On Thursday (Aug. 17), astronomers announced quite an unexpected update about one in all our solar system’s ice giants, Neptune: It will appear that the azure world’s clouds have all but disappeared.
Mainly, after images taken of the planet between the years 1994 and 2022, the team noticed an odd pattern starting in 2019. Across the planet’s mid-latitudes, cloud coverage looked as if it would start fading. Eventually, all evidence of clouds totally vanished.
“I used to be surprised by how quickly clouds disappeared on Neptune,” Imke de Pater, an emeritus professor of astronomy on the University of California, Berkeley and senior writer of a study on the findings, said in an announcement. “We essentially saw cloud activity drop inside just a few months.”
Intrigued by this discovery, de Pater and fellow researchers decided to dig deeper. And, sure enough, they got here up with a fairly fascinating explanation. It’s likely, the team suggests, that Neptune’s clouds are inextricably linked with the best way our sun behaves during its 11-year-long activity cycle.
What do you mean it is the sun’s fault?
The solar cycle, in essence, refers to the best way our host star’s magnetic fields change over the course of time — specifically, over 11 years.
Despite what it looks like, the sun is not exactly a blazing hot chunk of land. Slightly, it’s more of a large, orb-shaped ocean fabricated from charged particles, collectively often known as plasma, which suggests its structure can generally flow around and mold itself over time. Along side such movement, the sun’s magnetic fields, directly related to all those charged particles, get snarled.
As these fields get tangled, they exert an increasing number of “tension” on our host star, so to talk, until the yellow glowing ball cannot handle it anymore. Then, every 11 years, type of as a reset, the sun’s magnetic fields flip, meaning the north pole becomes the south pole and vice versa. From there, the saga repeats itself.
Related: NASA’s Latest Horizons will investigate Uranus from the rear (Neptune, too). Here’s the way you might help
During those 11 years, though, other kinds of things occur as a result of magnetic field alterations, too. As an illustration, magnetic-field knots can result in an increased number and intensity of solar flares, that are incredibly powerful ejections of radiation out into space. These flares can sometimes be so strong they even interfere with Earth-orbiting satellites. And so they’re often related to giant eruptions of solar plasma often known as coronal mass ejections, which might shower our planet with charged particles that create temporary mini-blips in communication lines.
But most significantly for the team’s Neptune evaluation, one phenomenon known to occur through the solar cycle is that the sun emits a bunch of ultraviolet radiation as its magnetic fields transition. Considering how utterly massive the sun is, that radiation type of “floods” the remainder of the solar system, because the researchers put it.
And naturally, it is easy to consider that this whole situation might affect a planet or two — including Neptune, regardless that the distant, windy planet sits some 2.8 billion miles (4.5 billion kilometers) from our beloved star.
Where does this leave Neptune?
To dissect where Neptune’s clouds have gone, the team gathered 30 years of stunning images of the planet taken by powerful observatories, including NASA’s Hubble Space Telescope and the W. M. Keck Observatory situated in Hawaii.
What they found was that there appeared to be a transparent correlation between the variety of clouds on Neptune and the purpose at which our sun’s solar cycle found itself. More specifically, roughly two years after the cycle’s peak — aka, the principal event of magnetic field flipping — Neptune exhibited some solid cloud coverage. It was only after that peak when the clouds appeared to fade away above the planet’s hydrogen, helium and methane atmosphere. (That methane content is what makes Neptune look so very blue).
Potentially, this implies the sun’s UV radiation — strongest at solar peak — could also be fostering a photochemical response, sparked by the absorption of energy in the shape of sunshine, to supply Neptune’s cloudy cap.
And possibly that response takes something like, say, two years to take effect? This is able to explain why, two years post-solar peak, the team witnessed Neptunian clouds galore.
“These remarkable data give us the strongest evidence yet that Neptune’s cloud cover correlates with the sun’s cycle,” de Pater said.
Moreover, the team saw that the more clouds there have been on this frozen blue world, the brighter it appeared to be, because there was more sunlight reflecting off those clouds.
“Potential correlations of variations in Neptune’s brightness with changing seasons and the solar activity cycle have been explored, but to this point no single cause has been identified,” the study authors wrote of their paper. “While seasonal effects are most probably vital for the slow gradual changes, secular variations in brightness will need to have a special origin.”
To get into just a few details, these results are all of the consequence of 2.5 cycles of cloud activity recorded over the three-decade-long period of Neptune observations the team laid out. And through this time, by way of that brightness finding, the researchers say that the planet’s “reflectivity” increased in 2002, dimmed in 2007, became vivid again in 2015, then darkened in 2020 — when the clouds looked as if it would have completely disappeared.
“Even now, 4 years later, essentially the most recent images we took this past June still show the clouds have not returned to their former levels,” Erandi Chavez, a graduate student on the Center for Astrophysics, Harvard-Smithsonian and study lead, said within the statement. “This is incredibly exciting and unexpected, especially since Neptune’s previous period of low cloud activity was not nearly as dramatic and prolonged.”
It’s actually quite striking that every one of those changes are clearly visible in the pictures provided by the team, further underlining the importance of maintaining observatories comparable to Keck and Hubble. “It’s fascinating to give you the option to make use of telescopes on Earth to check the climate of a world greater than 2.5 billion miles away from us,” Carlos Alvarez, an astronomer at Keck Observatory and co-author of the study, said within the statement.
In the long run, Alvarez and colleagues will proceed to observe Neptune’s cloud activity to see when these cirrus-shaped features are on the return. Actually, over the past couple of years, as solar UV rays have increased a bit, they have been seeing some cloud resurgence already.
“We have now seen more clouds in essentially the most recent Keck images that were taken through the same time NASA’s James Webb Space Telescope observed the planet,” de Pater said. “These clouds were particularly seen at northern latitudes and at high altitudes, as expected from the observed increase within the solar UV flux over the past roughly two years.”
Don’t fret, Neptune: Your clouds shall return in due time.
A paper on these findings is available within the November issue of the journal Icarus.