Scientists can finally explain why Neptune is bluer than Uranus

Neptune and Uranus are solar system neighbours with a lot in common, including similar masses, diameters, and atmospheric compositions. However, Neptune appears to be bluer than Uranus. According to new study lead by Professor Patric Irwin of the University of Oxford’s Department of Physics, the varying tints of blue are caused by a hazy layer that exists on both worlds. Both planets would appear blue if it weren’t for the smog.

The Hubble Space Telescope, the NASA Infrared Telescope Facility, and the Gemini North telescope were utilised by a group of worldwide researchers to study aerosol layers in the atmospheres of both planets.

“This is the first model to fit reflected sunlight observations from ultraviolet to near-infrared wavelengths at the same time.” In a press release, Irwin, the lead author of the article published in the Journal of Geophysical Research: Planets, said, “It’s also the first to explain the difference in visible colour between Uranus and Neptune.”

In the atmospheres of Neptune and Uranus, the team’s model anticipates three haze layers at varying heights. On Uranus, the middle layer of haze particles is said to be thicker than on Neptune.

Methane ice condenses on haze particles in the middle layer, forming a methane snow shower that drags haze particles deeper into the atmosphere. The haze particles can then stimulate the formation of hydrogen sulphide ice, resulting in a distinct, deeper layer of haze.

The atmosphere of Neptune is more active and turbulent than that of Uran, implying that the former is better at churning up gaseous methane into the haze layer, where it can condense on the haze particles and make this snow. This removes more haze and maintains Neptune’s haze layer thinner, giving Neptune a bluer appearance. The extra haze on Uranus accumulates and gives the planet a softer tone.

The investigation also revealed the presence of a second, deeper layer in the model, which, when darkened, might explain the dark areas seen on Neptune and Uranus on rare occasions. The black patches on both planets were already known to astronomers, but scientists didn’t know which haze layer was creating them.