Cassini Probe Sees Electric Link With Saturn And One Of Its Moons

PASADENA, Calif. -- NASA is releasing the first images and sounds of
an electrical connection between Saturn and one of its moons. The
data collected by the agency's Cassini spacecraft enable scientists
to improve their understanding of the complex web of interaction
between the planet and its numerous moons. The results of the data
analysis are published in the journals Nature and Geophysical Research Letters.

Scientists previously theorized an electrical circuit should exist at
Saturn. After analyzing data that Cassini collected in 2008,
scientists saw a glowing patch of ultraviolet light emissions near
Saturn's north pole that marked the presence of a circuit, even
though the moon is 150,000 miles (240,000 kilometers) away from the planet.

The patch occurs at the end of a magnetic field line connecting Saturn
and its moon Enceladus. The area, known as an auroral footprint, is
the spot where energetic electrons dive into the planet's atmosphere,
following magnetic field lines that arc between the planet's north
and south polar regions.

"The footprint discovery at Saturn is one of the most important fields
and particle revelations from Cassini and ultimately may help us
understand Saturn's strange magnetic field," said Marcia Burton, a
Cassini fields and particles scientist at NASA's Jet Propulsion
Laboratory in Pasadena, Calif. "It gives us the first visual
connection between Saturn and one of its moons."

The auroral footprint measures approximately 750 miles (1,200
kilometers) by less than 250 miles (400 kilometers), covering an area
comparable to California or Sweden. At its brightest, the footprint
shone with an ultraviolet light intensity far less than Saturn's
polar auroral rings, but comparable to the faintest aurora visible at
Earth without a telescope in the visible light spectrum. Scientists
have not found a matching footprint at the southern end of the
magnetic field line.

"Cassini fields and particles instruments found particle beams aligned
with Saturn's magnetic field near Enceladus, and scientists started
asking if we could see an expected ultraviolet spot at the end of the
magnetic field line on Saturn," said Wayne Pryor, a lead author of
the Nature study released today, and Cassini co-investigator at
Central Arizona College in Coolidge, Ariz. "We were delighted to find
the glow close to the 'bulls-eye' at the center of our target."

Jupiter's active moon Io creates glowing footprints near Jupiter's
north and south poles, so scientists suspected there was an analogous
electrical connection between Saturn and Enceladus. It is the only
known active moon in the Saturn system with jets spraying water vapor
and organic particles into space. For years, scientists used space
telescopes to search Saturn's poles for footprints, but none were found.

In 2008, Cassini detected a beam of energetic protons near Enceladus
aligned with the magnetic field and field-aligned electron beams. A
team of scientists analyzed the data and concluded the electron beams
had sufficient energy flux to generate a detectable level of auroral
emission at Saturn. A few weeks later, Cassini captured images of an
auroral footprint in Saturn's northern hemisphere. In 2009, a group
of Cassini scientists led by Donald Gurnett at the University of Iowa
in Iowa City detected more complementary signals near Enceladus
consistent with currents that travel from the moon to the top of
Saturn's atmosphere, including a hiss-like sound from the magnetic
connection. That paper was published in March in Geophysical Research Letters.

The water cloud above the Enceladus jets produces a massive, ionized
"plasma" cloud through its interactions with the magnetic bubble
around Saturn. This cloud disturbs the magnetic field lines. The
footprint appears to flicker in these new data, so the rate at which
Enceladus is spewing particles may vary.

"The new data are adding fuel to the fire of some long-standing
debates about this active little moon," said Abigail Rymer, the other
lead author of the Nature study and a Cassini team scientist based at
the Johns Hopkins University Applied Physics Laboratory in Laurel,
Md. "Scientists have been wondering whether the venting rate is
variable, and these new data suggest that it is."

The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. JPL manages the
mission for NASA's Science Mission Directorate in Washington.

To see a video and hear the sounds of the electrical connection, visit:

http://www.nasa.gov/cassini

Source: NASA

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