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) wide 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 perplexing mysteries about our Solar System’s largest planet — why it’s so much hotter than models predict.
It’s the permanent auroras flickering at Jupiter’s poles that could provide the extra energy to heat the gas giant to temperatures much hotter than we expect – and likely, along with a dense solar wind, is responsible for the heat.
“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 inkling that there was something fancy going on 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 4% of the solar radiation that reaches Earth.
Its upper atmosphere should average around -73 degrees Celsius (-99 degrees Fahrenheit). Instead, it sits at about 420 degrees Celsius – comparable to Earth’s upper atmosphere and much higher than can be due to solar heating alone.
That means there must be something else going on at Jupiter, and the first heat maps obtained by O’Donoghue and his colleagues and published last year pointed to a solution.
Jupiter is crowned by the most powerful auroras in the Solar System, burning at wavelengths invisible to the human eye. We also know that auroras here on Earth cause negligible heating of our own atmosphere.
Jupiter’s auroras are very similar to those on Earth: an interaction between charged particles, magnetic fields and molecules in the planet’s atmosphere. And they are also very alien. Earth’s auroras are born from gusts of particles blown by strong solar winds. They are sporadic, based on this irregular introduction.
Jupiter’s auroras are permanent, created by particles from the moon Io, the most volcanic object in the Solar System, which constantly spews sulfur dioxide. This forms a torus of plasma around Jupiter, which is channeled to its poles via magnetic field lines, where it rains down into the atmosphere.
Et voilà – saddle. Previous heat maps of Jupiter revealed hot spots just below the auroral oval, suggesting a connection between the two.
But then it got more interesting. Io’s contribution does not mean that there is no auroral contribution from the Sun, and this is what O’Donoghue and colleagues observed.
As they gathered observations of Jupiter and its strange temperatures, a dense solar wind slammed into the gas giant. As a result, the team noticed an improvement in the heating of the saddle.
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Because the hot gas expands, this is likely what sent the heat wave spilling out of the auroral oval and rolling toward the equator at speeds of up to thousands of kilometers per hour.
So, as it spread, this would have delivered a significant amount of additional heat to the Jovian atmosphere.
“While auroras continuously transmit heat to the rest of the planet, these heat wave ‘events’ represent an additional, important source of energy,” explains O’Donoghue.
“These findings add to our knowledge of Jupiter’s weather and climate in the upper atmosphere and are a great help in trying to solve the ‘energy crisis’ problem that plagues research on the giant planets.”
Jupiter is not the only planet in the Solar System that is warmer than it should be. Saturn, Neptune, and Uranus are hundreds of degrees warmer than solar heating can explain.
While none of the others have Jupiter-scale auroras, this finding represents an avenue for exploration that may go some way toward solving the puzzle.
The team presented their findings at the Europlanet Science Congress 2022.