An astronomer’s colorful animation shows how Saturn’s disappearing rings act like a ‘mini solar system’

saturn rings radio
Saturn’s rings, imaged based on radio data from NASA’s Cassini spacecraft. Green indicates regions with particles smaller than 5 centimeters; purple is where no particles are that small. The white area is so dense that it blocked radio signals.

  • Saturn’s seven icy rings each spin at their own speed, behaving like a “mini solar system.”
  • Planetary scientist James O’Donoghue made a beautifully simple animation to show how it works.
  • But the rings are temporary: Saturn is slowly swallowing them, according to O’Donoghue’s research.
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If star-hopping aliens ever visited our solar system, Saturn is probably the planet they’d remember.

The seven giant rings circling its equator make Saturn the most distinct planet orbiting the sun. It may not be obvious in images of the hula-hoop planet, but the ice and rock chunks that make up those rings are circling Saturn at rates nearly 70 times the speed of sound. What’s more, each ring is moving at its own pace.

“In a way, the ring system is like a mini solar system,” James O’Donoghue, a planetary scientist at Japan’s space agency, JAXA, told Insider. “Objects close to Saturn orbit faster otherwise they would fall in, while objects far away can afford to go slower. This is the same for planets.”

In his free time, O’Donoghue makes animations about physics and the solar system. Some of his others have demonstrated that there’s no “dark side” of the moon, the true center of the solar system isn’t the sun, and Earth has two types of day.

When he put his skills to work to depict Saturn’s rings, O’Donoghue created an animation (below) that shows how the each ring moves through its own motions in a beautiful, circular dance.

In the animation, the line labeled “synchronous orbit” is synced up with the spin of Saturn itself, so it shows which parts of the rings you would see over time if you stood at that spot on the planet.

Saturn’s slowest, outermost ring spins at about 37,000 mph (16.4 kilometers per second) – slower than the rotation of Saturn itself. The innermost chunks of ice and rock shoot through space at about 52,000 mph (23.2 kilometers per second).

saturn rings illustration
An illustration of Saturn’s rings up close.

Up close, Saturn’s rings aren’t as chaotic as their speeds might make them seem. According to O’Donoghue, grains of ice on neighboring tracks are only moving at a few centimeters per minute relative to each other.

“That speed is like walking one step every 30 minutes, or similar to rush hour traffic,” he said on Twitter. “So collisions aren’t very dramatic.”

Saturn is slowly swallowing its rings

In addition to being incredibly fast-moving, Saturn’s rings are very long and thin. If you unfurled them – as O’Donoghue did in the image below – all the planets would fit comfortably within their length.

saturn rings solar system o'donoghue

But in total, the rings have just 1/5,000th the mass of our moon.

“In other words, our moon could be used to make 5,000 Saturn ring systems,” O’Donoghue told Insider. “This highlights how extremely thin and fragile the rings of Saturn are.”

This fragility is a subject of O’Donoghue’s scientific research. In studying Saturn’s upper atmosphere, he and his colleagues found that the rings are slowly disappearing. Thousands of kilograms of ring material rain onto the planet every second. At that rate, the rings shouldn’t last more than 300 million years in their current “full” form, he said.

“Saturn’s ring system is not exactly stable, appearing to be more like a temporary debris field of some ancient moon or comet which got too close and broke apart, rather than a permanent feature,” O’Donoghue added. “We can count ourselves lucky we live in a time when Saturn’s rings have such an enormous presence in the solar system.”

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Mercury, Jupiter, and Saturn are clustering in the night sky in a rare, three-planet conjunction event. Here’s how to see it on Monday.

jupiter saturn conjunction
Saturn (above) and Jupiter (below) in the sky above a church in New York City, December 2020.

Mercury, Jupiter, and Saturn are currently clustering together in the night sky.

Monday is the final night that the three planets will be lined up and visible at twilight. They appeared the closest they’d been in more than two decades on Sunday, forming an equilateral triangle.

“This shape is just a blip in time,” Amy Oliver, a spokeswoman for the Harvard-Smithsonian Center for Astrophysics, told the Boston Globe. “We won’t see it exactly like this ever again, since it probably isn’t going to happen again in this exact same way – at least not in your lifetime.”

An astronomical event in which celestial bodies align like this is called a conjunction. A triple alignment like this is known as a planetary trio.

If you hold your palm up to the sky and all three planets cluster within a circle that fits in the space between your ring finger and your pointer finger, that’s a trio. 

Here’s how to see the planetary trio before it’s gone.

Head out at twilight, and bring binoculars

mercury
The surface of Mercury, as photographed by the Mariner 10 spacecraft in 1974.

On Monday, head out at twilight, between half an hour and 45 minutes after sunset. Look to the southwestern sky. The clearer the sky is, and the father from city lights you are, the easier it will be to see the conjunction. 

Jupiter will look brightest to the naked eye (it’s about 10 times bright than Saturn), followed by Mercury, then Saturn. 

Since Saturn is so dim, it may not be distinguishable from the sun’s afterglow with the naked eye. So the best way to spot the planetary triangle is to focus your eyes on Jupiter, which will be near the top, then point a pair of binoculars at it. Mercury and Saturn should appear in the same binocular field as Jupiter, according to EarthSky

After Monday, Jupiter and Saturn will dip below the horizon and no longer be visible, while Mercury will continue rising in the sky night after night – moving steadily away from the other two planets.

Although the three worlds seem to almost touch during the planetary trio, Jupiter and Saturn are actually separated by almost five times the distance between Earth and the sun. Mercury and Saturn are separated by nearly twice that distance. 

The last time these 3 planets aligned so closely was in 2000

saturn
A photo of Saturn and two of its moons, taken by Voyager 1 in 1980.

Astronomers turned their telescopes skyward last month to catch another conjunction event, when Jupiter and Saturn aligned more closely than they had for centuries.

In the last 2,000 years, there were just two times that Jupiter and Saturn came closer in the sky: One was in 1623, but the sun’s glare made it impossible to see. The other was in 1226. 

Planetary trios, by contrast, are far more common. The last one was in October 2015. Another trio, involving Mercury, Venus, and Jupiter, will happen on February 13, according to EarthSky.

The last time Mercury, Jupiter, and Saturn formed a triangle was in May 2000.

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