[meteorite-list] Cassini Prepares to Fly by Walnut-Shaped Moon (Iapetus)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 7 Sep 2007 09:00:29 -0700 (PDT)
Message-ID: <200709071600.JAA01190_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2007-096

Cassini Prepares to Fly by Walnut-Shaped Moon
Jet Propulsion Laboratory
September 05, 2007

PASADENA, Calif. - Cassini will make its only close flyby of Saturn's
odd, two-toned, walnut-shaped moon Iapetus on Sept. 10, 2007, at about
1,640 kilometers (1,000 miles) from the surface.

This flyby will be 100 times closer than Cassini's 2004 encounter, and
will be the last time the spacecraft will aim its instruments at this moon.

Iapetus (pronounced eye-APP-eh-tuss) has a ridge of surprisingly large
mountains -- the so-called "belly-band" -- that lies directly on top of
the equator. The moon also has a distinct difference in the brightness
of its leading and trailing hemispheres, one as bright as snow and the
other dark as tar. The irregular shape, the mountain ridge and Iapetus?
brightness contrast are among the key mysteries scientists are trying to
solve.

There are several different ideas on the origin of the dark material. Is
it from inside or outside of Iapetus? Is it residue from some other moon
or moons? Is it due to impacts by meteoroids or comet debris?

"We are on the search for the brush that may have painted Iapetus's dark
side," said Dennis Matson, Cassini project scientist at NASA's Jet
Propulsion Laboratory, Pasadena, Calif.

"This dark stuff appears in several places in the Saturn system and
might be present not just on Iapetus but many other moons,? said JPL
scientist Amanda Hendrix of Cassini?s ultraviolet imaging spectrograph
team and lead author of a paper soon to be published in the journal
Icarus that explores the possible sources of the Iapetus dark material.

There?s a reddish tint to the Iapetus dark stuff, an important clue in
tracing its origin, she said. Saturn's moon Hyperion, which shows
evidence of a violent disruption in its past, has a reddish tint, too.
"It may be that the event that disrupted Hyperion deposited reddish
material onto Iapetus," she said. "Hyperion may be the artist that?s
painting Iapetus dark."

Yet another Icarus paper on Iapetus by Dale Cruikshank at NASA's Ames
Research Center, Moffett Field, Calif., and colleagues, reports that the
dark material on Iapetus and Saturn's small moon Phoebe may be composed
of the same complex, prebiotic hydrocarbons that appear to play a
fundamental role in the origin of life. These chemicals, called
polycyclic aromatic hydrocarbons, exist on objects ranging from backyard
barbeques to comets, meteorites and the stardust that forms planets and
flows between stars. They are important markers in studies of the origin
of life in the universe.

An array of Cassini instruments will home in on Iapetus during the
flyby. The full menu of objectives includes plans to: characterize the
chemical composition of the surface; look for evidence of a faint
atmosphere or erupting gas plumes; and map the nighttime temperature of
the surface. This will be the first Cassini flyby of an icy moon, other
than Titan, that's close enough and slow enough to perform radar imaging
with Cassini's Synthetic Aperture Radar. A large swath of terrain will
be covered, including the equatorial ridge and regions of craters and
basins. These measurements may provide the height of some of the features.

"What is really neat is that we are doing radar of an icy object for
which we actually have pictures," said Steve Ostro, a radar scientist at
JPL. Until now, he said, the radar had been used to reveal the surface
of cloud-covered Titan. Iapetus? surface is easily visible. "This will
be a lesson on how to interpret radar images on an icy body. With Titan,
because of the cloud cover, we don't know what we are looking at much of
the time, but for Iapetus we will know very well," he said.

In coming weeks, scientists will be analyzing data from multiple
instruments. Some results of that analysis will be presented at a
planetary science conference in Orlando, Fla., in mid-October.

More information on the Cassini-Huygens mission is available at:
http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. JPL, a division of
the California Institute of Technology in Pasadena, manages the Cassini
mission for NASA's Science Mission Directorate, Washington, D.C. JPL
designed, developed and assembled the Cassini orbiter.

Media contacts: Carolina Martinez 818-354-9382,
Jet Propulsion Laboratory, Pasadena, Calif.

2007-096

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http://saturn.jpl.nasa.gov/news/events/iapetus/index.cfm

Iapetus Flyby - Sept. 10, 2007

Cassini's Closest Visit of Iapetus

On Sept. 10, the Cassini spacecraft performs its closest flyby during
the entire mission of the odd moon Iapetus, passing by about 1,640
kilometers (1,000 miles).

Iapetus is a world of sharp contrasts. The leading hemisphere is as dark
as a freshly-tarred street, and the white, trailing hemisphere resembles
freshly-fallen snow. Scientists want to know more about the composition
of the dark material that coats Iapetus. They also want to learn more
about Iapetus' distinctive walnut shape and the chain of mountains along
its equator.

Iapetus at a Glance

Iapetus Flyby
Sept. 10, 2007 (SCET)

Altitude
1,644 km (1,022 miles)

Speed
2.4 km/sec (5,368 mph)

Details
+ Iapetus Mission Description PDF ( 2.4 MB)
<http://saturn.jpl.nasa.gov/multimedia/products/pdfs/20070910_Iapetus_mission_description.pdf>
Received on Fri 07 Sep 2007 12:00:29 PM PDT