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Roses are red. Neptune is deep blue.
Why did scientists wonder, isn’t Uranus the same?
This is an intriguing question. The two outermost planets of our solar system, Uranus and Neptune, are both ice giants—cold worlds composed of part gas, part ice with similar chemical compositions.
Uranus is 15 times Earth’s and Neptune 17 times. And they’re both about four times the size of Earth, with Uranus slightly larger.
Yet the two worlds look decidedly different. Uranus first appeared with NASA’s transit Voyager 2 spacecraft In 1986, it is a featureless light blue blotch. When that same spacecraft encountered Neptune in 1989, it revealed a world with the strongest winds in the solar system, tearing apart a royal blue atmosphere. giant storms and even a mysterious dark spot. Why the difference?
Patrick Irwin, a planetary physicist at the University of Oxford, and his colleagues have now developed an answer. They put together a detailed understanding of each world’s atmosphere using the Gemini North telescope in Hawaii. Hubble space telescope and other observations.
Both worlds are blue because they have methane in their atmospheres, which absorbs the red color from sunlight. But a significant middle layer of methane haze on Uranus appeared to be twice as thick as the layer on Neptune. It is the presence of this additional haze that leads to different appearances.
Dr. “This haze is kind of whitish in appearance,” Irwin said. “This is why Uranus looks paler than Neptune.”
Research Published Tuesday Journal of Geophysical Research: Planets.
The finding makes sense, said planetary scientist Imke de Pater of the University of California at Berkeley. “The methane abundances on the two planets are very similar,” he said. “Something needs to explain the difference in color.”
The reason Uranus has a thicker layer of haze than Neptune may be the result of a giant impact early in its life that turned the planet sideways, says planetary scientist Leigh Fletcher of the University of Leicester in England. paper.
“All its internal energy and heat sources could have been released in this enormous collision,” he said. “So what you see today is a more stable world.”
Both worlds would lose haze as the methane ice pulled it into the lower atmosphere and fell as methane snow. But on the more active Neptune, methane snow falls more often, leading to a thinner layer of haze.
Erich Karkoschka, a planetary scientist at the University of Arizona, said he “wouldn’t make this assumption”, which explains why Uranus’ collision with another object explains why it is less active than Neptune. He suggested that worlds could be physically different enough to account for differences in their atmospheres.
Dr. Irwin said the study could also explain the origin of Neptune’s large and mysterious dark spots.
A future Uranus orbiter and atmospheric probe now top priority for NASA It will be released in the 2030s. This could give scientists more insight into the haze layers and James Webb Space Telescope.
Dr. “There’s 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 drop a probe into these deep atmospheres.”
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