Diving into Jupiter's Great Red Spot

The Juno spacecraft recently passed over the poles of the overwhelmingly huge planet Jupiter for the ninth time. Its orbit is extremely elongated, so when it dives in and screams over the jovian cloud tops, it only sees a fairly narrow strip of real estate up close.

So it didn't fly over Jupiter's iconic Great Red Spot until July 2017, zipping past it at 200,000 kilometers per hour (that’s fast) at a soul-freezing 9,000 km above clouds. The images it returned are as devastatingly awesome as you might expect, but now we're getting the science from it as well.

Planetary scientists have been analyzing the data returned on the Spot by Juno, and discovered some interesting things about it. We've known for a long time the Spot is a gigantic storm bigger than Earth, a high-pressure vortex that's been spinning for centuries (at least). But how deep is it?

Juno can see below the Great Red Spot’s surface layer to the warmer depths below using a detector sensitive to microwaves. This allows scientists to map the regions under the spot to a depth of hundreds of kilometers. Credit: NASA/JPL-Caltech/SwRI

Photo: NASA/JPL-Caltech/SwRI

Deep. The "roots" of the storm go down about 300 kilometers. That's fairly shallow compared to its 16,000 km extent (the ratio is about the same as the width of a stack of 50 sheets of writing paper to their thickness), but still deep; storms on Earth are not even a tenth that tall. Of course, Jupiter is atmosphere for a long way down, hundreds or even thousands of kilometers before the pressure squeezes it into a weird form of liquid.

The folks at JPL put together a video that combines Juno data with an animation to give you a feel for this:

I'm not sure how much that helps^*, but it does give a sense of the scale of the clouds to the depth of the storm.

So how did they do this? The clouds in the Spot are opaque to visible light, but there are other types of light, like microwaves. These have far longer wavelengths than the kind of light we see, and can more easily penetrate the clouds. The warm layers under the Spot emit this kind of light, and by looking at different wavelengths, Juno's Microwave Radiometer can "see" into different depths. It's like peeling away the Great Red Spot in layers.

We've all been drooling over the magnificent JunoCam images coming back from the spacecraft, but it's important to remember that this particular camera was installed primarily as a public service, specifically to take those jaw-dropping images. We do get science from them, of course, but Juno is loaded with other instruments that are designed to understand Jupiter's interior.

Which, I'll note, we don't understand all that well. We're not even sure if Jupiter has a core! Early results from Juno indicate Jupiter might have a core, but it's indistinct and bigger than previously thought. Hopefully that knowledge will tighten up as the mission progresses.

Another instrument, the Jupiter Energetic Particle Detector Instrument — yes, abbreviated JEDI — is designed to detect subatomic particles flung about by the planet’s immensely strong magnetic field. We've known for a long time that Jupiter has several belts of radiation around it, akin to the Earth's Van Allen belts, but new data from Juno show there's a new one, previously unknown, very close to the cloud tops. It was detected because Juno flew through it! In it, hydrogen, sulfur, and oxygen ions (atoms stripped of their electrons, becoming positively charged and therefore able to be affected by the magnetic fields) are getting whipped around at seriously high velocities, large fractions of the speed of light. The sources of these atoms may have been Europa and Io, two of Jupiter's big moons.

The amount of radiation in Jupiter's magnetosphere is intense, enough to kill an unprotected human pretty quickly (of course, unprotected you'd also have issues with the lack of air and freezing solid, too). Juno is armored like a tank to protect it, but even then it won't last forever. It should be operable into 2019 at least, but we'll see. Jupiter is terrifying.

Jupiter's also cool. But it's best, I think, viewed from a safe distance. I'm happy to let Juno be there and do that for us fragile, gloppy humans.

^* I think they borrowed the soundtrack from Space:1999.