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On October 24, 2017, the Juno spacecraft swung low over Jupiter’s poles for the ninth time. Accelerating by the giant planet’s powerful gravity to the nearly unbelievable velocity of 60 kilometers per second — fast enough to cross the continental United States in a minute and a half — it screamed over the cloud tops, taking scientific data to send back to Earth.
It also took a series of images using the JunoCam, a camera designed not for science but for public outreach. These shots of the solar system’s largest planet are meant primarily to excite the public about astronomy and planetary science, with the science itself being secondary.
And oh yeah, these images are very, very exciting. Behold!
That is a giant cyclone in Jupiter’s clouds. If I’ve read the metadata correctly, the main body of this system is about 3,000 km across (roughly the size of Earth’s Moon), and the spiral arms extend to over 7,500 km. That’s comfortably larger than the U.S.
This image was taken when Juno was about 10,000 km above Jupiter’s clouds, and the cyclone (a swirling mass of air around a low-pressure system that rotates counterclockwise in the northern hemisphere) is at the northern mid-latitudes. You can see brighter spots along the main system as well as in the arms; given the shadowing that betrays 3D structure, those look like storm clouds rising via convection in Jupiter’s troposphere.
It may be an illusion (it can be hard to tell), but the whole system looks like it’s above the other cloud tops, too. But that fits: On Earth, clouds are white due to water vapor, but in general whiter clouds on Jupiter are from ammonia ice. So if these clouds are higher, it would be cooler, and ammonia ice could form.
[Caveat videntium: I am not an expert here, so my interpretation of this may be off.]
This image was created by Gerald Eichstädt, who does the raw image processing, and Seán Doran, who taken “an aesthetic pass” at them to improve the colors and composition. If their names are familiar, they’ve done incredible work on Juno images that I’ve featured on this blog before. Also, I just wrote about some of Doran’s other amazing work creating art with space-based data.
The storms on Jupiter are powered in part by the Coriolis effect, which I have explained in detail for storms on Earth. But Jupiter is 11 times wider than our planet, and spins almost 2.5 times faster (its day is just under 10 hours long), so this effect is 25 times stronger on Jupiter than Earth! This is why there is so much swirling in the giant planet’s atmosphere.
Oh wow. Taken from above Jupiter at a distance of about 19,000 km, the center of this image is at about a Jovian latitude of 57° north, which on Earth would be, for example, around the middle of Alberta, Canada (north is roughly to the right; you can see the more southern swirl I showed earlier to the left).
Look at all that gorgeous activity! As you get farther north on Jupiter the familiar banding disappears and is replaced with a chaos of cyclones and anticyclones (high-pressure systems that rotate the opposite sense of cyclones). Again, you can see white clouds towering above the others, and to the best of my knowledge it’s not totally understood why the atmosphere appears blue here … though it’s certainly due to temperature and composition — Jupiter’s atmosphere is a mess of chemicals like hydrogen, helium, ammonia, methane, water, hydrogen sulfide (the molecule that makes rotten eggs stink), and more. Part of Juno’s mission is to understand this better.
Although the colors aren't as vivid, there's a surprise in it: The moons Io and Europa! Jupiter's moons aren't a primary target for Juno; on its orbit it never really gets close to them. But it's always nice to see them; it somehow makes Jupiter seem less alien to me.
This close pass (called perijove) was the ninth overall, and the eighth one where science instruments were on and taking data. Originally, the probe was to drop into a lower orbit and make 37 orbits of the planet. This would put Juno on a path through Jupiter’s intense radiation belts (powered by its magnetic field and fed by the solar wind and particles blasted into space by its moon Io), degrading the spacecraft electronics.
However, a stuck valve prevented the orbital maneuver, and it’s been on the current 53-day orbit for over a year now. The current trajectory keeps it out of the worst of the radiation, and also is designed to keep it in direct sunlight so that the solar arrays get power. This has extended the mission, which may go beyond 2019. The science instruments are deep inside the body of the spacecraft and well protected, but JunoCam is on the outside, and may feel those effects sooner.
Doran and Eichstädt have put more amazing images on their Perijove 9 Flickr page, and you can find more of Doran’s work on his Flickr page, too (the JunoCam page has images from the public as well). Since we don’t know when JunoCam will eventually succumb to its environment, you should gawk at these testaments to Jovian majesty while you can.