Winds measured on Saturn's moon Titan to help robot lander (Forwarded)

Bill Steigerwald
NASA Goddard Space Flight Center, Greenbelt, MD

(Phone: 301/286 5017)

Catherine Ishida
Subaru Telescope, Hilo, HI

808-934-5086

June 29, 2004

Release 04-28

WINDS MEASURED ON SATURN'S MOON TITAN TO HELP ROBOT LANDER

On top the windswept summit of a Hawaiian volcano, a NASA instrument attached to
the Japanese Subaru telescope measured distant winds raging on a strange world
-- Titan, the giant moon of Saturn -- to help the robotic Huygens probe as it
descends through Titan's murky atmosphere next January.

When combined with previous observations, new research with the Heterodyne
Instrument for Planetary Wind And Composition (HIPWAC) joined to the large
aperture of the Subaru telescope supports the model that Titan has currents or
jet streams at high latitudes racing through its upper atmosphere (stratosphere)
at speeds of approximately 756 km/hour (470 miles/hr.). The new observations
reveal that the wind travels in the same direction as Titan's rotation, and that
the stratospheric winds are milder (about 425 km/hr. or 264 miles/hr.) near the
equatorial regions, as the jet stream model predicts. HIPWAC was designed and
built at NASA's Goddard Space Flight Center in Greenbelt, Md. The Subaru
telescope is operated by the National Astronomical Observatory of Japan.

Wind direction on Titan is difficult to measure remotely because Titan's upper
atmosphere consists of an orange haze of hydrocarbons (molecules of hydrogen and
carbon) with no global features that show movement.

The observations were originally encouraged by the Cassini mission, an
international mission of NASA, the European Space Agency (ESA) and the Italian
Space Agency (ASI) that will employ a large robotic spacecraft to explore Saturn
and its system of 31 known moons beginning this July. The Huygens probe, built
by ESA, is attached to the Cassini spacecraft and will separate in December on a
22-day course ending with a plunge into Titan's atmosphere. NASA's Jet
Propulsion Laboratory in Pasadena, Calif., manages the Cassini mission for NASA.

"Our observations will complement local wind measurements by the Huygens probe
during its descent, because we offer a global view. Acquiring the direction and
speed of global winds is important for understanding the dynamics of planetary
atmospheres, particularly dynamics of those bodies that rotate slowly on their
axes. Titan's 'day' is 16 Earth days," said Dr. Theodor Kostiuk of NASA Goddard.

"We hope to be able to repeat our success during the probe's descent so we can
have detailed local information from Cassini and the Huygens probe and a global
portrait from HIPWAC and Subaru from the same time," said Professor Hiroshi
Karoji, Director of the Subaru telescope, Mauna Kea, Hawaii.

Titan, the second largest moon in the solar system, is larger than the planet
Mercury and is the only known moon with a thick atmosphere, actually 1.5 times
more dense than Earth's. Because it is far from the Sun, Titan is extremely cold
(surface temperature of about minus 178 Celsius (minus 289 Fahrenheit), allowing
a hydrocarbon rain that may form gasoline-like seas. Scientists are eager to
explore Titan because its atmosphere may resemble the Earth's atmosphere shortly
after our planet's formation, when it was rich with hydrocarbon molecules that
became the building blocks of life.

HIPWAC can measure wind speed and direction on Titan, even though the moon's
atmosphere lacks apparent features, because the instrument relies instead on the
faint, infrared glow of the hydrocarbons in Titan's atmosphere. Infrared light,
invisible to the human eye, can pass through Titan's hydrocarbon haze and is
detectable by special instruments. HIPWAC measures the very slight color
(frequency) change of the hydrocarbon's infrared light caused by the motion of
these molecules as they are carried by Titan's winds. This is called a Doppler
shift, and is similar to the change in tone of an ambulance siren as it races
by. Since the hydrocarbons are moved along by Titan's winds, the Doppler shift
of their emitted light gives the wind velocity.

To measure such miniscule Doppler shifts, HIPWAC must be capable of
distinguishing among infrared colors, or frequencies, to a very fine degree.
This is called spectral resolution, and HIPWAC possesses a spectral resolution
200 times better than any instrument in regular use today. It also must measure
specific infrared frequencies very accurately, and HIPWAC can identify a
frequency to one part in a hundred million.

Subaru telescope brings to HIPWAC the light gathering power of a modern large
aperture telescope. Subaru's 8.2-meter (27- foot) diameter mirror is the largest
single-piece mirror in the world that is currently in regular operation. Since
HIPWAC achieves its high spectral resolution by finely dividing light into
different frequencies, the more light it has to work with the better. Other
institutions contributing to this research include the Challenger Center for
Space Science Education, University of Maryland, University of Hawaii, and the
University of Cologne, Germany.

For images and more information, refer to:
http://www.gsfc.nasa.gov/topstory/2004/0615hipwac.html

Joint Subaru release:
http://www.naoj.org/Pressrelease/2004/06/29/index.html

For information about the Cassini mission, see:
http://www.nasa.gov/cassini