How a hidden magnetic field might be shutting down Jupiter's atmospheric jet streams
The famous multicolored bands that run across the face of Jupiter have raised many questions for astronomers since the first observations of the gas giant, and when NASA's Juno orbiter recently began streaming back data they finally started getting some answers. Among them was the discovery that these bands extend thousands of kilometers below the surface, but this posed another question, why do they stop where they do? A new study has put forward an explanation, describing a complex magnetic field that essentially stops these globe-circling jet streams in their tracks.
These jet streams in Jupiter's atmosphere are ever-changing in terms of their width and their intensity, while their white, red, brown and yellow shades are caused by clouds of ammonia in the outer atmosphere that get swept up and taken along for the ride. One thing we didn't know until recently, was how deep beneath the surface these jet streams go.
"There were many theories with answers that vary from just a few kilometers below the clouds to all the way deep inside Jupiter's interior," Australian National University's Dr Navid Constantinou tells New Atlas. "Nobody really knew the answer until just before the spacecraft Juno arrived at Jupiter. After Juno arrived, it made precise measurements to determine, amongst other things, how deep these jets go. It was discovered that they go as deep as 3,000 km (1,900 mi) and then they terminate abruptly."
Naturally, scientists began to wonder after penetrating so deeply beneath the surface, what could be bringing them to such a sudden halt? One possible explanation had to do with the pressure, which is much greater at those depths than it is on the surface, in much the same way the pressure builds the deeper you dive into the ocean here on Earth.
At 3,000 km, this pressure is thought to be so high that it knocks the electrons off molecules of hydrogen and helium, leaving them to float freely and create electric and magnetic fields. Scientist theorized that this magnetic field was responsible for terminating the jet streams, but with no evidence this was mere speculation.
Constantinou, who researches climate and fluid physics, together with Jeffrey Parker from Lawrence Livermore National Laboratory in the United States, have set out to join the dots. They've developed a mathematical model that predicts where these magnetic fields might be strong enough to shut the jets down, and found that things lined up very nicely.
"So, we used principles from statistical physics and turbulence theory to derive a theoretical model for the interaction of magnetic fields and jets," explains Constantinou. "Then we used our theoretical model to predict what would be the tendency for the formation of jets with and without magnetic fields. Last, we compared our predictions with results from computer simulations, done by other authors, and found very good agreement. This gave credibility to our theoretical model and to the conclusions deriving from it."
Further to better understanding Jupiter's atmosphere, the team's theory on how the strong magnetic field suppresses the jet streams could help explain some of the other mysteries of the universe.
"Both jets and magnetic fields are prevailing in rotating bodies around the universe," Constantinou says. "Therefore, this theory could also be important for understanding dynamics in other stellar bodies or gaseous planets. For example, a place where this can be applicable is the Sun's interior, and specifically a region called the 'Solar Tachocline,' where magnetic fields are strong."
The research was published in The Astrophysical Journal.
Source: Australian National University