Wind Shields Keep Jupiter’s Polar Storms in Place

This image shows Jupiter’s south pole, as seen by NASA’s Juno spacecraft, from an altitude of 32,000 miles. The oval features are cyclones, up to 600 miles in diameter. (NASA/JPL-Caltech/SwRI/MSSS/Betsy Asher Hall/Gervasio Robles)

(CN) — New models suggest that shields surrounding the numerous storms circling Jupiter’s north and south poles may be the reason why more than a dozen large tempests have circled the gas giant’s extremes without either merging or dissipating in the past four years.

Juno, the NASA space probe orbiting Jupiter, has kept its camera on Jupiter’s raging storms since it entered the planet’s polar orbit in July 2016.

The spacecraft has continuously circled the solar system’s largest and most massive planet, monitoring its stormy poles: eight massive vortexes circling a central storm on the planet’s north pole, and five swirling around a middle storm near its south pole.

The storms are massive, many times the size and ferocity of Earth’s Category 5 hurricanes. One of the shorter storm’s radius measures at about 1,250 miles long — nearly one-third the radius of the entire Earth — and others measure over 2,100 miles in one direction.

On its 20th flyby to Jupiter, the JIRAM instrument onboard the Juno spacecraft found a seventh vortex, lower right, trying to join the original family of six vortices. (Credit: Alessandro Mura/National Institute for Astrophysics)

Their winds whip at a hair under 179 miles per hour, and each is surrounded by a shield of vicious “anticyclonic” winds, spiraling in the opposite direction of the vortices, like gears pushing against one another in a machine.

Despite their massive, tempestuous nature, these storms have remained stable since August 2016 – not one, on either pole, has dissipated or merged since then.

Cheng Li, a University of California at Berkeley astronomer, and three colleagues published new research Monday in PNAS, the official journal of the National Academy of Sciences, finding that anticyclonic shields are the key to the storms’ unusual stability.

Several theories try to account for the idiosyncrasies of Jupiter’s’ vortices. For instance, they tend to move poleward, just as cyclones do on Earth.

“[Cyclones] originate at lower latitudes on Earth, and then they migrate to higher latitudes — to Texas, to New Orleans — and they all originate near the equator, then they go up,” Li said in an interview. “Those hurricanes will die on Earth once they hit and they lose their energy source, from the warm oceans.”

But Jupiter has neither land nor ocean – like Saturn, the solar system’s other gas giant, Jupiter has no topology to speak of. For its part, the ringed planet features only one cyclone at each of its poles.

Models for Saturn’s cyclones fail to account for the unique polygonal patterns seen on Jupiter. Its systems of vortices are arranged geometrically. A pentagon surrounds the south pole while an octagon dances around its north – for years they have neither merged nor dissipated.

To account for these oddities, Li and his colleagues modeled the behavior of Jupiter’s storms to find what variables made the difference between stable and unstable polar vortexes.

“We basically answer the question, ‘Why are they stable?’ We would like to come up with a simple explanation, and that simple explanation will involve very few parameters. They describe the basic features of the atmosphere. We would like to look at what parameters separate the space between merging and not merging,” Li said.

It turns out that there is a “sweet spot” of anticyclonic shielding that keeps Jupiter’s numerous polar vortices stable, a kind of Goldilocks zone between too little shielding, which would see the storms lose their polygonal formation and allow them to merge, and too much shielding, which would overtake and dispel the massive tempests.

Though it’s impossible to say without more data, this could also explain why Saturn features only one cyclonic vortex on each of its poles.

“We can speculate that on Saturn, probably the cyclones are not shielded,” Li said. “But we cannot say for sure why.”

It remains a mystery how Jupiter’s vortices formed: did they form in place, or did they drift in from lower latitudes? The latter is Li’s guess, but he says that future research — which he said he is already preparing — could help determine their origin.

%d bloggers like this: