Carolina
Martinez (818) 354-9382
Jet Propulsion
Laboratory, Pasadena, Calif.
News
Release: 2005-024
February 9, 2005
NASA Observations
Help Determine Titan Wind Speeds
Strong
westerly winds of up to about 400 kilometers per hour (250 miles per hour)
buffeted the Huygens probe as it descended through Titan's upper
atmosphere last month, according to NASA-led observations of the probe
transmissions with Earth-based radio telescopes.
The winds
eased to a mild breeze near the surface of Titan, Saturn's largest
moon.
A
preliminary estimate of the wind variations with altitude from about 110
kilometers (68 miles) down to the surface has been recovered by a joint
team of researchers from NASA's Jet Propulsion Laboratory, Pasadena,
Calif., collaborating with the Huygens Doppler wind experiment team led by
Dr. Michael Bird in Bonn, Germany, and with the ground-based European Very
Long Baseline Interferometry team led by Dr. Leonid Gurvits.
A network
of radio telescope facilities, located around the world, received the
radio signals transmitted by the Huygens probe to the Cassini orbiter
during the probe's descent and landing on Titan on Jan. 14. “The
information from the radio telescopes was originally intended to
supplement similar wind data received from the Huygens Doppler wind
experiment. However, the
onboard experiment failed to return data.” said Dr. William Folkner, the
JPL principal investigator for the ground-based Doppler wind
experiment.
"Our
ground-based work salvaged the Doppler wind experiment," said Sami Asmar,
a JPL co-investigator on the Huygens Doppler wind experiment. He had reported detecting the
signal on the ground from the Green Bank Telescope facility in West
Virginia. "The signal from
the Huygens probe was not designed to be detected on Earth -- sometimes it
pays to eavesdrop," said Asmar.
Winds are
determined by the "Doppler shift" of the signal. Doppler shift is a change in the
frequency when received at Earth due to the probe's motion in Titan's
atmosphere, similar to the change in pitch of a passing train
whistle.
"We
provided the only real-time confirmation that the probe transmitted a
signal at the expected time, released the stabilizer parachute and then
impacted the surface," said Asmar. "We did this by monitoring the
Doppler shift in the frequency of the signal received at the Green Bank
Telescope and the Parkes Telescope in Australia."
"The
Huygens Doppler team worked closely with the Joint Institute for Very Long
Baseline Interferometry team in Europe, which coordinated the scheduling
of many radio telescopes around the globe for complementary measurements
that monitored the change in probe position," said Dr. Robert Preston,
chief scientist of the Interplanetary Network Directorate at
JPL.
The Deep
Space Network lent the JPL team two special Radio Science Receivers and
had one shipped to Green Bank from its complex in California and another
to Parkes from its complex near Canberra. These receivers allowed for the
real-time detection and confirmation of the Huygens radio signal. The same type of receivers were
used at Deep Space Network stations for receiving the Cassini signal
during Saturn orbit insertion in June 2004 and the Mars Exploration Rover
signal during entry, descent and landing in January 2004.
The Green
Bank Telescope and other participating U.S. telescopes are part of the
National Radio Astronomy Observatory. The Parkes radio telescope is
operated by the Australia Telescope National Facility. The radio astronomy support was
coordinated by the Joint Institute for Very Long Baseline Interferometry
in Europe.
For the
latest images and information about the Cassini-Huygens mission,
visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.
The
Cassini-Huygens mission is a cooperative mission of NASA, the European
Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a
division of the California Institute of Technology in Pasadena, manages
the mission for NASA's Office of Space Science, Washington, D.C. The Cassini orbiter was designed,
developed and assembled at JPL. ESA built and managed the development of
the Huygens mission and was in charge of Huygens operations.
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