PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
 
PHOTO CAPTION                                     July 17, 1996
                                                  P-47109 color

The mottled face of Jupiter's volcanically active moon Io [pronounced
"EYE-oh" or "EE-OH"], viewed by the camera onboard NASA's Galileo
spacecraft, shows dramatic changes since it was seen 17 years ago by the
exploratory NASA spacecraft Voyagers 1 and 2. This Galileo image, taken on
June 25, 1996 at a range of 2.24 million kilometers (1.4 million miles), is
centered on the Media Regio area and shows details of the volcanic regions
and colored deposits that characterize Io. North is at the top of the
picture and the Sun illuminates the surface from the east (right). The
smallest features that can be discerned here are approximately 23 kilometers
(14 miles) in size, a resolution comparable to the best Voyager images of
this face of Io.

Io's surface is covered with volcanic deposits that are thought to contain
ordinary silicate rock, along with various sulfur-rich compounds that give
the satellite its distinctive color. In the brighter areas the surface is
coated with frosts of sulfur dioxide. Dark areas are regions of current or
recent volcanic activity. Planetary scientists say many changes are evident
in the surface markings since this region of Io was imaged 17 years ago by
the Voyager spacecraft. The bright regions near the eastern limb of the moon
are much more prominent in the Galileo images than they were previously.
Surface details have also changed dramatically in the vicinity of the
eruptive volcano Masubi (the large, predominantly white feature seen near
the 6 o'clock position in this view). Masubi was discovered as an active
volcano during the Voyager encounters of Io in 1979.