Home LATEST NEWS Haze makes Uranus paler than Neptune

Haze makes Uranus paler than Neptune


Uranus and Neptune are the most distant planets in the solar system (seventh and eighth), orbiting respectively 2.9 billion and 4.5 billion kilometers around our star. Two icy and little explored worlds – only a probe, Voyager 2, flew over them in the late 1980s.

Since then, thanks to terrestrial and space observatories, astronomers have learned to better understand these giants, both made of gas. They were able to observe great similarities in diameter (50,000 km each, i.e. five times more than the Earth), temperature (about -200°C), mass and composition of their atmospheres.

Illustration depicting the planet Uranus and its rings.

Illustration depicting the planet Uranus and its rings.

Photo: NASA

The presence of methane, a gas that absorbs infrared radiation, gives the two sisters this same bluish color, contrasting with the warm colors of Jupiter and Saturn, the two other gaseous planets of the solar system.

But at visible wavelengths, Neptune’s blue appears brighter than Uranus’, a difference astronomers struggled to explain until new research found a single cause.

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Published Tuesday in the Journal of Geophysical Research (JGR), they suggest the existence of an existing haze layer on both planets, but thicker on Uranus. What whitens the appearance of his complexion, explains to AFP Patrick Irwin, planetary scientist at Oxford University, lead author of the study.

To reach this conclusion, he and his team combined old data collected by Voyager 2 with more recent data from the Hubble and Gemini North telescopes (Hawaii). And they developed a model describing the different atmospheric layers of the ice giants, over a wide range of wavelengths (ultraviolet, visible and near-infrared) – previous research focused on specific wavelengths.

One such layer containing photochemical haze particles was found to be twice as thick on Uranus. These particles absorbing the Sun’s ultraviolet rays, they would be the cause of the lowest UV reflectivity observed on the planet. They would also explain this paler blue visible to the human eye, since these particles reflect on a visible spectrum close to whitedetails the study.

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As Neptune’s atmosphere is renewed more quickly, it would be more effective in driving out the layer of haze at the origin of Uranus’ pallor.

It is also in these atmospheric mists that the key to the mystery of the dark spots often visible on Neptune, more rarely on Uranus could reside.says Professor Irwin.

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