All of Neptune's clouds have mysteriously disappeared, and the sun may be to blame

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The disappearance of the gas giant's clouds is tied to the sun's 11-year cycle.

An artist's illustration of Neptune, with faint streaks of wispy white clouds.
An artist's illustration of Neptune, with faint streaks of wispy white clouds. (Image credit: Getty Images)

All of Neptune's clouds have vanished, and scientists think the sun is to blame.

The disappearance of the wispy, white strands of frozen methane that usually streak Neptune's azure face has been linked to changes in ultraviolet (UV) radiation as the sun's activity climbs to an 11-year maximum.

The sun's activity rises and falls in 11-year cycles, but recently, the sun has been far more active than expected, with sunspot appearances nearly double the number predicted by the National Oceanic and Atmospheric Administration's Space Weather Prediction Center. Scientists anticipate that the sun's activity, initially thought to reach its maximum in 2025, could peak as soon as the end of this year. 

Astronomers have pegged the loss of cloud cover to the effects of sunlight hitting Neptune's atmosphere. By analyzing data collected by the Hubble Space Telescope, the Keck Observatory in Hawaii, and the Lick Observatory in California, astronomers observed that, following a two-year delay, peaks in the sun's activity generate more cloud cover over Neptune, while lows cause it to dissipate.

What, exactly, is causing the change isn't known for certain. The most likely explanation is that UV light from the sun starts chemical reactions in Neptune's upper atmosphere, ultimately creating the clouds.

"It's fascinating to be able to use telescopes on Earth to study the climate of a world more than 2.5 billion miles away from us," study co-author Carlos Alvarez, a staff astronomer at the Keck Observatory, said in the statement. "Advances in technology and observations have enabled us to constrain Neptune's atmospheric models, which are key to understanding the correlation between the ice giant's climate and the solar cycle."

Ben Turner
Ben Turner
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Ben Turner is a U.K. based writer and editor at Live Science. He covers physics and astronomy, tech and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess.