Jupiter is renowned for being a cold planet, with normal temperatures averaging roughly -145 degrees Celsius. On the gas giant, however, JAXA (Japanese Aerospace Exploration Agency) scientists have found an unexpected 700 degrees Celsius 'hot wave' that stretches over 130,000 kilometres. About 12,742 km is the diameter of the Earth.

To put that in perspective, the temperature of Jupiter's top atmosphere should be -70 degrees Celsius. Instead, they are recording a temperature of almost 400 degrees Celsius at the cloud top. For a planet that receives only 4% as much sunshine as Earth, this is extraordinarily hot.

'Last year, we created the first maps of Jupiter's upper atmosphere that could pinpoint the main sources of heat, which we then presented at EPSC2021. These maps allowed us to show that Jupiter's auroras might be a mechanism to account for these temperatures, according to JAXA's James O'Donoghue. The research's findings were presented by O'Donoghue at the Granada-based Europlanet Science Congress (EPSC) 2022.

Solar wind causes auroras to appear near Jupiter's poles, however unlike Earth, where auroras only appear when solar activity is particularly active, auroras on Jupiter are always present. The area around the poles is being heated to approximately 700 degrees Celsius by these auroras. The heat is subsequently redistributed about Jupiter by the planet's global winds.

O'Donohogue and his team located the heat wave just below the northern aurora and found that it was moving at thousands of kilometres per hour in the direction of the planet's equator. The planet's magnetic field was presumably affected by a pulse of amplified solar wind, which caused the heat wave. As a result, gases were compelled to expand and travel closer to the equator, increasing auroral warmth.

'These heat wave 'events' constitute an extra, major energy source, while the auroras continue to provide heat to the rest of the earth. These discoveries deepen our understanding of Jupiter's upper atmosphere and environment and greatly aid our efforts to address the 'energy dilemma' that impedes research on the big planets, said O'Donohogue.