A diagram of the magnetic field in Jupiter’s northern hemisphere, showing the Great Blue Spot. Graphic : Moore et al ( Nature 2018 )

Jupiter is strange for a number of reasons. It’s the biggest planet in our S olar S ystem, of course. It harbors perhaps the most intense radiation environments. And, according to a new study, it has a magnetic field unlike that of any other known planet .


NASA’s Juno orbiter, a basketball court-sized spacecraft, is observing the gas giant as it circles the planet at varying distances. Scientists recently mapped Jupiter’s magnetic field at four depths, and noticed a strange hemispheric dichotomy: The northern hemisphere’s magnetic field was nothing like the southern hemisphere’s.



“It’s a baffling puzzle,” the study’s first author, Harvard Ph.D student Kimberly Moore, told Gizmodo. “Why is it so complicated in the northern hemisphere but so simple in the southern hemisphere?”


Many s cientists believe that magnetic fields come from electricity-conducting metals moving around inside of planets—moving electric charge results in a magnetic field. Rotating columns of metal in Earth’s outer core give it a magnetic field that looks like that of a tilted bar magnet. Saturn, too, has a field like a bar magnet, though its field aligns with its rotational axis. Uranus and Neptune have weaker, more complicated fields, as if they had several, crisscrossing bar magnets.

But then there’s Jupiter. The Juno scientists mapped the planet’s magnetic field at four places, at the planet’s surface and three different depths below. They found that t he southern hemisphere has just one magnetic pole , but the northern hemisphere has a complex field . The map revealed an intensely magnetic spot near the equator that they called the Great Blue Spot, and a longer band from which the field emanated closer to the pole. The field also seems more concentrated at lower depths, according to the paper published today in Nature.

The obvious differences between the magnetic fields of the planet’s northern (left) and southern (right) hemispheres. The blue spot in the righthand picture is the southern hemisphere’s single magnetic pole. The red band in the lefthand picture is the odd magnetic field of the northern hemisphere. Graphic : Moore et al ( Nature 2018 )

Now, the scientists need to try and understand what’s going on. “We think we may be able to explain it based on Jupiter’s interior,” Moore told Gizmodo. On the Earth, our magnetic field is generated by the inner core heating the liquid outer core and driving motion. But perhaps Jupiter’s core is more spread out with more complex motion, leading to the tangled magnetic field. Or maybe there are liquids of different compositions sloshing around which can change the way the magnetic field works.




It’s important to note that Juno has higher - resolution images of Jupiter’s northern hemisphere than of its southern hemisphere. But Moore told Gizmodo that the probe has taken enough data to conclude that the differences are real and not artifacts of the data.



The researchers Gizmodo spoke with who were not involved with the study found its results exciting. The “unexpected discovery of the northern hemisphere flux band, ‘Great Blue Spot’, and predominantly dipolar southern hemisphere challenge existing dynamo models, which means we have more to learn,” Krista Soderlund, r esearch a ssociate at the University of Texas at Austin, told Gizmodo in an email. She thought that the possibility of measuring magnetic field variations over time could be a powerful tool to understand how fluid moves below the planet’s surface.




It could also help scientists learn more about planetary magnetic fields in general, like why Jupiter and Saturn have such different fields, she said.

Juno will continue to orbit Jupiter until 2022, taking data along the way. “There’s a lot more data to collect, so hopefully there will be more things to investigate,” said Moore. “The internal structures we propose are speculative. One, or multiple, or none could be true.”


[Nature]

