Jupiter’s Crazy Magnetic Field is Unlike Anything Ever Seen Before

Jupiter’s magnetic field is not like anything scientists have seen before, with new measurements from NASA’s Juno spacecraft showing it is confined almost entirely to the northern hemisphere.

Juno was launched into space in 2011 and has spent the last two years orbiting the gas giant. Its primary goal is to understand the origin and evolution of Jupiter—as the biggest planet in our solar system by far, it could provide key insights into planetary systems of other stars.

One of the key features of Jupiter is its huge magnetic field. This huge feature accounts for the planet’s magnetosphere and the incredible aurora that appear at the poles. Understanding the magnetic field can help answer questions about Jupiter’s inner structure—something that is still very much a mystery. 

In a study published in Nature, scientists from the U.S. and Denmark have created a map of Jupiter’s magnetic field, showing it in unprecedented detail. They discovered the field was unlike any planetary magnetic field seen before—it is non-dipole and this is almost entirely confined to the northern hemisphere. On Earth, in contrast, the non-dipolar part of the magnetic field is evenly distributed between the northern and southern hemispheres.

The team mapped the magnetic field at a range of depths and found that most of the activity takes place from a narrow band in the northern hemisphere that re-enters the planet near the Great Blue Spot, close to the equator.

Corresponding author Kimberly Moore, from Harvard University, told Newsweek: “We were not expecting Jupiter’s field to look this way. Before the Juno mission, our best maps of Jupiter’s field resembled Earth’s field.

“The main surprise was that Jupiter’s field is so simple in one hemisphere and so complicated in the other. None of the existing models predicted a field like that. We were also surprised to learn the Great Blue Spot is a singular feature in the field. When we first observed it on Juno’s first orbit, we thought there would be others like it, but that’s not the case.”

Colorful swirling cloud belts dominate Jupiter’s southern hemisphere in this image captured by NASAs Juno spacecraft_NASA cropped Colorful swirling cloud belts dominate Jupiter's southern hemisphere in this image captured by NASA's Juno spacecraft. NASA

She said that while the magnetic field in each hemisphere is completely different, it is too early to say whether the hemispheres are different in other ways. The team put forward a number of scenarios that could explain the unusual magnetic field—it could be related to Jupiter’s core, which at the moment is considered either to be a solid mass or more of a liquid. There could also be stable layers of liquid inside the planet, creating regional zones where the fluid can flow.

“A common picture of Jupiter’s interior is that there is a tiny core of solid rock and ice in the middle,” Moore explained. “However, rock and ice may dissolve in liquid metallic hydrogen at the high temperatures and pressures present at depth. So any rocky material inside Jupiter might just be mixed into the liquid hydrogen—like salt dissolved in water.

This can create layers, because the density differences that drive convection inside Jupiter are very small. One option is that both layers flow independently from each other (a “double dynamo”), but the other option is for the bottom layer to be stable. In this case, the fluid does not convect.”

The researchers say they will need more measurements from Juno to get a better understanding of the magnetic field. They should be able to get this in the second half of the spacecraft’s 34-orbit mission. 

NASA’s John Connerney, one of the study authors, said: "We have thus far developed our new model of Jupiter's magnetic field using only the first eight orbits from an expected total of 34 orbits; so this first glimpse is a lower resolution version of what is to come.

"We expect much more detail as the mission progresses. We also expect to learn something about secular variation of the field, the slow time variation of the magnetic field strength and direction that will reveal new information about fluid motion in the interior. It's going to be very exciting to see this story unfold in the years to come."

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