Parachuting to Titan

http://science.nasa.gov/headlines/y2004/30dec_titan.htm

Parachuting to Titan
NASA Science News
December 30, 2004

On Jan. 14, 2005, the European Space Agency's Huygens probe will
descend
to the surface of Saturn's largest moon.

December 30, 2004: Get ready for two of the strangest hours in the
history of space exploration.

Two hours. That's how long it will take the European Space Agency's
Huygens probe to parachute to the surface of Titan on January 14th.
Descending through thick orange clouds, Huygens will taste Titan's
atmosphere, measure its wind and rain, listen for alien sounds and,
when
the clouds part, start taking pictures.

No one knows what the photos will reveal. Icy mountains? Liquid methane

seas? Hot lightning? "It's anyone's guess," says Jonathan Lunine, a
professor of planetary science at the University of Arizona and a
member of the Huygens science team. "We might not even understand
what we see, not immediately."

Such is Titan--the biggest mystery in the solar system.

Astronomers have been watching Titan, Saturn's largest moon, for
centuries. From Earth it looks like a pinprick of light orbiting the
ringed planet - nothing extraordinary. But when NASA's Voyager
spacecraft
flew by Titan in 1980, observers realized it was something special.
Titan is huge: bigger than the planets Mercury and Pluto. It has a huge
atmosphere, too: three times taller than Earth's and one and a half
times as massive. The air on Titan is choked with organic compounds
akin
to smog. Some of these molecules are building blocks of life. Could
life
begin on a world where the surface temperature dips 290o F below zero?
"Probably not," says Lunine, but, again, no one knows.

Titan's orange clouds hide its surface and, maybe, some pretty bizarre
things. There's methane (CH4) in Titan's atmosphere. Here on Earth
methane comes from, e.g., cows and bogs. On Titan - no one knows where
it comes from. Because Titan is so cold, its methane can liquefy and
rain down from the skies possibly filling lakes and seas on the ground.
Liquid methane has about the same appearance and viscosity as ordinary
water, but it's some 300o F colder. Lakes on Titan, if they exist,
might
look like lakes on Earth, but they certainly won't be the same.

The Huygens probe, about the size of a small car and shaped like a
flying saucer, will penetrate the clouds and investigate first hand.
"We're so hopeful that Huygens will succeed," says Alfred McEwen, a
colleague of Lunine's at the University of Arizona and a member of the
Cassini imaging team. "We're pulling our hair out trying to understand
Titan."

Huygens rode to Saturn onboard NASA's Cassini spacecraft. The trip
lasted 7 years. Cassini arrived in July 2004 and is now orbiting
Saturn.
Huygens remained onboard until Dec. 25th when it separated from its
mothership and headed for Titan. The probe is scheduled to enter
Titan's
atmosphere at 10:13 GMT (5:13 a.m. EST) on January 14, 2005.

On the way down, Huygens will collect air samples for analysis by
onboard gas chromatographs and mass spectrometers. This will tell
researchers exactly what Titan's atmosphere is made of. Huygens'
external sensors will measure temperature, pressure, winds and
electromagnetic fields that might come from lightning. Lightning is
important. Seething-hot strokes can fuse simple organic molecules into
more complicated and interesting things. Some scientists think this is
how life began on Earth billions of years ago. A microphone onboard
Huygens will listen for thunder (a sign of lightning) and other sounds.
For the first time, we'll get to hear what another world sounds like.

Huygens is going to descend during daylight hours. Sunlight filtering
through the clouds probably casts an orange glow across the landscape
"like 1000 full moons," says McEwen. That's bright enough to read a
newspaper, but still about 1000 times dimmer than a sunlit day on
Earth.
Just before Huygens lands it will turn on an intense flashlight and
shine it on the terrain below. This is done to improve pictures of the
landing site and help the probe's spectrometers get better readings of
elements and minerals in the soil--or whatever's down there.

"We don't know what we're going to land on," notes Lunine. Huygens
might
go tumbling down a cliff. It might splash into a lake or sea (Huygens
is
designed to float). Or it might thump down on a smooth icy plain. "Just
about anything is possible."

If the probe survives touchdown, the Surface Science Package attached
the bottom of the saucer can measure the properties of the landing
site:
thermal and electrical conductivity, index of refraction, sonar depth
and many other things. Mission planners hope Huygens survives on the
"ground" for at least 30 minutes before Titan's bitter cold and unknown
hazards shut it down. Even a few minutes of data would be cause for
celebration.

While all this is happening, the Cassini spacecraft will be flying
overhead, recording Huygens' transmissions. Later, Cassini will turn
toward home and relay the pictures and sounds and priceless
measurements. Radio signals from Saturn take 1 hour and 8 minutes to
reach Earth. "We can't wait to get the data," says McEwen.

What's down there? No one knows, but it's bound to be strange. Get
ready.