrobiologist at NASA's Jet Propulsion Laboratory
in California, said the arrangement might be like this: at the top,
a layer of ice on the moon's surface, with a layer of water below
that, then a second layer of ice, another layer of water underneath
that, then a third layer of ice, with a final layer of water at the
bottom above the rocky seafloor.
"That would make it the largest club sandwich in the solar system,"
Vance said in a telephone interview. "I suppose I'm also a fan of
club sandwiches. My fiancée points out that I order them every time
we go out to eat." Ganymede boasts a lot of water, perhaps 25
times the volume of Earth's oceans. Its oceans are estimated to be
about 500 miles (800 km) deep.
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With enough salt, liquid water on Ganymede could become so dense
that it sinks to the very bottom, the researchers said. That means
water may be sloshing on top of rock, a situation that may foster
conditions suitable for the development of microbial life.
Some scientists suspect that life first formed on Earth in bubbling
thermal vents on the ocean floor.
"Our understanding of how life came about on Earth involves the
interaction between water and rock. This (research) provides a
stronger possibility for those kinds of interactions to take place
on Ganymede," added Vance, whose study was published in the journal
Planetary and Space Science.
Ganymede is one of five moons in the solar system thought to have
oceans hidden below icy surfaces. Two other moons, Europa and
Callisto, orbit the big gas planet Jupiter. The moons Titan and
Enceladus circle the ringed gas planet Saturn.
"We're providing a more realistic view into ocean structure in
Ganymede's interior. We're showing that the salinity has a tangible
effect on the ocean," Vance said.
(Reporting by Will Dunham; Editing by Lisa Shumaker)
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