Herschel links Jupiter’s water to comet impact

23 April 2013 - ESA's Herschel space observatory has solved a long-standing mystery as to the origin of water in the upper atmosphere of Jupiter, finding conclusive evidence that it was delivered by the dramatic impact of comet Shoemaker-Levy 9 in July 1994. During the spectacular week-long collision, a string of 21 comet fragments pounded into the southern hemisphere of Jupiter, leaving dark scars in the planet's atmosphere that persisted for several weeks. The remarkable event was the first direct observation of an extraterrestrial collision in the Solar System. It was followed worldwide by amateur and professional astronomers with many ground-based telescopes and the NASA/ESA Hubble Space Telescope. ESA's Infrared Space Observatory was launched in 1995 and was the first to detect and study water in Jupiter's upper atmosphere. It was widely speculated that comet Shoemaker-Levy 9 may have been the origin of this water, but direct proof was missing. Scientists were able to exclude an internal source, such as water rising from deeper within the planet's atmosphere, because it is not possible for water vapour to pass through the 'cold trap' that separates the stratosphere from the visible cloud deck in the troposphere below.