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