Ice Volcanoes on Saturn's Moon Enceladus (Forwarded)

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March 14th, 2006

News SP / 2006 (27)

Ice Volcanoes on Saturn's Moon Enceladus

International team of researchers discovers ice volcanoes on Saturn's moon
Enceladus

Scientists from the Max Planck Institute for Nuclear Physics and the
University of Potsdam have found ice volcanoes -- or what could be called
"ice geysers" -- on the surface of Saturn's moon Enceladus. They made the
discovery using a combination of computer simulations and measurements
from the dust detector on the space probe CASSINI. The ice volcanoes are
located at geologically young, warm structures in the icy moon's southern
polar region. The ice particles probably are created from steam deep in
crevices. Volcanic activity is now known to exist in three bodies in our
solar system: Enceladus, Earth, and Jupiter's moon Io (Science, March 10,
2006).

Saturn's E ring, the largest ring around any planet in our solar system,
is not only remarkable for its huge size. What is also astounding is that
current optical measurements show it to be made of ice particles of nearly
equal size -- a radius of 0.3 to 2 micrometres. The icy moon Enceladus
was, however, expected to feed the ring with significantly larger pieces.
The ring's mass distribution must thus somehow be tied up with the
dynamics of the particles. Until now, however, scientists did not know
how. Directly measuring ice particles near Enceladus promised to deliver a
better understanding of the E Ring's complex nature.

On July 14, 2005, the CASSINI space probe came within 175 kilometres of
Enceladus, which is suspected of being the source of Saturn's E Ring. This
made it possible to measure dust distribution deep inside the area of
Enceladus' gravitational pull. The scientists could thus investigate how
the moon refreshed the ring with dust particles.

Until now, it was assumed that new ice particles were created by
interplanetary micrometeorites, or ring particles themselves, bombarding
the moon's surface. In this model, most of the fresh particles form a
nearly isotopic dust cloud around the moon. In the other model, faster
particles feed the ring. Indeed, the dust detector on the space probe
GALILEO had already discovered dust clouds surrounding Jupiter's Galilean
moons.

Measurements from the High Rate Detector (HRD) of CASSINI's "Cosmic Dust
Analyser" (CDA), taken by scientists from the Max Planck Institute for
Nuclear Physics in Heidelberg and the University of Chicago are however
not consistent with this assumption. Observations showed that the maximum
rate of impact was reached before the probe moved to its closest point to
Enceladus. This can only be explained if there exists a strong anisotropic
-- that is, directionally dependent -- dust distribution on the moon.

The dust detector was not the only instrument which came to show
unexpected discoveries. Photographs of Enceladus' southern polar region
clearly showed geologically young structures. Infrared images also
indicated a warmer area -- a "hot spot" -- in that southern region. This
led scientists from the University of Potsdam to model dust distribution
on the moon under the assumption that there is an additional, tightly
confined, dust source on its surface. The models indicated a contained
dust source in the southern polar region. This turned out to be consistent
with the probe's measurements.

This convincing match between models and HRD measurements (see image 2)
led the Cassini camera team to look for, and find, volcanic activity.
Enceladus is thus the second moon in our solar system where volcanic
activity has been discovered.

Original work:

Frank Spahn, Jürgen Schmidt, Nicole Albers, Marcel Hörning, Martin Makuch,
Martin Seiß, Sascha Kempf, Ralf Srama, Valeri Dikarev, Stefan Helfert,
Georg Moragas-Klostermeyer, Alexander V. Krivov, Miodrag Sremcevic,
Anthony J. Tuzzolino, Thanasis Economou, Eberhard Grün
Cassini Dust Measurements at Enceladus and Implications for the Origin of
the E Ring
Science, March 10, 2006

IMAGE CAPTIONS:

[Fig.1:
http://www.mpg.de/bilderBerichteDoku.../Web_Zoom.jpeg
(162KB)]
An artificially coloured image of Saturn's moon Enceladus. Clearly visible
over the southern polar region are dust fountains, caused by ice volcanic
activity (lower left corner).

Image: NASA/JPL/Space Science Institute

[Fig.2:
http://www.mpg.de/bilderBerichteDoku...2/Web_Zoom.gif
(91KB)]
A comparison of the rate of impact from CASSINI's HRD sensor and numerical
simulation of the dust clouds around Enceladus. Right: the modelled dust
distribution if there is an ice volcano in its southern polar region.
Left: the dust distribution without volcanic activity.

Image: University of Potsdam/Max Planck Institute for Nuclear Physics