A team of researchers from the Australian National University and the Lawrence Livermore National Laboratory has solved the mystery underlying Jupiter’s colored bands in a study on the interaction between atmospheres and magnetic fields.
Magnetic fields around Jupiter can overpower zonal jets that affect atmospheric circulation. Image credit: JAXA.
Jupiter is the Solar System’s largest planet. Unlike Earth, Jupiter has no solid surface — it is a gaseous planet, consisting mostly of hydrogen and helium.
So-called ‘zonal flows’ (also known as zonal jets) flow west to east in Jupiter’s atmosphere that are, in a way, similar to Earth’s jet streams.
Clouds of ammonia in the Jovian outer atmosphere are carried along by these flows to form Jupiter’s colored bands, which are shades white, red, orange, brown and yellow.
Previous work performed simulations that showed a magnetic field suppressed zonal flows.
The new study, published in the Astrophysical Journal (arXiv.org preprint), provides a mechanism explaining that suppression.
It shows that with magnetic fields present, even a weak shear flow causes subtle but coherent correlations in the magnetic fluctuations that oppose zonal flows.
This image captures a high-altitude cloud formation surrounded by swirling patterns in Jupiter’s North North Temperate Belt region. The North North Temperate Belt is one of Jupiter’s many colorful, swirling cloud bands. Scientists have wondered for decades how deep these bands extend. Gravity measurements collected by NASA’s Juno orbiter during its close flybys discovered that these bands of flowing atmosphere actually penetrate deep into the planet, to a depth of about 1,900 miles (3,000 km). Image credit: NASA.
“Because magnetic fields are prevalent in the Universe, this theory could be important for understanding dynamics at the solar tachocline where a strong magnetic field exists, and also potentially applicable to zonal flows deep in the interior of Jupiter, Saturn and other gas giants,” said study co-author Dr. Jeff Parker, a physicist at the Lawrence Livermore National Laboratory.
Zonal flows act as a barrier and don’t allow for fluid from the two sides to exchange properties (such as heat or carbon). Thus, they have a large impact on the Earth’s weather because they separate cold and warm air. But just how deep do these zonal jets dive in Jupiter?
“The zonal flows have an indirect effect on the gravitational field of Jupiter. With detailed measurements of the gravitational field, we can infer how deep the zonal flows are,” said co-author Dr. Navid Constantinou, a postdoctoral researcher in the Research School of Earth Sciences at the Australian National University.
NASA’s Juno spacecraft is in orbit around Jupiter doing precisely these sorts of measurements.
Preliminary evidence shows that jet streams reach as deep as 1,900 miles (3,000 km) below Jupiter’s clouds. This is still ‘shallow’ when compared to the radius of the gas giant (approximately 43,500 miles, or 70,000 km).
“It has been a long-standing question about how deep zonal flows penetrate into the interior of Jupiter and other gas giants,” Dr. Parker said.
“Some have argued they exist only on the surface, and others thought they should persist deep into the planet.”
“Only in the last year are we are starting to get answers to these questions, thanks to Juno. It’s an exciting time.”
“Since magnetic fields prevail within Jupiter’s interior, our research could shed light on why the jets don’t go any deeper.”
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Navid C. Constantinou & Jeffrey B. Parker. 2018. Magnetic Suppression of Zonal Flows on a Beta Plane. ApJ 863, 46; doi: 10.3847/1538-4357/aace53
