Jupiter and its moon Ganymede in 2007. Image credit: NASA, ESA, and E. Karkoschka (University of Arizona)

 
One of Jupiter's most baffling mysteries might be solved at last. The problem: Jupiter's upper atmosphere shouldn't be as hot as it is. The planet is simply too far from the Sun, and scientists have long puzzled over the reason for this phantom heat. Where is it coming from? At last, they think they've found the source, and it's the most conspicuous place on the planet: its characteristic Great Red Spot.

Scientists with the Center for Space Physics at Boston University used NASA's Infrared Telescope in Hawaii to map the temperatures of the gas giant. They found the upper atmosphere of Jupiter to range between 800°F and 1700°F—expected numbers based on previous observations, though still perplexing, as solar heating should leave the atmosphere somewhere around -100°F. Over the red spot, however, they were astonished to find measurements as high as 2400°F. Heat—and a lot of it—is somehow radiating from it. This upper atmosphere is the hottest region of the entire planet. So what is going on up there? 

FROM SOUND WAVES TO HEAT GENERATION

The red spot itself is a giant, continuous storm that's been going for at least 300 years. It's bigger than Earth, and it grows and contracts over time. (It once was three times the size of Earth, but it's since shrunk.) How turbulent is it? So turbulent that scientists now think the sound waves it generates are warming the planet. According to the study, published last week in Nature, as the storm swirls, its roar essentially blasts the upper atmosphere, exciting particles there and thus raising its temperature. This is surprising because scientists didn't expect phenomena from so much lower in the atmosphere (the spot) to affect something so high (the upper atmosphere).

Of course, that isn't the only action heating the planet; the interplay of stripes—some moving one direction, clouds moving in the other—also create heating. Its magnetic field, meanwhile, heats its poles as particles zip around at just under the speed of light. But the Great Red Spot's heat vortex is a newly discovered phenomenon.

How mysterious is Jupiter? Quite. It's a giant weather ball that's always in flux. We don't even know why the Great Red Spot is red, let alone why it doesn't stay red. Sometimes the red spot is pink. Sometimes stripes disappear and reappear

ANSWERS ARE COMING

There is hope for our understanding of Jupiter, and it is already in orbit around that planet. NASA's Juno spacecraft, which entered orbit around Jupiter on July 4, 2016, is designed precisely to analyze the planet's composition, among many other things, and to study its powerful winds, the makeup of its atmosphere deep into the planet, and even ascertain whether there's a rocky core at the center of it all.

This past weekend, the spacecraft reached "apojove," the most distant point of its highly elliptical orbit around Jupiter. It is presently 5 million miles from the planet, on an orbit that will take it as close as 2600 miles. This is the first of two such orbits, each lasting 53.5 days. The science phase of the mission, when the bulk of data is collected, is set for late October. It will involve an orbit that's much faster and tighter: 4900 miles to 2600 miles over a period of 14 days. It will perform 32 such orbits before plunging to its doom into Jupiter. 

So much is unknown about Jupiter that will take years for scientists to work through all of the data that is collected. They will construct models and hypotheses for what they find, and slowly piece together how the planet works. These latest findings by the Center for Space Physics help in that effort and give Juno one more thing to investigate while it's there.