Saturn's
moon Titan may be worlds away from Earth, but the two bodies have some
characteristics in common: Wind, rain, volcanoes, tectonics and other
Earth-like processes all sculpt features on Titan, but act in an environment
more frigid than Antarctica.
"It is
really surprising how closely Titan's surface resembles Earth's," said
Rosaly Lopes, a planetary geologist at NASA's Jet Propulsion Laboratory (JPL)
in Pasadena, Calif., who is presenting the results of two new studies at the
annual meeting of the of the International Astronomical Union (IAU) in Rio de
Janeiro, Brazil on Friday. "In fact, Titan looks more like the Earth than
any other body in the solar system, despite the huge differences in temperature
and other environmental conditions."
This view
of Titan comes from observations made by the Cassini-Huygens mission, which has
revealed details of Titan's geologically young surface, showing few impact
craters, and featuring mountain chains, dunes and even "lakes."
The RADAR
instrument on the Cassini orbiter has now allowed scientists to image a third
of Titan's surface using radar beams that pierce the giant moon's thick,
smoggy atmosphere. As its name implies, Titan is no small moon, with a size
approaching that of Mars.
Titan gets
about 1 percent the amount of sunlight Earth receives.
Titan is
the only moon in the solar system known to possess a thick atmosphere, and it
is the only celestial body other than Earth to have stable pools of liquid on
its surface. Lakes that pool on Titan's surface are thought to be filled not
with water, but with
liquid hydrocarbons, such as methane and ethane.
"With
an average surface temperature hovering around -180 C [-292 degrees
Fahrenheit], water cannot exist on Titan except as deep-frozen ice as strong as
rock," Lopes said.
On Titan,
methane takes water's place in the hydrological cycle of evaporation and
precipitation (rain or snow) and can appear as a gas, a liquid and a solid.
Methane rain cuts channels and forms lakes on the surface and causes erosion,
helping to erase the meteorite impact craters that pockmark most other rocky
worlds, such as our own moon and the planet Mercury.
Other new
research presented at the IAU General Assembly points to current volcanic
activity on Titan, but instead of scorching hot magma, scientists think these
"cryovolcanoes"
eject cold slurries of water-ice and ammonia.
The ammonia
signature seems to vary, which suggests that ammonia frosts are ejected and
then subsequently dissipate or are covered over. Although the ammonia does not
stay exposed for long, models show that it exists in Titan's interior,
indicating that a process is at work delivering ammonia to the surface. RADAR
imaging has indeed found structures that resemble terrestrial volcanoes near
the site of suspected ammonia deposition.
New
infrared images of this region, with ten times the resolution of prior
mappings, will be unveiled at the IAU meeting.
"The
images provide further evidence suggesting that cryovolcanism has deposited
ammonia onto Titan's surface," said Robert M. Nelson, a senior research
scientist, also at JPL, who presented results on Wednesday.
The
presence of ammonia and hydrocarbons could have interesting implications for
the possibility of life existing on Titan.
"It
has not escaped our attention that ammonia, in association with methane and
nitrogen, the principal species of Titan's atmosphere, closely replicates the
environment at the time that life first emerged on Earth," Nelson said.
"One exciting question is whether Titan's chemical processes today support
a prebiotic chemistry similar to that under which life evolved on Earth?"
Yet more
terrestrial-type features on Titan include dunes
formed by cold winds, and mountain ranges. These mountains might have
formed tectonically when Titan's crust compressed as it went into a deep
freeze, in contrast to the Earth's crust, which continues to move today,
producing earthquakes and rift valleys on our planet.
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