Lava flows on IoSource image: GIF (186K) TIF (820K)

Lava flows similar to those found in Hawaii are seen in the
black and white image at top, taken by NASA’s Galileo spacecraft.
It is one of the highest resolution images (7 meters or 23 feet
per picture element) ever obtained of Jupiter’s volcanic moon Io.
The two horizontal black stripes are places where data were lost
during transmission to Earth.

The image shows the textures of lava flows on the floor of
the caldera Chaac, which is shown in false color at lower
resolution (185 meters or 607 feet per pixel element) in the
bottom image. Calderas are depressions caused by collapse during
volcanic eruptions. The one shown here is approximately 100
kilometers (63 miles) long and 30 kilometers (19 miles) across.
Using shadow lengths from the new high-resolution observations,
the northeastern (upper right) scarp, or line of cliffs, has been
estimated to be 2.8 kilometers (9200 feet) high.

The lava flows are similar in texture to lava flows within
the caldera at Hawaii’s Kilauea volcano. This suggests that the
floor of Chaac has been covered by a combination of lava flows
and lava lakes.

The light-colored material surrounding the caldera may be
composed of sulfur-dioxide frost or some other sulfur-rich
material on the surface of Io. Galileo scientists believe that
the greenish color on the caldera floor is a form of contaminated
sulfur created when sulfur-rich material escaping from volcanic
vents reacts chemically with warm lava flows. The high-
resolution view shows numerous lava flows. The darkest flows are
thought to be the most recent because they have not been covered
by the sulfurous materials which coat most of Io’s surface.

The top image was acquired by Galileo on February 22, 2000.
It was taken at a distance of 600 kilometers (370 miles) and is
centered at 11.9 degrees north latitude and 157.6 degrees west
longitude. North is to the top, and the Sun illuminates the
surface from the right.

The color image was created by combining a black and white
image taken on February 22, 2000 at a distance of 18,800
kilometers (11,700 miles) from Io with lower-resolution (1.3
kilometers or 0.81 miles per picture element) color images taken
on July 3, 1999 at a distance of 130,000 kilometers (81,000
miles). The image is centered at 11.6 degrees north latitude and
157.7 degrees west longitude. North is to the top and the Sun
illuminates the surface from the left.

The Jet Propulsion Laboratory, Pasadena, CA manages the
Galileo mission for NASA’s Office of Space Science, Washington,
DC. JPL is a division of the California Institute of Technology,
Pasadena, CA.

This image and other images and data received from Galileo
are posted on the Galileo mission home page at . Background information and
educational context for the images can be found at .