The Great Red Spot is the largest atmospheric vortex in the solar system. A storm larger than our whole planet, that has been swirling through the Jovian atmosphere for at least two centuries. And now, scientists have worked out how deep it goes.

In two studies published in Science, researchers have used the instruments on NASA’s Juno spacecraft to probe the vortices of Jupiter even more and have discovered just how deep they are churning its atmosphere.

And they are deeper than expected, with the Great Red Spot reaching up to a depth of 500 kilometers (310 miles) in depth. A new impressive record for a storm 16,000 kilometers (almost 10,000 miles) in diameter.

In one of the papers, Dr Scott Bolton and colleagues use microwave observations to study the motion of the tremendous storms of the planet. The team studied the Great Red Spot and two other storms, one located at 19 degrees North and the other at 33 degrees North. Employing the Microwave Radiometer, they measured the emission of different layers of the atmosphere up to a depth of 600 kilometers (372 miles).

The Great Red Spot and the vortex at 19 degrees North are anticyclones – areas of high atmospheric pressure. The team find behaviors in these vortices consistent with the theoretical model but also found that the midplane of the storm is around the altitude where water and ammonia condenses, that’s where the bottom of the clouds are. And the Great Red Spot is even deeper than the other two, extending tens of kilometers below that.

This finding suggests that there are processes at work that allow for precipitation of water and ammonia below the cloud levels. And even more insight into the deeper layers came from the second paper, authored by Dr. Marzia Parisi and colleagues.   

This was studied using the motion of the spacecraft itself. As Juno flew above the Great Red Spot, gravitational anomalies due to localized densities slightly change the velocity in its orbit around the planet. These measurements can be used to work out the depth of the atmospheric structure, and the team found that two independent methods get the same answer for the depth of the incredible storm, no more than 500 kilometers (311 miles).

Even more interestingly, while the Great Red Spot’s roots are deeper than expected, the surrounding atmospheric jets are six times as deep. These jets are crucial in powering the Great Red Spot, so the difference in depth adds to the mystery of just how exactly the Jovian atmosphere can produce such spectacular storms.