Echoes from a comet that crashed in 1994 have revealed new data about Jupiter


It collided with Jupiter in 1994, but Comet Shoemaker-Levy 9 apparently still has things to teach us about the largest planet in the Solar System.

A new analysis of the impact traces of the comet, which still orbits Jupiter’s atmosphere, has yielded the first direct measurement of the gas giant’s powerful stratospheric winds, in the clear middle layer of the atmosphere.

There, narrow bands of wind known as jets, like Earth’s jet streams, blow up to 400 meters per second at high latitudes. That’s around 1,440 kilometers per hour (895 mph), far exceeding maximum wind speeds of around 620 km / h seen in the Great Red Spot cyclonal storm.

The team’s detection and analysis suggest that these jets could act as a colossal vortex, some 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.”

The death of Comet Shoemaker-Levy 9 was one of the most spectacular events we have seen in the Solar System. First, when the icy rock veered near Jupiter, it was ripped 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 fireworks display.

The 1994 Shoemaker-Levy Impact 9. (ESO)

For the scientists, it was an incredible gift. The impact churned Jupiter’s atmosphere, revealing new molecules and scarring Jupiter’s surface for months. This allowed measurements of wind speed and further studies of Jupiter’s atmospheric composition, as well as its magnetic field.

The comet impact also added new molecules that were not yet present on Jupiter. These included ammonia, which was gone within a few months, and hydrogen cyanide, which can still be detected in the Jovian stratosphere to this day.

It was this hydrogen cyanide that a team of scientists tracked using 42 of the 66 antennas from the Atacama Large Millimeter / Submillimeter Array in Chile. Using this powerful instrument, the astronomers observed the Doppler shift of hydrogen cyanide, the way in which the wavelength of the molecule’s electromagnetic emission lengthens or shortens depending on whether the observer is zoomed in or out.

“By measuring this change, we were able to deduce the speed of the winds in much the same way as you can deduce the speed of a passing train by changing the frequency of the train’s whistle,” said planetary scientist Vincent Hue of Southwest Research. Institute in the 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, strong jets of stratospheric wind blow at average speeds of around 600 kilometers per hour. All time. Here on Earth, the maximum wind speed ever recorded was 407 km / h (253 mph), and that was during a wild tropical cyclone.

However, one of the most intriguing jets was found directly below Jupiter’s permanent auroral oval, several hundred kilometers 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 believes that this jet is the lower tail of the auroral wind.

Previous studies had predicted that auroral winds would decrease in strength as altitude decreases, dissipating before reaching the stratosphere, so this came as a surprise – a beautiful demonstration of invisible atmospheric complexity on a planet we already knew to be. incredibly atmospherically complex.

And it sets the stage for future observations of upcoming missions, such as the European Space Agency’s JUpiter ICy moons Explorer (JUICE) probe and the Extremely Large Terrestrial Telescope currently under construction.

“These ALMA results open a new window for the study of Jupiter’s auroral regions,” said Cavalié.

The research has been published in Astronomy and Astrophysics.

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