When the
Cassini spacecraft reached Saturn's largest moon Titan and deployed its Huygens
probe to study the surface, it lifted a shroud that had hung over a world possibly
containing conditions for life's building blocks.
Now a
planetary scientist and an astronomy writer have laid out Cassini's findings and
Titan's enduring mysteries in a new book, "Titan Unveiled" (Princeton
University Press, 2008).
As Cassini entered
Saturn's orbit in 2004 and began snapping images during flybys of Titan later
that year, scientists realized that Titan has sand dunes
not unlike those in the Sahara desert. They had assumed little sand would exist
at the moon because of a lack of erosion processes, and that Titan's winds
lacked the strength to create dune patterns.
"Both
hypotheses were wrong for interesting reasons," said Ralph Lorenz, co-author
and planetary scientist on the Cassini-Huygens mission at Johns Hopkins
University Applied Physics Lab in Maryland.
The sand
had originated not from erosion pounding rocks into small grains, but instead
from chemicals that drizzled down from Titan's clouds. Cassini also found
powerful near-surface winds at Titan due to the gravitational influence of
Saturn on the atmosphere.
Another
surprise arose from "just how glaring the influence of rainfall and rivers was
in the Huygens
landing," Lorenz told SPACE.com. Titan's surface and atmosphere
contain methane, which acts like liquid water under the frigid temperatures of
roughly -290 degrees F (-179 degrees C) on the surface.
Falling and
flowing methane may only form a temporary feature on Titan's surface, but
Cassini also detected larger
bodies of liquid such as lakes, using optical cameras and radar. However, the
south polar region of Titan appears to have fewer lakes — just one of the
differences between the north and south poles that has become an "emerging
mystery," Lorenz said.
An added
bombshell came from the discovery that Titan's icy surface slides around like cheese on
pizza sauce. That suggests the moon harbors a hidden ocean that may consist
of water and ammonia.
Yet one of
Titan's most noticeable features remains a mystery. An orange shroud of methane
has long hidden the moon's surface from astronomers' eyes, but remains despite
getting steadily destroyed by the sun's harsh ultraviolet rays and making up
just 5 percent of the mainly nitrogen atmosphere. Scientists suspect the methane
may get replenished by underground lakes or volcanic vents.
Strangeness
aside, Titan still astounds scientists who "didn't expect it to be so
Earth-like and varied," Lorenz noted. The dunes, lakes, rivers and rain all
appear strikingly familiar and suggest a constantly changing climate that goes
with Titan's seasons.
Cassini
will continue to map Titan and explore its surface as the probe swings by
during the course of its extended Saturn mission. But Lorenz and other
scientists eagerly await a dedicated Titan mission that can thoroughly examine
the moon — although it may have to compete
with Europa as an attractive destination.
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