for National Geographic News
"Missing" moonlets, a huge volcanic eruption, and new maps of possible ocean ice are among the results of a recent flyby of Jupiter's moons.
The observations were made as NASA's New Horizons spacecraft whipped around the gas giant this past spring on its way to rendezvous with the dwarf planet Pluto in 2015.
(Read "NASA Probe Heads to Pluto" [January 19, 2006].)
Using Jupiter's gravity like a slingshot allowed New Horizons to shave years off its travel time to distant, icy Pluto.
The approach was also the first time a probe had been that close to Jupiter since the Galileo mission ended in September 2003.
Several teams of scientists used the opportunity to capture detailed images that allowed them to study different aspects of Jupiter.
Their findings appear in this week's issue of the journal Science.
No Tiny Moons
Perhaps the most surprising find for astronomers was an absence of tiny moonlets within the planet's rings.
Prior missions had revealed four small moons orbiting inside the orbit of the large moon Io.
The smallest of these are Adrastea, at 12 miles (20 kilometers) in diameter, and Metis, at 25 miles (40 kilometers) in diameter.
Earlier instruments weren't sensitive enough to spot moons much smaller than these. But scientists presumed that moonlets existed, because where there are big objects, there are usually lots of smaller ones.
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