Either Saturn likes playing role-playing games, or it has really weird weather patterns... and we know it has weird weather patterns.
Behold, Saturn's northern hexagon!
This odd six-sided pattern -- which is over 20,000 kilometers across -- was first seen in Voyager images back in the 1970s. When Cassini arrived at Saturn it was winter in the planet's northern hemisphere, so the hexagon was shrouded in darkness. Cassini's infrared cameras were able to get some images, and while they did reveal needed info on the feature, astronomers really wanted higher-res visible light images.
Finally, earlier this year the Sun started peeking over into Saturn's arctic regions as the Equinox approached. When dawn broke over the north pole, astronomers pointed Cassini's higher-resolution visible light cameras there. This new image, taken in January, is a mosaic from those observations. It reveals quite a bit about the hexagon. You can easily see that the clouds are darker inside the hex than outside, for example. The borders of the hexagon have multiple walls of clouds, too, and the feature extends all the way to the top of Saturn's atmosphere (the earlier IR imagery showed the hex goes deep into the atmosphere as well).
Cassini scientists took 55 of the images and created this nifty mosaicked animation, showing the jet stream feature in motion. It moves at about 100 meters per second as it circles Saturn at 77 degrees north latitude.
This planetary stop sign is long-lived; it's been around at least 30 years, and who knows how long it existed before that. Earth has atmospheric features that can stick around; our jet stream is a good example. But most terrestrial weather patterns come and go quickly, of course, like storms and hurricanes. But on the giant outer planets they can last decades or, in the case of Jupiter's Great Red Spot, even centuries. At least part of that is because the planets spin rapidly, and the Coriolis effect helps power these behemoth storms. The heat source for these storms is different than on Earth, too: it comes partly from the Sun, but also from the interior of the planets themselves, and that plays a role.
But the weird shape of this jet stream is likely to puzzle and delight scientists for some time to come. These new images will give them critical clues to figure it out... and after all, isn't that why we explore in the first place?