False color image of Jupiter's great red spot, as seen by Galileo's camera using near-infrared filters.
NASA/JPL/Cornell University
Galileo, the first spacecraft to orbit any of the large planets beyond Mars, may have been the most delayed mission in NASA’s history. It was originally scheduled to launch in 1982, reach Jupiter three years later, and wrap up by 1987. But a series of setbacks with the space shuttle and Galileo’s attached booster rocket pushed the launch to 1989 and arrival to 1995.
Although the looping tour through the Jovian system was planned to end two years later, Galileo’s mission was extended twice so scientists could get closer pictures of Europa, with its iced-over ocean, and the other large satellites: Io, Ganymede, and Callisto. Finally, though, it came time to say goodbye. In September 2003, with hardly any maneuvering fuel left, Galileo ended its last orbit with a plunge into Jupiter’s atmosphere.
See the gallery below for a sampling of the spacecraft’s remarkable images.
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Tohil Mons, a 19,700-foot-high mountain, is at the center of this mosaic of images taken during Galileo’s close flyby of Io on October 16, 2001. One of the highest-resolution pictures taken during the six-year mission, the scene shows details measuring as little as 160 feet. Flanking the mountain are two paterae, or volcanic craters, with a web-like pattern of lava flows visible at the upper right. Galileo tried to take another round of pictures of Io in January, but the blistering radiation near Jupiter caused the spacecraft to shut down temporarily.
NASA
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Caught between the gravitational tugs of Jupiter and other moons, Io is racked by tidal forces that constantly squeeze and heat the crust, producing volcanoes—lots of them. The moon’s mottled coloring comes from different minerals erupting onto the surface.
NASA
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Jupiter’s turbulent atmosphere, as seen in natural color (top) and false color. At near-infrared wavelengths (above), the cloud layers appear more distinct. Bluish clouds are high and thin, reddish clouds are low, and white clouds are high and thick. This image of a “hotspot” near the equator covers an area about 21,100 by 6,800 miles. Galileo’s photos were the first to show different cloud layers on Jupiter.
NASA
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A remarkable closeup of Io, taken by Galileo last October, shows an eroded cliff (the amphitheater-shaped structure at the center) estimated to be 3,300 to 6,600 feet high. Material can be seen slumping in a southeast direction from the sharp edge of the cliff—the legacy of past erosion on a world where volcanism and lava flows continually rework the surface, so that most geological features are young.
NASA
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Shooting from a distance of 1.4 million miles, Galileo’s digital camera needed four frames to capture this elegant mosaic view of Jupiter’s thin ring system, made of dust particles. The pictures were taken in November 1996, when the spacecraft was in Jupiter’s shadow, looking back toward the sun. The arc at right is due to sunlight scattered by small particles in the planet’s atmosphere.
NASA
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When the spacecraft’s namesake, Galileo Galilei, first trained his telescope on Jupiter in 1610, he saw only four moons: Io, Europa, Ganymede, and Callisto (arranged in this artificial montage from top to bottom). Now astronomers count 39. Yet the objects of greatest interest continue to be the Galilean moons. Even Earth-based telescopes show the planet’s Great Red Spot, the most prominent storm on the planet. It has persisted for at least 300 years, with winds blowing counterclockwise around the center at 250 mph.
NASA
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The key pieces of evidence in nailing down the presence of an ocean on Europa were Galileo’s high-resolution pictures of “rafts” of ice that shift over time. The size and orientation of these rafts, which typically are miles across, suggest that they float on liquid or soft ice, then refreeze in a new place. The area shown here is about 21 by 26 miles.
NASA
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Even before Galileo arrived at Jupiter, scientists had speculated that a liquid ocean lies underneath Europa's cracked, icy crust. High-resolution photographs taken by Galileo in February 1997 all but settled the matter. The lines in this image are cracks in the ice where the surface has shifted—the reddish tint is a result of contaminants in the ice. Scientists have now advanced the argument from whether there is an ocean to how deep it lies, and whether life exists there. NASA is making long-term plans for a Europa orbiter to take the investigation further.
NASA
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Because Galileo had to cross through the asteroid belt on its way to the outer solar system, mission managers were able to chalk up another first. After years of guessing what the surface of an asteroid looks like, Galileo delivered to astronomers the first closeups of Gaspra (the smaller object) and Ida in October 1991 and August 1993, respectively. Both asteroids proved to be irregularly shaped rocks, and Galileo discovered a tiny moon, Dactyl, circling Ida. The 10-mile-long Gaspra was photographed from a distance of 3,300 miles, and the 35-mile-long Ida from around 2,200 miles.
NASA
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Galileo took this backward-glance photo of Earth and its moon from 3.9 million miles away, just eight days after the spacecraft made its second swing past Earth, in early December 1992.
NASA
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