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Shoemaker-Levy 9 impact site G
Shoemaker-Levy 9 impact site G

Herschel solves mystery of Jupiter's water

24 April 2013

Jupiter, the largest planet in the Solar System, is mostly made of the gases hydrogen and helium. Tiny amounts of water have been found in its upper atmosphere, but, until now, no one was sure where this water came from. The answer to the long-standing mystery has been given by ESA’s Herschel space observatory, the most sensitive infrared telescope ever launched. Herschel has found conclusive evidence that the water was delivered by multiple comet impacts in July 1994!

Collisions with incoming cosmic debris are a continuous threat to the planets of the Solar System, including Earth. However, few impacts have actually been observed by scientists. The first direct observation of such an event occurred at Jupiter, 19 years ago. Astronomers watched in astonishment as 21 pieces of comet Shoemaker-Levy 9 plunged into the planet’s upper atmosphere and exploded.

Water in Jupiter's atmosphere
Water in Jupiter's atmosphere
ESA’s Infrared Space Observatory, launched in 1995, was the first to detect and study water in Jupiter's upper atmosphere. Scientists were able to exclude an internal source, such as water rising from below. But if the water was delivered from outside, where did it come from?

It was widely speculated that comet Shoemaker-Levy 9 may have been the origin of this water, but direct proof was missing. Now Herschel’s sensitive infrared eyes have solved the mystery. The space observatory has found 2-3 times more water in the southern hemisphere of Jupiter than in the northern hemisphere. The traces of water are only found at high altitudes and most of it is concentrated around the sites of the 1994 comet impacts.

Even more detailed observations of the gases that make up Jupiter’s massive atmosphere will be made by ESA’s JUICE mission, which is planned for launch towards the giant world in 2022.

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