While Earth's magnetic field is distributed symmetrically around the planet, Jupiter's is much stronger in the northern hemisphere than in the south. And whereas Earth's magnetic field lines converge rather neatly at the poles a bit like a giant bar magnet, Jupiter's field lines look helter-skelter on a map created from the data. The lines emanating from Jupiter's north return not to one point but to two: one near Jupiter's south pole and the other near its equator.
"Now we know that Jupiter's field is very different from Earth's field," Kimberly Moore, a graduate student in the Department of Earth & Planetary Sciences at Harvard University and the lead author of a paper describing the research, told NBC News MACH in an email. "The main puzzle of our study is why Jupiter's field is so simple in one hemisphere and so complicated in the other."
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The scientists who conducted the research don't expect a quick solution to the puzzle.
"We're just starting to work out the possible answers," said Scott Bolton, the principal investigator of the Juno mission and a co-author of the paper, which was published Sept. 5 in the journal Nature. "Whatever's going on inside Jupiter isn't like what's going on inside other planets."
Earth's magnetic field is believed to result from the circulation of liquid iron in our planet's outer core; as this electrically conductive material moves about — driven by heat from a solid inner core — it generates a "dipolar" magnetic field.
But the new research indicates that something very different must be happening within Jupiter. One possibility that's consistent with the new data, Bolton said, is that Jupiter's magnetic field is generated not by one mechanism, as on Earth, but by two: one occurring in a layer deep within the planet and another in a layer closer to the surface. As these hypothetical fields interact, they might interact to cause the strange field seen in the Juno data, Bolton said, adding, "Maybe there is some sort of double thing here."
Additional data to be collected by Juno could help explain the mystery — but that will take years.
The new magnetic field map is a coarse one, generated from data collected by Juno over the course of eight close passes over Jupiter's surface as it skims the planet's surface at speeds of up to 150,000 miles per hour. Bolton said the final, detailed map, to be made from data collected from a total of 32 passes, would be completed in 2021.
It will take that long because it takes Juno 53 days to compete one orbit of Jupiter — and Juno is close enough to Jupiter to collect the necessary data for only a few hours of each orbit.
Juno launched in 2011 from Cape Canaveral Air Force Station in Florida.