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It collided with Jupiter in 1994, but Comet Shoemaker-Levy 9 apparently still has something to teach us about the largest planet in the solar system.
A new analysis of the traces of the comet’s impact – still zooming around Jupiter’s atmosphere – gave the first direct measurement of the gas giant’s powerful stratospheric winds, in the cloudless middle layer of the atmosphere.
There, narrow bands of wind known as jets – like Earth’s jet streams – blow at up to 400 meters per second at high latitudes. This works out to about 1,440 km / h (895 mph) – far exceeding the maximum wind speeds of around 620 km / h seen in cyclonal storm Great Red Spot.
The team’s detection and analysis suggests that these jets could act like a colossal vortex, about 50,000 kilometers in diameter and 900 kilometers in height.
“A vortex of this size,” said astronomer Thibault Cavalié of the Bordeaux Astrophysics Laboratory in France, “would be a unique meteorological beast in our solar system.”
The death of Comet Shoemaker-Levy 9 was one of the most spectacular events we have ever seen in the solar system. First, as the icy rock veered near Jupiter, it was torn apart by the planet’s immense gravitational pull.
The fragments spent two Earth years in ever-closer orbit, until finally, in July 1994, they collided with Jupiter’s atmosphere in a fascinating spectacle of fireworks.
The 1994 Impact of Shoemaker-Levy 9. (ESO)
For scientists, it was an incredible gift. The impact lifted Jupiter’s atmosphere, revealing new molecules and marking Jupiter’s surface for months. This allowed for wind speed measurements and further studies of Jupiter’s atmospheric composition, as well as its magnetic field.
The impact of the comet also added new molecules that were not already present on Jupiter. These included ammonia – which disappeared within months – and hydrogen cyanide, which can still be detected in the Jovian stratosphere to this day.
It is this hydrogen cyanide that a team of scientists tracked using 42 of the 66 antennas of the Atacama Large Millimeter / Submillimeter Array in Chile. Using this powerful instrument, astronomers have observed the Doppler shift of hydrogen cyanide – the way in which the wavelength of the molecule’s electromagnetic emission lengthens or shortens depending on its size. moves away or approaches the observer.
“By measuring this offset, we were able to deduce the wind speed just as we could deduce the speed of a passing train by the change in frequency of the train’s whistle,” said planetologist Vincent Hue of the Southwest Research Institute in United States.
Analyzing the duration of these changes allows scientists to calculate the speed at which hydrogen cyanide is moving.
Around the planet’s equator, powerful stratospheric jets of wind blow at average speeds of around 600 kilometers per hour. All the time. Here on Earth, the maximum wind speed on record was 253 mph (407 km / h), and that was during a wild tropical cyclone.
One of the more intriguing jets, however, was found directly beneath Jupiter’s permanent auroral oval, several hundred miles below the auroral winds. It was clockwise in the north and counterclockwise in the south, at speeds of up to 300 to 400 meters per second. The team believe that this jet is the lower tail of the auroral wind.
Previous studies had predicted that the strength of auroral winds would decrease as altitude decreased, dissipating before reaching the stratosphere, so this was a surprise – a beautiful demonstration of the invisible atmospheric complexity of a planet we already knew that it was incredibly complex from an atmospheric point of view.
And it sets the stage for future observations from upcoming missions, such as the European Space Agency’s JUpiter ICy moons Explorer (JUICE) and the Extremely Large Earth Telescope currently under construction.
“These ALMA results open a new window for the study of the auroral regions of Jupiter,” Cavalié said.
The research was published in Astronomy and astrophysics.
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