Neptune's Clouds Suddenly Disappeared; What Happened?

Neptune's clouds suddenly mysteriously vanished, and scientists suspect the incident is linked to the planet's solar cycle.

The disappearing clouds have been visible for the last three decades by the W.M. Keck Observatory in Maunakea, Hawaiian, and NASA's Hubble Space Telescope. The observatories have recently observed that the big blue planet's clouds have all but disappeared, except the ones at the south pole.

Neptune's Clouds Disappeared

The recent findings were published in the journal Icarus, and continued research showed a relationship between Neptune's disappearing clouds and the planet's solar cycle. This is a surprising development as it is the farthest major planet from our solar system's sun and only receives 1/900th of the sunlight that we do on our planet.

A team of astronomers from the University of California (UC) Berkeley led the discovery of the abundance of clouds that are normally seen at the planet's mid-latitudes starting to fade in 2019. In a statement, the study's senior author, Imke de Pater, said that he was surprised by the speed at which the clouds on Neptune disappeared, as per Phys.org.

A graduate student at Harvard University's Center for Astrophysics, Erandi Chavez, who led the study when she was an undergraduate astronomy student at UC Berkeley, said that even after four years, the images that they took in June showed that the clouds on Neptune have not yet returned to their former levels.

They added that the situation was extremely exciting and unexpected, particularly because the big blue planet's previous low cloud activity period was nowhere near as dramatic and prolonged.

Chavez and her team analyzed the images taken from 1994 to 2022 to monitor the evolution of the planet's appearance. They used the Keck Observatory's second-generation Near-Infrared Camera (NIRC2) paired with the equipment's adaptive optics system since 2002. They also analyzed observations from Lick Observatory, from 2018 to 2019, and the Hubble Space Telescope since 1994.

Correlation Between Solar Cycle and Neptune's Cloud Cover

De Pater and his team, when digging deeper into the phenomenon, theorized that the disappearance of the clouds on Neptune could have been affected by our sun's behavior during its 11-year-long activity cycle, according to Space.

Every cycle, the sun experiences a reset where its magnetic fields flip, which means that the north pole becomes the south pole and vice versa. This phenomenon occurs when the fields get tangled up increasingly, exerting increasing "tension" until it reaches its limit.

The team monitoring the situation found that the number of clouds on Neptune increased two years after the peak of our sun's solar cycle. The researchers later found a positive correlation between the number of clouds on the planet and the brightness from the sunlight reflecting off it.

De Pater noted that the data they have acquired provides the strongest evidence yet that Neptune's cloud cover is somehow affected by our sun's solar cycle. He added that the team's findings support the theory that UV rays, if they are strong enough, could trigger photochemical reactions that, in turn, produce Neptune's clouds, said NASA.