Postcards from Jupiter: New Aurora Details Seen

March 8, 2001


Guy Webster/Jet Propulsion Laboratory (818) 354-6278

Robert Brown/for University of Michigan (919) 791-2081

Bright auroras on parts of Jupiter where those shimmering
glows have not previously been seen appear in new images taken
from NASA's Hubble Space Telescope by University of Michigan

The images come from a joint study in December 2000 and
January 2001 using both the Earth-orbiting Hubble and NASA's
Cassini spacecraft, currently near Jupiter, to examine how
Jupiter's aurora is affected by the solar wind, an outbound
flow of particles from the Sun.

Jupiter's aurora

For higher resolution image, click here.

QuickTime movie, click here.

The new pictures of Jupiter's aurora are also available online
from NASA's Jet Propulsion Laboratory, Pasadena, Calif, at:

or from the University of Michigan, Ann Arbor, at: .

"I've been observing Jupiter's aurora for 22 years and
these images have provided an enormous amount of new and
interesting data," said Dr. John T. Clarke, senior research
scientist at the University of Michigan's College of
Engineering and principal investigator for the Hubble
observations. "We've just begun to study the data and have
already found some new features, including bright aurora in
places we've never seen them before."

While Hubble observes the aurora, a team of Cassini
scientists led by University of Michigan's Dr. David Young,
principal investigator for the Cassini plasma spectrometer
instrument is measuring variations in the solar wind that
might be causing the auroral fluctuations. "We know from
earlier data that the solar wind has some control over the
aurora, but this is the first chance we've had to study the
connection up close," Young said. By learning more about
Jupiter's aurora, scientists hope to gain better understanding
of how Earth's aurora behaves and of ways the two planets

Like Earth's aurora, often called the northern lights or
southern lights, Jupiter's auroral glows occur at high
latitudes. They frequently appear as ovals encircling
Jupiter's magnetic poles. At both planets, auroras are useful
indicators of conditions in the magnetic field surrounding the
planet, since particles steered by the magnetic field toward
the planet's poles are what stimulate the glow. In that
sense, the aurora serves a TV screen displaying what's
happening in the magnetic field. The axis of Jupiter's
magnetic field is tilted from Jupiter's axis of rotation, so
the auroral ovals seem to wobble around the rotational poles
as the planet turns. One newly observed phenomenon is a series
of fast fluctuations in brightness inside the southern oval,
previously seen only in the north. These are known as "polar
cap flares."

The new images also capture a distinct brightening inside
the northern oval over the portion of the planet rotating
toward the Sun. "We see the main oval, then all of a sudden we
see a curtain of auroral emission start up on the dawn side,
just poleward of the auroral oval," said University of
Michgan's Dr. Hunter Waite, team leader for one of Cassini's
scientific instruments and a co-investigator for the Hubble
observations. Jupiter's "dawn storms" resemble certain auroral
storms on Earth in that they persist for hours, but differ
from them by appearing on the planet's dawn flank, instead of
its night side.

Researchers are studying features of the aurora and
examining possible relationships to how the solar wind affects
Jupiter's magnetosphere, a vast environment of charged
particles surrounding the planet under the influence of
Jupiter's magnetic field. Just as Earth's auroras are
triggered by disturbances in Earth's magnetic fields, auroras
on Jupiter are linked to that planet's much greater magnetic

"We have collected more data in two weeks than we've
amassed in several years." Waite said. "This new data helps us
determine if our theories about how the aurora behaves are on

During a second phase of the joint study, after Cassini
had passed Jupiter, Cassini took nightside pictures while
Hubble captured dayside images. "It's a rare chance to view
Jupiter from two vantage points simultaneously," Waite said.
"As the planet rotates and the solar wind changes, we can
collect images and solar wind data without interruption.
That's something we've never been able to do before."

In addition to visible imagery, researchers collected
ultraviolet and infrared images of the planet. The project
involves collaboration between NASA's Goddard Space Flight
Center and several leading research universities, including
University of Michigan, University of Arizona, University of
Colorado and the California Institute of Technology.

"These joint observations are a welcome opportunity for
collaboration with Hubble", said JPL's Dr. Linda Spilker,
deputy project scientist for Cassini. "The ability to
understand and model Jupiter's aurora is clearly enhanced with
combined measurements from both Cassini and Hubble. The
combined data sets are more valuable than either data set

The Hubble Space Telescope is a project of international
cooperation between NASA and the European Space Agency (ESA).
It is managed for NASA by the Space Telescope Science
Institute, Baltimore, Md.

Additional information about Cassini-Huygens is online at

The Cassini spacecraft is scheduled to arrive at Saturn in July 2004 to
begin a four-year exploration of the ringed planet and its moons. The
Cassini mission is managed by NASA's Jet Propulsion Laboratory in Pasadena,
Calif., for NASA's Office of Space Science, Washington, D.C. JPL is a
division of the California Institute of Technology in Pasadena.

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