Press release from the NASA Goddard Space Flight Center
(http://www.gsfc.nasa.gov/topstory/2004/0615hipwac.html)
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 minuscule 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.
Images and more information:
|
This
artist's rendition shows the Huygens probe as
it reaches
the surface of Titan. The Cassini spacecraft
(top left corner of the image) flies over with
its High
Gain Antenna pointed at the probe. Saturn is
seen in the background through Titan's thick
atmosphere
of methane, ethane and (mostly) nitrogen. Thin
methane clouds dot the horizon, and a narrow
methane spring or "methanefall" flows
from the cliff at left and drifts mostly into
vapor. Smooth
ice features rise out of the methane/ethane
lake, and crater walls can be seen far in the
distance.
Image by David Seal.
Credit: David Seal/NASA
|
|
Subaru is an optical-infrared
telescope at the 4,200m summit of Mauna Kea
on the island
of Hawaii operated by the National Astronomical
Observatory of Japan. Subaru has one of the
world's largest single piece primary mirrors
with an
effective aperture of 8.2 meters, and uses
various revolutionary technologies to achieve
superb
image quality. An active support system that
maintains an unprecedentedly high mirror surface
accuracy, a new dome design to suppress local
atmospheric turbulence, an extremely accurate
tracking mechanism using magnetic driving systems,
seven observational instruments installed at
four foci, and an auto-exchanger system to
use the observational instruments effectively
are
just some of the unique features of this telescope.
Credit:
Subaru Telescope/NAOJ
|
|
This is a photo of the HIPWAC instrument
on its interface table at the Subaru telescope.
The detector and guide system face the viewer,
and one of the electronics racks can be seen to
the right.
Credit: NASA/Subaru
Telescope
|
|
This image of Titan, taken by a Voyager
spacecraft, shows Titan to be completely shrouded
by a thick atmosphere. The atmosphere is about
95% nitrogen, the remainder methane as well as
other hydrocarbons and hydrogen cyanide.
Credit:
NASA
|
|
This artist's conception shows Titan's
surface with Saturn appearing dimly in the background
through Titan's thick atmosphere of mostly nitrogen
and methane. The Cassini spacecraft flies overhead
with its high-gain antenna pointed at the Huygens
probe as it nears the surface.
Titan's surface may hold lakes of liquid ethane
and methane, sprinkled over a thin veneer of
frozen methane and ammonia. Most of the brownish-orange
color comes from more heavily processed hydrocarbons
present in Titan's atmosphere and on its surface.
Artistic license has been used to exaggerate
the size of the orbiter, the sharpness of the
icy features, the tilt of Saturn's rings, and
the visibility of the planet through Titan's
atmosphere.
Credit: NASA/JPL
- Caltech
|
Information about the Cassini
mission: http://www.nasa.gov/cassini
Contact:
Bill Steigerwald
NASA Goddard Space Flight Center
301 286 5017
Catherine Ishida
Subaru Telescope
808 934 5086
