Jupiter has the most intense planetary magnetic field in the solar system, causing a pile-up where the solar wind is slowed down (known as the bow shock). Juno first passed through this region and into the Jovian magnetosphere on June 24. At its closest approach, the strength of Jupiter’s magnetic field was twice as strong as any model had predicted and much more irregular.
That’s important, because it suggests that the magnetic field could be generated at shallower depths than expected, above the “metallic hydrogen” layer that is thought to exist at very high pressures. If proven, this has substantial implications for studies of magnetic fields at all of the giant planets. Perhaps the Cassini mission will be able to confirm whether this is the case as it makes its final measurements of Saturn’s magnetic field before it crashes into the planet in September.
Chaos at the poles
If you’ve ever been lucky enough to see Jupiter through a telescope, you’ll be familiar with the organised, striped structure of whiter zones and dark brown belts. These colourful bands are bordered by powerful jet streams whizzing east and west around the planet. On Saturn, this organised, banded structure persists all the way to the poles, with one jet showing a strange hexagonal wave pattern encircling a hurricane-like polar cyclone. But Jupiter’s poles are different. Gone is the organised structure of jets. There’s no evidence for hexagons or anything like it. And instead of one cyclone, we see multitudes, surrounded by a whole host of chaotic and turbulent features.
With the ability to see structures as small as 50km, Juno’s camera has revealed numerous bright cyclones of a variety of appearances – some appear sharp, some have clear spirals, some are fluffy and diffuse, and the largest is some 1400km across. That’s about the same distance between London and Majorca. These bright storms sit on top of dark clouds, giving the appearance of “floating” on a dark sea, and it will be some time before we understand the lifetimes and motions of these storms.
You might imagine that, faced with throwing out models that have taken careers to develop, scientists might be a little glum. But the exact opposite is true. A mission like Juno, accessing regions that no robotic spacecraft has ever probed before, is designed to test the models to the extreme. If they break, then the search to find the missing pieces of the puzzle will provide deeper insights into the physics of the Jovian system. All these surprises have come from just the first perijove encounter, and I’m sure there are plenty more revelations to come.