The first close-up observations from Nasa’s Juno spacecraft have captured towering clouds, swirling cyclones and dramatic flows of ammonia that drive giant weather systems on the largest planet in the solar system.

The $1.1bn probe swung into orbit around Jupiter in July last year on a mission to peer through the thick clouds that shroud the planet and learn how the alien world, and ultimately all of the planets in the solar system, formed around the nascent sun 4.5bn years ago.



“We were all jumping up and down with excitement when the images came down,” said Fran Bagenal, a planetary space physicist at the University of Colorado, who joined the Juno mission more than a decade ago. “You’ve got to be patient, but the rewards are fantastic.”



Once every 53 days the Juno spacecraft swings close to Jupiter, speeding over its clouds. In just two hours, the spacecraft travels from a perch over Jupiter’s north pole through its closest approach (perijove), then passes over the south pole on its way back out. Photograph: Credits: NASA/SWRI/MSSS/Gerald Eichstädt/Seán Doran

The spacecraft survived an almost six-year, 2.8bn km voyage across the depths of space to reach its destination, where it ducked beneath Jupiter’s intense radiation belts, turned on its suite of instruments, and swept into an orbit that loops over the planet’s north and south poles.



From 5,000km above the brown-orange blanket that covers the planet, Juno’s camera snapped pictures of tall, white storm clouds standing high above the rest. Some were so high, they stood out even on the nightside of the planet, betrayed by the feeble light of the sun glinting off them.



Yet more images revealed flashes of lightning that illuminate the Jovian sky. “The weather is dramatic,” said Bagenal. “What we thought we knew about Jupiter, we underestimated. It’s more variable, there are more features, there is much more detail the closer you look.”



Described as a “planet on steroids” by Scott Bolton, the mission’s principal investigator at the Southwest Research Institute in San Antonio, Jupiter is an enormous gas giant made from hydrogen and helium. Compared with Jupiter and the sun, the rest of the solar system is an afterthought. All of the other planets, the asteroids and comets, would fit within Jupiter, a planet 11 times wider than Earth.



Writing in two papers in the journal Science today, the Juno team describe fresh images and measurements of the planet’s atmosphere, magnetic field and the brilliant non-stop lightshows that constitute the aurorae at Jupiter’s poles.



An image of the North polar region of Jupiter. Photograph: MSSS/SwRI/JPL-Caltech/NASA

Its sensors peering down as it swooped around the planet, Juno spotted chaotic scenes with bright oval-shaped features swirling in the clouds. Time-lapse images revealed them to be enormous cyclones, rotating counter-clockwise in the northern hemisphere. The storms reached up to 1,400km wide, more than ten times the size of the largest cyclones on Earth. Deep inside the atmosphere, the scientists found evidence for what they called an “equatorial plume” – a massive and unexpected overturning of gas driven by a steady upward stream of ammonia from around the planet’s equator. It seems to mirror the Hadley cell convection currents on Earth, where warm air rises at the equator and falls again about 30 degrees to the north and south. But “It looks like a band that goes all the way round the middle of Jupiter,” said Bagenal. The question is where does it go down?”

Another instrument on Juno measured the magnetic field of the planet and found it to be twice as strong as scientists expected, at about ten times greater than the field that surrounds Earth. During observations of the planet’s intense aurorae, Juno detected streams of electrons hurtling down into Jupiter’s upper atmosphere, where they potentially power the spectacular light shows.



Over the coming months, Juno will build up an unprecedented map of the planet’s interior before its instruments succumb to the harsh radiation and the spacecraft plunges into the clouds at the end of its mission. Along for the ride are three Lego crew members: the Roman god Jupiter, his wife Juno, and a telescope-wielding Galileo, who discovered four of Jupiter’s 53 moons.



One mystery scientists are keen to clear up is whether Jupiter has a solid core. With more data from the orbiting Juno, it is a puzzle they hope to answer. “We’re having to put together this 3D puzzle,” Bagenal said. “And surprise, surprise, it isn’t like Earth.”

