Planets

Jupiter's Clouds Float On Waves of Ammonia

The discovery sets the stage for NASA's upcoming Juno mission, which will probe for water in the giant planet's atmosphere.

<p>NASA/ESA</p>

Beneath Jupiter's colorful bands, giant spots and swirling clouds lay giant waves of ammonia that rise and fall from deep within the planet's turbulent atmosphere, a new study shows.

The unprecedented global peek beneath Jupiter's clouds comes from the recently upgraded Very Large Array, a network of 27 radio telescopes in New Mexico.

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Previous attempts to study Jupiter's atmosphere have been hampered by the planet's rapid spin. Since a day on Jupiter lasts just 10 hours, conventional radio images, which take hours to produce, tend to smear.

The VLA upgrade, combined with a new data-processing technique, removed the smearing, allowing astronomers to make global measurements of the temperatures, pressures and motions of gases up to about 100 kilometers, or 62 miles, beneath Jupiter's clouds.

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"We in essence created a three-dimensional picture of ammonia gas in Jupiter's atmosphere," said astronomer Imke de Pater, with University of California, Berkeley.

By comparing the radar maps with visible-light images taken at nearly the same time, scientists have a better idea of the dynamics and structure of Jupiter's atmosphere.

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The radio map shows ammonia-rich gases rising into and forming the upper cloud layers, which consist of an ammonium hydrosulfide cloud at a temperature of about minus-100 degrees Fahrenheit and an ammonia-ice cloud at about minus-170 degrees.

The maps also reveal ammonia-poor air sinking into the planet and a belt of ammonia-poor "hot spots," which appear bright in radio and infrared images, located north of Jupiter's equator.

In between the spots are ammonia-rich plumes that swell up from deeper inside the planet.

The VLA radio map (top) of the region around the Great Red Spot in Jupiter's atmosphere shows complex upwellings and downwellings of ammonia gas that shape the colorful cloud layers seen in the approximately true-color Hubble Space Telescope map (bottom). | Radio image by Michael H. Wong, Imke de Pater (UC Berkeley), Robert J. Sault (Univ. Melbourne). Optical image by NASA, ESA, A.A. Simon (GSFC), M.H. Wong (UC Berkeley), and G.S. Orton (JPL-Caltech).

Jupiter's radiation blocks VLA from probing deeper in the atmosphere, a problem that won't affect NASA's Juno spacecraft, which is due to put itself into an unprecedented polar orbit around Jupiter on July 4.

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Juno will fly between Jupiter's radiation belts and its cloud tops. Scientists will be on the hunt for a layer of water that may be responsible the ammonia wave, the Great Red Spot and other structures in Jupiter's atmosphere.

Determining the amount of water in the atmosphere also will provide clues about where and how the giant planet formed.

"I was not surprised by the VLA results," Juno lead scientist Scott Bolton, wrote in an email to DNews. "The limits of what can be done by the VLA illustrate the reason for Juno."