[meteorite-list] Cassini Finds an Atmosphere on Saturn's Moon Enceladus

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Mar 21 13:24:57 2005
Message-ID: <200503162038.j2GKc2I10836_at_zagami.jpl.nasa.gov>

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

Carolina Martinez (818) 354-9382
Jet Propulsion Laboratory, Pasadena, Calif.

Press Release: 2005-046 March 16, 2005

Cassini Finds an Atmosphere on Saturn's Moon Enceladus

The Cassini spacecraft's two close flybys of Saturn's icy
moon Enceladus have revealed that the moon has a significant
atmosphere. Scientists, using Cassini's magnetometer
instrument for their studies, say the source may be
volcanism, geysers, or gases escaping from the surface or
the interior.

When Cassini had its first encounter with Enceladus on Feb.
17 at an altitude of 1,167 kilometers (725 miles), the
magnetometer instrument saw a striking signature in the
magnetic field. On March 9, Cassini approached to within 500
kilometers (310 miles) of Enceladus' surface and obtained
additional evidence.

The observations showed a bending of the magnetic field,
with the magnetospheric plasma being slowed and deflected by
the moon. In addition, magnetic field oscillations were
observed. These are caused when electrically charged (or
ionized) molecules interact with the magnetic field by
spiraling around the field line. This interaction creates
characteristic oscillations in the magnetic field at
frequencies that can be used to identify the molecule. The
observations from the Enceladus flybys are believed to be
due to ionized water vapor.

"These new results from Cassini may be the first evidence of
gases originating either from the surface or possibly from
the interior of Enceladus," said Dr. Michele Dougherty,
principal investigator for the Cassini magnetometer and
professor at Imperial College in London. In 1981, NASA's
Voyager spacecraft flew by Enceladus at a distance of 90,000
kilometers (56,000 miles) without detecting an atmosphere.
It's possible detection was beyond Voyager's capabilities,
or something may have changed since that flyby.

This is the first time since Cassini arrived in orbit around
Saturn last summer that an atmosphere has been detected
around a moon of Saturn, other than its largest moon, Titan.
Enceladus is a relatively small moon. The amount of gravity
it exerts is not enough to hold an atmosphere very long.
Therefore, at Enceladus, a strong continuous source is
required to maintain the atmosphere.

The need for such a strong source leads scientists to
consider eruptions, such as volcanoes and geysers. If such
eruptions are present, Enceladus would join two other such
active moons, Io at Jupiter and Triton at Neptune.
"Enceladus could be Saturn's more benign counterpart to
Jupiter's dramatic Io," said Dr. Fritz Neubauer, co-
investigator for the Cassini magnetometer, and a professor
at the University of Cologne in Germany.

Since the Voyager flyby, scientists have suspected that this
moon is geologically active and is the source of Saturn's
icy E ring. Enceladus is the most reflective object in the
solar system, reflecting about 90 percent of the sunlight
that hits it. If Enceladus does have ice volcanoes, the
high reflectivity of the moon's surface might result from
continuous deposition of icy particles originating from the
volcanoes.

Enceladus' diameter is about 500 kilometers (310 miles),
which would fit in the state of Arizona. Yet despite its
small size, Enceladus exhibits one of the most interesting
surfaces of all the icy satellites.

For images and information on the Cassini mission visit
http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini .

The Cassini-Huygens mission is a cooperative project of
NASA, the European Space Agency and the Italian Space
Agency. The Jet Propulsion Laboratory, a division of the
California Institute of Technology in Pasadena, manages the
Cassini-Huygens mission for NASA's Science Mission
Directorate, Washington, D.C. The Cassini orbiter was
designed, developed and assembled at JPL.

                            -end-
Received on Wed 16 Mar 2005 03:38:01 PM PST