Uranus and Neptune have colors closer than we imagined – 01/05/2024 – Science

A new study could change common sense regarding two planets in our Solar System. Neptune is normally imagined and represented with brighter blue colors; Uranus is considered more greenish. The reality is that the coloring of the two is very close, something like a greenish blue.

The research that reveals the proximity of the tones of these ice giants was published, this Friday (5), in the magazine Monthly Notices of the Royal Astronomical Society.

However, the colors we imagined for the planets to be incorrect is not a big surprise. The images of these planets obtained during the last century, such as those from NASA’s Voyager 2 mission, had been captured in different colors and, later, combined — which generated some inaccuracy in the result.

In the case of Neptune, an increase in contrast was also used to better observe its clouds. For experts, it could even be clear that this was an image far from reality, but this idea was apparently lost over time.

The authors of the new study then took data from the Hubble Space Telescope and the Muse instrument on the VLT (Very Large Telescope). In the images coming from each, each pixel is a continuous spectrum of colors, which helps to achieve a more realistic tone of the planets.

Scientists then reprocessed images from Hubble’s Voyager 2 and WFC3 (Wide Field Camera 3).

There is a slight color difference between the two planets. Neptune has a little more blue, due to a thinner layer of haze.

In addition to the issue related to Neptune, the study also seems to help clarify another point: the change in color of Uranus during the 84-year orbit it makes around the Sun.

Basically, at solstices Uranus appears greener, while at equinoxes, it appears bluer. The planet’s rotation is unusual, with an angle of almost 90° in relation to the plane of its orbit. This makes it appear to rotate sideways. Therefore, at the solstices of Uranus, the planet has one of its poles pointed towards the Sun and the Earth.

Using a model, scientists saw that the polar regions of Uranus are more reflective in green and red wavelengths, which, in part, must be related to methane, which absorbs red, which is less present at the poles.

Still using the model created, the scientists added a layer of ice fog, which has already been observed during the planet’s summer. It would be formed by methane ice particles. In the model, such particles increased the reflection of green and red in the polar regions of Uranus, which would explain the greener tones of the planet at the solstice.