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 has shown that these clouds are actually located lower in the atmosphere than we thought and are made of ammonium hydrosulfide mixed with smog.
Hubble’s photo of Jupiter displays the ever-changing landscape of its turbulent atmosphere. Image credit: NASA / ESA / Hubble / Amy Simon, NASA’s Goddard Space Flight Center / Michael H. Wong, University of California, Berkeley / Joseph DePasquale, STScI.
Citizen scientist Steve Hill previously showed that he could map the planet’s atmosphere by using only specially colored 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 and a team of professional astronomers from the University of Oxford, the University of Leicester and British Astronomical Association used the 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,” they said.
Their study shows that the new approach with backyard telescopes or VLT/MUSE can map the abundance of ammonia in Jupiter’s atmosphere with surprising accuracy.
As for clouds, they concluded that Jupiter’s atmosphere is much like a layered cake.
Clouds of ammonium hydrosulfide 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 unraveling the secrets still lying within our Solar System.
“We test the reliability of the filter-imaging technique by applying it to VLT/MUSE observations of Jupiter and show that the method yields surprisingly reliable results that agree closely with more sophisticated analyses of these observations, and which are also consistent with observations made at microwave wavelengths by NASA’s Juno spacecraft and the Very Large Array,” the astronomers said.
“We show that the main level of reflection at red wavelengths is from the 2-3 bar level, which is well beneath the expected ammonia ice cloud condensation level at 0.7 bar, and conclude that ammonia ice cannot be the main cloud constituent.”
“We also show that the same technique can be applied to MUSE observations of Saturn and find that ammonia maps extracted agree very well with the ammonia abundance determined by NASA’s Cassini spacecraft and the NASA/ESA/CSA James Webb Space Telescope at pressures greater than 2 bar.”
The findings appear in the Journal of Geophysical Research: Planets.
_____
Patrick G.J. Irwin et al. 2025. Clouds and Ammonia in the Atmospheres of Jupiter and Saturn Determined From a Band-Depth Analysis of VLT/MUSE Observations. JGR Planets 130 (1): e2024JE008622; doi: 10.1029/2024JE008622
