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Posts Tagged ‘Saturn’s rings’

This story caught my attention back in April, the possible creation of a new Saturn moon on the outskirts of its famous ring system (I’m not sure why it has taken me so long to blog about it, probably because in April I was working frantically finishing up my book on the Cosmic Microwave Background). The particles in Saturn’s rings are basically small lumps of rocky water-ice, and so are pretty good at sticking together if they collide. What we think is happening is that this little moon is being created by the collisions of the particles in the ring system, which is slowly building up a new moon. Quite spectacular really, to see the possible birth of a new moon!



A story about the birth of a "new" moon about Saturn.

A story about the birth of a “new” moon about Saturn.



We don’t fully know the origin of Saturn’s rings, there are two competing theories. One is that a larger moon which would have formed at the same time as Saturn (i.e. 4.6 billion years ago) and at some time in the past came too close to Saturn and was torn apart by Saturn’s gravitational tidal forces. The point at which an extended body will be torn apart by tidal forces is called the Roche limit, and once an object is closer than this the gravitational forces on e.g. the near and the far side are too different and the object gets torn apart. The size of Roche limit depends on the planet (so would be different for the Earth and Saturn), but also on the size of the object. So, the Roche limit for a larger moon will be different (at a larger distance) than for a smaller object.

The other theory is that they formed from debris left over from Saturn’s formation, just as the asteroid belt is debris left over from the formation of the Solar System. The problem with this theory is that the rings are thought to be just a few hundred million years old, whereas if they are left over debris we would expect them to be as old as Saturn. As of writing this, we are not sure which of these two competing theories is correct. Or, maybe there is another explanation entirely!

Galileo looked at Saturn through his telescope back in 1610, but was not able to make out the rings as such. He saw that Saturn had what looked like “ears”, but it was the Dutch astronomer Christian Huygens who was the first to describe them as rings. They are a complex system, and it would take several blogs to describe them, but suffice it to say that in the time that we have been sending space probes past or to Saturn (e.g. Voyager, Pioneer, and now Cassini), we have been learning more and more about how complex a system the rings are.

Saturn is not the only planet with a ring system, it may surprise you to hear that Jupiter, Uranus and Neptune also have ring systems, but none is as spectacular as Saturn’s. Here is an amazing photograph taken by Cassini of Saturn and her ring system, looking back towards the Sun. It also shows several of Saturn’s moons, Mars, Venus and even the Earth!!



This amazing photograph, taken by NASA's Cassini space probe, shows the rings back-lit by the Sun. The photograph also shows Mars, Venus and the Earth!

This amazing photograph, taken by NASA’s Cassini space probe, shows the rings back-lit by the Sun. The photograph also shows Mars, Venus and the Earth!



The Cassini probe has been an overwhelming success. Launched in 1997, it arrived at Saturn in 2004, and some of you may remember it sent a little probe called Huygens which landed on the surface of Titan in January 2005. For the last ten years it has been orbiting Saturn and some of its moons, and has made numerous discoveries in doing so. It is scheduled to remain in operation until 2017. Here are some remarkable images from the probe, together with a model of Enceladus based on the observations that Cassini has made of it.



A Cassini image of Enceladus, showing plumes of water coming from its pole.

A Cassini image of Enceladus, showing plumes of water coming from its pole.




One of the surprises of the Cassini mission has been the moon xxxx, which shows geysers of water shooting out from its poles. Because of the presence of water, xxxx has become a prime candidate to  look for life beyond our Earth.

One of the surprises of the Cassini mission has been the moon Enceladus, which shows geysers of water shooting out from its poles. Because of the presence of water, Enceladus has become a prime candidate to look for life beyond our Earth.




A Cassini image showing the rings nearly edge-on, with the moon Dione in the background.

A Cassini image showing the rings nearly edge-on, with the moon Dione in the background.



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There are not too many planets visible this summer. Venus will be visible very low in the Western sky in the evening in early summer. Jupiter will be visible as the Sun is setting, also over towards the West. But really the only planet visible when night has fallen this summer is Saturn, which is currently in the constellation Libra.


Where to find Saturn this summer. It is to the South of Arcturus, and to the East of Spica.

Where to find Saturn this summer (2013). It is in the constellation Libra; to the South of Arcturus, and to the East of Spica.


The image above shows where Saturn is to be found at about 21:45. The easiest way to find it is to find the bright star Arcturus (the second brightest star in the summer sky after Vega), and to the South of it is Saturn. You can also check that Spica, the brightest star in the constellation Virgo, is to the West of it.

Throughout the summer, Saturn will have a magnitude of about +1.1, which makes it roughly the same brightness as Spica and about 2.5 times fainter than Arcturus. Even with the naked eye you should be able to see the colour difference between Spica and Saturn. Whereas Spica is a bluish-white, Saturn is a distinctly brown colour.

In mid-July, Saturn will be rising at about 14:45, transiting at about 19:50 and setting at about 01:00. So it will be at its highest in the night-time sky a little before sunset in northern latitudes.

Although Saturn is easily visible to the naked eye, it is well worth looking at through a small telescope, as when one does so the famous rings become visible. If the atmosphere is particularly stable, you should be able to make out the Cassini division in the rings. You may also be able to spot Titan, Saturn’s largest moon, which is indicated in the photograph below.


Saturn as seen through a small telescope, with its largest moon Titan visible to the right.

Saturn as seen through a small telescope, with its largest moon Titan visible to the right.


Titan is a fascinating moon, and one which has become quite well studied by the spacecraft Cassini and the space probe Huygens, which plunged through its atmosphere in January 2005 and landed on its surface. It is thought to be one of the most likely places beyond the Earth in our Solar System to harbour life. I will do a blog about Titan and what we so far know about it in the near future.

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