A hot spot in Jupiter's upper atmosphere is caused by the planet's most recognisable feature, according to scientists.
The Great Red Spot, a massive storm system three times wider than the Earth that is readily apparent in photographs of the gas giant, is heating the atmosphere high above it to temperatures hundreds of degrees warmer than anywhere else on the planet.
Scientists made the discovery after observing Jupiter's infrared light emissions, which allowed them to make temperature measurements.
At high altitude, some 800km above the planet's visible cloud tops, temperatures were much greater than would be expected as a result of warming by the distant Sun.
"We could see almost immediately that our maximum temperatures at high altitudes were above the Great Red Spot far below – a weird coincidence, or a major clue?" said Dr James O'Donoghue, a member of the team from Boston University in the US.
The Great Red Spot (GRS) was first officially recorded in 1831 but may have been the same ‘permanent spot’ identified by Italian astronomer Giovanni Cassini in 1665.
It consists of a hurricane-like system of gases swirling at speeds of up to 684km/h. Because of its size, the winds can take six days to complete one revolution.
Study co-author Dr Luke Moore, also from Boston University, said: "The Great Red Spot is a terrific source of energy to heat the upper atmosphere at Jupiter, but we had no prior evidence of its actual effects upon observed temperatures at high altitudes."
The scientists concluded that the GRS produces ‘acoustic waves’ of energy, waves that vibrate in the direction of their travel, that heat the upper atmosphere.
A similar effect on a much smaller scale has been observed over the Andes mountains on Earth.
The Juno probe, an armour-shielded spacecraft on an exploration mission, reached Jupiter earlier this month after completing its five-year, 2.2-billion-kilometre journey from Earth.
But the Boston researchers took their data from the Earth-bound SpeX spectrometer at Nasa’s Infrared Telescope Facility on Mauna Kea, Hawaii.
Using the three-metre infrared telescope, the team observed non-visible infrared light hundreds of miles above the gas giant where they found temperatures to be much higher in certain latitudes and longitudes in Jupiter’s southern hemisphere, where the spot is located.
SpeX lies on the same site as the partially completed Thirty Meter Telescope, which has been beset with delays following protests from local Hawaiians who say it would damage sacred lands.