Aurora Glow

Jupiter Night-Side Auroras, North and South


February 5, 2001

Oval-shaped auroras glow in night-side areas near Jupiter's north and
south poles in these images taken by NASA's Cassini spacecraft on Jan. 13,
2001. The lower frame is the first to capture the southern aurora on the
planet's night side. Blue lines of longitude and latitude have been added
in each frame to indicate position of the glows.

Jupiter's auroral ovals are similar to Earth's auroras, often called the
northern lights or southern lights, although fluctuations in solar
activity play a more important role in the auroras at Earth than at
Jupiter. Energetic particles are constantly streaming towards Jupiter on
magnetic field lines that intersect the planet's atmosphere on a ring
around the magnetic pole. Where the energetic particles hit the upper
atmosphere, they cause emission of light, similar to the glow in a
fluorescent bulb. In the north (upper image), the magnetic pole is offset
from the rotational pole, which is where the blue longitude lines
converge, just to the left of the imaged area. The auroral oval appears
like a draped necklace that is carried around by the rotation of the
planet. In the south (lower image), the magnetic and rotational poles are
nearly coincident, so no significant offset is visible.

Cassini had passed its closest to Jupiter about two weeks before taking
these pictures, so it was in position to see the night side of the planet.
It was about 16.5 million kilometers (10.3 million miles) from the planet
and about 2.5 degrees below the plane of Jupiter's equator. The smallest
features visible are about 100 kilometers (about 60 miles) across. The
images were taken by Cassini's narrow-band camera through a filter
centered on a light-wave frequency at which hydrogen emits light when it
is excited. They have been processed to remove scattered light from the
overexposed sunlit crescent of the planet. Hydrogen is a major ingredient
of Jupiter's atmosphere.

It is not understood why the auroral oval rings are so thin. Cassini
images will help scientists figure out what brings about the narrow nature
and other features of the auroras, such as the break in the northern oval
visible in the upper image.

Cassini 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
mission for NASA's Office of Space Science, Washington, D.C.

Credit: NASA/JPL/University of Arizona

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