Spacecraft snaps close-ups of a lava flow on Io

The latest Galileo images of a lava flow in Io (top); calderas near Io's south pole (center); and the surface of Europa (bottom)

April 20, 2000
Web posted at: 11:07 AM EDT (1507 GMT)

By Richard Stenger
CNN Interactive Writer

PASDENA, California (CNN) -- Belching fissures, lava flows and sulfur frost dominate new high-resolution pictures of Io, obtained by the Galileo spacecraft during its closest flyby yet of the Jupiter moon.

The images help scientists understand the fiery volcanic activity on Io, which in many ways resembles geologic processes on Earth, said NASA scientists who released the images this week.

The top image captures lava flows on the floor of a caldera, or depression created by collapse during volcanic eruptions. They resemble volcanic lava flows in Hawaii, according to NASA's Jet Propulsion Laboratory, which manages the Galileo mission.

The light-colored material around the caldera could consist of sulfur-dioxide frost or some other sulfur-rich substance, JPL said.

The caldera is about 100 kilometers (63 miles) long and 30 kilometers (19 miles) wide. Galileo snapped this color enhanced picture in late February from a distance of only 600 kilometers (370 miles).

The second picture captures a region near Io's south pole. Three black spots are small calderas about 10-20 kilometers (6-12 miles) across. They are dark because recent lava flows cover their floors, said Duane Bindschadler, a Galileo mission scientist.

The whitish material concentrated near the cliffs could be sulfur-dioxide frost that forms through a dramatic vaporization process. Scientists theorize that liquid sulfur dioxide seeps out at the base of cliffs, vaporizes into a plume of gas, liquid and solid, and then condenses again on the surface.

The composite combines black and white images snapped in February from 34,000 kilometers (21,000 miles) and color images taken in July from about 130,000 kilometers (81,000 miles).

Europa's Jupiter face revealed

The new collection of images includes a picture of Europa, another jovian moon. The high-resolution snapshot is the best view ever of hemisphere facing Jupiter, according to Bindschadler.

The superimposed false-color image, obtained by Galileo's near-infrared mapping spectrometer instrument, reveals the presence of materials with differing compositions on Europa's surface.

The differences in surface matter suggest the presence of sulfuric acid, possibly from an underground ocean, according to NASA. "But there's not an agreement as to the exact materials," Bindschadler said.

"The surface is composed mainly of water ice. The trace material may reflect geologic events, like ice eruptions, that bring up materials underneath. It's analogous to magma on Earth," Bindschadler said. Galileo has orbited Jupiter and its moons since 1995. It has functioned well beyond its primary mission, which ended in 1997. Galileo will conduct joint observations with the Cassini spacecraft when it arrives in the system at the end of the year.

Io, slightly larger than Earth's moon, is Jupiter's third largest satellite. Europa is the fourth.

Galileo, Cassini to study Jupiter in joint expedition
March 9, 2000
Galileo images offer color-coded clues about Io
Roaming Galileo returns to heart of Jupiter system
February 1, 2000
Scientist: Jupiter radiation could mean life on Europa
January 28, 2000
Galileo returns closeups of volcanic Io
August 27, 1999

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