Imagine looking up and not seeing a single cloud in the sky.
Now, imagine that happening on Neptune, a planet known for its clouds!
For the first time in almost 30 years of watching, scientists have noticed that Neptune’s clouds have almost completely disappeared.
Researchers used the W. M. Keck Observatory in Hawaiʻi and NASA’s Hubble Space Telescope to study the big blue planet. From 1994 to 2022, they saw lots of clouds, but suddenly, almost all were gone except near the south pole.
What’s causing this? Scientists from the University of California (UC) Berkeley think it’s related to the sun’s activity.
This might sound odd because Neptune is so far away from the sun and gets very little sunlight. But the data suggests that when the sun is more active and gives off more ultraviolet (UV) light, Neptune gets cloudier.
Imke de Pater, a professor from UC Berkeley, was surprised at how fast the clouds vanished. “In just a few months, the cloud activity dropped a lot,” she said.
Four years later, they still haven’t fully come back. This is unusual because Neptune has had fewer clouds in the past, but not for this long or this few.
Erandi Chavez, who led the study, and her team looked at pictures of Neptune taken from 1994 to 2022. They noticed a pattern.
Neptune had more clouds when the sun was more active, and less when it was calm. This sun activity, called the solar cycle, changes about every 11 years.
The sun affects many things in our solar system, including the weather on distant Neptune. “Our data shows that Neptune’s clouds seem to be linked with the sun’s activity,” said de Pater.
“The sun’s UV rays might be causing a reaction that creates Neptune’s clouds.”
Over the past 29 years, Neptune’s brightness changed with the solar cycle. It was brighter (more clouds) in 2002, then dimmer (fewer clouds) in 2007, bright again in 2015, and very dim in 2020. That’s when most clouds disappeared. However, it’s not just the sun’s activity.
There are other factors, like storms on Neptune that aren’t related to the sun, that can affect its clouds.
Neptune is an interesting planet. It’s blue and has a chaotic atmosphere with very fast winds, faster than any other place in our solar system.
In 1989, NASA’s Voyager 2 spacecraft flew by Neptune and took pictures of a big storm called the “Great Dark Spot.” Since then, other big storms and spots have been seen.
Carlos Alvarez, who also worked on the study, said, “It’s amazing that we can use telescopes on Earth to study the weather on a planet billions of miles away.” The team will keep watching Neptune, especially since the recent images in 2023 showed some clouds coming back.
This study is not just about Neptune. By understanding how Neptune’s atmosphere works, scientists can also learn more about planets outside our solar system, called exoplanets.
In summary, something strange is happening on Neptune: its clouds are vanishing. And the sun, even from its great distance, might be the reason why!
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Source: W. M. Keck Observatory.
