Jupiter's raging thunderstorms a sign of 'global upheaval'
来源：未知 作者：法笥 时间：2019-02-26 11:16:00
By David Shiga (Image: NASA/IRTF/Zac Pujic) (Image: NASA/ESA/GCP-UPV/EHU) Towering storms more than 100 kilometres tall have been caught punching up through Jupiter’s cloud deck for the first time, thanks to a series of Hubble Space Telescope and ground-based observations. The rare storms – a sign of recent turmoil on the planet – are helping scientists deduce what lies hidden beneath the clouds that shroud the solar system’s largest planet. The Hubble Space Telescope captured the first of the two clouds by chance just as it was forming on 25 March 2007. A second, very similar cloud appeared just 9 hours later in an image taken by a team of amateur astronomers from the ground. Hubble, the Infrared Telescope Facility in Hawaii, US, and telescopes owned by a network of amateur astronomers called the International Outer Planet Watch then tracked the development of the clouds, and the observations are reported in a study led by Agustin Sanchez-Lavega of Universidad del Pais Vasco in Bilbao, Spain. Once they appeared, the two clouds grew horizontally to span about 2000 kilometres in a little more than a day, eventually reaching 4000 kilometres across – wider than the Moon – before disappearing in May. The clouds are similar to thunderstorm clouds on Earth, only much, much bigger, as Earth’s clouds grow to only 10 km in height, says Kunio Sayanagi of the University of Louisville in Kentucky, US, who is not a member of the team. “What they are seeing are the very tops of thunderstorms on Jupiter,” he told New Scientist. Such clouds probably come complete with lightning, which has been observed in smaller storms on Jupiter before, he says. The thunderstorm-like clouds are rare, and distinct from the larger hurricane-like storms on Jupiter, including the Great Red Spot, which is three times the width of Earth. The Great Red Spot has persisted for centuries, but the thunderstorm-like clouds are fleeting and rare – they have been spotted only twice before in 1990 and 1975. The new observations are the first to show the clouds in the process of forming and rising, revealing them in unprecedented detail. The two big storms appear to be the result of plumes of warm hydrogen gas rising from at least a few dozen kilometres below the cloud deck, according to the authors’ simulations. The plumes rose more than 120 kilometres, punching through the normal cloud deck to tower 30 kilometres above it. The bright white appearance of the clouds probably comes from icy particles made of frozen water and ammonia, materials dredged up from below, the study suggests. The storms appeared during a dramatic, planet-wide disturbance on Jupiter that is ongoing. The cause of the disturbance has yet to be explained, but it has changed the colour of some of the planet’s stripes. “It’s pretty clear that there’s a lot going on in Jupiter’s atmosphere right now – much more than usual – and these storms are probably tied in with that so-called global upheaval,” says co-author Imke de Pater of the University of California in Berkeley, US. The appearance of the two storms provides information on the atmosphere below the cloud deck, de Pater says. In order to successfully reproduce the appearance of the storms in simulations, the researchers had to set the amount of water vapour below the clouds to very high levels – about 300 times that measured by the Galileo spacecraft, which sent an entry probe into an unusually cloud-free region on Jupiter in 1995. The higher amount of water vapour agrees better with other studies of Jupiter’s chemical composition, which suggest the planet is enriched in elements heavier than hydrogen compared to the Sun. Nature (DOI: