The stripy bands on Jupiter are made from roaring winds that penetrate deep below its surface and circle round the entire planet.
An international team of physicists studied the gas giant’s atmosphere by measuring its gravity field using using radio waves emitted by NASA’s Juno spacecraft during close flybys. Their results have been published in Nature.
As Juno edges closer, Jupiter’s gravity pulls on the spacecraft and shifts the wavelength of its radio signals by a small amount. The change in wavelength provides a way to indirectly calculate the planet’s gravity field and its atmospheric and interior flows.
The researchers found powerful wind belts that extend to a depth of about 3000 kilometers – much deeper than previously thought – and have lasted hundreds of years at least. Jupiter’s atmosphere makes up 1 per cent of its total mass – it might sound like a small proportion, but its huge compared to the Earth’s atmosphere which is only a millionth of its total mass.
Yohai Kaspi, co-author of the paper and a professor at the Weizmann Institute of Science, Israel, who led the research said: “That is much more than anyone thought and more than what has been known from other planets in the Solar System. That is basically a mass equal to three Earths moving at speeds of tens of meters per second."
As these winds ripple around the planet, it disturbs the distribution of mass and makes the strength of the gravity field vary at different points.
“Since Jupiter is basically a giant ball of gas, the initial expectation was that there would be no asymmetries in the gravity field between the north and south," Kaspi said.
But the researchers' expectations were proven wrong, as there were clear anomalies between the gravitational field strength at the north and south.
The asymmetry of the gravitational field allowed the researchers to estimate the depth of its atmosphere. In a recent, separate paper also published in Nature, another team of physicists studied this asymmetry in more detail and found that the gas floating beneath Jupiter’s winds rotates synchronously as if it were a single solid body.
It’s still unclear if Jupiter has a solid core at its center or is just one giant gaseous orb. Next, Kaspi and his colleagues hope to study its famous Great Red Spot to find out why this particular storm has been dwindling over time. ®