Io and Red Spot
Photojournal: PIA02852
Published: December 16, 2004

This image taken by NASA's Cassini spacecraft on Dec. 1, 2000, shows
details of Jupiter's Great Red Spot and other features that were not
visible in images taken earlier, when Cassini was farther from Jupiter.

The picture is a color composite, with enhanced contrast, taken from a
distance of 28.6 million kilometers (17.8 million miles). It has a
resolution of 170 kilometers (106 miles) per pixel. Jupiter's closest
large moon, Io, is visible at left.

The edges of the Red Spot are cloudier with ammonia haze than the spot's
center is. The filamentary structure in the center appears to spiral
outward toward the edge. NASA's Galileo spacecraft has previously observed
the outer edges of the Red Spot to be rotating rapidly counterclockwise,
while the inner portion was rotating weakly in the opposite direction.
Whether the same is true now will be answered as Cassini gets closer to
Jupiter and interior cloud features become sharper. Cassini will make its
closest approach to Jupiter, at a distance of about 10 million kilometers
(6 million miles), on Dec. 30, 2000.

The Red Spot region has changed in one notable way over the years: In
images from NASA's Voyager and Galileo spacecraft, the area surrounding
the Red Spot is dark, indicating relatively cloud-free conditions. Now,
some bright white ammonia clouds have filled in the clearings. This
appears to be part of a general brightening of Jupiter's cloud features
during the past two decades.

Jupiter has four large moons and an array of tiny ones. In this picture,
Io is visible. The white and reddish colors on Io's surface are due to the
presence of different sulfurous materials while the black areas are due to
silicate rocks. Like the other large moons, Io always keeps the same
hemisphere facing Jupiter, called the sub-Jupiter hemisphere. The opposite
side, much of which we see here, is the anti-Jupiter hemisphere. Io has
more than 100 active volcanoes spewing very hot lava and giant plumes of
gas and dust. Its biggest plume, Pele, is near the bottom left edge of
Io's disk as seen here.

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.

For higher resolution, click here.


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