Planets Uranus and Neptune almost the Same Color: Light Greenish-Blue

[lpetrich]

Neptune and Uranus seen in true colours for first time - BBC
Uranus and Neptune Reveal Their True Colors - The New York Times
noting
Modelling the seasonal cycle of Uranus’s colour and magnitude, and comparison with Neptune | Monthly Notices of the Royal Astronomical Society | Oxford Academic by Patrick GJ Irwin et al.

We may all be familiar with pictures of Uranus showing it light greenish-blue and Neptune showing it dark blue. But the latter picture was the result of image editing to make some clouds more easily visible, and PGJI et al. have reassessed the two planets' colors, finding them much alike.

BBC:

In the recent study, the researchers used data from the Hubble Space Telescope Imaging Spectrograph and the Multi Unit Spectroscopic Explorer on the European Southern Observatory's Very Large Telescope.

...
The analysis revealed that Uranus and Neptune are a similar shade of greenish blue, although researchers found a slight difference. Neptune has a slight hint of additional blue, which the model reveals to be because of a thinner haze layer on that planet.

The study also showed that Uranus appears a little greener during its summer and winter, when one of its poles is pointed towards the Sun. But during spring and autumn, when the Sun is over the equator, it has a bluer tinge.

NYT:

They also reviewed an immense observational record of both planets captured by Lowell Observatory in Arizona between 1950 and 2016.

The results confirm that Uranus is only slightly paler than Neptune, because of the thicker layer of aerosol haze that lightens its color.

The Lowell data set also shed new light on the mysterious color shifts that Uranus experiences over its extreme seasons.

For years, astronomers have puzzled over why Uranus is tinted green during its solstices but radiates a bluer glow at its equinoxes. The pattern is linked to Uranus’s odd position — tilted almost entirely on its side. Over the course of an 84-year orbit around the sun, Uranus’s poles are plunged into decades of perpetual light or darkness in the summers and winters, while the equatorial regions face the sun near the equinoxes.

Uranus’s shifting colors can be partly explained by atmospheric methane. Because methane absorbs red and green light, the equator ends up reflecting more blue light; by contrast, the poles, which have half as much methane, are tinted slightly green. The new study confirms this dynamic, and shows that a “hood” of ice particles coalesces over the sunlit poles of Uranian summer, boosting the greening effect.