It collided with Jupiter in 1994, but comet Shoemaker-Levy 9 still seems to have something to learn about the largest planet in the solar system.
A new analysis of the comet’s impact – still growing around Jupiter’s atmosphere – led to the first direct measurement of the gas giant’s strong stratospheric winds in the atmosphere’s cloudless middle layer.
There, narrow bands of wind known as jets – such as the Earth’s jet streams – blow up to 400 meters per second at high latitudes. It is about 1,440 kilometers per hour (895 mph) – far exceeding the maximum wind speed of about 620 km / h observed in the cyclone storm of the Red Spot.
The team’s detection and analysis suggest that these jets could act as a colossal whirlwind, about 50,000 kilometers in diameter and 900 kilometers high.
“A whirlwind 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 ever seen in the solar system. First, as the frozen rock approached Jupiter, it was torn apart by the planet’s immense gravitational pull.
The fragments spent two years on Earth in closer and closer orbit, until finally, in July 1994, they collided with Jupiter’s atmosphere in a captivating fireworks show.
Shoemaker-Levy Impact 9. 1994 (ESO)
For scientists, it was an incredible gift. The impact shook Jupiter’s atmosphere, revealing new molecules and scarring Jupiter’s surface for months. This allowed the measurement of wind speed and new studies of the atmospheric composition of Jupiter, as well as its magnetic field.
The impact of the comet also added new molecules that were not already present on Jupiter. These include ammonia – which disappeared in a few months – and hydrogen cyanide, which can still be detected in the Jovian stratosphere to this day.
This hydrogen cyanide was tracked by a team of scientists using 42 of the 66 antennas of the Atacama Large Millimeter / Submillimeter Array in Chile. Using this powerful tool, astronomers have observed the Doppler change of hydrogen cyanide – the way in which the wavelength of the electromagnetic emission of the molecule is prolonged or shortened depending on the distance to or from the observer.
“By measuring this change, we were able to deduce the speed of the winds just as we could deduce the speed of a train passing by changing the frequency of the train’s whistle,” said planetary scientist Vincent Hue of the Southwest Research Institute in the United States.
Analyzing the length of these changes allows scientists to calculate the speed at which hydrogen cyanide moves.
Around the planet’s equator, strong jets of stratospheric wind blow at average speeds of about 600 kilometers per hour. Always. Here on Earth, the maximum wind speed ever recorded was 407 km / h (253 mph) and this was during a wild tropical cyclone.
However, one of the most interesting jets was found just below the permanent auroral oval of Jupiter, a few 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 have predicted that auroral winds will decrease in strength as they drop in altitude, dissipating before reaching the stratosphere, so this was a surprise – a beautiful demonstration of the unseen atmospheric complexity on a planet we already knew it is unusually complex from an atmospheric point of view.
And it sets the stage for future observations of future missions, such as the European Space Agency’s JUpiter ICy moons Explorer (JUICE) spacecraft and the extremely large ground-based telescope under construction.
“These ALMA results open a new window for the study of Jupiter’s aurora regions,” Cavalié said.
The research was published in Astronomy and astrophysics.