Fwd: Cassini and Galileo spacecraft analyse volcanic ashes at Jupiter

From: Amara Graps (Amara.Graps@mpi-hd.mpg.de)
Date: Wed Jan 10 2001 - 06:00:21 MST

I see that our press release finally made it out, delayed by a couple
of months for some strange reason. This was written in November,
before we acquired our measurements, and the data is, simply, great.



From: Andrew Yee <ayee@nova.astro.utoronto.ca>
Newsgroups: sci.astro
Date: Tue, 09 Jan 2001 16:03:19 GMT

Max-Planck-Institut für Kernphysik
Heidelberg, Germany

Eberhard Grün
Max-Planck-Institut für Kernphysik
Postfach 10 39 80
69029 Heidelberg
Tel. +49-6221-516-478 (office)
E-Mail: Eberhard.Gruen@mpi-hd.mpg.de

Harald Krüger
Max-Planck-Institut für Kernphysik
Postfach 10 39 80
69029 Heidelberg
Tel. +49-6221-516-563 (office)
E-Mail: Harald.Krueger@mpi-hd.mpg.de

Ralf Srama
Max-Planck-Institut für Kernphysik
Postfach 10 39 80
69029 Heidelberg
Tel. +49-6221-516-423
E-Mail: Ralf.Srama@mpi-hd.mpg.de


Cassini and Galileo spacecraft analyse volcanic ashes at Jupiter

In December 2000, when NASA's Cassini spacecraft will pass by Jupiter,
scientists from the Max Planck Institut für Kernphysik in Heidelberg,
Germany, will analyse microscopic ash particles from volcanoes on the
giant planet's satellite Io. It will be the first in-situ analysis of surface
material from a planetary satellite of our solar system other than the
Earth's moon.

On 30 December 2000 NASA's Cassini spacecraft, on its journey to
Saturn, will pass by the giant planet Jupiter. Another NASA spacecraft --
Galileo -- has been exploring Jupiter since 1995. From different vantage
points both spacecraft will study Jupiter, its satellites and its huge
magnetosphere in a joint observation campaign between October
2000 and March 2001. This is the first time that two spacecraft
simultaneously investigate the same gas giant planet from a close

Cassini and Galileo have highly sensitive instruments for the analysis
of microscopic dust particles on board which were built by the
Max-Planck-Institut für Kernphysik in Heidelberg, Germany. The
Max-Planck scientists will study streams of ash particles, finer than
cigarette smoke, originating from volcanic plumes on Jupiter's moon Io.
Patterns in the streams as they pass one spacecraft first, then the
other, could give information about the particles' movement. These
streams can serve as a monitor of Io's plume activity. Identification
of the particles' composition would be sampling Io's surface material.

Io is the only moon in the solar system with presently active volcanism,
being volcanically more active than the Earth. "The volcanic ash particles
released from Io are accelerated to speeds of 300 km/sec by Jupiter's
magnetic field," said Prof. Eberhard Grün, leader of the joint
Cassini/Galileo dust investigations. "By measuring the particles' flight
time between the two spacecraft which are more than 20 times the
Earth-moon distance apart we can directly measure their speed. The
particles are 4000 times faster than formula 1 world championship
winner Michael Schumacher in his racing car. Only because the particles
are so small (a thousandth of the thickness of a human hair) can they
gain such high speeds in Jupiter's magnetosphere," explains Grün.

"With our Galileo dust instrument we have seen a surprisingly large
amount of dust while Galileo was 20 million kilometers (50 times the
Earth-moon distance) away from Jupiter in September this year,"
explains Dr Harald Krüger, leader of the dust investigations with Galileo.
"If matter gets dispersed in space you usually expect more material to
be close to the source than far away, just like water released from a
hose is dispersed. We measured exactly the opposite which tells us
that the particles accumulate due to the interaction of Jupiter's
magnetosphere and the interplanetary magnetic field, a fact which
we do not understand yet."

Furthermore, during the past five years of the Galileo dust exploration
in the Jupiter system, large variations in the detected amount of
dust have been found which could be due to changes in the Jovian
magnetosphere, or to variations in the dust production of Io's
volcanoes, or both. "If we better understand the movement of the
dust particles in the magnetosphere we can use our dust measurements
to monitor Io's volcanic activity," said Eberhard Grün. "Our joint
Cassini/Galileo measurements can be a major step forward towards
understanding these effects."

Large amounts of dust were also recognized with the Cassini dust
instrument even further away from Jupiter. "In September this year
we have measured the first dust particles from Io while Cassini was
still 45 million kilometers away from Jupiter," explains Ralf Srama,
responsible for the Cassini dust instrument. "By analysing the dust
grains millions of kilometers away from Io we can analyse the moon's
surface composition. Our Cassini measurements have confirmed that
the particle composition resembles that of Io's surface."

With the Galileo dust detector various types of dust grains have
been found throughout the Jupiter system: the planet's moons are
surrounded by faint clouds of dust particles ejected from the moons'
surface by impacts of interplanetary meteoroids. The planet itself
is surrounded by a dusty ring system, part of which can be seen
on images taken with large Earth-based telescopes. Only with the
continuous Galileo dust measurements going on for five years now
could Io be identified as the source of the ash particles detected
even in interplanetary space 300 million kilometers (750 times the
Earth-moon distance) away from Jupiter. More is presently known
about cosmic dust in Jupiter's system than about natural (i.e.
non-artificial) dust in the Earth environment.

In interstellar space, stars and planets form out of clouds of gas and
dust permeated by magnetic fields. Since Io's dust particles behave
like ions in a magnetic field, the Jovian system can serve as a
laboratory for studying the processes of star and planet formation.
With their dust detector on board ESA's Ulysses spacecraft, the
scientists from Heidelberg successfully identified and analysed
interstellar dust sweeping through our solar system. Due to their
high speeds, the Io particles eventually become interstellar dust.

Only with the highly sensitive dust detectors on board Cassini and
Galileo which measure dust grains hitting a 1000 cm2 metal target,
could these particles be detected. In the case of the Io particles the
dust concentration is so low that only one grain can be found in a cube
with about 3 meters on a side. Although these ash particles are very
interesting scientifically, they do not cause a danger to spacecraft.

The Cassini and Galileo dust instruments were built by an international
team of scientists and engineers under the leadership of Prof. Dr.
Eberhard Grün at the Max-Planck-Institut für Kernphysik in Heidelberg,
Germany, with financial support from the German national space agency

The Cassini and Galileo programs are international cooperative efforts
involving NASA, ESA and several European academic and industrial
contributors. Galileo has been orbiting Jupiter since December 1995,
and has currently completed five very successful years of exploring
the Jupiter system. Cassini/Huygens will reach Saturn in 2004 and
explore the second-largest planet of our solar system and its satellites
during a four-year orbital mission. Cassini's Huygens probe was built by
ESA and will descend into the atmosphere of Titan, the largest of the
Saturnian moons. Galileo and Cassini are operated by the Jet Propulsion
Laborary which is a division of Caltech, Pasadena, CA.

More information:

* Heidelberg dust team
* NASA's joint Cassini/Galileo campaign


[Figure 1: http://www.mpi-hd.mpg.de/galileo/gal_cas_meas/img2.gif]
Cassini spacecraft before launch (NASA/JPL). The arrow 'CDA'
indicates the Cosmic Dust Analyser.

[Figure 2: http://www.mpi-hd.mpg.de/galileo/gal_cas_meas/img3.gif]
Jupiter's moon Io as seen by the cameras of the Galileo spacecraft
(NASA/JPL) with one of its volcanic plumes visible at the limb. The Galileo
dust detector found Io's volcanic ash particles at distances out to 300
million kilometers from Jupiter. Io has about the size of the Earth's moon.

[Figure 3: http://www.mpi-hd.mpg.de/galileo/gal_cas_meas/img4.gif]
Galileo (red) and Cassini (blue) at Jupiter. From two vantage
points the two spacecraft will measure streams of dust particles
originating from Io. On 29 December 2000 the streams (green) can
first be detected by the Galileo dust detector and 9 hours later by
the Cassini dust analyser.


********************************************************************* Amara Graps | Max-Planck-Institut fuer Kernphysik Interplanetary Dust Group | Saupfercheckweg 1 +49-6221-516-543 | 69117 Heidelberg, GERMANY Amara.Graps@mpi-hd.mpg.de * http://www.mpi-hd.mpg.de/dustgroup/~graps ********************************************************************* "Never fight an inanimate object." - P. J. O'Rourke

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