Neptune's Clouds Will Decrease in the Years to Come

Saturday - August 19 2023, 10:09 UTC - 1 year ago

Neptune's cloud cover is decreasing due to the waxing and waning of the Sun's magnetic fields. This has been observed due to thirty years of archived data from the Hubble, Keck and Lick Observatories since 1972 and was confirmed by a University of California Berkeley team in 2019. Currently, the planet's cloud cover is sparse with clouds hovering mainly at the south pole.

Weather forecast for Neptune: After sunny weather for the past few Earth years, we’ll see increasingly more clouds over the next few years.

In 1989, NASA’s Voyager 2 spacecraft provided the first close-up images of linear, bright clouds, reminiscent of cirrus clouds on Earth, seen high in Neptune’s atmosphere. They form above most of the methane in Neptune’s atmosphere and reflect all colors of sunlight, which makes them white.

On that frozen frontier, the Sun is still influential regarding the Neptunian weather that produces cloud cover. At Neptune’s distance of nearly 3 billion miles, the Sun appears starlike at 1/30th the diameter of the full Moon. This feeble radiation is a mere 1% of the amount of starlight as received on Earth.

Yet the Sun’s influence on Neptune became increasingly obvious when astronomers looked at 30 years of Neptune observations with the Hubble and Keck telescopes. Neptune’s abundance of clouds waxes and wanes over an 11-years cycle. The Sun also has an 11-year cycle where it becomes stormy as its magnetic fields become entangled, increasing sunspot number and rate of violent outbursts.

Recent observations from the Hubble Space Telescope show that Neptune’s clouds are almost completely disappearing! Credit: NASA’s Goddard Space Flight Center .

Astronomers have uncovered a link between Neptune’s varying cloud abundance and the 11-year solar cycle, in which the waxing and waning of the Sun’s entangled magnetic fields drive solar activity.

This discovery stems from three decades of Neptune observations captured by NASA’s Hubble Space Telescope and the W. M. Keck Observatory in Hawaii, as well as data from the Lick Observatory in California.

The link between Neptune and solar activity is surprising to planetary scientists because Neptune is our solar system’s farthest major planet and receives sunlight with about 0.1% of the intensity Earth receives. Yet Neptune’s global cloudy weather seems to be driven by solar activity, and not the planet’s four seasons, which each last approximately 40 years.

Currently, Neptune’s cloud coverage is notably sparse, with the exception of some clouds hovering over the giant planet’s south pole. A University of California (UC) Berkeley-led team of astronomers discovered that the abundance of clouds normally seen at the icy giant’s mid-latitudes started to fade in 2019.

"I was surprised by how quickly clouds disappeared on Neptune," said Imke de Pater, emeritus professor of astronomy at UC Berkeley and senior author of the study. "We essentially saw cloud activity drop within a few months," she said.

"Even now, four years later, the most recent images we took this past June still show the clouds haven’t returned to their former levels," said Erandi Chavez, a graduate student at the Center for Astrophysics | Harvard-Smithsonian (CfA) in Cambridge, Massachusetts, who led the study when she was an undergraduate astronomy student at UC Berkeley. "This is extremely exciting and unexpected, especially since Neptune’s previous period of low cloud activity was not nearly as dramatic and prolonged." .

To monitor the evolution of Neptune’s appearance, Chavez and de Pater accumulated years of archive data from the Hubble and Keck telescopes and compared them to data from the Lick Observatory, a historical archive going back to 1972 when fish-eye photographs were taken of the giant planet.