Jupiter’s clouds are not made of ammonia ice

Astronomers have long thought that the upper clouds of Jupiter, which create the planet’s iconic pale brown belts, are made of frozen ammonia. But a new study, that brought together amateur and professional astronomers, has shown that these clouds are actually located lower in the atmosphere than we thought and are made of something completely different: most likely ammonium hydrosulphide mixed with smog.

Citizen scientist Steve Hill previously showed that he could map the planet’s atmosphere by using only specially coloured filters and his backyard telescope. These results provided initial clues that the clouds were too deep within Jupiter’s warm atmosphere to be consistent with clouds made of ammonia ice. To check, Hill joined forces with Patrick Irwin at Oxford University, whose team had previously used the sophisticated MUSE instrument on ESO’s Very Large Telescope (VLT) to study the atmosphere of gas giants.

MUSE is capable of scanning the atmosphere of Jupiter at different wavelengths, mapping out the different molecules that make up the planet’s atmosphere. This animated image, based on real MUSE data, shows how the gas giant looks at different wavelengths.

The new study shows that this new approach with backyard telescopes or VLT/MUSE can map the abundance of ammonia in Jupiter’s atmosphere with surprising accuracy. As for clouds, the team concluded that Jupiter’s atmosphere is much like a layered cake. Clouds of ammonium hydrosulphide cover the upper layers, but sometimes there may be a decoration of ammonia ice clouds, brought to the top by strong vertical convection. The entire cake’s structure, though, is not yet fully known, and the work of citizen scientists will be key to uncovering it. So next time you are looking at Jupiter or Saturn from your backyard, you may also be unravelling the secrets still lying within our Solar System.