Powerful stratospheric winds measured for the first time on Jupiter
Using the Atacama Large Millimeter / Submillimeter Array (ALMA), a partner of the European Southern Observatory (ESO), a team of astronomers has directly measured the winds in Jupiter's middle atmosphere for the first time. Analyzing the effects of a comet collision in the 1990s, researchers found incredibly powerful winds of up to 1,450 kilometers per hour near the poles of Jupiter. They may represent what the team described as "a unique meteorological monster in our solar system."
Jupiter is known for its distinctive red and white stripes, swirling clouds of moving gas that astronomers traditionally use to track winds in Jupiter's lower atmosphere. Astronomers have also seen bright auroras near Jupiter's poles, known as auroras, which appear to be associated with strong winds in the planet's upper atmosphere. But until now, researchers have not been able to directly measure the wind patterns between these two atmospheric layers in the stratosphere.
Measurement of wind speed in the stratosphere of Jupiter using cloud tracking methods is not possible due to the lack of clouds in this part of the atmosphere. However, astronomers were provided with an alternative means of measurement in the form of comet Shoemaker-Levy 9, which impressively collided with the gas giant in 1994. This collision produced new molecules in Jupiter's stratosphere, where they always moved with the winds. as.
A team of astronomers led by Thibaut Cavalier at the Bordeaux Astrophysics Laboratory in France tracked one of this molecules-hydrogen cyanide-to directly measure stratospheric jets on Jupiter. Scientists use the word "jets" to refer to narrow bands of wind in the atmosphere, such as the Earth's jet streams.
"The most impressive result is the presence of strong jets at speeds of up to 400 meters per second, which are under the auroras near the poles," says Cavalier. These wind speeds, equivalent to about 1,450 kilometers per hour, are more than twice the maximum storm speeds achieved in Jupiter's Great Red Spot, and more than three times the wind speeds measured on the strongest tornadoes on Earth.
"Our discovery indicates that these jets may behave like a giant vortex with a diameter four times the diameter of the Earth and a height of about 900 kilometers," explains co-author Bilal Benmahi, also from the Bordeaux Astrophysics Laboratory. "A vortex of this size would be a unique meteorological beast in our solar system," adds Cavalier.
Astronomers were aware of strong winds near Jupiter's poles but much higher up in the atmosphere, hundreds of kilometers above the focus of the new study, which is published today in Astronomy & Astrophysics. Previous studies have predicted that these winds in the upper atmosphere will decrease in speed and disappear long before they reach the stratosphere. "The new ALMA data tells us otherwise," Cavalier says, adding that the discovery of these strong stratospheric winds near Jupiter's poles was "a real surprise."
The team used 42 of ALMA's 66 high-precision antennas, located in the Atacama Desert of northern Chile, to analyze hydrogen cyanide molecules that moved in Jupiter's stratosphere after the Shoemaker-Levy impact 9. ALMA's data allowed them to measure the Doppler shift - tiny changes in the frequency of radiation emitted by the molecules-caused by winds in this region of the planet. "By measuring this shift, we were able to determine the wind speed in the same way that you would determine the speed of a passing train by changing the frequency of the train whistle," explains study co-author Vincent Hugh, a planetary scientist. at the Southwest Research Institute of the United States.
In addition to the amazing polar winds, the team also used ALMA for the first time to confirm the existence of strong stratospheric winds around the planet's equator by directly measuring their speed. The planes seen in this part of the planet reach an average speed of about 600 kilometers per hour.
ALMA's observations, required to track stratospheric winds at both the poles and the equator of Jupiter, took less than 30 minutes of telescope time. "The high level of detail we've achieved in this short time really demonstrates the power of ALMA observations," says Thomas Greathouse, a scientist at the Southwest Research Institute in the US and a co-author of the study. "It's amazing to me to see the first direct measurement of these winds."
"These ALMA results open a new window for studying the auroral regions of Jupiter, which was really unexpected just a few months ago," says Cavalier. "They also set the stage for similar but more extensive measurements to be made by the JUICE mission and its submillimeter-wave instrument," Greathouse adds, referring to the European Space Agency's Jupiter Icy moons Explorer program, which is expected to launch next year.
This research is presented in the paper "The First Direct Measurement of Auroral and Equatorial Jets in the Jupiter Stratosphere," published today in the journal Astronomy & Astrophysics.