Lightning Strikes, Changing Climate Revealed on Jupiter

Anne Minard
for National Geographic News
October 9, 2007
A quick flyby of Jupiter by NASA's New Horizons probe has yielded the most detailed glimpse yet of the weather on the gas giant.

Images sent back from New Horizons earlier this year show stormy features similar to Earth's, including lightning on both of Jupiter's poles.

The images suggest the storms are caused by the heat from the planet itself, rather than the sun, and are maintained by circulation patterns that could be global in scale.

Perhaps even more important, Jupiter's weather appears to be different than it was when NASA probes last visited the gas giant, experts say.

"Jupiter has changed," said Dennis Reuter of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

"There's been a whole environmental change on this massive planet since Voyager and Galileo were there [in 1979 and 2003, respectively]."

Reuter is the lead author of one of several studies on Jupiter that appear in this week's issue of the journal Science.

Mysterious Disturbance

Astronomers have observed lightning on other planets before, but until now polar lightning was only known to happen on Earth.

In a few brief exposures taken by New Horizons' cameras, lightning was shown to strike about every other second at Jupiter's poles.

(See related photo: "Jupiter Auroras 'Northern Lights on Steroids'" [March 30, 2007].)

A study of the images led by Kevin Baines at Caltech's Jet Propulsion Laboratory (JPL) showed roughly equal amounts of lightning in the planet's northern and southern hemispheres.

This countered a prevailing theory that lightning was more common in Jupiter's northern region.

Overall similarities in the lightning at the poles and at the equator suggest that internal heat is driving the storm systems, the study authors wrote.

Something on the planet is generating atmospheric waves like those that flow out from a disturbance on the surface of a pond, Reuter, of NASA's Goddard Center, said.

What's causing the disturbance remains a mystery for now.

"On Earth you see these [circulation patterns] over mountain ranges," he said. "As air flows over, it goes high and sinks back down again. On Jupiter there's no surface to do that."

Reuter said he hopes a full analysis of New Horizons' data will reveal what's causing the circulation patterns.

Jupiter's Climate Change

Meanwhile, the study led by Baines at JPL found that cloud cover on Jupiter has thinned significantly since the Cassini-Huygens probe made its flyby in 2000.

That means climate on the gas giant varies over the long term, possibly seasonally.

New Horizons also captured images of fresh ammonia clouds. Reuter's team studied these images and found that storms that were bringing ammonia up from lower in the atmosphere.

"We were lucky enough to watch a full storm develop," Reuter said.

While the results from both studies provide tantalizing new insights into Jupiter's atmosphere, they raise questions that will remain unanswered indefinitely.

Adam Burrows, an astronomer at the University of Arizona in Tucson, called the results interesting but "not epochal."

"It would be wonderful if this mission could have loitered around Jupiter," he said. "It's a pity that they can't really follow up."

Long Gone

By now New Horizons is long gone from Jupiter, on its way to Pluto and the Kuiper Belt, a region of the solar system beyond the major planets.

(See an interactive map of the solar system.)

The mission is NASA's fastest to date, with the probe expected to reach Pluto by 2015.

(Read about New Horizons' mission.)

Scientists see the Jupiter flyby as a test for what's in store at Pluto, since the probe was designed to peer at planets floating in near-darkness.

"These instruments will be used to study Pluto for the first time," Burrows pointed out. "And they seem to work."

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