Everyone knows Jupiter’s Great Red Spot, but now it has a Great Blue Spot too. It plays a key role in operation of the planet’s uniquely-weird magnetic field, as shown in the graphic above.
The spot was discovered when astronomers analysed the first direct measurements of the magnetic fields within the planet. The readings were captured by NASA’s Juno space probe, which has been orbiting the planet since July 2016.
Unlike Earth’s highly uniform field with poles at opposite ends of the planet and identical field patterns in both hemispheres, Jupiter’s field is highly irregular and asymmetric.
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The magnetic field generated inside the planet flows outwards into space through a zone of the northern hemisphere—the red-brown region in the graphic. The field re-enters Jupiter to complete its circuit by converging on the Great Blue Spot, the dark blue patch to the right in the graphic, just below Jupiter’s equator.
Not true blue
The spot is not actually blue – it gets its name from the colour scale the team used to analyse the magnetic field.
“It makes for a nice parallel with the Great Red Spot,” says Kimberly Moore of Harvard University in Cambridge, Massachusetts, who led the work. “It’s a region of Jupiter where the field is very strong and densely concentrated.”
The team had expected to see many such spots, but Juno’s readings suggest it is unique. “We’re still working to understand its cause, and should hopefully learn more as the 34-orbit mission continues,” says Moore.
