During the Huygens
probes 147-minute descent toward Titans surface on Jan. 14, it carried
onboard a microphone poised to record any sounds from Saturns largest
moon, from a booming clap of thunder to the tiny splash of methane raindrops.
But while Huygens was listening to Titan, 750 million miles away, scientists
on Earth were listening to Huygens.
As the Huygens probe descended through Titans smoggy atmosphere, scientists on Earth were able to listen in on sounds from the moons surface. Formed when sunlight interacts with hydrocarbons, a 300-kilometer-thick layer of orange smog covers Titans surface, preventing light from escaping. Courtesy of ESA.
As part of an experiment to determine wind speeds on Titan, radio telescopes in the United States, China, Japan and Australia honed in on the radio signal emitted by Huygens. The plan was for Cassini (the spacecraft that carried Huygens to Titan and is still orbiting Saturn) to focus on detecting east-west winds, and the radio telescopes to focus on any north-south winds, but things didnt go as planned.
The National Radio Astronomy Observatory in Green Bank, W.V., was the first to detect the probes successful deployment from Cassini. But after waiting 67 minutes for the transmission delay to pass, scientists were crestfallen when no data arrived from the orbiter. Fortunately, however, the radio astronomers who were eavesdropping on the Huygenss signal intended for Cassini were able to reconstruct the lost data.
Ive never felt such exhilarating highs and dispiriting lows than those experienced when we first detected the signal from the Green Bank Telescope, indicating alls well, and then discovering that we had no signal at the operations center, indicating alls lost, said Michael Bird, the radio astronomer at the University of Bonn, Germany, who led the Doppler Wind Experiment, part of the larger European Space Agency/NASA Cassini-Huygens project, in a press release. The truth, as weve now determined, lies somewhat closer to the former than the latter.
As Huygens descended through Titans thick atmosphere, it also drifted in the wind. These subtle changes in position caused the frequency of its radio signal to shift slightly producing longer wavelengths as it moved farther away from observers on Earth and shorter wavelengths as it moved closer, a phenomenon called Doppler shift. Scientists analyzing the Doppler shift from the weak signal were then able to reconstruct Huygens motion and then calculate the wind strength.
Researchers found that Titans winds move from west to east at all altitudes, in the same direction that the moon rotates. The highest wind speed, 270 miles per hour, was detected at an altitude of 75 miles, and the lowest was found near the surface where a light breeze blows. Wind speeds increased at altitudes up to 37 miles, where Huygens encountered some turbulence. Scientists interpreted the turbulence as vertical wind shear, but they are still investigating it.
Green Bank and the other radio telescopes are using the radio signal to reconstruct a 3-D record of Huygens position, orientation and motion throughout the Titan mission, despite how weak it is. A typical cell phone on the moon would provide a considerably more powerful signal, Bird says. Scientists are also still analyzing the acoustic data from Huygens microphone.
Listening to Titans atmosphere should provide crucial information about weather and storms that may hold clues to how life began on Earth. For example, lightning could supply electrical energy for certain organic chemical reactions. Titans atmosphere and surface are thought to closely resemble those of early Earth.
Geotimes contributing writer
To hear Titan, click here to download files from the ESA Web site, of sounds picked up by the acoustic sensor aboard Huygens.
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