The unmanned Galileo spacecraft has captured stunning close-up pictures of Ganymede, providing the most detailed views ever of the stark planet-size moon that circles Jupiter.
"Nobody could have imagined what these look like: tremendous structure on the surface that is just about mind-boggling," Bill O'Neil, Galileo project manager, said Tuesday.NASA's Jet Propulsion Laboratory was to release mosaic views of Jupiter's largest companion Wednesday. Each high-resolution image is made up of four shots from a camera capable of capturing features as small as 33 feet.
Until now, scientists had only very remote views of Ganymede's terrain snapped by NASA's two Voyager spacecraft in 1979. All that changed as Galileo passed within 524 miles of the giant moon on June 26.
Astronomers have been aiming their telescopes at Ganymede since Italian astronomer Galileo Galilei spotted it through his lens in 1610. At three-quarters the size of Mars, Ganymede is the largest moon in the solar system. Its 3,269-mile diameter nearly equals the distance from California to Bermuda. Earth's moon is 2,155 miles across.
Scientists believe Ganymede's ridges, icy grooves and craters hint at an Earthlike crust that pulls apart and fills in with flowing rock. Galileo's observations will help test theories that a huge mantle of water and ice covers a rock core.
The pictures were taken on the first of Galileo's four Ganymede flybys. The encounter was a highlight of Galileo's two-year tour of Jupiter and the planet's four major moons: Ganymede, Europa, Io and Callisto.
Galileo, fitted with 10 scientific instruments, went into orbit in December around Jupiter, the solar system's largest planet.
O'Neil, who has steered the mission through a series of setbacks since its 1989 launch, remains optimistic despite new glitches.
One instrument automatically shut down before last month's Ganymede encounter. Although the energetic particles detector appears to be working again, scientists missed several days of readings on high-energy particles in Jupiter's radiation belt.
In addition, O'Neil said that scientists recently discovered that another instrument, the Near Infrared Mapping Spectrometer, was working erratically days after the Ganymede flyby. The glitch could have ruined some long-range observations of other Jupiter moons.
Investigators don't expect to know much more before week's end.