Uranus is pale blue, while Neptune is a much deeper shade of blue . Why this color difference? Currently, the only information scientists have is the data sent back from the Voyager 1 and 2 probes more than 30 years ago and from telescopes here on Earth and in orbit. Now scientists think they know the answer.
The reason lies, according to the team of researchers led by the University of Oxford (United Kingdom), in the fact that Uranus has a layer of haze in its atmosphere that is approximately twice the thickness of Neptune, which gives it a much darker color. more clear.
“This explains why Uranus is a paler blue color than Neptune,” says Patrick Irwin, lead author of the study.
Scientists have named this layer Aerosol-2 , and it would likely appear whitish at visible wavelengths . It serves to lighten the appearance of this planet, similar to how tracing paper makes more vibrant colors appear duller.
Using data from the Hubble Space Telescope and ground-based observatories, as well as information obtained from the Voyager 2 spacecraft, Patrick Irwin of the University of Oxford and colleagues have developed detailed models of the two worlds’ atmospheres that could explain the color difference.
The models showed that both planets have nearly equal atmospheric pressure and that both contain large amounts of hydrogen sulfide, ice and photochemicals. In the same way, both have a cloudy upper atmospheric layer with a lower pressure. The researchers suggest that the haze on both planets is produced by materials in the atmosphere being pushed up until they concentrate and methane condenses. Later, they turn into seeds that lead to the formation of flakes, which fall until their particles are released and used as part of the formation of new clouds.
In this approach, Uranus’ atmosphere would be thicker than Neptune’s, giving Neptune its much darker blue color. (The reason they’re both blue is because methane reflects blue light.)
“Since these particles were found to absorb UV, it would explain the observed lower UV reflectivity of Uranus and also explains why Uranus appears to have a paler blue color to the human eye than Neptune, since these particles are found to have a roughly white visible reflectivity spectrum, ” the researchers wrote in their paper.
Future observations will help answer more questions about these interesting icy worlds, experts say, and here the James Webb Space Telescope will have a lot to say. Observations of Neptune and Uranus are already planned during Webb’s first year of operation.
Referencia: Patrick G.J. Irwin et al, Hazy blue worlds: A holistic aerosol model for Uranus and Neptune, including Dark Spots. arXiv:2201.04516v1 [astro-ph.EP], arxiv.org/abs/2201.04516