A Little Moon of Saturn Makes its Presence Known (Forwarded)

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

Contact:

Dr. Geraint Jones
Max Planck Institute for Solar System Research
Katlenburg-Lindau, Germany
Tel.: +49 5556 979205
Fax: +49 5556 979240

Elias Roussos
Max Planck Institute for Solar System Research
Katlenburg-Lindau, Germany
Tel.: +49 5556 979413
Fax: +49 5556 979240

Dr. Chris Paranicas
Applied Physics Laboratory, The Johns Hopkins University
Laurel, MD 70723, USA
Tel.: +1 240 228 5000

Prof. Michele K. Dougherty
Imperial College London
London, United Kingdom
Tel.: +44 2075947757

March 10th, 2006

News / SP / 2006 (25)

A Little Moon of Saturn Makes its Presence Known

Max Planck researchers detect sub-surface material from the moon Enceladus
in the magnetosphere around Saturn

The effects of plumes of ice and gas released from a small icy moon of
Saturn can be detected over a million kilometers from the moon itself. The
report, led by a team of scientists from the Max Planck Institute for
Solar System Research in Katlenburg-Lindau, Germany, details how an
instrument aboard the NASA/ESA Cassini spacecraft has detected "holes" in
the magnetosphe a bubble of charged particles surrounding Saturn. These
holes are caused by Enceladus and material it has spewed out through open
vents near its south pole. The results of these observations are reported
in the journal Science (Science, 10 March 2006).

Enceladus measures only 500 km across, and is coated in a highly
reflective layer made mostly of water ice. The NASA-led international
Cassini mission is in orbit about Saturn, making countless new discoveries
about the planet and its many moons. During 2005, Cassini's passed by
Enceladus, and its instruments revealed the moon to be geologically active
even today, billions of years after its formation.

The MIMI instrument on the Cassini spacecraft is led by Johns Hopkins
University Applied Physics Laboratory. One of its detectors, LEMMS, was
built at the Max Planck Institute for Solar System Research (Max Planck
Institut für Sonnensystemforschung). LEMMS measures the energy and
direction of high energy ions and electrons.

Like the Earth, Saturn is surrounded by a belt of these high-energy
particles, called the radiation belts. Enceladus orbits the planet within
the radiation belt, and is constantly being pelted by these particles.
This bombardment of Enceladus causes material to be lost to the moon's
surface, and these losses are observed by LEMMS as holes or dropouts when
passing close to the moon's orbital path. Rather than seeing a clean
dropout as is usually observed near icy moons, LEMMS observations show
that the holes caused by Enceladus come in various depths and widths.
Something is varying the way that Enceladus is interacting with Saturn's
magnetosphere, and the MIMI team suggest that it is the ice eruptions on
Enceladus that are the cause. As these eruptions change in activity, the
plume of gas and icy dust that lies near Enceladus also changes, causing
the holes to change shape and depth.

"What we're effectively doing is detecting from far away how this changing
activity on Enceladus is affecting Saturn's magnetosphere", says Dr.
Geraint H. Jones from the Max Planck Institute for Solar System Research.
"This complements very well what other Cassini instrument teams are seeing
with completely different instruments on close passes to Enceladus.
Scientists are studying the moon's inside, its surface, atmosphere, and
the effects on the magnetosphere. It's a fantastic interdisciplinary
study."

The Cassini mission's phenomenal success is set to continue. Currently
halfway through its 4-year survey of the Saturn system, scientists are
anticipating further groundbreaking discoveries to take place.

Original work:

G. H. Jones, E. Roussos, N. Krupp, C. Paranicas, J. Woch, A. Lagg, D. G.
Mitchell, S. M. Krimigis, and M. K. Dougherty
Enceladus' Varying Imprint on the Magnetosphere of Saturn
Science, 10 March 2006

IMAGE CAPTION:
[http://www.mpg.de/bilderBerichteDoku.../Web_Zoom.jpeg
(65KB)]
Saturn's moon Enceladus is bombarded by highly-energetic electrons that
flow opposite to its motion around the planet (red arrow). On July 14th,
2005, the Cassini spacecraft passed downstream of this high-energy
electron stream, and the LEMMS portion of the spacecraft's MIMI instrument
recorded the sharp decrease in energetic electron fluxes (inset) in the
region shadowed by the moon (green). Observations such as this one have
allowed the MIMI team to investigate the interaction between Enceladus and
the charged particles trapped around Saturn. Varying signatures at low
electron energies indicate that Enceladus's plumes of water change in
activity over the timescale of days or weeks.

Image: Max Planck Institute for Solar System Research