Great Red Spot makes Jupiter hot
Jupiter’s Great Red Spot has fascinated scientists for hundreds of years. The centuriesold, hurricane-like storm — once three times as large as Earth, but now around half that size — runs on the kind of time and size scale that reminds us just how tiny our own world really is. According to a study published Wednesday in Nature, the Great Red Spot, or GRS, may help solve a longstanding Jovian mystery: The upper atmosphere of this gaseous planet is much, much hotter than it should be, and tumultuous winds down below may be to blame.
Jupiter, the king of the solar system by measures of both age and size (and even by mass, which is pretty impressive given that it’s made of gas) is five times farther away from the sun than Earth is. But somehow, its upper atmosphere is nearly as hot as our own.
“We call this question the energy crisis, and it’s been going on since the late ’70s,” said Boston University’s James O’Donoghue, lead author of the new Nature study. “It’s relentless.”
By rights, O’Donoghue explained, Jupiter’s upper atmosphere should be around -100 degrees Fahrenheit. Instead, the temperatures average from between 800 degrees to 1,700 degrees — a massive discrepancy. So if the sun’s rays aren’t to blame, what’s causing things to heat up?
Jupiter has the most tumultuous magnetic field of any planet in the solar system. The charged particles that zip up and down its poles — nearly at the speed of light — are so powerful that NASA’s recently inserted Juno probe needed a 400-pound titanium shield to protect its computer components from being shredded. That activity could explain why the poles get as hot as they do — around 1,700 degrees Fahrenheit — but, O’Donoghue said, “the rest of the planet really has no excuse.”
He and his colleagues used the Infrared Telescope Facility on Mauna Kea, Hawaii, to look at heat signatures across the entire upper atmosphere, hoping that creating a global temperature map would help them pick out trends. Sure enough, the atmosphere just above the Great Red Spot stood out as a great big hotspot, reaching temperatures of over 2,400 degrees Fahrenheit — the highest ever detected on the planet.
The researchers believe the energy that heats the upper atmosphere may come up from below, with the GRS providing an extreme example. The rest of the atmosphere’s heat may come from Jupiter’s swirling bands: Some move hundreds of miles per hour in one direction while bands of cloud below move just as quickly in the opposite direction. That turbulence could produce gravity waves (which aren’t the same thing as the gravitational waves produced by black hole collisions and the like — gravity waves form when fluids meet and gravity tries to restore equilibrium between them, like when the wind meets the ocean and creates a wave or tsunami) that carry energy up into the atmosphere.
Now that NASA’s Juno probe is in orbit, the king of the planets could get a lot less mysterious. O’Donoghue’s work will continue to mostly rely on groundbased telescopes, but he hopes that some of the probe’s data will help inform this energy mystery. An infrared instrument on board could help confirm the GRS temperature readings, and might be able to detect hotspots over other, smaller storms. Juno, which will use its instruments to probe below Jupiter’s cloud cover for the first time ever, could also help answer basic questions about those swirling gasses: We don’t know how deep the GRS or the rotating bands go, or whether there’s a rocky core hiding beneath them.