Planetary Profile: Strange Saturn

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Yay, it’s time for the next entry in my weird solar system series (see here for entries on why Mercury, Venus, Earth, Mars, the asteroids, and Jupiter are all weird in their own special ways), and next up we have a big one: the ringed planet Saturn!

As with each world in the solar system, Saturn has a wide array of features that are bizarre when you consider them up against everything else, so I’m going to have to pick and choose which ones to focus on. But I think we all know what I’m going to start with, because it’s the Saturnian elephant in the cosmos. 

Put a Ring on It

Now obviously Saturn is not strange for having rings. All of the outer planets have a ring system of some sort. But you cannot deny that Saturn’s rings stand out. Jupiter, Uranus, and Neptune all have very thin, fine, faint rings mostly made out of dusty material knocked off of moons over the eons. When it comes to Saturn’s rings, “thin”, “fine”, and “faint” are not the words that come to mind.

Saturn’s rings are truly enormous. In fact, they’re much bigger than you probably think they are. When you think of Saturn’s rings, you likely picture the main ring system, which largely consists of the A and B rings, with the Cassini Division appearing as a big gap between them. These are the densest and brightest parts of the rings, but they’re not the only parts.

The C and D rings are fainter and interior to the A and B rings, but there are others much farther out. How far out is actually unknown, with a possible tenuous outer ring whose full structure is still unclear possibly extending as far out as 10 million miles (16 million km) from Saturn itself (compare that to Jupiter’s ring system, which can be measured in hundreds of thousands of miles).

And of course the main rings, at least, are very bright! That’s because they’re largely made up of ice. If you’ve ever seen sunlight reflecting off of fresh fallen snow, you know frozen water bounces light very well, making the rings of Saturn a very visible target through even a small telescope. Heck, even Galileo was able to see them 400 years ago through his not-very-good telescope. 

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Saturn’s main rings probably come from the death of at least one (and possibly a few, according to a new theory) moon, which got shredded by the planet’s gravity. The rocky core(s) got swallowed by the planet and icy outer layers turned into the rings. If I had to pick a favorite ring it would probably be the faint, fuzzy E ring. This one also comes from a moon, but not like the other ones. This one is caused by all the watery material the moon Enceladus is shooting out from its insides via its famous geysers. It’s a ring made entirely of moon spit.

This fabulous piece of planetary jewelry is certainly the most obvious way Saturn stands out among the planets, but it’s hardly the only way.

Shapely Skies

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When the two Voyager spacecraft each flew by Saturn in 1980 and 1981 their images revealed something unexpected going on at Saturn’s north pole. Then, when the Cassini spacecraft actually entered orbit around Saturn in 2004, astronomers got some really clear images of the area, leaving no doubt: Saturn has a polar hexagon.

It’s a bit of a head-scratcher, actually. Saturn’s north polar region is dominated by a very strong jet stream several thousand miles long moving at over 200 mph (322 kph) and encircling a central vortex. And for some not entirely understood reason those jet streams are forming an almost perfect hexagonal shape. 

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The fact that both Voyagers and Cassini saw this pattern means it’s a persistent feature. It’s also enormous, with each side of the hexagon stretching roughly 9,000 miles (14,500 km), and it rotates in sync with the planet, unlike other cloud features. It’s also suspected to be up to hundreds of miles tall, because nothing about Saturn is small.

And we don’t see this pattern anywhere else. Not on the other giant worlds, and not even on Saturn itself! Its southern pole has a central vortex, but is completely lacking the surrounding hexagon shape. And, again, we don’t know where that hexagon comes from! I mean, we know it’s a wind pattern, but why it looks like that is still a big question with many proposed answers.

Also, thanks to the fact that Cassini was observing this structure for years, we know it changes colors sometimes. And I love that about it. 

Cute and Fluffy

You might have heard the factoid before that if you could find a bathtub big enough, Saturn would float. That’s because Saturn is the least dense of the planets, the only one to have a density lower than that of water (Saturn’s density, if you’re curious, is 0.687 g/cm³. Water is 1 g/cm³, so anything with a density less than that will float).

This is just over 10% of Earth’s density, which is perhaps an unfair comparison because Earth is actually the densest of the planets. But Mars, the least dense of the rocky worlds, is still over five times Saturn’s density. Looking at the outer worlds, Saturn’s density is less than half that of Jupiter or Neptune. It’s about half that of Uranus. 

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What this means practically is that Saturn is fluffier than any of the other planets. It’s letting its mass spread out a little. I don’t mean to suggest that Saturn is a lightweight by any means—it’s still hauling around over 95 times the mass of the Earth. But it’s doing it in a package that could fit a whopping 763 Earths within it. To compare to Jupiter again, our largest planet is shoving 317 Earth masses into a volume less than twice that of Saturn. 

Couple this fluffiness with Saturn’s rapid spin (the second shortest day in the solar system, after Jupiter, at 10.7 hours), and you get a planet with a serious spare tire around the middle. The planet is protruding along its equator as its spin causes all of its insides to bulge outward. This is not unusual—Earth has an equatorial bulge of its own—but Saturn’s is very pronounced.

This also leads to a weird fun fact about Saturn’s gravity. When you’re standing on the surface of a planet, how powerfully you feel its gravity is at least somewhat determined by how the planet’s mass is distributed beneath you. Saturn, of course, doesn’t have a solid surface to stand on, but let’s imagine that you could. 

The uneven distribution of Saturn’s mass (spread out so much farther from its core near the equator than it is near the poles) means that along the equator you’d feel a gravitational force almost identical to that on Earth. But at the poles, the gravitational pull would be a bit stronger. That means you’d weigh less at Saturn’s equator than you would at Saturn’s poles, which is nutty.

Moon Madness

I’m not going to go into too much detail about Saturn’s moons because I’m still contemplating an entire weird solar system entry all about moons, but I’d be remiss if I didn’t at least touch upon them. Because Saturn is bizarrely blessed with moons!

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The last several years have seen each of the outer planets up their confirmed moon counts, as we continue to get better and better at finding little squib moons orbiting farther from their planets, but Saturn has had an absolute moon bonanza. At the beginning of 2023 I was telling my Planetarium audiences that Jupiter was in the lead for moon count with 92, ahead of Saturn’s 82.

Today I have to spout very different numbers. As of the day I’m writing this Jupiter’s moon count has finally edge up over a hundred, with 101 currently confirmed moons, while Saturn sits very comfortably in the lead with 285. 

This is not necessarily because Saturn actually has more moons than Jupiter. Newer moon surveys using more advanced technology have, to a certain extent, focused more on Saturn than its larger sibling if only because Saturn’s smaller size and greater distance from the Sun mean it’s not as bright as Jupiter. That makes it slightly easier to spot tiny little pinpricks of light that are previously unknown moons. I personally think Jupiter is raring for a comeback in the moon race. But boy does it have a lot of ground to catch up.

More Than a Pretty Ring

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Rings, moons, and polar hexagons—I’m beginning to think Saturn is just far better at accessorizing than any of the other planets. Whatever the reasons behind Saturn’s extra bling, it goes far beyond its famous ring system (which itself might be the end result of a beautiful series of gravitational dominoes falling in just the right way).

So the next time you think of Saturn, think of it in all its fluffy, weird, moon-hoarding glory. But at the same time if you want to dwell on that ring system in particular, I can’t blame you. I’ve never seen anything so consistently marvel someone looking through a telescope as Saturn’s magnificent rings, which even a small telescope can see. When you got it, flaunt it, after all. And Saturn has definitely got it.