Radio map unveils ammonia gas in Jupiter's atmosphere

Astronomers have produced the most detailed radio map yet of the atmosphere of Jupiter, unveiling massive movement of ammonia gas under the colourful bands, spots and whirling clouds visible to the naked eye.

The University of California, Berkeley (UC Berkeley) researchers used the upgraded Karl G Jansky Very Large Array in New Mexico to measure radio emissions from Jupiter's atmosphere in wavelength bands where clouds are transparent.

They were able to see as deep as 100 kilometres below the cloud tops, a largely unexplored region where clouds form.

The planet's thermal radio emissions are partially absorbed by ammonia gas. Based on the amount of absorption, the researchers could determine how much ammonia is present and at what depth.

By studying these regions of the planet's atmosphere, astronomers hope to learn how global circulation and cloud formation are driven by Jupiter's powerful internal heat source.

These studies also will shed light on similar processes occurring on other giant planets in our solar system and on newly discovered giant exoplanets around distant stars.

"We, in essence, created a three-dimensional picture of ammonia gas in Jupiter's atmosphere, which reveals upward and downward motions within the turbulent atmosphere," said Imke de Pater, a professor at UC Berkeley.

The radio map shows ammonia-rich gases rising into and forming the upper cloud layers: an ammonium hydrosulfide cloud at a temperature near minus 73 degrees Celsius and an ammonia-ice cloud in about minus 113 degrees Celsius. These clouds are easily seen from Earth by optical telescopes.

Conversely, the radio maps show ammonia-poor air sinking into the planet, similar to how dry air descends from above the cloud layers on Earth.

The map also shows that hotspots -- so-called because they appear bright in radio and thermal infrared images -- are ammonia-poor regions that encircle the planet like a belt just north of the equator.

Between these hotspots are ammonia-rich upwellings that bring ammonia from deeper in the planet.

"With radio, we can peer through the clouds and see that those hotspots are interleaved with plumes of ammonia rising from deep in the planet, tracing the vertical undulations of an equatorial wave system," said Michael Wong of UC Berkeley.

The final maps have the best spatial resolution ever achieved in a radio map: 1,300 kilometres, researchers said.

"We now see high ammonia levels like those detected by Galileo from over 100 kilometres deep, where the pressure is about eight times Earth's atmospheric pressure, all the way up to the cloud condensation levels," de Pater said.

The observations are being reported just a month before the July 4 arrival at Jupiter of NASA's Juno spacecraft, which plans, in part, to measure the amount of water in the deep atmosphere where the Very Large Array looked for ammonia.

The study was published in the journal Science.