Think of Uranus and Neptune, the outermost planets in the solar system, and you can imagine two different shades: pale turquoise and cobalt blue. But the Astronomers say the true colors of these distant ice giants are more similar than their popular portraits.
Neptune is a little bluer than Uranus, but the difference is not as great as it appears in common images, according to a new study.
“There is a subtle difference in the blue hue between Uranus and Neptune, but subtle is the key word,” said Leigh Fletcher, a professor of planetary sciences at the University of Leicester in England, and an author of the study.
In the 1980s, NASA's Voyager 2 became the first (and still only) spacecraft to visit the two planets. Scientists at the time artificially enhanced the blue of images of Neptune taken by Voyager's cameras to highlight the planet's many curiosities, such as its south polar wave and dark spots. But to the human eye both Neptune and Uranus appear pale blue-green.
Enhanced images of Neptune often include captions addressing artificial color, but the concept of a deep blue planet has endured.
Patrick Irwin, a professor of planetary physics at the University of Oxford and an author of the study, and his colleagues used advanced instruments on the Hubble Space Telescope and the Very Large Telescope in Chile to resolve the colors of the planets as accurately as possible. They also reviewed an immense observation record of both planets captured by the Lowell Observatory in Arizona between 1950 and 2016.
The results confirm that Uranus is only slightly paler than Neptune, due to the thicker layer of aerosol haze that lightens its color.
Lowell's data also shed new light on a mystery that has baffled astronomers for years: why Uranus turns green during its solstices, but radiates a bluer glow at its equinoxes. The pattern is related to the strange position of Uranus—tilted almost completely 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.
Because atmospheric methane absorbs red and green light, the equator ends up reflecting more blue light; In contrast, the poles, which contain half as much methane, are tinted slightly green. The study confirms this dynamic and shows that a “hood” of ice particles forms over the poles during the Uranian summer, enhancing the green effect.
“I hope that for the public this paper can help undo decades of misinformation about Neptune's color,” said Heidi Hammel, an astronomer who worked on the Voyager imaging team in 1989 and is now vice president of the Association of Universities for the Research in Astronomy.
“There has never been an intention to deceive, but there has been an attempt to tell a story with these images by making them aesthetically pleasing to the eye so that people can enjoy these beautiful scenes in a way that, perhaps, is more meaningful than a amorphous, gray, blurry blur in the distance,” Fletcher said.
By: BECKY FERREIRA
THE NEW YORK TIMES
BBC-NEWS-SRC: http://www.nytsyn.com/subscribed/stories/7092500, IMPORTING DATE: 2024-01-31 03:22:03
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