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ZL2VAL > SPACE 15.10.03 21:39l 121 Lines 5065 Bytes #999 (0) @ WW
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Subj: Huygens, Touchdown or Splashdown?
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From: ZL2VAL@ZL2AB.#46.NZL.OC
To : SPACE@WW
Titan Probe May Get All Wet
By Robert Roy Britt
Senior Science Writer
posted: 06:17 am ET
14 October 2003
No craft has ever landed in a lake or ocean beyond our home planet. A
new study suggests that could change in 2005 when the Cassini spacecraft
sends its detachable Huygens probe parachuting down to Saturn's moon Titan.
Since well before the mission launched, exactly 6 years ago tomorrow,
astronomers have wondered whether Huygens would touch down or splash
down. Titan is no waterworld, but it may be a liquid methane world,
mounting evidence suggests.
The mystery moon
Titan is half again as large as Earth's Moon. It is the only satellite
in the solar system with a serious atmosphere. Like Earth's air, Titan's
is mostly nitrogen. Problem is, Titan's atmosphere is so thick with
natural smog that astronomers can hardly see through it, so they know
little about what exists at the surface.
For decades, researchers have speculated that Titan could harbor liquid
lakes or seas made of hydrocarbons, which would rain out of the
atmosphere as a result of sunlight breaking down methane, also prevalent
in the air.
In the new study, published Oct. 3 in the online edition of the journal
Science, scientists peered through the smog to get a direct glimpse of
the surface.
Radar is not hampered by smog. So the astronomers sent microwave signals
to Titan from the National Science Foundation's 1,000-foot (305-meter)
Arecibo Observatory in Puerto Rico, waited more than 2 hours, then
gathered the feeble returns with the Arecibo dish along with the
328-foot (100 meter) Robert C. Byrd Green Bank Telescope in West Virginia.
Like sunlight glinting off the ocean, the radar signals showed bright
spots interpreted to be liquid hydrocarbon.
"Those new observations are remarkable," Huygens Project Scientist
Jean-Pierre Lebreton, of the European Space Agency, told SPACE.com. "The
likelihood of Huygens splashing in a sea of hydrocarbons is most exciting."
Lebreton was not involved in the study. But he pays close attention to
these sorts of ground-based studies, which dominate current views of the
mysterious moon. Not since the Voyager era has Titan been visited up close.
Uncontrolled landing
Titan has a preplanned entry course, but the specific landing site
cannot be chosen, said Lebreton. Wind could carry the probe to sites as
potentially distant as the Bahamas are from Miami.
Since the Huygens capsule is designed to take pictures and sense its
environment on the way in, beaming the data back to Cassini, researchers
should learn exactly what happens after Cassini relays the data to Earth.
"Images by the camera a few kilometers above the surface and a few
minutes before landing should show if we are coming down on land or
sea," Lebreton explained.
The 700-pound (318-kilogram) probe will report on Titan's surface for as
brief as three minutes or as long as a half-hour, according to NASA,
which manages the Cassini mission.
Several instruments -- an impact sensor, accelerometer and tilt sensor
-- should confirm what sort of surface the probe lands on or in,
Lebreton said. "After impact, an acoustic sonar will measure the depth
of the sea down to about 1 kilometer [0.62 miles]" if it indeed lands in
liquid.
A sea landing has one clear advantage: The probe will bob into an
upright position -- important for getting data up to Cassini.
High hopes
Built by the European Space Agency, the detachable probe aboard Cassini
is named for Christiaan Huygens (1629-1695), a Dutch astronomer who
discovered Titan and also figured out that Saturn had rings (Galileo had
earlier spied the rings, which looked like lobes on the planet, and he
could not explain what he saw).
Cassini will arrive at Saturn early next year, study the planet and its
rings and also gather more data on Titan's atmosphere. It will release
Huygens several months later.
Scientists have high hopes for the combined assault on the smoggy satellite.
much as 75
percent of Titan’s surface could be covered in this way." Scientists
have long theorized that Titan could be mottled by craters, much like
Earth's Moon. And other studies have indeed indicated Titan's topography
is not simple.
Only Huygens -- which will reach Titan on Jan. 14, 2005 -- will provide
a definitive look the veiled surface, and astronomers can't wait.
"The radar data," Lorenz said, "suggest that on Titan itself, as well as
in the terrestrial media, this event will make quite a splash."
==============================
73 de Alan
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Brain Cramps
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