NASA's Cassini Spacecraft Marks Mission Halfway Point

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

News Release: 2006-088 June 27, 2006

NASA’s Cassini Spacecraft Marks Mission Halfway Point

As the Cassini spacecraft reaches the halfway mark in
its four-year tour of the Saturn system, discoveries
made during the first half of the mission have
scientists revved up to find out what’s in store for
the second act. Cassini has been orbiting Saturn since
June 30, 2004, studying the planet, its rings and moons.

“The spacecraft has spent a considerable amount of time
studying the moon Titan during 15 separate flybys so far.
In the second half of its prime mission, ending June
2008, Cassini will swing by Titan 30 more times,” said
Robert T. Mitchell, Cassini program manager at NASA’s
Jet Propulsion Laboratory, Pasadena, Calif. “The past
two years have been just like a warm-up.”

“We especially focused on Titan because we thought it
could tell us something about the early Earth,” said Dr.
Toby Owen, Cassini interdisciplinary scientist at the
University of Hawaii at Manoa.

Owen added, “Examining this world frozen in time, we
find evidence that Earth may have begun with the same
methane-ammonia atmosphere that marked the birth of
Titan. Because of our world’s closeness to the Sun,
Earth has oceans of liquid water, which Titan lacks.
The resulting chemistry in Earth’s warm environment
ultimately led to the origin of life, whereas on Titan
we find only a frozen echo of early Earth: methane,
nitrogen, and a suite of small organic molecules.
Our planet’s carefully balanced, warm global climate
is the underlying reason that we are investigating
Titan, instead of Titanians investigating Earth.”

Cassini’s tour of the Saturnian system is about to
take on a new pace. "This summer we will begin our
express-ticket ride. That’s 11 months with 17 Titan spacecraft’s orbit
orientation with respect to the
sun by nearly 180 degrees, resulting in a
bird’s-eye view of Saturn’s glorious rings. This
gradual transfer will take about one year.

“One of the biggest mysteries confronting Cassini is the
changes we’ve seen in Saturn’s radio emissions” said
Dr. Bill Kurth, Cassini scientist at the University of
Iowa, Iowa City. “We’ve seen the radio period, the
frequency of emissions that tell scientists how fast or
slow the planet is rotating, change by as much as one
percent (or a few minutes) over just 10 years, and we
don’t know why. Pinning down how long the day is on
Saturn is key to understanding other things, such as
wind speed.”

Cassini has quite a job to do during the second half
of the mission to match the potpourri of discoveries
in its first half.

The wealth of information from the Cassini spacecraft
and the European Space Agency’s Huygens probe, which
descended through Titan’s murky atmosphere to its
surface, shows that Titan is remarkably Earth-like.
There is evidence for methane rain, erosion,
drainage channels, dry lake beds, possible
volcanoes and vast dune fields that run for miles.

In addition to the Titan findings, Cassini also
discovered three new moons, and some of the
previously-known moons provided surprises. One of
the most bizarre discoveries is a giant mountain
range that runs the full length around the equator
of Saturn’s moon Iapetus. The mountains rival
Olympus Mons on Mars, which is nearly three times
the height of Mt. Everest. Other moons look like
rubble piles.

Cassini also acquired the highest resolution images
ever taken of the planet’s rings. Strange structures
in the rings became apparent on the first day of
the tour. Waves rip through the rings, while knots
and banded structures shape them. Clumps of ice
several kilometers wide are now appearing. Scientists
also witnessed moons influencing the rings. The moon
Prometheus was caught stealing particles from the
F-ring, while Enceladus seems to be contributing
particles to Saturn’s expansive E-ring. A whole new
class of small moonlets may lie within Saturn’s rings.
New rings have also appeared, which may indicate the
presence of tiny moonlets.

The true showstopper was the discovery of giant,
icy geysers gushing from the surface of Enceladus.
This evidence leads some scientists to believe there
may be liquid water close to the surface. With all
these discoveries in the first two years, it’s little
wonder Cassini scientists are anxiously waiting to see
what else remains for their instruments to reveal in
the next two years.

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