For 50 years, researchers have struggled to explain one of Jupiter’s lingering mysteries: Why is its upper atmosphere so hot? Based on the intensity of sunlight Jupiter receives, its highest levels should be -100 degrees Fahrenheit (-73 degrees Celsius). Instead, they sizzle at around 800 F (426 C).
One hypothesis held that Jupiter somehow generates heat from below – possibly from storms lower in its atmosphere. Or, some have speculated, his insides could still settle down by gravity and release heat.
But the main suspect has been Jupiter’s auroras, which are produced when the planet’s magnetic field traps charged particles and sends them to its poles. When these particles break into molecules in the atmosphere, they cause them to glow and inject a huge amount of energy into the poles in the process.
While in principle this could heat the entire planet, atmospheric models have predicted that the planet’s strong winds trap heat at the poles and prevent it from spreading to lower latitudes.
But a study in Nature published on August 4 suggests that these models may be missing something. An international team of researchers used the Keck Observatory in Hawaii to measure the infrared emission of hydrogen molecules in Jupiter’s atmosphere, producing a high-resolution temperature map of the planet.
Their analysis found that the polar regions directly below the aurora were about 720 F (400 C) warmer than equatorial climates, clear evidence of the aurora’s ability to heat the poles. And on the team’s second night of sightings (January 25, 2017, about nine months after the first), they also found evidence that this heat can spread elsewhere: a warm band appeared south of the main auroral oval, 360 F (200 C) warmer than its surroundings and enveloping half the planet.