It collided with Jupiter in 1994, but Comet Shoemaker-Levy 9 apparently still has things to teach us about the solar system’s largest planet.
A new analysis of the comet’s traces – still zooming around Jupiter’s atmosphere – has provided the first direct measurement of the gas giant’s powerful stratospheric winds in the cloudless middle layer of the atmosphere.
There, narrow wind bands known as jets – like Earth’s jets – blow up to 400 meters per second at high latitudes. That’s about 1,440 kilometers per hour (895 mph) – well above the top wind speeds of about 620 km / h seen in the cyclonic storm Great Red Spot.
The team’s detection and analysis suggests these jets could act like a colossal vortex, about 50,000 kilometers in diameter and 900 kilometers high.
“A vortex of this size,” said astronomer Thibault Cavalié of the Laboratoire d’Astrophysique de Bordeaux in France, “would be a unique meteorological beast in our solar system.”
Comet Shoemaker-Levy 9’s death was one of the most spectacular events we have ever seen in the solar system. First, as the icy rock swerved close to Jupiter, it was torn apart by the planet’s immense gravity.
The fragments spent two Earth years in ever-narrowing orbit, until finally, in July 1994, they collided with Jupiter’s atmosphere in a compelling fireworks display.
The impact of Shoemaker-Levy 9 in 1994 (ESO)
It was an incredible gift to scientists. The impact stirred up Jupiter’s atmosphere, revealing new molecules and scarring Jupiter’s surface for months. This allowed measurements of wind speed and new studies of Jupiter’s atmospheric composition, as well as its magnetic field.
The comet impact also added new molecules not yet present on Jupiter. These include ammonia – which disappeared within a few months – and hydrogen cyanide, which can still be detected in the Jupiter stratosphere to this day.
It was 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 observed the hydrogen cyanide’s Doppler shift – the way in which the wavelength of the molecule’s electromagnetic emission gets longer or shorter depending on whether it moves away from or towards the observer.
“By measuring this shift, we were able to derive the speed of the wind as you could infer the speed of a passing train from the change in the frequency of the train whistle,” said Southwest planetary scientist Vincent Hue. Research Institute in the USA.
By analyzing the length of these shifts, scientists can calculate the speed at which the hydrogen cyanide moves.
Strong stratospheric winds blow around the planet’s equator at average speeds of about 600 kilometers per hour. Always. Here on Earth, the maximum wind speed ever recorded was 253 mph (407 km / h), and that was during a wild tropical cyclone.
One of the most intriguing jets, however, was found directly below 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 thinks this jet is the bottom tail of the auroral wind.
Previous studies had predicted that the auroral winds would diminish in strength as altitude decreased, disappearing before reaching the stratosphere, so this was a surprise – a wonderful demonstration of the invisible atmospheric complexity on a planet we already knew was insanely atmospheric. complex.
And it paves the way for future sightings of upcoming missions, such as the European Space Agency’s JUpiter ICy moons Explorer (JUICE) probe and the terrestrial Extremely Large Telescope currently under construction.
“These ALMA results open a new window for the study of Jupiter’s auroral regions,” said Cavalié.
The research is published in Astronomy and Astrophysics