We all know Jupiter, the absolute unit of the Solar System. Hey, you could cram like 1,300 Earths inside Jupiter, so you know the big ball of hydrogen gas means business. Except for the Sun, since the Sun is literally 99.8% of the Solar System’s mass, and you could cram like 1,000 Jupiters inside of it. But we’ve talked about the Sun a lot before so let us look back at Jupiter–which you’ve probably heard of for both being really big, and having that big spot on it. We call it the Great Red Spot, except it’s not like our celestial overlords just painted part of Jupiter’s bottom half red. So what is the Great Red Spot?
Noticing the Spot
We probably first noticed the Great Red Spot in 1665 when Cassini wrote about a permanent storm kicking around on Jupiter. It’s possible a guy by the name of Robert Hooke noticed it in 1664, but he noticed a spot North of Jupiter’s equator–and the Great Red Spot is South of it. There were recorded observations in the 1700s too, but it’s entirely that these independent observations were of different spots on Jupiter–rather than the same one.
The same one has been observed since 1831, though. We started looking more deeply into it by 1879. Since we started gazing into this red vortex, the Great Red Spot has been progressively shrinking–though we generally maintain that the Spot is about as wide as two Earths placed end to end. By 1966 we figured out the Great Red Spot rotates counterclockwise–and that its wind speeds push 270 miles per hour (about 434 kilometers per hour)–newer imaging pushes 350 miles per hour. That’s like going top speed in one of the fastest sports cars in a circle all the time for at least 190 years and counting.
Keeping the Spot Going
You might be wondering what keeps the Great Red Spot going, and you can thank jet streams for that. As a planet with an atmosphere, Jupiter has winds. As you’ve probably figured out, Jupiter is also very… Windy. It’s an eastward and westward jetstream pushing gas in opposite directions that creates the Great Red Spot. Kind of like if you put some food coloring in water and spun it around. Now make your hypothetical water bowl twice the diameter of Earth.
In case you were wondering, we have jet streams on Earth too-they can make hurricanes and other storms sometimes. Jupiter is just… Really intense and angry about it. It’s probably aided by how big the planet is–and the fact that Juipiter is basically a big ball of gas. Even though it spins like Earth does (Jupiter is not tidally locked), the gas on Jupiter’s surface doesn’t all move at the same speed. That’s why astronomers have 3 different systems for measuring latitude and longitude on Jupiter.
Speaking of keeping the Great Red Spot going, there was a time when amateur astronomers thought the Great Red Spot was going to die. In 2019 the thing started spitting off red flakes. The Spot isn’t dead though, so we got that going for us.
The Great White Spot
Turns out, Jupiter isn’t the only planet that has weird storm spots. Saturn does too, and it’s called the Great White Spot. It’s kind of a misnomer though, since unlike the Great Red Spot, the Great White Spot comes and goes. The current running theory for Great White Spots is that they’re caused by convection of Saturn’s gases. Hot gases rise and colder gases sink down, where they heat up again and rise.
Bam, Great White Spots.
More consistently weird on Saturn is its hexagon. No really, on Saturn’s north pole there’s an almost perfectly hexagonal cloud–each of its sides is probably as long as the Earth is. You might think the hexagon would be present on Saturn’s south pole–it’s not. Similarly to the Great Red Spot, Saturn’s hexagon is likely also caused by jet streams. Though instead of two streams pushing gas to make a vortex, the one that makes Saturn’s hexagon behaves kind of like a wall.
See if you know more things about Jupiter here.