Date: Thu, 17 Oct 1996 16:26:05 -0400
From: NASANews@luna.osf.hq.nasa.gov (NASA HQ Public Affairs Office)
To: press-release-net@venus.hq.nasa.gov
Subject: Hubble Follows Rapid Changes in Jupiter's Aurora
Don Savage
Headquarters, Washington, DC October 17, 1996
(Phone: 202/358-1547) EMBARGOED UNTIL: 4 P.M.(EDT)
Tammy Jones
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-5566)
Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone: 410/338-4514)
RELEASE: 96-210
HUBBLE FOLLOWS RAPID CHANGES IN JUPITER'S AURORA
Hubble Space Telescope's sharp view of the rapid,
spectacular dance of luminescent gasses high in Jupiter's
atmosphere -- better known as aurora -- is allowing
astronomers to map Jupiter's immense magnetic field and
better understand how it generates such phenomena.
"Now that we have pinpointed the general location of
the auroral curtains and have mapped their daily changes,
eventually we should be able to find out what causes the
aurora on Jupiter," said John T. Clarke, an astronomer at the
University of Michigan's College of Engineering.
The new Hubble observations simultaneously show warped
oval rings at the north and south poles (offset from
Jupiter's spin axis by 10-15 degrees), as well as an auroral
"footprint" created by a river of electrical current of about
one million amperes flowing between Jupiter and the volcanic
moon Io.
The Hubble images provide enough detail to allow
Clarke and his colleagues to record daily changes in the
auroras' intensity and motion. They find that changes in
brightness occur over the course of a Jovian day, perhaps due
to compression of Jupiter's magnetic field on the sun-facing
side of the planet. They also find emission features that
are fixed on the planet, co-rotating with it.
This global view is complemented by in situ
measurements of the magnetic field and charged particles by
the Galileo spacecraft, now orbiting Jupiter. By comparing
close-up and global views scientists expect to refine
theories about how Jupiter creates and maintains its
electrical, incandescent light shows.
The team of scientists, at the University of Michigan,
Ann Arbor, NASA's Jet Propulsion Laboratory, Pasadena, CA,
University of Wisconsin, Madison, and other institutions,
studied Jupiter's auroras for two years with the telescope's
Wide Field and Planetary Camera 2. Their results have led to
two papers, one first authored by Clarke and the other by
Gilda Ballester, also of the University of Michigan's College
of Engineering. Both papers appear in the October 18 issue of
Science. The images, taken in ultraviolet light, are the
most sensitive and sharply-detailed views of the auroras to
date. Previous observations of Jupiter's aurora have been
recorded by Hubble's Faint Object Camera and by ground-based
telescopes using near-infrared filters. Hubble sees
features as small as 186 miles across (300 kilometers). This
allows Clarke and his colleagues to watch small-scale, rapid
changes in the auroral pattern, map changes in both magnetic
poles, and pinpoint the effects of emissions from Io.
Auroras occur when charged particles (electrons,
protons, and positive ions) are captured in the magnetic
field surrounding a planet. Falling toward the magnetic north
and south poles, they collide with molecules and atoms in a
planet's upper atmosphere. The atoms become energized and
release the extra energy in the form of light, just as gas in
florescent and neon lights glows when an electric current is applied.
By studying images of Jupiter's entire disk, the
investigators found, surprisingly, the auroras mirror each
other at the north and south poles. Though Earth's auroras
at each pole also are carbon copies of each other, previous
spatially-unresolved observations and theories for Jupiter
suggested that some locations on the auroral ovals should be
brighter. That's because, in Jupiter's case, the magnetic
field has large asymmetries and more charged particles
trapped in the field could, under specific mechanisms,
eventually fall into the atmosphere at the weaker locations,
and would thus create a brighter light show.
A critical difference is that auroras on Earth are
triggered by a barrage of charged particles from the Sun.
This process is different on Jupiter, although not well
understood. Fundamentally, the planet's immense magnetic
field, coupled with its fast, 10-hour rotation, helps
generate auroras that are 1,000 times more powerful than
Earth's spectacular light shows.
The situation is complicated by material released by
Jupiter's moon, Io. Scientists believe that volcanic
eruptions on Io churn out particles that become ionized,
expand radially, and are trapped by Jupiter's immense
magnetic field. These charges are forced to co-rotate with
the planet, creating an immense sheet of current that in turn
modifies Jupiter's magnetic field. What has not been clear
on Jupiter is the balance of the internal processes versus
the Sun-driven processes, and how these processes produce the
auroral lights.
On Earth, magnetic storms are triggered by large
changes in the solar particles, producing very bright
auroras. These storms can disrupt radio signals and
communications systems, interfere with airplane navigation
and cause power outages. One storm in 1989 knocked out a
Quebec power station serving 9 million people. The team has
found that energetic auroral storms also occur on Jupiter,
but that these storms may be triggered instead by internal
processes.
Some of the material released by Io produces a fierce
current of charged particles. The particles become ionized
and are then drawn into Jupiter's intense magnetic field
along an invisible "flux tube," which bridges both worlds.
This creates small auroral spots just outside the ovals
around both magnetic poles. By studying changes in the
intensity of these spots, Clarke and his colleagues were able
to map Jupiter's magnetic field as Io orbits through it. The
scientists linked the spots to Io's "flux tube" because the
auroral emissions rotate with Jupiter while the spots remain
in a fixed location underneath Io.
"The size of the aurora at the magnetic footprint of
Io is 600 to 1,200 miles (1,000 to 2,000 kilometers) across,"
Clarke said. "If you were at Jupiter's cloud tops, under
Io's footprint, the aurora would fill the entire sky. You
would see an explosion as the gasses 250 miles above you
rapidly heated to more than 10,000 degrees Fahrenheit. The
aurora would speed overhead from east to west at more than
10,000 miles per hour (5 kilometers per second) because
Jupiter's fast rotation moves it rapidly underneath Io, which
orbits more slowly."
Clarke and his colleagues hope that future
observations will yield more information about the auroras.
The team is sharing data with the scientists operating the
Galileo spacecraft, which moves through Jupiter's magnetic
field repeatedly as it orbits the giant planet and surveys
the Galilean satellites. Galileo can record the type of
charged particles (ions, protons, electrons) in the field,
their location and energy. Information from Hubble and
Galileo is important because scientists can create a more
accurate picture of the charged particles which produce the
auroral lights, which eventually could lead them to its
source on Io.
The Space Telescope Science Institute is operated by
the Association of Universities for Research in Astronomy,
Inc., for NASA, under contract with the Goddard Space Flight
Center, Greenbelt, MD. The Hubble Space Telescope is a
project of international cooperation between NASA and the
European Space Agency.
- end -
EDITOR'S NOTE: An image accompanying this release is
available to news media by calling the Headquarters Imaging
Branch on 202/358-1900. Photo numbers are:
Color: 96-HC-679
B&W: 96-H-679
Image files in GIF and JPEG format and captions may be
accessed on Internet via anonymous ftp from ftp.stsci.edu in
/pubinfo.
GIF JPEG
PRC96-32 Jupiter Aurora gif/jupaur.gif jpeg/jupaur.jpg
Higher resolution digital versions (300 dpi JPEG) of the
release photograph will be available temporarily in
/pubinfo/hrtemp: 96-32.jpg (color) and 96-32bw.jpg
(black/white).
GIF and JPEG images, captions and press release text are
available via World Wide Web at:
http://www.stsci.edu/pubinfo/PR/96/32.html
and via links at:
http://www.stsci.edu/pubinfo/Latest.html
or
http://www.stsci.edu/pubinfo/Pictures.html
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