Pale blue and dark blue: how Uranus and Neptune got their colors – 06/01/2022 – The science

Roses are red. Neptune It is dark blue.

Because Uranus is not it? The scholars asked.

It’s an interesting question. Uranus and Neptune, the two outer planets in our solar system, are ice giants – cold worlds made of gas and ice, with similar chemical compositions.

They also do not differ much in mass, since Uranus is 15 times larger than the planet Earth and Neptune is 17 times larger. Both are roughly four times the size of Earth, and Uranus is slightly larger.

However, the two worlds look completely different. Uranus, as first revealed by a spacecraft Voyager 2 Give NASA In 1986, it was a pale blue bubble without special features.

When the same spacecraft encountered Neptune in 1989, it revealed a world with the strongest winds in the Solar System, riven through a true blue atmosphere, with giant storms and even a mysterious dark spot. Why the difference?

Patrick Irwin, a planetary physicist at the University of Oxford, in United kingdom, and his colleagues developed an answer. They collected detailed information about the world’s atmosphere using the Gemini North telescope in Hawaii Hubble Space Telescope And other notes.

The two planets are blue because they contain methane in their atmosphere, a gas that absorbs the red color of sunlight. But an intermediate layer of methane haze on Uranus appears to be twice as thick as Neptune’s layer. It is the presence of this additional fog that produces the various shapes.

“This fog looks kind of white,” Irwin said. “That’s why Uranus appears paler than Neptune.”

The research was published Tuesday in the Journal of Geophysical Research: Planets.

The finding makes sense, said Emke de Pater, a planetary scientist at the University of California, Berkeley. “The abundance of methane on the two planets is very similar,” she said. “Something should explain the color difference.”

Lee Fletcher, a planetary scientist at the University of Leicester in the UK and co-author of the study, said the reason Uranus has a thicker haze layer than Neptune’s may be the result of a giant impact early in its existence that upended the planet.

“All of its energy and internal heat sources could have been released in this huge impact,” he said. “So what we see today is a much more stagnant world.”

Both worlds will lose their fog as methane ice pulls it into the lower atmosphere, falling as methane ice. But on more active Neptune, methane snows fall more often, resulting in a thinner haze layer.

He “wouldn’t make that assumption,” said Eric Karkoschka, a planetary scientist at the University of Arizona, that the collision of Uranus with another object would explain why it was less energetic than Neptune. He suggested that the planets might be physically different enough to explain the differences in their atmospheres.

The work may also explain the origin of the vast, mysterious black spots on Neptune, Irwin said, which appear to be caused by the dimming of fog particles, possibly due to the evaporation of hydrogen sulfide ice.

The future atmospheric probe and the Uranus probe are a priority for NASA, scheduled for launch in 2030. They can reveal more to scientists about the layers of haze, as can observations using James Space Telescope web.

“There is still a lot of uncertainty,” Irwin said. “We don’t really know what the particles are made of. The only way to really know what’s going on is to launch a probe into these deep atmospheres.”

^{Translated by Luis Roberto M. Gonsalves}