Free Astronomy Magazine

49 JULY-AUGUST 2022 ASTRO PUBLISHING A stronomers may now understand why the similar planets Uranus and Neptune are different colors. Using observa- tions from the Gemini North telescope, the NASA Infrared Tele- scope Facility, and the Hubble Space Telescope, researchers have developed a single atmospheric model that matches ob- servations of both planets. The model reveals that excess haze on Uranus builds up in the planet’s stagnant, sluggish atmos- phere and makes it appear a lighter tone than Neptune. [Im- ages and Videos: International Gemini Observatory/NOIRLab/ NSF/AURA/J. da Silva/NASA /JPL-Caltech /B. Jónsson, J. Pollard, E. Mastroianni, ESA/Hubble, M.Kornmesser. Image Processing: M. Zamani (NSF’s NOIRLab). Music: Stellardrone − Airglow] Planetary Physics at Oxford Univer- sity, developed to describe aerosol layers in the atmospheres of Nep- tune and Uranus. Previous investi- gations of these planets’ upper atmospheres had focused on the appearance of the atmosphere at only specific wavelengths. However, this new model, consisting of mul- tiple atmospheric layers, matches observations from both planets across a wide range of wave- lengths. The new model also in- cludes haze particles within deeper layers that had previ- ously been thought to contain only clouds of methane and hydrogen sulfide ices. “This is the first model to si- multaneously fit observa- tions of reflected sunlight from ultraviolet to near-in- frared wavelengths,” ex- plained Irwin, who is the lead author of a paper pre- senting this result in the Journal of Geophysical Re- search : Planets. “It’s also the first to explain the difference in visible color between Uranus and Neptune.” The team’s model consists of three layers of aerosols at different heights. The key layer that affects the colors is the middle layer, which is a layer of haze particles (referred to in the paper as the Aerosol-2 layer) that is thicker on Uranus than on Neptune. The team suspects