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This Week on Galileo?
July 10 - 16, 2000

Galileo Continues to Return Data from February's Flyby of Io

The Galileo spacecraft continues to orbit Jupiter this week, returning science data acquired during a flyby of Io performed this past February. Data playback is interrupted once this week. On Thursday, the spacecraft performs standard maintenance on its tape recorder and propulsion systems.

Io is the most volcanically active body in our solar system. A little larger than Earth's moon, Io is the third largest of Jupiter's moons, and the fifth one in distance from the planet. Of the four largest of Jupiter's known 16 moons, Io is the closest to Jupiter. The largest four of Jupiter's moons are also known as the Galilean moons. Io is close enough to Jupiter that the huge planet causes tremendous tidal forces on the smaller, more volatile moon. The tidal forces can cause the surface to bulge up and down (or in and out) by as much as 100 meters (330 feet)! By comparison, typical ocean tides on Earth amount to only 2 meters (6.5 feet) between low and high tides, and this for water, not solid ground! The tides in the solid body of the Earth are much smaller still. This tidal pumping generates a tremendous amount of heat within Io, keeping much of its subsurface crust in molten form. The heat seeks any available escape route to relieve the pressure, causing volcanic plumes rise as high as 300 kilometers (190 miles) above the surface.

Two observations from the February flyby are transmitted to Earth this week. The observations were performed by the Solid-State Imaging camera (SSI) and the Near-Infrared Mapping Spectrometer (NIMS), but both observations focused on the same region of Io, the Amirani volcanic region. Previously known as Amirani-Maui, this region was originally thought to contain two separate volcanoes. Galileo data have shown that Maui is actually the leading edge of a lava flow that originates at the Amirani volcanic vents. The Amirani-Maui flow is more than 250 kilometers (160 miles) long and is one of the longest volcanic flows known to exist. The SSI observation consists of color imaging of the region, while NIMS returns spectral scans.

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