Jupiter’s Great Red Spot is one of the most intriguing features in the solar system. It’s a storm that’s big enough to swallow Earth – but getting smaller.

Winds at its perimeter blow much faster than any hurricane on Earth. And it has a bright reddish orange color. Despite a century and a half of study, though, it’s still mysterious. Scientists don’t know why it’s red, why it’s getting smaller, or how it fired up in the first place.

They do know that the storm drifts westward around the planet. And a recent study found that it “inches” along like a garden slug.

Scientists monitored the storm for three months with Hubble Space Telescope. They already knew that the Great Red Spot goes through a 90-day cycle. But this was the first time they plotted the changes in detail.

The images revealed that the spot stretches and squeezes as it moves. When it’s moving slowest, it’s stretched out. When it’s moving fastest, it’s more compressed, so it’s a little rounder. The storm’s width varies by about a hundred miles, and its height by a bit more.

The spot’s average width is more than 8,000 miles. That’s only a third the size when it was first seen. No one knows whether it will continue to shrink – and eventually disappear.

Look for Jupiter close to the right of the Moon in tomorrow’s dawn twilight. It looks like a bright star. But it’s so low that you need a clear horizon to spot it.

Script by Damond Benningfield