It’s definitely shrinking, but no one knows why. (NASA/ESA)

Storms on Earth are worsening amid global warming, but it’s a different story on Jupiter. The humanless planet’s trademark red spot — a giant windstorm — has shrunk to the smallest size ever measured.

“We have no reason why this storm should’ve lasted as long as it did. That’s one of the big mysteries,” said Amy Simon, who studies planet atmospheres at NASA, during a Google Hangout Thursday. “Will it go away? Part of the problem is we don’t understand what is sustaining it in the first place.”

Observers have noticed since the 1930s that the spot is shrinking. In 2003, Simon estimated that given its shrinkage rate, the spot could disappear around 2030. Since then it has shrunk even faster, and become more of a circle than an oval. Although reduced, the spot remains massive at 10,250 miles across.

The earliest reports of a red spot on Jupiter date to the 1600s, but it’s unclear if it’s the same spot we’re viewing today. Definite observations of today’s red spot date to the 1870s. Without more devoted funding and research, Jupiter’s shrinking spot appears likely to remain a mystery.

“It seems ironic due to money that we send probes into the atmosphere of Venus, which is one of most homogeneous,” said Glenn Orton, a NASA planetary astronomer. “We could send one into Jupiter, that is the least homogeneous. But that’s life. Jupiter is far away, Venus is a lot closer.”