Juno Explores the Great Red Spot on Jupiter

Tracking an Ancient Storm

Jupiter is an amazing sight — even in our night skies. Sure, it looks like a bright dot of light, but you can explore it with binoculars or a reasonable backyard-type telescope pretty easily to spot some details. With the binos, you can find the four largest moon. The telescope will give you a hint of the most amazing storm in the solar system: the Great Red Spot. This giant windstorm has been whirling around the planet for hundreds of years. Its size changes over time, from a whopping three Earths across to a mere one Earth-wide storm. The color shifts, too. It used to be much redder, now it’s more of an orange-pink. You can detect all those changes from Earth, but to get the real story on the Great Red Spot, it’s necessary to look at spacecraft views.

Juno Zeroes in on the Red Spot

For more than a year, the Juno spacecraft and its ever-busy JunoCam have been circling the planet and sending images and data about Jupiter back to Earth. The views have been fantastic. Image after image shows swirling cloud decks, belts, and zones.  One target has always been the Great Red Spot, so in early July 2017, the spacecraft swooped low over the planet to get a closer look. The raw images revealed a little of the complexity of the storm, and image processing by qualified citizen scientists brought out the rest. Couple that with data from the craft’s other science instruments, and the spot turns out to be a trove of information. It will answer questions about the longevity of this storm, the processes that formed it, and perhaps even why it seems to shift size and change color.

There are some clues to the changes provided by the chemistry of the clouds that make up the spot. They contain ammonia, ammonium hydrosulfide, and water (plus traces of other gases). Somehow the chemical reactions in these clouds are involved in the changing colors, although it’s not clear what reaction causes the shift. The planet is also bombarded by cosmic rays and has its own highly charged radiation environment. So, could those together explain why the Great Red Spot (sometimes pinkish orange) is as colorful as it is? Planetary scientists are still trying to figure that out. The Juno measurements may help solve the puzzle, and mission scientists are working on its data now.

The Great Red Spot’s Structure

Just by looking at the images of the spot, you might conclude that it’s about the same altitude as the rest of the clouds. Turns out that’s not quite right. The spot is actually some kilometers higher in the atmosphere than the clouds it appears to be a part of; it’s also colder. It whirls around the planet about once every six Earth days and is a very stable type of storm. No one is sure how long it will last, although it has been observed from Earth since the 1800s. So, it’s a long-lasting, color-changing storm blasting its way through a giant planet’s atmosphere. The more we look at it, the more we learn about Jupiter’s atmospheric dynamics (that is, its motions and changes).

After the Great Red Spot Flyby, What about Juno?

The Juno mission is slated to do 37 orbits around Jupiter. It arrived at the giant planet in summer 2016 and began its long, looping orbits right away.  Its nominal mission should be done by mid-September 2017. Any extra time after that will be used to do more imaging until the instruments fry in Jupiter’s strong radiation belts, or fail for some other reason. The spacecraft will be deorbited into the Jovian cloud tops after that, plummeting in sometime during 2018 or 2019. Its mission is to study the planet, help determine more details about its composition, measure the magnetic field and gravity, and look for more clues about how the planet formed and evolved. While the general idea is that Jupiter is largely a gas-rich world, current theories also suggest it has more hidden than we know about. That includes a rocky interior about the size of our planet, and it may harbor significant reserves of water well beneath the cloud masses. Here’s hoping that Juno’s mission data will help solidify our understanding of Jupiter and its active atmosphere.

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