Exploration of Jupiter - Flyby Missions - Cassini (2000)

Cassini (2000)

In 2000, the Cassini probe, en route to Saturn, flew by Jupiter and provided some of the highest-resolution images ever taken of the planet. It made its closest approach on December 30, 2000, and made many scientific measurements. About 26,000 images of Jupiter were taken during the months-long flyby. It produced the most detailed global color portrait of Jupiter yet, in which the smallest visible features are approximately 60 km (37 mi) across.

A major finding of the flyby, announced on March 6, 2003, was of Jupiter's atmospheric circulation. Dark belts alternate with light zones in the atmosphere, and the zones, with their pale clouds, had previously been considered by scientists to be areas of upwelling air, partly because on Earth clouds tend to be formed by rising air. But analysis of Cassini imagery showed that the dark belts contain individual storm cells of upwelling bright-white clouds, too small to see from Earth. Anthony Del Genio of NASA's Goddard Institute for Space Studies said that "the belts must be the areas of net-rising atmospheric motion on Jupiter, the net motion in the zones has to be sinking".

Other atmospheric observations included a swirling dark oval of high atmospheric-haze, about the size of the Great Red Spot, near Jupiter's north pole. Infrared imagery revealed aspects of circulation near the poles, with bands of globe-encircling winds, with adjacent bands moving in opposite directions. The same announcement also discussed the nature of Jupiter's rings. Light scattering by particles in the rings showed the particles were irregularly shaped (rather than spherical) and likely originated as ejecta from micrometeorite impacts on Jupiter's moons, probably on Metis and Adrastea. On December 19, 2000, the Cassini spacecraft captured a very low resolution image of the moon Himalia, but it was too distant to show any surface details.