Saturn gets more and more mysterious with each new discovery. Earlier this year, NASA scientists reported seeing UFOs in Saturn’s rings, which then appeared to be “torn” by something possibility flying out of the planet. Meanwhile, frequent discoveries made by the Cassini spacecraft keep hinting at the possibility of life on Saturn’s moons. Now, the planet itself is drawing the attention of astronomers and armchair scientists alike thanks to an unexplained phenomenon happening to one of Saturn’s most iconic and mysterious features.

According to NASA’s Jet Propulsion Laboratory, the massive hexagonal storm on Saturn has changed colors from blue to gold and astronomers have no explanation for it. A JPL press release states that the current hypothesis is that the change in the hexagon’s colors stems from “photochemical hazes” reacting to shifts in temperature as Saturn changes seasons:

[…] the change from a bluish color to a more golden hue may be due to the increased production of photochemical hazes in the atmosphere as the north pole approaches summer solstice in May 2017. Other effects, including changes in atmospheric circulation, could also be playing a role. Scientists think seasonally shifting patterns of solar heating probably influence the winds in the polar regions.

Saturn’s years last the equivalent of 29 Earth years, and the ringed planet’s seasons change only once every seven years. Since we have only been sending probes to observe Saturn close-up for a few decades, it’s plausible that the change in color is merely our first observation of a regularly recurring cycle.

Saturn’s hexagon was discovered in 1988 by the Voyager spacecraft but was not confirmed until almost thirty years later when the Cassini probe collected high-resolution photographs and data about the six-sided storm.

Scientists now believe the hexagon to be a type of hurricane-like storm kept in place by powerful jet currents in Saturn’s atmosphere. How the hexagon was originally formed still remains a mystery, however.