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      Saturn's Hula-Hoops

                                                               Written for the KidsKnowIt Network by:
                                                                         Gemma Lavender, MPhys, FRAS

 
  Image: NASA-JPL

 

Saturn

Each ring travels around Saturn at a different speed.

 

 

 

 

 

 

 

 

 

 

Neptune's rings
Neptune's rings. Image: NASA-JPL

 

 

An image of Saturn in 1980 taken by Voyager.
Image: NASA

 

Saturn

Earth's moon could fit through the Cassini Division.

 

 

 

The Cassini spacecraft took this natural color image of Saturn's rings in 2004.
Image: NASA/JPL/Space Science Institute

 

Saturn

A few years after Galileo first saw Saturn and its rings (which he thought were Saturn and two other planets close together) they disappeared. He thought that perhaps Saturn had eaten his sons. This was because the rings were in their flat plane phase in relation to Earth. Galileo died without ever knowing what the rings really were.

 

 

Saturn with its moons Tethys and Dione.
Image: NASA/JPL

 

 

Saturn

Every 29.5 years, Saturn's rings seem to disappear to us here on Earth.  This is because Saturn tilts on its axis, just like Earth. When Saturn reaches the mid point of its tilt, the rings are in a flat plane with Earth, making them disappear from our view. During this time, researchers can search for more moons around Saturn because the glare of the rings is absent. See below photo. Saturn's moon Rhea is seen below the rings.

Saturn's rings in the flat plane.
Image: NASA/JPL


Do you have a favorite planet? Which one is it? It might be the gas giant Jupiter, or it could be red, rocky Mars. If your favorite is Saturn, however, then you are in for a treat as we’re going to have a look at this planet - but rather than talking about this gaseous world as a whole, we’re going to focus on one of its very important and most obvious features - its rings. These unusual features, which circle the planet like hula hoops, might be the reason why it’s your favorite - they certainly make Saturn stand out from the crowd and they are also very beautiful. Some astronomers say that it makes Saturn look like it’s got ears - at least, depending on what angle the rings are tilted towards the Earth - maybe you disagree and think that Saturn looks like a cup with two handles on either side!






You might be surprised to learn that Saturn is not the only planet with rings - Jupiter, Neptune and Uranus have them too - they’re just not as obvious as Saturn’s when you look through a small telescope. Do you know why this is? The answer is because they are very bright (because they reflect the Sun’s light). They are also the largest rings in our Solar System spanning up to 175,000 miles - that’s about three quarters of the distance from our planet to the Moon. So now you can see; the more thick, massive rings there are, the more light that they reflect! If you or your parents have a telescope why not have a go at trying to find Saturn in the night sky? Maybe you can sketch what you see! Are the rings tilted a certain way?

So who was lucky enough to spot Saturn’s rings in the first place? Stepping back to 1610, astronomer Galileo Galilei was the first person to see them through his telescope. However, at the time, his telescope was not strong enough to see details and he therefore did not realize that what he saw were rings around the planet and, ever since his sightings, early astronomers wondered what they could be.

     Galileo Galilei  Christiaan Huygens
     Galileo Galilei                       Christiaan Huygens

In 1655, amazed by what Galileo saw, Dutch astronomer Christiaan Huygens suggested that Saturn had a disc surrounding it. To get an idea of what Huygens described imagine a Pogo Ball - they are bouncy balls with a disc around them - you might have one in your garden or your parents might have had one when they were little. If you don’t have one on hand, why not get a football (soccer ball) and cut out a disc to make your very own Saturn!

You may have noticed that we prefer to use the word “rings” rather than Huygen’s idea of a disc. The reason behind this is because rather than being similar to a frizbee with a hole in the middle, Saturn really does have ring-like structures around it and astronomers have given a name to each of them as well as the gaps that separate them.

Saturn's equinox
Image: NASA

There are 7 rings in total and, as expected, they are named in the order they were discovered. Because they are named in an ordered system, astronomers have named the rings as letters such as Ring A, Ring B and Ring C all of the way up to Ring G. While you might think that the names of these rings are quite boring, they helped astronomers refer to them quickly and easily - after all, Saturn’s rings are quite complicated! So we have got some rings, what do we call the spaces in between them? That’s right - they’re called gaps and while you might think that these are going to have even duller names, think again! Scientists decided to have a bit more fun naming those! Before you carry on reading about them, maybe have a think about what you would call the rings and gaps if you were asked to name them!

Now let’s learn about the gaps. You have probably noticed them in a picture that you have looked at of Saturn - but you wouldn’t be the first to spot them! Back in 1795 Giovanni Cassini, an astronomer (who now has a mission named after him called Cassini) saw a large obvious gap which we now know as the Cassini Division. This gap is gigantic - it would be pretty much impossible for you, or even your parents to be able to jump over it! Near the edge of the rings is another gap that we now refer to as the Encke gap. How do you think that this gap got its name? That’s right! It was named after its discoverer Johann Encke - a German astronomer.

The Cassini gap is the large gap in the middle. The Encke gap is near the outer faint ring.
Image: NASA/JPL Space Science Institute

 

So how do you think that gaps like these were made? Have a guess before you watch the video below to find out!

 


Watched the video? If you have, then it’s time for a small test! If you imagine for a moment that you are an astronomer back in the times of Cassini, then the next question that you would have wondered, as soon as the disc was uncovered, was: what is this disc made of? Do you remember from the video that you have just watched?

That’s correct - the rings are made mostly of pure water ice (the frozen water that you’re very likely to find in the fridge). But that’s not all - there’re some lumps of rocks that scientists call tholins and silicates in there too. As mentioned, the rings are not solid and that means that there must be more gaps in the rings - we just can’t see them from Earth. With the help of missions to Saturn (such as Cassini and Voyager), we have been able to see lots of other spaces in the rings. Below is a table that shows the main ones - why not cover up the first column and have a go at guessing what the name of the gaps are by using the “Named after” column as a clue?


Name

Distance from Saturn (miles)

Width (miles)

Description

Named after

D Ring

41,570 - 46,298

4,660

Faint innermost ring made of smaller rings.

None

C Ring

46,390 - 57,166

10,874

Wide faint ring made of dark material

None

B Ring

57,166 - 73,061

15,845

Largest and brightest of the rings. Has spokes and an embedded moonlet (S/2009 S1).

None

Cassini Division (Gap)

73,061 - 75,913

2,920

Gap between A Ring and B Ring. The Huygens Gap is at the edge of the Cassini Division.

Giovanni Cassini

A Ring

75,913 - 84,988

9,072

Contains the Encke Gap, Keeler Gap and many moonlets discovered by the Cassini spacecraft.

None

Roche Division (Gap)

84,988 - 86,607

1,616

Separates the A Ring and the F Ring.

Édouard Roche

F Ring

87,104

19-311

Active ring with features that change every few hours.

None

Janus/Epimetheus Ring

92,584 - 95,691

3,107

Faint dust ring around the region occupied by the orbits of Saturn’s moons, Janus and Epimetheus.

Saturn’s moons Janus and Epimetheus

G Ring

103,148 - 108,740

5,592

Thin, faint ring that lies between the F ring and E ring.

None

Methone Ring Arc

120,689

Unknown

A faint ring arc thought to be made by dust ejected from impacts with Saturn’s moon Methone.

Saturn’s moon Methone.

Anthe Ring Arc

122,823

Unknown

A faint ring arc thought to be made by dust ejected from impacts with Saturn’s moon Anthe.

Saturn’s moon Anthe.

Pallene Ring

131,109 - 132,663

1,553

A faint dust ring thought to be made by dust ejected from impacts with Saturn’s moon Pallene.

Saturn’s moon Pallene.

E Ring

111,847 - 298,258

186,411

Outermost ring and extremely wide.

None

Phoebe Ring

~2,485,485 - >8,077,826

None

A disk of material close to the orbit of Saturn’s moon, Phoebe.

Saturn’s moon Phoebe.

Remember that “~” means “around” or “approximately” and “>” means “greater than”
or “more than”.

 

Here is a video about strange findings in Saturn's F Ring.

 

Saturn

Like Earth, Saturn's atmosphere reflects blue light from the Sun. This only happens across the northern hemisphere, however. Scientists aren't quite sure why this is.  One idea is that it is a seasonal effect. Can you spy the two moons in the photo below? Titan is seen in the lower right corner. Mimus is the faint dot to the right of the rings.

Saturn's blue atmosphere.
Image: NASA/JPL

 




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