ALMA Detects Strong Winds in Stratosphere of Jupiter | Astronomy

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have revealed incredibly powerful winds — with speeds of up to 1,450 kmh (901 mph) — near Jupiter’s poles.

This image shows an artist’s impression of winds in Jupiter’s stratosphere near the planet’s south pole, with the blue lines representing wind speeds; these lines are superimposed on a real image of Jupiter, taken by the JunoCam imager aboard NASA’s Juno spacecraft. Image credit: ESO / L. Calçada / NASA / JPL-Caltech / SwRI / MSSS.

Astronomers were aware of strong winds near Jupiter’s poles, but much higher up in the atmosphere, hundreds of kilometers above the focus area of the new study.

Previous studies predicted that these upper-atmosphere winds would decrease in velocity and disappear well before reaching as deep as the stratosphere.

“The new ALMA data tell us the contrary. Finding these strong stratospheric winds near Jupiter’s poles was a real surprise,” said Dr. Thibault Cavalié, an astronomer in the Laboratoire d’Astrophysique de Bordeaux.

Dr. Cavalié and colleagues used ALMA to analyze hydrogen cyanide molecules that have been moving around in Jupiter’s stratosphere since the impact of comet Shoemaker-Levy 9, which collided with the gas giant in 1994.

The ALMA data allowed the team to measure the Doppler shift — tiny changes in the frequency of the radiation emitted by the molecules — caused by the winds in this region of the planet.

“By measuring this shift, we were able to deduce the speed of the winds much like one could deduce the speed of a passing train by the change in the frequency of the train whistle,” said Dr. Vincent Hue, a planetary scientist at the Southwest Research Institute.

“The most spectacular result is the presence of strong jets, with speeds of up to 1,450 kmh, which are located under the aurorae near the poles,” Dr. Cavalié said.

These wind speeds are more than twice the maximum storm speeds reached in Jupiter’s Great Red Spot and over three times the wind speed measured on Earth’s strongest tornadoes.

“Our detection indicates that these jets could behave like a giant vortex with a diameter of up to four times that of Earth, and some 900 km (559 miles) in height,” said Dr. Bilal Benmahi, an astronomer in the Laboratoire d’Astrophysique de Bordeaux.

In addition to the surprising polar winds, the astronomers used ALMA to confirm the existence of strong stratospheric winds around the planet’s equator, by directly measuring their speed, also for the first time.

The jets spotted in this part of the planet have average speeds of about 600 kmh (373 mph).

“These ALMA results open a new window for the study of Jupiter’s auroral regions, which was really unexpected just a few months back,” Dr. Cavalié said.

The findings were published in the journal Astronomy & Astrophysics.

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T. Cavalié et al. 2021. First direct measurement of auroral and equatorial jets in the stratosphere of Jupiter. A&A 647, L8; doi: 10.1051/0004-6361/202140330