ESA Science News Release – SNR 3-2005
Using a global network of radio telescopes, scientists have measured the speed of the winds faced by Huygens during its descent through the atmosphere of Titan. This measurement could not be done from space because of a configuration problem with one of Cassini’s receivers. The winds are weak near the surface and increase slowly with altitude up to about 60 km, becoming much rougher higher up where significant vertical wind shear may be present.
Preliminary estimates of the wind variations with altitude on Titan have been obtained from measurements of the frequency of Huygens’ radio signals recorded during the probe’s descent on 14 January 2005. These "Doppler" measurements, obtained by a global network of radio telescopes, reflect the relative speed between the transmitter on Huygens and the receiver on the Earth. Winds in the atmosphere affected the speed of Huygens’ descent and produced a change in the frequency of the signal received on Earth, in a manner similar to the commonly heard change in a siren's pitch from a speeding police car.
Leading the list of large radio antennas involved in the programme were the NRAO Robert C. Byrd Green Bank Telescope (GBT) in WestVirginia, USA, and the CSIRO Parkes Radio Telescope in Australia. Special instrumentation designed for detection of weak signals was used to measure the "carrier" frequency of the Huygens radio signal during this unique opportunity. The initial detection, made with the "Radio Science Receivers" on loan from NASA’s Deep Space Network, provided the first unequivocal proof that Huygens had survived the entry phase and had begun its radio relay transmission to Cassini.
signal detection on Earth provided a surprising turnabout for the
Cassini-Huygens Doppler Wind Experiment (DWE), whose data could not
be recorded on the Cassini spacecraft due to a commanding error
needed to properly configure the receiver. “Our team has now
taken a significant first step to recovering the data needed to
fulfil our original scientific goal, an accurate profile of Titan's
winds along the descent trajectory of Huygens,” said DWE’s
Principal Investigator Dr Michael Bird (University of Bonn, Germany).
The ground-based Doppler measurements were carried out and processed
jointly by scientists from the NASA Jet Propulsion Laboratory (JPL,
USA) and the Joint Institute for VLBI in Europe (JIVE, The
Netherlands) working within the DWE team.
“Major mission events, such as the parachute exchange about 15 minutes into the atmospheric flight and impact on Titan at 13:45 CET, produced Doppler signatures that we can clearly identify in the data,” Bird said.
“This is a stupendous example of the effectiveness of truly global scientific cooperation,” said Jean-Pierre Lebreton, ESA Huygens Project Scientist. “By combining the Doppler and VLBI data we will eventually obtain an extremely accurate three-dimensional record of the motion of Huygens during its mission at Titan,” he concluded.
support of the Huygens mission is coordinated by JIVE and JPL and
involves the Netherlands Foundation for Research in Astronomy
The Netherlands), the University of Bonn (Germany), Helsinki
University of Technology (Espoo, Finland), the MERLIN National
Facility (Jodrell Bank, UK), the Onsala Space Observatory (Sweden),
the NASA Jet Propulsion Laboratory (Pasadena, USA), the National
Radio Astronomy Observatory (NRAO, Green Bank, USA, and Socorro,
USA), the CSIRO Australia Telescope National Facility (ATNF, Sydney,
Australia), the University of Tasmania (Hobart, Australia), the
National Astronomical Observatories of China, the Shanghai
Astronomical Observatory (Shanghai and Urumqi, China) and the
National Institute of Information and Communications Technologies
(Kashima Space Research Center, Japan).
Joint Institute for
VLBI in Europe is hosted by ASTRON and funded by the national
research councils, national facilities and institutes of The
Netherlands (NOW), the United Kingdom (PPARC), Italy (CNR), Sweden
(Onsala Space Observatory, National Facility), Spain (IGN) and
Germany (MPIfR). The National Radio Astronomy Observatory is operated
by Associated Universities, Inc., under a cooperative agreement with
the National Science Foundation. The Australia Telescope is funded by
the Commonwealth of Australia for operation as a National Facility
managed by CSIRO. The Jet Propulsion Laboratory is operated by the
California Institute of Technology under contract to NASA.
The Cassini-Huygens mission is a cooperation between NASA, ESA and ASI, the Italian space agency. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, is managing the mission for NASA's Office of Space Science, Washington DC. JPL designed, developed and assembled the Cassini orbiter while ESA operated the Huygens atmospheric probe. For more information about Cassini-Huygens please see:
For further information please contact:
Dr Jean-Pierre Lebreton
Huygens Project Scientist
European Space Agency
Noordwijk, The Netherlands
Tel: +31 71 565 3600
E-mail: jplebret @ rssd.esa.int
Dr Michael Bird
University of Bonn
Tel: +49 228 733 651
E-mail: mbird @ astro.uni-bonn.de
Dr Leonid Gurvits
Joint Institute for VLBI in Europe
Dwingeloo, The Netherlands
Tel: +31 521 596 514
E-mail: lgurvits @ jive.nl
Dr Guido De Marchi
Science Communication Office
European Space Agency
Noodrwijk, the Netherlands
Tel: +31 71 565 8332
E-mail: gdemarchi @ rssd.esa.int
Media Relations Division
European Space Agency
Tel: +33 1 5369 7155
Fax: +33 1 5369 7690