Electrons Flying "Backwards" in Saturn's Sky (Forwarded)

Press and Public Relations Department
Max Planck Society for the Advancement of Science
Munich, Germany

Contact:

Prof. Joachim Saur
University of Cologne, Institute of Geophysics and Meteorology
Tel.: +49 221 470-2310
Fax: +49 221 470-5161

Dr. Norbert Krupp
Max Planck Institute for Solar System Research, Katlenburg-Lindau
Tel.: +49 5556 979154
Fax: +49 5556 979-6154

March 6th, 2006

News SP / 2006 (23)

Electrons Flying "Backwards" in Saturn's Sky

Scientists at the Max Planck Institute for Solar System Research discover
unusual particle rays in Saturn's polar region

Polar lights are fascinating to look at on Earth. On other planets, they
can also be spectacular. Scientists from the Max Planck Institute for
Solar System Research in Katlenberg, Lindau, Germany, have now observed
Saturn's polar region using the particle spectrometer MIMI, on the Cassini
Space Probe. They discovered electrons not only being accelerated toward
the planet, but also away from it (Nature, February 9, 2006).

We can see polar lights on Earth when electrons above the atmosphere are
accelerated downwards. They light up when they hit the upper atmosphere.
Some years ago, researchers discovered that electrons inside the polar
region can also be accelerated away from the Earth -- that is,
"backwards". These anti-planetary electrons do not cause the sky to light
up, and scientists have been puzzled about how they originate.

Until now it has also been unclear whether anti-planetary electrons only
occur on Earth. An international team led by Joachim Saur at the
University of Cologne have now found electrons on Saturn that are
accelerated "backwards" -- that is, in an anti-planetary direction. These
particles were measured using "Magnetospheric Imaging Instruments" (MIMI)
on NASA's Cassini Space Probe. One of these instruments' sensors, the "Low
Energy Magnetospheric Measurement System" (LEMMS), was developed and built
by scientists at the Max Planck Institute for Solar System Research.

The rotation of the space probe helped the researchers to determine the
direction, number, and strength of the electron rays. They compared these
results with recordings of the polar region and a global model of Saturn's
magnetic field. It turned out that the region of polar light matched up
very well with the lowest point of the magnetic field lines in which
electron rays were measured.

Because the electron ray is strongly focussed (with an angle of beam
spread less than 10 degrees), the scientists were able to determine where
its source lies: somewhere above the polar region, but inside a distance
of maximum five radii of Saturn. Because the electron rays measured on the
Earth, Jupiter, and Saturn are so similar, it appears that there must be
some fundamental process underlying the creation of polar lights.

Doing these measurements, Norbert Krupp and his colleagues Andreas Lagg
and Elias Roussos from the Max Planck Institute for Solar System Research
worked closely with scientists from the Institute for Geophysics and
Meteorology at the University of Cologne and the Applied Physics
Laboratory of Johns Hopkins University in Baltimore. US scientists led by
Tom Krimigis are responsible for service and coordination of the
instrument on the Cassini Space Probe.

Original work:

J. Saur, B.H. Mauk, D. G. Mitchell, N. Krupp, K.K. Khurana, S. Livi, S. M.
Krimigis, P. T. Newell, D. J. Williams, P.C. Brandt, A. Lagg, E. Roussos,
M. K. Dougherty

Electron beams at Saturn indicate universality of anti-planetward auroral
acceleration
Nature, 439, 699-702 (09 Feb 2006)

IMAGE CAPTION:
[http://www.mpg.de/bilderBerichteDoku.../Web_Zoom.jpeg
(195KB)]
Beware -- particle rays! Researchers have measured electron rays, using
the instrument MIMI on the Cassini Space Probe. These rays fly "backwards"
-- that is, away from, rather than toward, the planet Saturn, in its polar
region.

Image: University of Cologne / Joachim Saur