Why Neptune and Uranus appear in different colors
Source: By The Indian Express
Neptune and Uranus have much in common — they have similar masses, sizes, and atmospheric compositions — yet their appearances are in different shades of blue. At visible wavelengths, Neptune is a rich, deep azure hue, while Uranus is a distinctly pale shade of cyan. Astronomers now have an explanation for why the two planets are different colours.
One reason why this difference had not been explained so far was the absence of similar data for comparison. Previous studies of the spectrum of each planet concentrated on individual wavelength regions. In the new comparison, researchers have developed a single atmospheric model that matches observations of both planets from the NASA/ESA Hubble Space Telescope, as well as the Gemini North telescope and the NASA Infrared Telescope Facility. The model shows that the haze around Uranus is thicker than that around Neptune, the researchers have reported in the Journal of Geophysical Research: Planets.
Uranus’s stagnant, sluggish atmosphere and makes it appear a lighter tone than Neptune. If there was no haze in the atmospheres of Neptune and Uranus, both would appear almost equally blue as a result of blue light being scattered in their atmospheres, a release on the ESA Hubble website explained.
The model leading to this conclusion describes three aerosol layers in the atmospheres of Neptune and Uranus. The key layer that affects the colours is the middle layer, which is a layer of haze particles that is thicker on Uranus than on Neptune. The team suggests that, on both planets, methane ice condenses onto the particles in this layer, pulling the particles deeper into the atmosphere. Because Neptune has a more active, turbulent atmosphere than Uranus does, the team believes Neptune’s atmosphere is more efficient at churning up methane particles into the haze layer. This removes more of the haze and keeps Neptune’s haze layer thinner than it is on Uranus, with the result that the blue colour of Neptune looks stronger.
