Recent studies by astronomers and astronomy enthusiasts have challenged the traditional belief that the main component of the “brown clouds” in Jupiter’s atmosphere is ammonia ice. They suggest that these clouds may be composed of other substances.
In the past, astronomers estimated that Jupiter’s atmosphere is composed of 71% hydrogen, 24% helium, and various condensable gases. These gases may condense in Jupiter’s convective layer to form clouds of ammonia-water/ice and ammonium hydrosulfide (a compound of sulfur and ammonia gas).
Previous missions sending unmanned spacecraft to fly over Jupiter have yielded mostly unsatisfactory results. These spacecraft could only measure partial pressure data of Jupiter’s cloud layers and confirm that the “brown clouds” are not pure ice.
Dr. Steven Hill, a astrophysics PhD from the University of Colorado who works on space weather forecasting, used commercial telescopes and special spectral filters to observe Jupiter and process the data. He found that Jupiter’s cloud composition is likely not ammonia ice but a mixture of ammonium hydrosulfide and haze.
To verify Dr. Hill’s simple analysis method, Professor Patrick Irwin from the Department of Physics at the University of Oxford and his team used the Multi-Unit Spectroscopic Explorer (MUSE) on the European Southern Observatory Very Large Telescope in the Atacama Desert in Chile to detect light in the 600 to 680 nanometer range in Jupiter’s atmospheric clouds. This spectral range includes absorption bands for methane (619 nm) and ammonia (647 nm). After analyzing the data and simulating Jupiter’s atmosphere with computer models, they found that the cloud-top pressures in these Jupiter cloud regions are between 2-3 bars, much higher than the 0.7 bar needed for ammonia gas to condense into ice. The temperatures in the cloud layers were also higher than originally expected.
Based on these findings, they concluded that pure ammonia ice is unlikely to be the main component of Jupiter’s clouds, with ammonium hydrosulfide being more probable. The team explained that moist, ammonia-rich air rises to form ammonia ice at a much slower rate than the destruction or mixing of the ammonia gas with other substances. Therefore, Jupiter’s main cloud layer is most likely composed of a mixture of ammonium hydrosulfide and photochemical haze, resulting in the commonly observed “reddish-brown blotches.”
Researchers noted that although similar results were found in previous analyses of MUSE observations, these results were obtained through extremely complex methods that only a few groups worldwide were capable of performing, making them difficult to confirm.
The team emphasized that Dr. Hill’s method is not only highly reliable, simple, fast, and accurate but also easily verifiable, significantly reducing the complexity of computational costs. Additionally, this method allows astronomy enthusiasts to track changes in ammonia and cloud-top pressures in Jupiter’s atmosphere, including features like Jupiter’s belts, small storms, and the Great Red Spot.
Professor Irwin and his team also applied this method to observing Saturn’s atmosphere and obtained similar results indicating that the clouds in Saturn’s atmosphere are unlikely to be ammonia ice.
Professor Irwin commented to the University of Oxford’s press office, “I am amazed that such a simple method can detect the deeper layers of the atmosphere so clearly and prove that the cloud layers are not pure ammonia ice! These results show that an innovative amateur enthusiast using modern cameras and special filters has opened up a new window for understanding Jupiter’s mysterious cloud properties, aiding in our comprehension of how Jupiter’s cloud layers operate.”
Dr. Hill added, “I enjoy conducting physical measurements with ordinary commercial equipment because I hope to find new methods that allow amateur enthusiasts to make useful contributions to professional work. However, at the time, I did not expect this method to yield such effective results!”
John H. Rogers, a research co-author and research fellow at the Royal Astronomical Society, further noted, “A special advantage of this technique is that it allows amateur enthusiasts to connect changes in ammonia with observable weather changes on Jupiter. Because changes in ammonia likely represent weather on Jupiter.”
The research results from Professor Irwin’s team were officially published in early January in the journal “Journal of Geophysical Research.”