The Huygens
probe landed on Saturn's moon Titan in 2005, but it never encountered chilly seas
of liquid methane as mission scientists had hoped--it landed in a mud field.
In spite of
the disappointment, scientists have recreated a turbulent picture of Titan's
atmosphere using data from sensors intended to measure oceanic properties. In
addition to showing Huygens probably plunged through turbulent methane ice
clouds, the research may aid in the design of balloon probes for future Titan
missions.
"We knew
Huygens had a bumpy ride down to Titan's surface. Now we can separate out
twenty minutes of air turbulence--probably due to a cloud layer--from other
effects such as cross winds or air buffeting," said Mark Leese, a Huygens
project manager at The Open University in the U.K.
Turbulent
Titan
The Huygens
probe jettisoned off of the
Cassini probe on Dec. 25, 2004 and reached Titan's surface in Jan. 14,
2005, deploying a parachute after entry into the moon's planet-like atmosphere
to begin a 2.5-hour descent.
Huygens
engineers did not intend to precisely measure the minor, chaotic changes in air
known as turbulence, but Lorenz and his team gleaned such data by looking at information
from two of the probe's sensors. One of the two, a "liquid density sensor,"
was designed to measure the properties of Titan's purported
methane seas if the probe had floated on one.
"Although
never designed with atmospheric measurements in mind, this device works as a
weakly damped accelerometer," write the study's authors in an upcoming
issue of the journal Planetary and Space Science. Accelerometers measure
changes in speed at extremely minute scales. NASA, for example, uses one on
NASA's space shuttle leading wing edges to detect vibrations caused by
micrometeoroid impacts, among other phenomena.
Lead author
Ralph Lorenz, a planetary scientist at the Johns Hopkins University in
Baltimore, Md. Lorenz and his colleagues partnered the density sensor's data with
that from a pendulum-like "tilt sensor" to create a play-by-play
picture of Huygens' atmospheric dive.
"Such
information may offer insights into the meteorological processes prevalent on
Titan, a world believed to share many characteristics with the Earth,"
Lorenz said.
The
researchers found that Huygens may have plunged into icy methane cloud layer--which
scientists have proposed to create a chilly methane "rain" --about
12 to 19 miles (20 to 30 kilometers) above the moon's surface.
Balloon
boon?
Although
the turbulence findings may not give airline passengers on Earth relief from
the nauseating buffets of wind, the information could be used to help design
balloon-like probes.
"Future
Titan exploration might use lighter-than-air vehicles, which would have to
compensate for wind gusts in order to keep above targets of interest for
sampling," the study's authors said.
Scientists
imagine such balloons would be outfitted not only with cameras to detail out the
moon's surface, but also spectrometers that could map mineral deposits on
Titan. NASA, however, has neither approved nor scheduled such a mission.
Lorenz and
his colleagues hope to use more Huygens data, including that from radio
emissions, to create a more detailed reconstruction of Huygens' descent as well
as Titan's nitrogen-thick atmosphere.
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