Cassini Flies Through
Watery Plumes Of Saturn Moon
(13 March 2008) NASA's Cassini
spacecraft performed a daring flyby of Saturn's moon Enceladus on Wed., March
12, flying about 15 kilometres per second (32,000 mph) through icy water
geyser-like jets.
The spacecraft snatched up precious samples
that might point to a water ocean or organics inside the little
moon.
Scientists believe the geysers could provide evidence that liquid
water is trapped under the icy crust of Enceladus. The geysers emanate from
fractures running along the moon's south pole, spewing out water vapour at
approximately 400 metres per second (800 mph).
The new data provide a
much more detailed look at the fractures that modify the surface and will give
a significantly improved comparison between the geologic history of the moon's
north pole and south pole.
This three-image mosaic is the highest resolution view yet obtained of Enceladus' north polar region. The view looks southward over cratered plains from high above the north pole of Enceladus. (courtesy: NASA/JPL/Space Science Institute)
New images show that compared to much of the
southern hemisphere on Enceladus--the south polar region in particular--the
north polar region is much older and pitted with craters of various sizes.
These craters are captured at different stages of disruption and alteration by
tectonic activity, and probably from past heating from below. Many of the
craters seem sliced by small parallel cracks that appear to be ubiquitous
throughout the old cratered terrains on Enceladus.
"These new images are
showing us in great detail how the moon's north pole differs from the south, an
important comparison for working out the moon's obviously complex geological
history," said Carolyn Porco, Cassini imaging team leader, Space Science
Institute, Boulder, Colo. "And the success of yesterday's daring and very
low-altitude flyby means this coming summer's very close encounter, when we get
exquisitely detailed images of the surface sources of Enceladus' south polar
jets, should be an exciting 'next big step' in understanding just how the jets
are powered."
This week's flyby and another one planned for Oct. 9,
2008, were designed so that Cassini's particle analysers could dissect the
"body" of the plume for information on the density, size, composition and speed
of the particles. Among other things, scientists will use the data gathered
this week to figure out whether the gases from the plume match the gases that
make up the halo of particles around Enceladus. This may help determine how the
plumes formed.
During Cassini's closest approach, two instruments were
collecting data--the Cosmic Dust Analyzer and the Ion and Neutral Mass
Spectrometer. An unexplained software hiccup with Cassini's Cosmic Dust
Analyzer instrument prevented it from collecting any data during closest
approach, although the instrument did get data before and after the approach.
During the flyby, the instrument was switching between two versions of software
programs. The new version was designed to increase the ability to count
particle hits by several hundred hits per second. The other four fields and
particles instruments on the spacecraft, in addition to the ion and neutral
mass spectrometer, did capture all of their data, which will complement the
overall composition studies and elucidate the unique plume environment of
Enceladus.
Cassini's instruments discovered evidence for the geyser-like
jets on Enceladus in 2005, finding that the continuous eruptions of ice water
create a gigantic halo of ice dust and gas around Enceladus, which helps supply
material to Saturn's E-ring.
This was the first of four Cassini flybys
of Enceladus this year. During Wednesday's flyby, the spacecraft came within 50
kilometres (30 miles) of the surface at closest approach, 200 kilometres (120
miles) while flying through the plume. Future trips may bring Cassini even
closer to the surface of Enceladus. Cassini will complete its prime mission, a
four-year tour of Saturn, in June. From then on, a proposed extended mission
would include seven more Enceladus flybys. The next Enceladus flyby would take
place in August of this year.
The Cassini-Huygens mission is a
co-operative 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-Huygens mission for NASA's Science Mission Directorate,
Washington. The Cassini orbiter was designed, developed and assembled at
JPL.
(source: NASA Jet Propulsion Laboratory)
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