Juno’s View of Jupiter’s Turbulent Poles

The imagery we’re getting of Jupiter’s polar regions is extraordinary. Juno’s Jovian Infrared Auroral Mapper instrument (JIRAM) works at infrared wavelengths, showing us a vivid picture of a massive central cyclone at the north pole and eight additional cyclones around it. In the image below, we’re looking at colors representing radiant heat, with yellow being thinner clouds at about -13 degrees Celsius, and dark red representing the thickest clouds, at about -118 degrees Celsius. JIRAM can probe down to 70 kilometers below the cloud tops.

Image: This composite image, derived from data collected by the Jovian Infrared Auroral Mapper (JIRAM) instrument aboard NASA’s Juno mission to Jupiter, shows the central cyclone at the planet’s north pole and the eight cyclones that encircle it. Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM.

This is hardly the orange, white and saffron belted world we are familiar with from telescope views of the lower latitudes. The scale of these storms is, as you would expect with Jupiter, quite impressive. Alberto Adriani is a Juno co-investigator based at the Institute for Space Astrophysics and Planetology in Rome:

“Prior to Juno we did not know what the weather was like near Jupiter’s poles. Now, we have been able to observe the polar weather up-close every two months. Each one of the northern cyclones is almost as wide as the distance between Naples, Italy and New York City — and the southern ones are even larger than that. They have very violent winds, reaching, in some cases, speeds as great as 350 kph. Finally, and perhaps most remarkably, they are very close together and enduring. There is nothing else like it that we know of in the solar system.”

Adriani’s work on the Jovian polar regions is part of a four-paper set of Juno findings just published in Nature (citations below). We also learn that the planet’s south pole likewise contains a central cyclone, surrounded by five other cyclones with diameters ranging from 5,600 to 7,000 kilometers (the eight northern circumpolar cyclones have diameters between 4,000 and 4,600 kilometers). As Adriani tellingly asks, “…why do they not merge?”

Contrast this situation with Saturn, which houses a single cyclonic vortex at each pole, and it becomes clear that the differences between gas giants can be striking. We also see evidence at Jupiter that the winds dominating its zones and belts run deep, a phenomenon put on display by gravity measurements Juno has collected during its close flybys. “Juno’s measurement of Jupiter’s gravity field indicates a north-south asymmetry, similar to the asymmetry observed in its zones and belts,” said Luciano Iess, Juno co-investigator from Sapienza University of Rome, and lead author on a Nature paper on Jupiter’s gravity field.

That such asymmetries in gravitational measurements exist — and the visible eastward and westward jet streams are likewise shown to be asymmetric — tells us a great deal about how deep these powerful flows extend. This JPL news release explains that the deeper the jets flow, the more massive they are, creating a stronger signal in the gravity field. Juno’s gravity asymmetries thus become a marker for how far down these weather patterns extend.

The massive Jovian weather layer, east-west flows extending to a depth on the order of 3,000 kilometers, contains about one percent of the planet’s mass. Yohai Kaspi, lead author of another of the recent papers in Nature explaining the result, says that seeing the depth of these weather jets and their structure takes us from a two- to a three-dimensional view, adding: “The fact that Jupiter has such a massive region rotating in separate east-west bands is definitely a surprise.” We have much work ahead to determine what drives these jet streams; their gravity signature is entangled with that of Jupiter’s core.

On that score, the surprises seem likely to continue. For a final Juno result now being released suggests that the planet rotates below its massive weather layer as a rigid body.

“This is really an amazing result, and future measurements by Juno will help us understand how the transition works between the weather layer and the rigid body below,” said Tristan Guillot, a Juno co-investigator from the Université Côte d’Azur, Nice, France, and lead author of the paper on Jupiter’s deep interior. “Juno’s discovery has implications for other worlds in our solar system and beyond. Our results imply that the outer differentially-rotating region should be at least three times deeper in Saturn and shallower in massive giant planets and brown dwarf stars.”

Let’s close with a Juno image of Jupiter’s south pole as processed from JunoCam imager data by citizen scientist Gerald Eichstädt.

Image: This image captures the swirling cloud formations around the south pole of Jupiter, looking up toward the equatorial region. NASA’s Juno spacecraft took the color-enhanced image during its eleventh close flyby of the gas giant planet on Feb. 7 at 1011 EST (1411 UTC). At the time, the spacecraft was 120,533 kilometers from the tops of Jupiter’s clouds at 84.9 degrees south latitude. Credit: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstadt.

All four papers are in Nature 555 (8 March 2018). They are: Adriani et al., “Clusters of cyclones encircling Jupiter’s poles,” 216-219 (abstract); Iess et al., “Measurement of Jupiter’s asymmetric gravity field,” 220-222 (abstract); Kaspi et al., “Jupiter’s atmospheric jet streams extend thousands of kilometres deep,” 223-226 (abstract); and Guillot et al., “A suppression of differential rotation in Jupiter’s deep interior,” 227-230 (abstract).