A heat wave the size of 10 Earths has been discovered rippling through Jupiter’s atmosphere.
It was 130,000 kilometers (about 81,000 miles) in diameter and 700 degrees Celsius (1,292 degrees Fahrenheit), traveling at speeds of up to 2,400 meters per second away from the Jovian north pole.
And that, scientists say, could solve one of the most puzzling mysteries about our Solar System’s largest planet: why it’s so much hotter than models predict.
It is the permanent auroras that shine at Jupiter’s poles that could provide the extra energy to heat the gas giant to temperatures much higher than we expect, and are likely, along with a dense solar wind, responsible for the heat wave.
“Last year we produced … the first maps of Jupiter’s upper atmosphere capable of identifying the dominant heat sources,” says astronomer James O’Donoghue of the Japan Aerospace Exploration Agency ( JAXA) in Japan.
“Thanks to these maps, we showed that Jupiter’s auroras were a possible mechanism that could explain these temperatures.”
The first hint that there was something fishy in Jupiter’s atmosphere came in the 1970s, about 50 years ago.
Jupiter is much further from the Sun than the Earth; about five times the distance, in fact. At this distance, it receives only four percent of the solar radiation that reaches Earth.
Its upper atmosphere should have an average temperature of about -73 degrees Celsius (-99 degrees Fahrenheit). Instead, it is at about 420 degrees Celsius, comparable to Earth’s upper atmosphere, and much higher than can be explained by solar heating alone.
That means there must be something more to Jupiter, and the first heat maps, obtained by O’Donoghue and colleagues and published last year, pointed to a solution.
Jupiter is crowned by the most powerful auroras in the Solar System, shining in wavelengths invisible to the human eye. We also know that auroras here on Earth cause a non-negligible warming of our own atmosphere.
Jupiter’s auroras look a lot like Earth’s: an interaction between charged particles, magnetic fields, and molecules in the planet’s atmosphere. And they are also very alien. Terrestrial auroras are born from bursts of particles blown in by powerful solar winds. They are sporadic, dependent on this irregular input.
Jupiter’s auroras are permanent, generated by particles from its moon Io, the most volcanic object in the Solar System, which constantly belches sulfur dioxide. This forms a torus of plasma around Jupiter, which is channeled to its poles by magnetic field lines, where it rains down into the atmosphere.
Et voila – aurora. Previous heat maps of Jupiter revealed hot spots directly below the auroral oval, suggesting a connection between the two.
But then it got more interesting. The contribution from Io does not mean that there is no auroral contribution from the Sun, and this is what O’Donoghue and his colleagues observed.
As they were collecting observations of Jupiter and its strange temperatures, a dense solar wind slammed into the gas giant. As a result, the team observed enhanced auroral heating.
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As the hot gas expands, this is likely what caused the heat wave to spill out of the auroral oval and roll towards the equator at speeds up to thousands of kilometers per hour.
Therefore, as it propagated, this would have delivered a significant amount of additional heat to the Jovian atmosphere.
“While auroras continuously provide heat to the rest of the planet, these heat wave ‘events’ represent an additional and important source of energy,” explains O’Donoghue.
“These findings add to our knowledge of the climate and climate of Jupiter’s upper atmosphere and are of great help in trying to solve the ‘energy crisis’ problem affecting research on the giant planets.”
Jupiter is not the only planet in the Solar System that is hotter than it should be. Saturn, Neptune, and Uranus are hundreds of degrees hotter than solar heating can account for.
While none of the others have Jupiter-scale auroras, this finding represents an avenue of exploration that may go some way to solving the puzzle.
The team presented their findings at the Europlanet Science Congress 2022.