Posted on 08/06/2004 12:03:51 PM PDT by ckilmer
Cassini Spacecraft Sees Saturn Lightning
Fri Aug 6,11:10 AM ET Add Science - AP to My Yahoo!
By JOHN ANTCZAK, Associated Press Writer
LOS ANGELES - The Cassini spacecraft's mission to Saturn has revealed a new radiation belt around the ringed planet and found that lightning in its atmosphere is occurring in different patterns than it did when NASA (news - web sites)'s Voyagers flew by in the early 1980s, scientists said.
AP Photo
AP Photo Slideshow: Cassini Saturn Mission
The discoveries announced Thursday are part of an early wave of information about the Saturn system from Cassini, which arrived June 30 on a $3.3 billion exploration expected to last four years.
"This is exactly the point of doing a mission like this," said Bill Kurth of the University of Iowa, the deputy principal investigator for Cassini's radio and plasma wave instrument, which detects "cracks" and "pops" from lightning like those that can be heard on an AM radio during a thunderstorm on Earth.
"Cassini now has evidence for changes in the thunderstorms that occur on Saturn over more than 20 years since we first started making measurements of these," Kurth said.
One difference is that lightning is occurring much more sporadically.
"Some days we see no lightning at all; other days we see evidence perhaps of more than one storm," Kurth said. "Back in the early 1980s on Voyager such storms were detected extremely regularly."
Another major difference is that the thunderstorms observed by Cassini are taking more time to rotate around the giant gas planet — about 10 hours and 45 minutes, compared to the 10 hours and five minutes in the 1980s.
Voyager scientists associated those storms with "superrotational clouds" near the equator, where a a high-velocity windstream can move them around Saturn faster than the planet itself rotates.
"The fact that Cassini is seeing a longer period suggests that the storms are coming from a higher latitude" where the winds don't move as fast, Kurth said.
Scientists suspect that the difference in the lightning patterns may be due to the difference in the way shadows from Saturn's rings are falling on the planet now, compared to in the early '80s.
Then, the sun was nearly on the same plane as the rings, and their shadow fell along a narrow band close to the equator. Now, the sun is illuminating the southern hemisphere and the rings' shadows are falling broadly across the northern hemisphere.
"They're no longer concentrated in one place and they're spread out over a large part of the planet," Kurth said.
The new radiation belt was discovered just above Saturn's cloud tops by a Cassini instrument, showing that the belts extend much closer to the planet than had been known.
Radiation belts are invisible, symmetrical, doughnut-shaped regions in space where high-energy ions and electrons are confined by a planet's magnetic field.
Over the long term, radiation belts have an important role in the evolution of a planet's atmosphere and any moons and orbiting gas and dust, said Donald G. Mitchell, a scientist for the magnetospheric imaging instrument, from Johns Hopkins University, in Laurel, Md.
Temperature and chemistry of a planet's upper atmosphere are also affected by radiation belts, he said.
Coolness bump.
Holy cow! They named a spacecraft for Oleg Cassini?
Did it record the thunder? New Zot Pictures!
"found that lightning in its atmosphere is occurring in different patterns than it did when NASA (news - web sites)'s Voyagers flew by in the early 1980s"
It's all Bush's fault!
It's all those SUV's on Saturn.
Yeah, I'm amazed they didn't name it after that war hero, John Kerry! /sarcasm off.
.
Not much use for a spacecraft which can only serve for four months.
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