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Storm clouds deeply rooted in Jupiter's atmosphere affect the white areas and colored belts of the planet, creating disturbances in their flow and even changing their color.
Thanks to the coordinated observations of the planet made in January 2017 by six ground-based optical and radio telescopes and the Hubble Space Telescope of NASA, a University of California at Berkeley, the astronomer and his colleagues were able to follow the effects of these storms – visible as luminous plumes above the ammoniacal ice clouds of the planet – on the belts in which they appear.
The observations will help planetary scientists to understand the complex atmospheric dynamics of Jupiter, which, with its large red spot and colorful stripes resembling layered cakes, makes it one of the most beautiful and changing gaseous giant planets in the world. solar system.
One of these feathers was noticed by amateur astronomer Phil Miles in Australia a few days before the first sightings of the Atma Large Large / Millimeter Array (ALMA) in Chile, and photos taken a week later by Hubble showed that the plume had generated a second plume. and left a disturbance downstream in the cloud band, the south equatorial belt. The rising plumes then interacted with the strong winds of Jupiter, which extended the clouds east and west from their point of origin.
Three months earlier, four bright spots were observed slightly north of the northern equatorial belt. Although these plumes disappeared in 2017, the belt has since widened to the north and its northern edge has changed color from white to orange-brown.
"If these plumes are vigorous and continue to have convective events, they can disrupt one of these bands over time, although it may take a few months," said study leader Imke de Pater, Professor Emeritus of Astronomy at the University of Berkeley. "With these observations, we see an ongoing plume and the after-effects of others."
The plume analysis confirms the claim that they are about 80 kilometers below the cloud top at a location dominated by clouds of liquid water. A document describing the results has been accepted for publication in the Official Journal. Astronomical Journal and is now online.
In the stratosphere
The atmosphere of Jupiter is mainly composed of hydrogen and helium, with traces of methane, ammonia, hydrogen sulphide and water. The highest cloud layer is composed of ammonia ice and includes brown belts and white areas that we see at the naked eye. Below this outer cloud layer is a layer of solid particles of ammonium hydrosulfide. Further still, about 80 kilometers under the upper cloud, is a layer of droplets of liquid water.
The storm clouds of Pater and his team revealed in the belts and zones a cloud of light and behaved like the cumulonimbus that precede the storms on Earth. The storm clouds of Jupiter, like those of Earth, are often accompanied by a lightning bolt.
However, optical observations can not see below the ammonia clouds. That's why, Pater and his team have explored radio telescopes, including ALMA, as well as the Very Large Array (VLA) in New Mexico, run by the National Science Foundation. National Observatory of Radioastronomy.
The first observations of Jupiter by the ALMA network took place from January 3 to 5, 2017, a few days after one of these luminous plumes was sighted by amateur astronomers of the southern equatorial belt of the planet. A week later, Hubble, the VLA, Gemini, Keck and Subaru observatories in Hawaii and the Very Large Telescope (VLT) in Chile captured images in the visible, radio and mid-infrared domains.
De Pater combined the ALMA radio observations with the other data, focusing specifically on the new storm as she was crossing the ammonia clouds of the upper deck.
The data showed that these storm clouds reached the tropopause – the coldest part of the atmosphere – where they spread a little like the anvil-like cumulonimbus that generates lightning and thunder on the Earth.
"Our ALMA observations are the first to show that high concentrations of ammonia are produced during an energy eruption," Pater said.
The observations correspond to a theory, called wet convection, on the formation of these plumes. According to this theory, convection brings a mixture of ammonia and water vapor high enough – about 80 kilometers below the top of the clouds – for the water to condense into liquid droplets. The condensation water releases heat that dilates the cloud and makes it rise quickly through other cloud layers, eventually piercing the ammonia ice clouds at the top of the atmosphere.
The momentum of the plume transports the ammonia cloud in supercooled over existing ammonia ice clouds until ammonia freezes, creating a white and bright plume that stands out from the colorful bands surrounding Jupiter.
"We were really lucky with these data because they were taken just days after amateur astronomers discovered a brilliant plume in the South Equatorial Belt," said de Pater. "With ALMA, we watched the whole planet and saw this plume .. Since ALMA probed under the cloudy layers, we could see what was going on beneath the clouds of ammonia."
Hubble took images one week after ALMA and captured two distinct light points, suggesting that the plumes originate from the same source and are transported east by the jet stream at high altitude, resulting in big disturbances in the belt.
Coincidentally, three months earlier, bright plumes had been observed north of the northern equatorial belt. The observations of January 2017 showed that the width of the belt was widened and that the band where the plumes had been seen had turned from white to orange. De Pater suspects that the northward expansion of the northern equatorial belt is a result of gas from plumes depleted of ammonia that fall back into the deeper atmosphere.
The colleague and co-author of De Pater, Robert Sault of the University of Melbourne in Australia, used special computer software to analyze ALMA data in order to obtain radio maps of the surface comparable to the photos taken by Hubble in visible light.
"Jupiter's rotation every 10 hours usually makes radio maps blurry because it takes hours to observe them," said Sault. "In addition, because of Jupiter's large size, we had to" scan "the planet to create a large mosaic at the end.We developed a technique to build a complete map of the planet."
The VLT data was provided by Leigh Fletcher and Padraig Donnelly from the University of Leicester in the UK, while Glenn Orton and James Sinclair from the Jet Propulsion Laboratory in California and Yasuma Kasaba from the University of Tokyo in Japan. provided the SUBARU data. Gordon Bjoraker of NASA's Goddard Space Flight Center in Maryland and Máté Ádámkovics of Clemson University in South Carolina analyzed Keck's data.
The work was supported by a NASA Global Astronomy Award (NNX14AJ43G) and a Solar System Observations Award (80NSSC18K1001).
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