Everyone’s heard of Jupiter’s four most famous moons Europa, Io, Callisto, and Ganymede—we’ve known about them for over 400 years, thanks to Galileo—but giant Jupiter has many more moons than that. To date there are thought to be 69 natural satellites orbiting Jupiter. 53 are officially named, while 16 are awaiting further confirmation. So you’d be forgiven for not being immediately familiar with all of them…it’s a big Jovian family!
The little world seen above is one of Jupiter’s smaller and lesser-known satellites and it holds a particular distinction. It’s called Metis (pronounced like “meet” in the present tense, not “met” in the past) and it’s only about 37 miles across and 21 miles high. It is the closest moon to Jupiter, orbiting within the planet’s main ring (yes, Jupiter has rings) at a distance of about 80,000 miles. It’s also Jupiter’s speediest moon—at 70,500 mph it completes a single orbit in just over 7 hours. That’s almost three hours less than a Jovian day!
If you think that Saturn’s polar storm systems are amazing then you’re gonna love this: Jupiter has them too, and not just a single central storm over each of its poles either. NASA’s Juno mission has revealed that Jupiter has not only polar vortices but also a ring of enormous cyclones spinning in formation around both of its poles—five around its south pole and a whopping eight around its northern one! Each of these cyclones is gargantuan in its own right, easily big enough to span the Atlantic Ocean, and somehow they all manage to avoid merging with their respective neighbors via some as-yet unknown process. It’s literally like nothing found anywhere else in the Solar System!
On this night in 1610 the Pisan astronomer Galileo Galilei looked up at a bright Jupiter at opposition through his handmade telescope and noted three little “stars” next to it, piquing his natural scientific curiosity. Further observations over the next few nights showed that the planet wasn’t moving relative to the little “stars” as it would have if they were indeed background stars. In fact the smaller objects (of which he soon saw four) were moving along with Jupiter, each in its own little path. He realized that the little objects weren’t stars at all but rather moons orbiting the giant planet—and, most importantly, not the Earth. This revelation helped change our entire view of the Solar System… and caused no end of trouble for Galileo as the Church didn’t appreciate a restructuring of their conveniently Earth-centered Universe. But it also opened the door for later discoveries of many more moons around other planets.
Saturn has its rings, Mars has its rusty landscape, Earth has its whales, water, and wi-fi…and Jupiter has its Great Red Spot. The giant gas planet’s enormous orange storm—once over twice the diameter of Earth but today “only” about 1.3 times as wide—is one of the most distinctive planetary features in our Solar System. It’s so well-known that even young children are sure to include its orangey oval when drawing Jupiter!
But as famous as it is, there’s a lot we still don’t know about Jupiter’s giant storm. NASA’s Juno spacecraft, launched in August 2011, has now been orbiting Jupiter since July 4, 2016 and has been using its suite of science instruments to investigate the planet’s complex atmosphere like never before possible. Thanks to Juno, for the first time scientists are able to “see” deep below Jupiter’s dense clouds (in microwave wavelengths, that is) and find out what’s happening inside the GRS. What they’ve discovered is a storm hundreds of miles deep with a hot base that powers its winds.
They’ve arrived! Images from NASA’s Juno spacecraft P7 pass have landed on Earth (a few days early no less) showing Jupiter’s Great Red Spot from the closest distance that it’s ever been imaged before. Captured on the night of July 10 (early July 11 morning UTC) the closest Junocam images were taken from a distance of only about 5,600 miles from the top of the storm’s clouds—that’s less than an Earth diameter away from a hundreds-year-old hurricane an Earth and a half wide!