Jupiter's "Jet Stream" Heated by Surface, Not Sun

Anne Minard
for National Geographic News
January 23, 2008
Jupiter's powerful weather jets—the giant planet's equivalent to Earth's jet stream—may be fired up by internal heat rather than radiation from the sun, a new study says.

A team of researchers found that Jupiter's jets seem to reach well beneath the visible cloud layer, which absorbs most of the sun's light. This suggests that the jets are being maintained by heat and winds near the surface of the planet itself.

The observations shed light on a longstanding debate over whether Jupiter's jets form in the "shallow" or "deep" atmosphere.

But the research could also unlock weather secrets on Earth, on other gas giants such as Saturn and Neptune, and even on Jupiter-like extrasolar planets that are being discovered at accelerated rates, the study authors say.

(Related: "First Proof of Wet "Hot Jupiter" Outside Solar System" [July 11, 2007].)

The research, led by Agustín Sánchez-Lavega from the Universidad del País Vasco in Spain, appears in tomorrow's issue of the journal Nature.

Eye on the Storm

Jupiter's jets—which are far more numerous and consistent than Earth's jet streams—dominate the circulation of the thick cloud layer that hides the interior.

What powers the jets and how they form vertical structures in the atmosphere, however, are "major open questions," the study authors note.

Scientists have proposed two basic models for the formation of the jets.

In the shallow scenario, the jets result from thunderstorms and other sun-driven events on the visible surface of the gas giant. In the deep scenario, Jupiter's internal heat drives the jets.

Opportunities to probe the jets are rare.

But in March of last year, major atmospheric turmoil hit Jupiter.

Using some of Earth's most technologically advanced cameras—the NASA/ESA Hubble Space Telescope, the NASA Infrared Telescope Facility in Hawaii, and telescopes in Spain's Canary Islands—scientists captured the closest-ever glimpse of the violent storms.

During the event, giant twin storms moved at speeds up to 370 miles (600 kilometers) an hour in Jupiter's middle northern latitudes.

"We saw the rapidly growing storm [go] from about 250 miles (400 kilometers) to more than 1,245 miles (2,000 kilometers) in size in less than one day," Sánchez-Lavega said.

(Related: "Lightning Strikes, Changing Climate Revealed on Jupiter" [October 9, 2007].)

Bright plumes turned out to be storm systems triggered in Jupiter's deep clouds. The systems moved up vigorously, injecting ammonia ice and water about 20 miles (30 kilometers) above the visible clouds that disturbed the jet.

Models of the 2007 event based on this data showed the jet stream extending deep in the atmosphere, more than 62 miles (100 kilometers) below the visible cloud tops, supporting the "deep" origin theory.

The findings support other—but tenuous—evidence for the "deep" theory.

For instance, NASA's Galileo Probe—which parachuted through Jupiter's atmosphere in 1995—measured strong winds just below the visible part of the atmosphere.

"[Our finding] confirms previous findings by the Galileo Probe when it descended through Jupiter's upper atmosphere in December 1995," Sánchez-Lavega said.

"All the evidence points to a deep extent for Jupiter's jets and suggest that the internal heat power source plays a significant role in generating the jet," he said.

"Patchwork" Approach

Adam Showman, a planetary scientist at the University of Arizona in Tucson, is not affiliated with the new study.

Showman's research, published in 2006 in the journal Icarus, showed that the jets could reach deeply regardless of their origin.

"Before about 2005, most people have assumed that if the jets extend deeper ... then they are powered by internal heat in Jupiter's interior," Showman said.

"Personally, I think that both shallow and deep processes are important in driving Jupiter's jets."

Sánchez-Lavega agrees that more observations and models will be the key to understanding Jupiter's jets—and March's giant storm.

The March 2007 storm shows surprising and unexplained similarities to events in 1975 and 1990, for instance, he and his co-authors note.

All three eruptions occurred with a periodic interval of about 15 to 17 years, and the storm has always erupted with exactly two plumes.

"Understanding this outbreak could be the key to unlock the mysteries buried in the deep Jovian atmosphere," they write.

Timothy Dowling, who directs the Comparative Planetology Lab at the University of Louisville, Kentucky, said the implications go even farther.

"Jupiter is the prototype for not only the other three gas giants in the solar system," he said, "but also the extrasolar gas-giants that are being discovered at a rapid rate."

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