Jupiter's planet shows its true colors

Wildcat File Photo Arizona Daily Wildcat Photo Courtesy of Planetary Image Research Laboratory This view of Jupiter's moon, Io, in eclipse (left) was acquired while the moon was in Jupiter's shadow. Gases above the satellite's surface produced a ghostly glow which could be seen at visible wavelengths (red, green, and violet). The vivid colors, caused by collisions between the atmospheric gases and energetic charged particles trapped in Jupiter's magnetic field, have not previously been observed. The green and red emissions are probably produced by mechanisms similar to those at work in the polar regions of Earth. Bright blue glows mark the sites of dense plumes of volcanic vapor, and may be places where Io is electrically connected to Jupiter. The viewing geometry is shown in the image on the right. The images were taken May 31.

Paul Geissler, a UA lunar and planetary laboratory senior research associate, assembled the spectacular red, green and blue photo from three of 16 images taken by the Galileo spacecraft.

Geissler, who applied different filters to the black-and-white images, never expected to create such a brilliant display of colors.

"It is kind of eerie, unexpected to me," he said. "Io is glimmering away in the darkness - it's spooky, plus it's close to Halloween."

Geissler is an affiliate of the Galileo imaging team, which works on the Galileo camera, known as the Silicon Charge Coupled Device. The camera uses the same technology as in a camcorder and is one of 11 instruments on the unmanned spacecraft, he said.

The image was taken with red, green and violet filters originally used to find "hotspots."

Hotspots are dark areas that glow inside like hot coals in a barbecue, indicating presence of extraterrestrial volcanoes spewing lava.

Geissler said he expected to see the hotspots show up as red areas in the photo but never anticipated getting a full-color image.

"It is as if you're looking over Galileo's shoulder - the visible colors can be seen with the naked eye," Geissler said. "We shouldn't be able to see at green and blue wavelengths, only at the red wavelengths."

In the photo, the top and outer edges of the moon's surface appear red, while green glows near the center. Two bright blue spots are seen on Io's left and right sides.

"This is interesting because we don't know what causes the glow, yet we do know the wavelength (color)," Geissler said.

The blue glow is somehow related to the north and south poles of Jupiter, which generate a 400,000-volt electrical current, Geissler said.

The electricity excites surface gases such as sulfur dioxide, which glows like a fluorescent lamp. Sulfur dioxide, created from sulfuric acid spewed by volcanoes, is found in higher concentrations near the hotspots, he said.

Still, scientists don't understand why different areas glow different colors, Geissler said.

One reason may be that gas composition varies from one area of Io to another. Another may be that the gases are stimulated differently.

Although Io - slightly larger than the Earth's moon - always glows, the location of each color varies, he said.

"The unidentified optical emission is cool because it was previously unknown and it's a spectacular light show that is in constant change," Geissler said.

Irene Hsiao can be reached via e-mail at Irene.Hsiao@wildcat.arizona.edu.