NASA’s Juno spacecraft made another of its close flybys of Jupiter on Dec. 11 and returned this new photo featuring a extraterrestrial pearl. But while a real pearl is a lustrous gem built around an irritant such a food particle in a mollusk, this pearl is a storm half the size of the Earth whirling counterclockwise in Jupiter’s upper atmosphere. Its picturesque clouds are composed largely of ammonia ice crystals ‘chillin’ at 190° below zero Fahrenheit (–125° C).
The pearl is but one in a string of eight in the gas giant’s southern hemisphere. Storms on Earth have lifetimes numbered in days and weeks, Jupiter’s can last for decades, even centuries. Since 1986, these white ovals have varied in number from six to nine. A few years back, several merged to form one larger, ruddy-colored storm that resembled a miniature version of the Great Red Spot nicknamed Red Spot Jr. There are currently eight white ovals visible, and they girdle the planet’s southern hemisphere.
Juno orbits the giant planet in a highly elongated (very oval-shaped) orbit and takes its most detailed photos and gathers essential data when it’s closest to the planet. Then it swings back out in a giant loop, slowing down while relaying the its data booty to Earth. When closest, the probe is speeding along at 129,000 mph (60 km/second). Good thing it gets out of there in hurry because it’s during these close brushes that the spacecraft is also most at risk from the maelstrom of high-speed atomic particles whipped around by Jupiter’s powerful magnetic field. To protect Juno’s instruments from harm, most of the electronics are shielded in a ~1/2 thick titanium vault.
Its next close flyby happens on Feb. 2, 2017. While Juno’s performing its loop de loop, you can always picture the action in your mind’s eye any clear morning around dawn. If you’re up around 6:30-7 a.m. face to the south-southeast, and you’ll see two bright “stars” paired together about halfway between the horizon and overhead point. The top one, much brighter, is Jupiter. Below it twinkles Spica, Virgo’s brightest star. Now imagine Juno as the tiniest gnat pestering the giant planet.