Posted on: Thursday, July 8, 2004

Scientists to probe Saturn moon

By Christie Wilson
Advertiser Neighbor Island Editor

A NASA instrument attached to the Subaru Telescope atop Mauna Kea has measured stratospheric wind currents of 470 mph on haze-shrouded Titan, Saturn's largest moon.

The research will help the robotic Huygens probe as it drops through Titan's murky, orange atmosphere in January. The probe is attached to the Cassini spacecraft, which began orbiting Saturn June 30 after a seven-year voyage.

Scientists are eager to explore Titan because its atmosphere may resemble the Earth's atmosphere shortly after the planet's formation. "We've been looking for life on Mars, and Titan is one of the few other places in the universe that may have conditions conducive to life," said Subaru researcher Catherine Ishida. "But we don't know what's going on underneath the haze and what the chemical environment is like."

The wind observations were accomplished by combining NASA's Heterodyne Instrument for Planetary Wind and Composition with the 27-foot-diameter Subaru Telescope, operated by the National Astronomical Observatory of Japan.

The observations revealed that the winds travel in the same direction as Titan's rotation, and that these winds are milder — about 264 mph — near the equatorial regions, similar to the jet streams on Earth.

Ishida said it was the first time scientists were able to obtain wind-speed measurements from different areas of the moon. The data also will be useful in providing more details about the area where Huygens will enter Titan's atmosphere, she said.

Titan has been difficult to study from afar because of its thick upper atmosphere and the lack of any features that might show wind movement.

According to a NASA news release, the Heterodyne Instrument measures wind speed and direction by relying on the faint, infrared glow of the hydrocarbons in Titan's atmosphere. The instrument measures the very slight color, or frequency, change of the infrared light caused by the motion of the molecules as they are carried by Titan's winds. This is called the Doppler shift.

The Subaru Telescope, with the world's largest single-piece mirror in regular operation, provides the light-gathering power needed for the Heterodyne Instrument to precisely distinguish among infrared frequencies, NASA said.

Astronomers involved in the wind experiments will return to the Big Island Jan. 14 to observe Titan again using the Subaru Telescope. Ishida said Mauna Kea will be an ideal watching post since, in addition to its array of observatories, it will be midnight in Hawai'i when the Huygens probe makes its descent to the surface on that day.

The ground observations from Mauna Kea, offering a broader view of Titan, will complement local wind measurements by the Huygens probe to provide even more detailed information, she said.

Other institutions involved include the Challenger Center for Space Science Education, the University of Maryland, the University of Hawai'i, and the University of Cologne in Germany. Information about the Cassini mission is available at www.nasa.gov/cassini.

Reach Christie Wilson at cwilson@honoluluadvertiser.com or (808) 244-4880.