The wicked winds of a soon-to-be-visited alien world are already being measured from Hawaii.
Astronomers are using ground-based telescopes atop the Mauna Kea volcano on the island of Hawaii to measure the speed and direction of winds on smog-shrouded Titan, Saturn's largest moon. What they have discovered is that Titan has upper atmosphere jet stream-like winds that race around the planet at about 470 miles per hour (756 km per hour).
At that rate a high-altitude wind-blown balloon could circumnavigate Titan in less than an Earth day (although Titan's days are 16 times longer than Earth's).
"The idea was to look at the east limb and west limb (of Titan) and compare," said Titan wind watcher Theodor Kostiuk of NASA's Goddard Space Flight Center. Measuring what is known as the Doppler shift of a narrow band of infrared light at the eastern and western edges of the face of Titan they can tell if the wind is blowing towards us on one edge and away from us on the opposite edge, and at what speed.
The Doppler shifts reveal this in the same way we can tell is a train is approaching or receded from the sound of its horn: the frequency sounds higher on approach and lower after it passes. A similar thing happens — but much more subtly — with an infrared glow of ethane gas in the clouds of Titan.
The wind measurements were made possible by combining the advanced Heterodyne Instrument for Planetary Wind and Composition (HIPWAC) with the 8.2-meter-diameter Subaru Telescope on Mauna Kea. That telescope enabled scientists to zoom in and look at just a third of Titan's face at a time.
The ability to watch Titan's winds from Earth will become even more important six months from now when the Huygens probe drops through the Titan murk, opens its parachutes and sends real-time wind speed data back to the Cassini spacecraft.
"(They) will be observing Titan again from the Subaru telescope on Mauna Kea on Jan. 14, 2005, when our group will also be measuring the direction and strength of Titan's wind as part of the Doppler Wind Experiment (DWE) of the Cassini/Huygens mission," said Michael Bird of the University of Bond, Germany, and principal investigator for the Huygens wind experiment.
In the case of Huygens wind measurements, it's the Doppler shift of the radio signals to Cassini from Huygens, as it is caught up in the Titan winds, that will reveal wind speeds, Bird explains. By combining the Huygens measurements with simultaneous wind measurements from earthbound telescopes, researchers will have a unique chance to gather local and global data of the solar system's largest moon, says Kostiuk.
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Titan's Winds Measured From Hawaii
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