A
comprehensive model of Saturn's magnetosphere and moons has revealed
that the
ringed planet's largest moon Titan gets its oxygen from the icy geysers
on
another.
Until now,
the method for oxygen making its way into Titan's
surface chemistry has remained a mystery, the scientists said
in a NASA
statement.
Icy geysers
on Saturn's moon
Enceladus shoot water
molecules into the planet's
magnetosphere, where they break down into oxygen and hydrogen as they
travel to
Titan, according to a model developed by scientists at NASA's Goddard
Space
Flight Center in Greenbelt, Md.
"Titan
and Enceladus, another icy moon of Saturn, are chemically connected by
the flow
of material through the Saturn system," said John Cooper, a plasma
spectrometer team scientist with NASA's Cassini mission to Saturn, in a
recent
statement.
Cooper and
fellow Cassini scientist Edward Sittler led two different studies into
the
transportation of oxygen between Enceladus and Titan. NASA announced
the
research this month.
Icy moon calls
the shots
Scientists
have known that Titan's
atmosphere receives an
infusion of oxygen ions
since 2004, when it was detected by the Cassini spacecraft currently
orbiting
Saturn.
At the time,
the very tiny amounts of the gas and their high energy surprised
scientists
accustomed to a Titan atmosphere composed mostly of nitrogen, but they
wrote it
off as the breakup of icy interplanetary grains of dust.
It was not
until Cassini's observations revealed the ice jets on Enceladus that
researchers understood "that Enceladus was dominating the whole
system," Sittler said. [Photos: Moons of
Saturn]
Though roughly
10 times smaller than Titan, Enceladus was observed dumping 661 pounds
(300 kg)
of frozen water every second into Saturn's magnetosphere, researchers
said. Gas
beneath a cavity of water on the moon's south pole continuously builds
up,
causing water to erupt from cracks on the icy surface.
The icy jets
escape Enceladus in plumes of vapor similar to the Old Faithful Geyser
at Yellowstone
Park in the U.S., reaching orbit easily because the moon's escape
velocity is
only a few hundred meters per second, Sittler said.
Titan's
hydrocarbons are key
In their
studies, the two researchers found that oxygen particles can attach to
soccer
ball-shaped carbon molecules called fullerenes on Titan after they
migrate to
the cloud-covered moon from Enceladus.
These
fullerene cages protect the oxygen reacting with the methane in Titan's
atmosphere and could ultimately reach the moon's surface attached to
dust
particles, the researchers said.
It's a
unique setup, and one that arises only because of Saturn and its
interactions
with its moons.
"That's
what's unique about this whole story: you need Titan, you need
Enceladus, and
you need the magnetosphere," Sittler told SPACE.com.
Furthermore,
the fullerene hydrocarbons form some of the building blocks of more
complex
compounds, Sittler said. When radiated by highly energetic cosmic rays,
the
oxygen immersed in these molecules can produce amino acids, the
foundation of pre-biological
chemistry.
The
fullerene link
At 10 hours
and 29 minutes, the rotation of Saturn subjects materials in its
magnetosphere
to velocities similar to those found in a particle accelerator, more
than
enough to break down water molecules from Enceladus into their
component parts.
By the time
molecules are ripped apart and headed for the upper atmospheres of
nearby
moons, they are energetic enough to pierce the cages of fullerene,
researchers
said.
"You
need energetic reactions to get the molecules in the fullerenes,"
Sittler explained,
likening the action to shooting a particle through a solid ball.
Once oxygen
atoms are trapped in the hollow fullerene balls, the molecules can
condense
into aerosols and act as protection and crucible for chemical
reactions.
Aerosols are
dust particles that can cause the reddish glow seen on Earth during
sunset.
They are large enough to gradually fall with time, making them a viable
path
for oxygen to be transported to the Titan surface, researchers
said. Without the
protection of the fullerenes in Titan's hydrocarbon-rich atmosphere,
oxygen
atoms would react with the moon's methane to produce carbon dioxide or
carbon
monoxide, they added.
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