[meteorite-list] Saturn Kicks Out Super-Fast Dust Streams

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Jan 19 19:49:07 2005
Message-ID: <200501200048.QAA03660_at_zagami.jpl.nasa.gov>

http://www.spacedaily.com/news/cassini-05p.html

Saturn Kicks Out Super-Fast Dust Streams
AFP
January 19, 2005

Paris - The US spacecraft Cassini ran into dramatic storms of dust
as it hurtled towards its rendezvous with Saturn last year, a study
published on Thursday says.

The microscopic grains smashed into Cassini with an impact speed of more
than 100 kilometers (62 miles) per second (360,000 kph, 225,000 mph) as
the craft was ferrying the European probe Huygens towards Saturn last year.

The dust probably came from the outermost ring of Saturn, called the A
ring, the authors believe.

Other possible sources were the planet's E ring, as well as dust clouds
around the icy Saturnian moons of Dione and Rhea.

The dust was first recorded by Cassini's onboard detectors about 60
million kms (37.5 million miles) from Saturn, and the bursts became more
frequent and intense as the craft neared the rendezvous in July.

The grains are believed to compose minute crystals of water ice which
carry a positive electrical charge.

They achieved their enormous velocity because they were flung into space
by the mighty whirling magnetic field generated by Saturn, the authors
suspect.

Scientists had expected that Saturn may be spewing out dust because the
phenomenon had already been spotted near Jupiter, where the main source
of the particles is the Jovian moon Io.

Lead author in the study, which appears in the British journal Nature,
is Sascha Kempf of the Max Planck Institute for Nuclear Physics in
Heidelberg, Germany.

Huygens last Friday descended to the surface of Titan, carrying out an
unprecedented array of experiments to assess its mysterious, thick
atmosphere.

Cassini-Huygens was launched in 1997, in a 3.2-billion-dollar
(2.46-billion-euro) transatlantic venture to explore the second largest
planet of the Solar System.

Objects in space can reach enormous speeds because there is no friction.
Meterorites enter the Earth's atmosphere at up to 72 kilometers (45
miles) per second, which causes them to burn up through friction with
atmospheric molecules.

---------------------------------------------------------------------

http://www.newscientist.com/article.ns?id=dn6902

Cassini finds high-speed dust streaming from Saturn
Kelly Young
New Scientist
January 19, 2005

The Cassini spacecraft has found high-speed streams of dust zipping away
from Saturn, astronomers revealed on Wednesday. Similar dust streams
have been found emanating from Jupiter, but this is a first for the
ringed planet.

"It was suspected that such a phenomenon could be observed there," says
the new study's lead author, Sascha Kempf, at the Max Planck Institute
for Nuclear Physics in Heidelberg, Germany. "What was not expected, when
Cassini was quite far away from Saturn, was the speed and size of the
grains."

The probe first felt the particles pelting its dust detector on 15
January 2004 when it was still about 70 million kilometres away from the
planet. The bursts became more intense as Cassini drew closer to Saturn,
suggesting that the particles came from the planet and were not just
interplanetary dust patches.

Kempf and his colleagues believe the dust comes from Saturn's wide A
ring. Cassini is unable to dive through this dense, bright ring - it
would probably be destroyed - so the dust streams provide a convenient
way to analyse the ring's particles from a distance.

Moon dust

In 1992, the Ulysses spacecraft detected dust streaming from Jupiter.
Later in the 1990s, the Galileo probe pinpointed the source of the dust
streams - the volcanic moon, Io.

Scientists initially suspected that the particles streaming from Saturn
originated in the dust clouds around two of the planet's icy moons,
Dione and Rhea. But the dust particles' speed and size did not support
this idea.

The flecks of dust from Saturn are tiny, measuring between 2 and 50
nanometres. The spacecraft's dust analyser was principally designed to
measure the larger particles in Saturn's E ring, but the tiny particles'
high speed allowed the analyser to detect them.

The dust particles are accelerated to speeds above 100 kilometres per
second. This is because solar radiation causes some particles in the
outer regions of the A ring to become positively charged. These are then
accelerated outwards by electrical fields generated by the interaction
of the charged particles and the planet's magnetic field.

Scientists now hope to use Cassini's instruments to learn more about the
origin and composition of the particles flowing away from Saturn.

The cumulative dust loss is probably negligible compared to the masses
of both the giant planets. Jupiter probably loses between 20 grams and 1
kilogram of dust per second, for example.

Earth dust

"The new finding tells us that such dust streams are a common phenomenon
for giant planets," Kempf told New Scientist.

In fact, the Earth may even have dust particles streaming away from it,
says Eberhard Gr?n, who leads the cosmic dust analyser group at the Max
Planck Institute in Heidelberg. Because of the Ulysses and Galileo
observations of Jupiter, we know less about the Earth's dust environment
than we know about Jupiter's, he says.

Cassini's next major milestone will be a return to Saturn's giant moon,
Titan, on 15 February 2005, a month after the European Space Agency's
Huygens probe successfully touched down.

Journal reference: Nature (vol 433, p 289)
Received on Wed 19 Jan 2005 07:48:56 PM PST