Scientists explain why Uranus and Neptune are different colors

The Hubble Space Telescope shows that the haze on Uranus makes it paler than Neptune and that the dark spots are caused by a second cloud.

Astronomers may be able to explain why Neptune and Uranus are different colors. Researchers have developed a single atmospheric model that matches the observations of both planets. The model shows that the haze on Uranus builds up in the stagnant atmosphere and makes it appear lighter than Neptune. The model shows the presence of a second, deeper layer that can be seen in the Great Dark Spot, which was observed by Voyager 2 in 1989.

Neptune and Uranus have the same mass, size, and atmospheric compositions, but their appearance is different. Astronomers have an explanation for why Neptune has a bluer color than Uranus.

A new research shows that a layer of haze on both planets is thicker than a similar layer on Neptune. If there was no haze in the atmospheres of Neptune and Uranus, both would be blue.

The model that led to this conclusion was developed by the international team led by Patrick Irwin, Professor of Planetary Physics at Oxford University. The appearance of the atmosphere at specific wavelength was the focus of previous investigations. This new model matches observations from both planets across a wide range of wavelength simultaneously. The new model includes haze particles at deeper layers that had been thought to only contain methane and hydrogen sulfide ices.

This is the first model to simultaneously fit observations of reflected sunlight from the ultraviolet to the near-IR wavelength.

The team has a model with three layers of aerosols. The middle layer is a layer of haze particles that is thicker on Uranus than on Neptune. The team suspects that on both planets, methane ice condenses onto the particles in this layer, pulling the particles deeper into the atmosphere in a shower of methane snow. The team believes that Neptune has a more efficient atmosphere than Uranus because Neptune has a more active, turbulent atmosphere. The haze layer on Neptune is thinner than it is on Uranus, making it bluer.

Mike Wong, an astronomer at the University of California, Berkeley, and a member of the team behind this result, said they hoped that developing this model would help them understand clouds and hazes in the ice giant atmospheres.

The model was created by analyzing a set of observations of the planets taken with the NASA/ESA Hubble Space Telescope.

The model helps explain the dark spots on Neptune and Uranus. Astronomers were aware of the presence of dark spots in the atmospheres of both planets, but they didn't know which aerosol layer was causing them or why the aerosols at those layers were less reflective. The dark spots seen on Neptune and occasionally on Uranus are the result of a darkening of the particles in the deepest layer of the model.

More information: P.G.J. Irwin et al, Hazy blue worlds: A holistic aerosol model for Uranus and Neptune, including Dark Spots, Journal of Geophysical Research: Planets (2022). DOI: 10.1029/2022JE007189. Journal information: Journal of Geophysical Research: Planets Citation: Scientists explain why Uranus and Neptune are different colors (2022, May 31) retrieved 31 May 2022 from https://phys.org/news/2022-05-scientists-uranus-neptune.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.