Saturn’s rings get all the glory, and no wonder: ever since 1610, when Galileo used his primitive telescope to spot what looked like bumps protruding from either side of the Solar System’s second-largest planet, telescopes and space probes have gradually unveiled the dizzying beauty and strange science of this extraordinary example of space architecture.
But the planet itself is plenty intriguing all on its own. Like its big brother Jupiter, Saturn is a huge ball of noxious clouds surrounding a small, solid core; and as with Jupiter too, those atmospheric gases, driven by powerful winds, organize themselves into massive storms which can last for decades, or even centuries.
Even experienced Saturn-watchers were taken aback, however, when they got their first good look at what lies right at the planet’s north pole: a hurricane so gigantic it could swallow Earth, with room to spare. The eye alone is more than 1,200 miles (1,900 km) across, and wind speeds at the vast cyclone’s outer edges reach 330 mph (531 k/h). When they first saw the storm’s image, said Caltech planetary scientist Andrew Ingersoll in a statement, “We did a double-take.”
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That reaction is all the more impressive because the Cassini probe, orbiting Saturn since 2004, had already detected hints of a wind vortex at the pole, lying within a bizarre hexagon of clouds astronomers first spotted during the Voyager flybys in 1980 and 1981. Cassini couldn’t photograph the vortex, though, because Saturn’s north pole was tilted away from the Sun, just as Earth’s tilt keeps the Arctic in darkness for months at a time. In the case of Saturn, however, which takes 29.7 years to complete a single solar orbit, winter is a whole lot longer.
But the planet’s motion has now taken the pole into sunlight, so Cassini’s controllers used a gravity assist from Saturn’s moon Titan to nudge the spacecraft into a more favorable orbit, allowing its cameras to capture the hurricane in detail.
While the storm is far bigger and more powerful than anything Earth has ever experienced, it’s structurally similar to the hurricanes that batter the U.S. and Caribbean islands every year. What’s markedly different is that those storms move across the planet; Saturn’s polar storm just sits at the top of the globe without budging. That’s not because the dynamics of Saturn’s atmosphere are fundamentally different from those of Earth: the giant planet has jet streams and prevailing winds just as we do.
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But on Earth, the combined effects of prevailing winds and the planet’s rotation tend to push hurricanes in the Northern Hemisphere further northward, as Irene and Katrina and Sandy all demonstrated in their own devastating ways. A storm that’s already sitting at the north pole, said Cassini imaging team member Kunio Sayanagi, “has nowhere else to go.”
On Earth, any hurricane that managed to reach the Arctic would quickly die, as the ocean heat that fuels tropical storms petered out. Saturn has no ocean, of course, so that’s not happening. In fact, it remains unclear exactly what does fuel this giant storm.
Water vapor is most likely involved somehow, say Cassini team members. But while the mystery of what lies at Saturn’s north pole has now been solved, the mystery of why it’s there will probably take years to unravel.
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