Saturn is the jewel of the solar system, with its magnificent rings and retinue of weird moons. It’s the faintest of the naked-eye planets—technically Uranus is sometimes bright enough to see, though you need good eyesight and a very dark site—but still fairly easy to pick out among the stars.
If you’re an early riser (or a late partier), then now is a decent time to look for Saturn, not because it’s brighter or closer to Earth than usual but because it’s made some news recently. New research indicates its rings are relatively young, cosmically speaking, and astronomers have also just announced the discovery of a whole passel of tiny Saturnian satellites that make the planet the current record holder for the greatest number of moons.
Saturn currently crests the horizon early in the morning local time and about an hour later rises high enough to spot low in the southeastern sky. If you get up shortly before dawn, it’ll be about 25 degrees above the horizon, or roughly 2.5 times the width of your outstretched fist—a universal unit of measure among astronomers. Don’t confuse it with the nearby star Fomalhaut, which is closer to the horizon than Saturn and has almost exactly the same brightness. Jupiter is closer to the eastern horizon (down and to the left of Saturn, for Northern Hemisphere observers), but it’s 15 times brighter and much easier to spot.
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If you’d prefer to avoid a predawn viewing, in this case, waiting is fine, too: Saturn’s rings and moons aren’t going to vanish (on human timescales anyway). And as summer progresses, the planet rises earlier and gets higher in the sky at a more reasonable time. By late June it rises around midnight in many locations, for example, and by late August it reaches the sky watching sweet spot: it rises at sunset and stays up all night.
Through binoculars, Saturn can look elongated or oval-shaped because of its rings. The sharper view from a small telescope will reveal the rings more clearly. Using one, you might even spot a couple of the planet’s moons; its largest, Titan, is bigger than Mercury and typically appears as a faint “star” adjacent to Saturn.
If you do brave the early hours to get a look at the gas giant, take a moment to contemplate what you’re really seeing. The pale, resplendent orb, so small in our sky, is a behemoth that is nine times wider than Earth and 95 times more massive. And despite centuries of observations, we’re still learning about this ringed wonder.
Saturn is iconic among its planetary siblings because of its rings, of course. Jupiter, Uranus and Neptune all have rings, too, but those are thin, faint and difficult to see without spacecraft or powerful telescopes. Saturn’s rings stretch an incredible 175,000 miles (282,000 kilometers) across—three quarters of the distance between Earth and our moon!
Even though they seem solid, Saturn’s rings are actually composed of countless chunks of nearly pure water ice, likely the remnants of a shattered moon. The largest chunks are probably less than ten meters across—with most being more like the size of the ice cubes you put in your drinks. Although the rings haven’t appeared to change much at all since humans started observing them through telescopes in the 1600s, their age and longevity have been contentious issues among experts for much of that time.
More recently, evidence has been mounting that the rings are far younger than the planet’s own approximately 4.5-billion-year age. The Cassini mission provided much of the data for this; the spacecraft orbited the planet for 13 years and sent a wealth of information to Earth.
New research, just published in the planetary science journal Icarus, reinforces the notion that not only are the rings young, but also they won’t last forever.
Micrometeoroids—tiny space rocks zipping around the solar system—were key to this new chronology. When they strike particles in Saturn’s rings, there are two overall consequences. One is that micrometeoroid dust pollutes and darkens the rings’ pristine water ice. The other is that those small collisions sap orbital energy from the ring particles, which respond by moving inward toward Saturn. Together, these effects should make the ring particles grow grimy over time and eventually rain down onto Saturn itself.
With Cassini data in hand, the scientists put numbers to these effects, finding that the rings are likely no older than about 120 million years, which is quite young for a planetary system. To put that into perspective, if early Cretaceous dinosaurs had invented telescopes, they would’ve seen Saturn without rings!
The researchers also found the rings are eroding at a rate that means they’ll disappear sometime between 15 million and 400 million years from now. That’s a long time in human terms but still only a fraction of the solar system’s age.
Ironically, although Saturn’s rings are fading away, it seems to have a growing number of moons. That is not the case literally or physically—we’re just getting better at finding them.
Scientists have just announced a new passel of 62 moons around Saturn, bringing the planet’s total to more than 140, blowing right past Jupiter’s previous record-holding count of about 90.
The researchers actually spotted many of these moons in observations taken in 2019 using a clever technique to enhance their visibility, but these tiny satellites were very faint and didn’t move very much in between observations. To confirm them, the astronomers needed to get more data. Over the past two years they’ve done just that and nailed down the reality of the moons, most of which are only a few kilometers across.
How many moons might Saturn actually have? Well, that depends on what you mean by “moon.” There are hundreds, certainly—maybe thousands bigger than a kilometer or so. But if you count each ring particle as a moon, then the answer is trillions. The trouble here is we don’t have a good definition of what makes a moon, especially with regard to what the lower size limit might be. So in that sense, trying to decide which planet has the most is a bit silly.
But still, if you venture out early and gaze at Saturn in the predawn spring skies, remember you are now armed with knowledge that would make the astronomers of just a few decades ago jealous. Hundreds of moons as big as mountains circle Saturn. Its rings are young and fleeting. In a very real sense, we’re lucky to be around to see them at all.