Neptune, a frigid planet decorated with supersonic storms, has been visited by only one spacecraft, Voyager 2, which zipped by in 1989. Consequently, little is definitively known about the planet, including the nature of its eccentric hydrocarbon clouds.

Until another robotic envoy pops over to greet Neptune, astronomers must rely on telescopes to decode its secrets. Interested in the nearly-naked status of the ice giant, a team led by Erandi Chavez, a graduate student now at the Harvard-Smithsonian Center for Astrophysics, set to work.

The researchers combined images taken by Hubble, the Keck Observatory in Hawaii and the Lick Observatory in California to create a 29-year photo album of Neptune going back to 1994. Then, they compared it with the sun’s cycles.

The sun goes through cycles of hyperactivity and tranquility, lasting from eight to 14 years, that are driven by the repeated inversion of the sun’s magnetic field. These cycles seem to rise and fall in sync with Neptune’s cloud cover. In 2002 and 2015, for example, Neptune showcased myriad clouds, hot on the heels of peak solar activity on both occasions. It’s thought that the bombardment of ultraviolet light triggers an alchemic, cloud-making reaction in the planet’s ethereal skies.

Conversely, during the sun’s nadir, Neptune’s vaporous veil fades away — although it isn’t known why the current dearth of clouds is so extreme compared with previous cycles.