A massive amount of ammonia gas lies beneath the colourful clouds on Jupiter, astronomers have revealed, a discovery coming just a month prior to the arrival of NASA’s Juno spacecraft at the planet on July 4.
Using the Karl G. Jansky Very Large Array in New Mexico, the researchers from University of California-Berkeley measured radio emissions from Jupiter’s atmosphere in wavelength bands where clouds are transparent.
The observers were able to see as deep as 100 km below the cloud tops, a largely unexplored region where clouds form.
Jupiter’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.
“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 principal author Imke de Pater, a UC Berkeley professor of astronomy.
The map bears a striking resemblance to visible-light images taken by amateur astronomers and the Hubble Space Telescope.
The study will shed light on similar processes occuring on other giant planets in our solar system and on newly-discovered giant exoplanets around distant stars.
The radio map shows ammonia-rich gases rising into and forming the upper cloud layers.
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 UC Berkeley research astronomer Michael Wong.
The observations were reported in the journal Science at a time when NASA’s Juno spacecraft plans, in part, to measure the amount of water in the deep atmosphere where the Very Large Array looked for ammonia.
“Maps like ours can help put their data into the bigger picture of what’s happening in Jupiter’s atmosphere,” de Pater noted.