MOST OF THE planet Jupiter is painted in red and white, with exquisite stripes and splotches brushed onto its face. But, it turns out, its poles are dark blue and marked by a multitude of cyclones that scientists have now seen up close.
Observations from NASA’s Juno spacecraft — which was the first to get a clear look at the gas giant’s poles — show the tempestuous curlicues clustered in geometric configurations, with several storms surrounding a central spiral. In the north, the storms are arranged in an octagonal shape. In the south, they form a pentagon.
Juno has been orbiting the planet since July 2016, and it snapped images of the planet in both visible and infrared light. These allowed scientists to measure the size and temperature of the violent spirals, most of which are at least as wide as the United States.
“Their centres are arranged on the [corners] of imaginary polygons,” says Alberto Adriani of Italy’s Istituto di Astrofisica e Planetologia Spaziali, who describes the storms Wednesday in the journal Nature.
Within each clump, the cyclones tend to drift or migrate, but they never disappear (at least not since Juno has been watching) and the polygonal groupings are unlike anything that’s been seen on another planet in the solar system. Saturn, the gas giant next door to Jupiter, wears a hexagonal shape on its north pole — but the geometry is all the work of a single storm. Now, scientists are trying to figure out how the Jovian polygons formed and are maintained.
“I think we were expecting to see what we see at Saturn, where you have the one big hexagon, or something a bit more like that,” says Fran Bagenal of the University of Colorado, Boulder. ”But here we are.”
These new revelations about the Jovian poles are among several reported together in Nature. Three studies describe the way the planet’s interior works, and for the first time resolve a debate about whether the patterns painted on the surface are merely superficial, or reflect the work of processes churning away inside the planet.
“People have been fighting about this since before I was born,” says Jonathan Fortney of the University of California, Santa Cruz. “There was no dataset capable of answering this question until Juno.”
Jupiter is 11 times wider than Earth, yet spins around itself in a meager 10 hours or so. It’s that almost unfathomably fast rotation that powers its iconic cloudy bands, whipped by winds hurtling alternately east and west like a ramped-up version of the trade winds on Earth. But for a long time, scientists didn’t know if those winds extended deeper within the planet or were a superficial weather phenomenon.
Juno is the first spacecraft that’s letting scientists peel back the planet’s banded skin to answer that question. As it orbits Jupiter, Juno sends radio waves back to Earth. By measuring minute changes in the frequency of those arriving waves, scientists can map Jupiter’s gravitational field and glean crucial clues about its innards.
One of the reports in Nature reveals that Jupiter’s gravitational field is asymmetric, meaning there’s some kind of mass imbalance between its north and south hemisphere.
“It’s gone pear-shaped, if you will,” Bagenal comments. “Maybe it’ll even out in the next millennium or something, or maybe even a few decades — we don’t know the time scale.”
A second study identifies the planet’s ferocious winds as a reason for the asymmetry. To move so much mass, the authors say, the winds must be deeply rooted. That study, and a third, both suggest that the surface patterns and blustery bands are linked to turbulence extending at least 3,000 kilometres beneath the planet’s surface.
A Rotating Rutabaga
Deeper than that, the third study says, and enormous pressures inside the planet begin jamming atoms together, turning it into a solid, rotating ball. Bagenal compares the pressure within Jupiter, which is roughly 100 million times that of Earth’s atmospheric pressure, to that beneath a thousand elephants standing on top of one another, with the bottom elephant perched on one leg. Wearing a stiletto heel.
At those pressures, a layer of metallic hydrogen exists, the swirling actions of which generate Jupiter’s magnetic field. Deeper still, there’s a core of dissolving rock and minerals swaddled inside that exotic hydrogen.
Together, these studies point to a planet that’s more perplexing than imagined, like an onion that just got a bit more layers??. Or … not.
“It might be more like a rutabaga,” Bagenal says. “A really big rutabaga.”
Like that vegetable, Jupiter has layers that are separate but connected, and it’s denser toward the centre. But left on their own, rutabagas don’t spin around themselves once every 10 hours, with their interiors rotating as solid objects beneath a swirling, turbulent skin of wind and clouds.
“We maybe should have anticipated that there would be more mixing or more structure than what’s in textbooks,” Bagenal says, noting that Jupiter could hold the key to understanding how other gas giant planets, including Saturn, work.
“One likes to think of Jupiter being the archetype of the giant planets around other star systems,” she says. “But who knows?”
Lead Image: Cyclones swirl around each other in a new infrared mosaic of Jupiter's south pole created by NASA's Juno spacecraft. COURTESY OF NASA, SWRI, JPL, ASI, INAF, IAPS