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Jupiter's Poles Have Lightning, By Jove

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By WARREN E. LEARY, The New York Times

Published: October 13, 2007

WASHINGTON - The NASA spacecraft on the way to Pluto has discovered lightning in the polar regions of Jupiter, scientists said Tuesday. It also found that the volcanically active moon Io belches out tons of material that travels hundreds of millions of miles down Jupiter's long magnetic tail.

The spacecraft, New Horizons, was launched in January 2006 and made a close pass to Jupiter on Feb. 28 of this year to get a slingshot-like gravity boost designed to cut three years off its trip to Pluto, which it is to reach in July 2015.

New Horizons scientists took advantage of the trip around Jupiter to test the craft's seven scientific instruments and operational procedures in a trial run for Pluto, and said the exercise produced 700 separate observations that resulted in fundamental new discoveries.

'What we found blew a lot of people away,' said S. Alan Stern, the principal investigator for the mission and head of the Science Directorate of NASA.

Besides confirming and amplifying findings from seven previous spacecraft that have visited Jupiter, it produced unexpected knowledge about the planet's environment, Stern said.

'We had a great set of instruments and showed up at the right time to make some fascinating observations,' Stern said. 'The results add tremendously to our understanding of Jupiter and its moons, rings and magnetosphere.'

The New Horizons team last spring presented early results from the encounter, but revealed more-detailed analyses of its data recently at a meeting in Orlando of the Division for Planetary Sciences of the American Astronomical Society.

The results are detailed in Wednesday's issue of the journal Science.

Jupiter has lightning strikes near both poles, the team found, a phenomenon previously observed only on Earth. Six flashes in the north polar region and seven in the south suggest that the planet circulates and radiates its heat uniformly through water clouds.

New Horizons made the first close observations of the Little Red Spot, a swirling storm 70 percent as large as Earth that appeared several years ago. The storm, in the planet's atmosphere, is half as large as the centuries-old Great Red Spot.

On the moon Io, the closest to Jupiter, the spacecraft spotted 11 volcanic plumes, three of which were seen for the first time, the team said.

One was a 200-mile-high eruption rising above the volcano Tvashtar that showed how the ejection became visible as particles in the plume cooled.

New Horizons' global map of Io confirms the moon's status as the most active body in the solar system, researchers reported, showing more than 20 geological changes since the Galileo Jupiter orbiter provided the last close-up look in 2001.

Departing Jupiter, New Horizons flew down the huge magnetic tail formed by energized solar wind particles affecting the planet's powerful magnetic field. The spacecraft spotted fluxes of charged particles flowing hundreds of millions of miles beyond the planet and evidence that Io's volcanoes produce tons of material moving down the tail as large, dense blobs.

Project scientists also said the spacecraft captured the clearest images so far of the tenuous ring system around Jupiter. Although images showed the tiny inner moons Metis and Adrastea shepherding the materials around the thin rings, a search for smaller moonlets inside the rings, possible new sources of the dusty material they contain, found no bodies wider than a mile.

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