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

Subject: Electrons Flying "Backwards" in Saturn's Sky Forwarded
From: Andrew Yee
Date: Mon, 06 Mar 2006 12:08:45 -0500
Newsgroups: sci.astro
Press and Public Relations Department
Max Planck Society for the Advancement of Science
Munich, Germany


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)

[ (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

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