PASADENA, Calif., April 23 (UPI) -- Astronomers say all the water present in a layer of Jupiter's atmosphere was delivered by comet Shoemaker-Levy 9, which famously struck the planet in 1994.
Data from the Herschel space observatory, a European Space Agency mission with NASA participation, reveal two to three times more water in Jupiter's southern hemisphere, where the impacts occurred, than in the north, a release from NASA's Jet Propulsion Laboratory in Pasadena, Calif., reported Tuesday.
The source of water in the upper atmospheres of the solar system's giant planets -- Jupiter, Saturn, Uranus and Neptune -- has been debated for almost two decades, scientists said.
Water in the lower layers of their atmospheres can be explained as internal in origin, but the presence of water molecules in their upper atmospheric layers is puzzling due to the scarcity of oxygen there, suggesting their origin was external.
The mystery has been solved, at least for Jupiter, by the discovery of an asymmetry in the distribution of water in its stratosphere, caused by the comet impact, researchers said.
"The asymmetry between the two hemispheres suggests that water was delivered during a single event and rules out icy rings or moons as candidate sources," said study leader Thibault Cavalie from the Laboratoire d'Astrophysique de Bordeaux in France.
The majority of the water in the upper atmosphere of Jupiter's southern hemisphere is concentrated around the sites of the 1994 comet impact, the astronomers said.
"Local sources would provide a steady supply of water, which over time would lead to a hemispherically symmetric distribution in the stratosphere," Cavalie said.
"According to our models, as much as 95 percent of the water in the stratosphere is due to the comet impact."