by Pete Spotts
But a team
of scientists using NASA's
Cassini spacecraft have now found
indirect but telltale signs of a subsurface sea, perhaps of water as
well as ammonia, which would act like antifreeze.
atmosphere is thought to mirror the composition of Earth's
atmosphere before the emergence of life some 3.8 billion years ago.
This image from NASA's Cassini spacecraft shows Saturn's largest moon, Titan,
passing in front of the planet and its rings.
A new study released Thursday suggests there may be an ocean below Titan's frigid surface.
Thursday's report represents "a nice step forward" in establishing
an ocean's presence on Titan, he says.
Neptune's moon Triton may also have a
subsurface ocean, and
Ganymede and Callisto, two more Jovian moons,
also are though to have under-ice seas (below video):
These readings allow the team to measure the strength of Titan's gravity in the regions Cassini overflies.
This process allows researchers to "weigh the moon, basically," says Sami Asmar, a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and a member of the team that reported its results on Sciencexpress, the web outlet of the journal Science.
If Titan was solid, its gravity field wouldn't change.
Even when the moon comes closest to Saturn on its elliptical orbit - experiencing Saturn's strongest tug - its mass would remain fairly evenly distributed throughout the object. But Titan's gravity changes as it progresses along its orbit, the team found.
The side of the moon that always faces Saturn bulged as Titan made its closest approach to the ringed planet.
This tidal bulge represents a redistribution of material within the
moon's interior - a telltale sign that there is likely a fluid layer
in the moon's interior.
It is as though Titan's rocky core with its icy cover was being
drawn through the global subsurface ocean toward Jupiter as the moon
made its closest approach, creating the bulge.