The Great Red Spot of Jupiter is one of the solar system’s most astonishing marvels. An elliptical storm with swirls of burnt orange and dulled copper, it is longer than the Earth is wide, and its winds go through the tops of the planet’s clouds at 400 mph.
The spot may seem like an unchanging fixture from a distance. But scientists have now discovered that it is jiggling and changing shape, repeatedly elongating and then contracting as it circumnavigates Jupiter’s southern hemisphere like a bright red kickball bouncing through a schoolyard.
Astronomers say that the Great Red Spot hasn’t always looked as it does today. But finding that it was able to transform during a 90-day period of observation came as a shock. “We were very surprised,” said Amy Simon, a planetary astronomer at NASA’s Goddard Space Flight Center and an author of a study published in The Planetary Science Journal. The storm “behaves like a slug, contracting and stretching as it moves around the planet,” said James O’Donoghue, a planetary astronomer at the University of Reading in England who wasn’t involved with the study.
But astronomers have no clue as to why the spot is behaving this way. The Great Red Spot, which rotates counterclockwise, has been continuously observed for the past 150 years.
That the storm has been around so long probably has something to do with two jet streams sandwiching it in place, O’Donoghue said. They keep the spot’s edges spinning while also preventing the storm from wandering off toward the equator or poles, where atmospheric forces and the planet’s rotation could tear it apart.
But the storm isn’t rooted in place. It “drifts slowly westward, taking a few years to circle the planet,” Simon said. And as it migrates, it speeds up and slows down over a three-month cycle. This cycle has yet to be explained. — ROBIN GEORGE ANDREWS /NYT
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