U.S. and European researchers are
lauding the effectiveness of a network of ground-based telescopes that has
apparently salvaged a wind experiment feared lost during a mission to the
surface of Saturn's moon Titan.
Astronomers
were able to use a global group of radio telescopes and a simple signal tone
bleated by Europe's Huygens probe during its
Jan. 14 Titan landing
to determine the moon's wind characteristics.
Early
analysis of the data has given researchers a good look at the winds of Titan,
despite a communications error
that prevented the probe's primary data target - NASA's Cassini
orbiter currently circling Saturn - from receiving wind observations from the
Huygens probe.
"The
original idea was to use Cassini's onboard receiver
for Doppler ranging and later the ground stations were for a second line of
sight," said Walter Brisken, a staff scientist for
the National Radio Astronomy Observatory (NRAO), in a telephone interview. "But
we were pretty sure we had the sensitivity needed and were fairly confident
that things would work out."
Brisken
worked at the NRAO's Green Bank Telescope (GBT) in
West Virginia which first detected the Huygens probe's signal announcing its
successful entry into Titan's atmosphere. Other ground-based telescopes,
including nine from the Very Large Baseline Array, monitored the Huygens signal.
The Huygens probe itself was built by the European Space Agency (ESA).
By
combining Doppler shift data from the Green Bank Telescope and other radio
instruments, astronomers now know that while Titan's winds are relatively weak
at the moon's surface, they reach nearly 270 miles (434 kilometer) an hour at
an altitude of about 75 miles (120 kilometers). At an altitude of about 37
miles (59 kilometers), Huygens found highly variable winds that may be a region
of vertical wind shear, mission scientists said.
"I've never
felt such exhilarating highs and dispiriting lows than those experienced when
we first detected the signal from the GBT, indicating 'all's well' and then
discovering that we had no signal at the operations center, indicating 'all's
lost,'" said Doppler wind experiment principal investigator Michael Bird, of
Germany's University of Bonn, in a written statement. "The truth, as we have
now determined, lies somewhat closer to the former than the latter."
Ground-based
observations of the Huygens probe's descent gave astronomers a glimpse at the
north-south attributes of Titan's winds, but it was the Cassini
spacecraft that was expected to return data on the moon's east-west wind
patterns. While that data is lost, Huygens researchers say the ground data was
able to track the spacecraft's Titan descent to within three-quarters of a mile
(one kilometer) and ultimately yield a three-dimensional picture of the probe's
landing.
"It's sort
of an awakening of sorts," Brisken said. "Now that we
have the technology to do this so easily, it might be a more normal thing in
the future."
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