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.
Image right: An artist's concept showing the Huygens probe descending to Titan. Image credit: ESA.
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.
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
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.
Carolina Martinez (818) 354-9382
Jet Propulsion Laboratory, Pasadena, Calif.