Scientists don't know what makes the Great Red Spot so long-lasting. Nor can they explain the chemistry behind its brilliant color. But thanks to NASA's Juno spacecraft, now on its second year of orbiting Jupiter, they know that the storm's roots go deep: The well of hot, swirling gas that powers the Great Red Spot extends some 217 miles into Jupiter's interior.
The finding was announced Monday at the annual meeting of the American Geophysical Union, along with other results from Juno's first eight flights past the solar system's largest planet. The spacecraft arrived in orbit around Jupiter in summer 2016 and has since performed looping orbits that take it skimming between Jupiter's cloud tops and radiation belts once every 53 days.
On Earth, the Great Red Spot would almost graze the orbit of the International Space Station. The highest clouds of our planet's worst hurricanes top out at around 10 miles.
But understanding the behavior of the Great Red Spot could improve scientists' understanding of weather on Earth, said California Institute of Technology planetary scientist Andy Ingersoll, a co-investigator for the Juno spacecraft. He called Jupiter's giant storm a good “stress test” for Earth-based weather models.
It isn't clear what the new find means for the future of the storm — Ingersoll said the spot already has stretched traditional weather models to their limits. But the spot has been shrinking steadily since the Voyager 2 spacecraft visited it in 1979; it used to be big enough to engulf two Earths.
High above the cloud tops, Jupiter is enveloped in radiation belts formed by charged particles that get trapped by the planet's magnetic field. On Monday, scientists said that Juno had discovered a new area of radiation just above the planet's atmosphere at the equator. The high energy particles in this region are even more intense than those that make up the radiation belt. But none of the eight spacecraft that preceded Juno at Jupiter had spotted it.
Juno's orbit meant “we literally flew through it,” said Heidi Becker, a physicist at NASA's Jet Propulsion Laboratory who leads Juno's radiation investigation team.
The radiation in this region is thought to stem from fast-moving atoms of hydrogen, oxygen and sulfur. These particles are produced in the gas clouds around Jupiter's moons, Io and Europa, but are stripped of electrons and become charged as they interact with Jupiter's atmosphere.
The spacecraft found another area of high-energy particles in Jupiter's inner radiation belt, where electrons move at nearly the speed of light. Becker and her colleagues are still studying the exact nature of these particles.
Juno's other discoveries at Jupiter include clusters of 600-mile-wide cyclones at the planet's poles and an uneven magnetic field that is weak in some places, but in others is 10 times as strong as anything found on Earth. The spacecraft's high resolution camera has also taken thousands of detailed images, revealing a planet that looks like a cross between a Van Gogh painting and the world's most elaborate latte foam art.
In a lecture, project scientist Scott Bolton pulled up one of Juno's images of Jupiter's blue-tinged polar storms and burnt sienna gas clouds.
“If you had shown us that five years ago, we couldn’t have guessed what planet it was,” he said.