Scientists say they have discovered new evidence that cloud activity on Neptune is linked to atmospheric changes on the planet caused by the sun.
Researchers say the evidence is based on observations collected by several telescopes over a period of nearly 30 years. Data was collected by the Hubble Space Telescope – operated by the American space agency NASA – as well as the W.M. Keck Observatory in Hawaii and the Lick Observatory in California.
Astronomers recorded atmospheric changes on Neptune as they examined the cloud data. The researchers found that the changes followed the sun’s natural cycle. Each natural cycle, known as the solar cycle, lasts about 11 years.
During this cycle, the sun’s magnetic field completely flips. This means the sun’s north and south magnetic poles change places. They then flip back after another 11 years. Before the flip, a major increase in solar activity happens. This can send powerful collections of solar particles shooting through space.
The scientists who examined the telescope data said they found that Neptune appeared brightest in 2002, then dimmed in 2007. The planet became bright again in 2015, but then darkened in 2020 to the dimmest level ever observed.
The team said the observations also showed Neptune lost nearly all of its clouds beginning in 2019.
Astronomers at the University of California, Berkeley (UC Berkeley) led the research. They recently reported their findings in a study in the publication Icarus.
Imke de Pater is a retired professor of astronomy at UC Berkeley and was the lead writer of the study. She said in a statement she was surprised by how quickly clouds disappeared on Neptune. She noted cloud activity had dropped sharply “within a few months.”
“Even four years later, the images we took this past June showed the clouds haven’t returned to their former levels,” said Erandi Chavez. She is a student at Harvard University’s Center for Astrophysics who took part in the study while at UC Berkeley.
“This is extremely exciting and unexpected,” Chavez said. She noted the finding was unusual “since Neptune’s previous period of low cloud activity was not nearly as dramatic and prolonged.”
Neptune, about four times wider than Earth, is the eighth and most distant major planet orbiting our sun, NASA says. It receives sunlight with only about 0.1 percent intensity of our planet. For this reason, the researchers found it surprising that Neptune would be heavily influenced by solar activity. The planet also receives intense winds that can blow around clouds.
The scientists looked at images captured by the different telescopes. They discovered clear patterns between seasonal changes in Neptune’s cloud cover and the solar cycle. The team found that during periods when the sun gave off more intense ultraviolet (UV) light, more clouds appeared on the planet two years later.
De Pater said the newly discovered data provides "the strongest evidence yet that Neptune's cloud cover correlates with the sun’s cycle." He added the findings "support the theory that the sun's UV rays, when strong enough, may be triggering a photochemical reaction that produces Neptune’s clouds." Photochemical is a term relating to how chemicals are affected by light.
The researchers are continuing to follow cloud activity on Neptune. They noted that the latest images taken of the planet, in June 2023, showed clouds started to return. The team says this finding further strengthens their evidence. This is because the scientists see a link between the increasing cloud cover and the release of intense UV light over the past two years.
The researchers say further study is needed to confirm their latest results. They say the research will be important not only for learning more about Neptune, but can also help scientists gain a better understanding of how similar planets outside our solar system behave.
I’m Bryan Lynn.
