Jupiter’s beautiful stripes move and morph from year to year. Giles Sparrow finds out how the Juno spacecraft revealed where these changes begin
Step out under the stars this month and you won’t be able to miss Jupiter. As well as being the largest planet in our Solar System, it is also at opposition this month, meaning it lies directly opposite the Sun as seen from Earth. That means the giant planet is not only visible all night but is also at its closest to us, giving backyard astronomers a great chance to observe its colourful cloud bands. These ever-changing patterns have fascinated sky-watchers for centuries, but now an international team of scientists say they’ve come a big step closer to understanding what drives their behaviour.
Jupiter is a bloated gas giant that could swallow 1,300 Earths, but it’s composed almost entirely of the lightweight gases hydrogen and helium. The uppermost layers of its deep atmosphere are wrapped in bands of cloud that run parallel to the planet’s bulging equator. Darker regions dominated by reddish, brown and blue clouds are called belts, while lighter, cream-coloured stripes are known as zones.
The striking colour differences between belts and zones are due to the way that various chemicals condense from gas into clouds of ice crystals or liquid droplets in different conditions.
The bright zones mark areas where gas is welling up from Jupiter’s interior, rising a few kilometres higher than their surroundings into colder, lower-pressure surroundings where crystals of ammonia ice can condense and form creamy-white clouds. The dark belts, in contrast, mark areas where gas is sinking deeper into the atmosphere, experiencing warmer temperatures and higher pressures. The clouds that condense in these conditions are made mostly from ammonium hydrosulphide, ammonium sulphide and water – although none of these chemicals can themselves explain the distinctive colours of the belts, which are probably due to a ‘soup’ of more elusive chemical compounds.
Jupiter can change its stripes
Alternating zones and belts form a series of stripes to the north and south of Jupiter’s equator, with each distinctive band named after the latitude where it resides. So the broad Equatorial
