NASA's Galileo spacecraft acquired its highest
resolution images of Jupiter's volcanic moon Io on July
3, 1999 during its closest pass by Io since it entered
orbit around Jupiter in December 1995. This color
mosaic uses the near-infrared, green and violet filters
(slightly more than the visible range) of the spacecraft's
camera, processed to enhance more subtle color
variations. Most of Io's surface has pastel colors,
punctuated by black, brown, green, orange, and red
areas near the active volcanic centers.
The improved resolution reveals small-scale color
areas which were not recognized previously and which
suggest that the lava and sulfurous deposits are
composed of complex mixtures (close-up A). Some of
the bright, whitish,
high-latitude (near the top and bottom) deposits have an
ethereal quality like a transparent covering of frost
(close-up B). Bright red areas were seen in previous
images only as diffuse deposits. However, they now
appear as both
diffuse deposits and sharp linear features like fissures
(close-up C). Some volcanic centers have bright and
colorful flows, perhaps due to flows of sulfur
(rather than silicate) lava (close-up D). In this region of
Io, bright, white material
can also be seen to emanate from linear rifts and cliffs.
Comparison of this mosaic to previous Galileo images
reveals many changes due to ongoing volcanic activity.
Galileo is scheduled to make two close passes of Io in
October and November.
Most of the high-resolution targets for these flybys are
seen on the hemisphere shown here.
North is to the top of the picture, and the Sun illuminates
the surface from almost directly behind the spacecraft.
This illumination is good for imaging color variations,
but poor for imaging topographic shading. However,
some topographic shading can be seen here due to the
combination of relatively high resolution (1.3 kilometers
or 0.8 miles per picture element) and rugged
topography over parts of Io. The mosaic is centered at
0.3 degrees north latitude and 137.5 degrees west
longitude. The images were taken at a distance of
about 130,000 kilometers (81,000 miles) by Galileo's
onboard solid state imaging camera.
Image produced by: Moses Milazzo,
Planetary Image Research Lab. (PIRL), Lunar and Planetary Lab. (LPL),
University of Arizona
The Jet Propulsion Laboratory, a division of the California Institute of
Technology in Pasadena, manages the Galileo mission for NASA's
Office of Space Science, Washington, D.C. Additional information about
Galileo and its discoveries is available on the Galileo mission
home page at http://galileo.jpl.nasa.gov/.
Background information and educational context for the images can be found at
http://galileo.jpl.nasa.gov/images/io/ioimages.html.
NASA's Planetary Photojournal PIA-02319
August 27, 1999