B-Ring It On!

 

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What do you think this picture might be? Could it be a microscope’s view of a hair? Could it be the pages of a really big book? They’re not bad guesses but they’re not correct.

This image focuses on a region in Saturn’s B ring, which is seen in twice as much detail as ever before, revealing a wealth of rich structure. It shows the incredible detail at which the international Cassini spacecraft is observing Saturn’s rings of icy debris as part of its dedicated close ‘ring grazing’ orbits. The spacecraft was at a distance of about 51 000 km from the rings

Saturn’s rings are composed mainly of water ice and range from tiny dust-size specks to boulders tens of metres across. Some of the patterns seen in Cassini’s close images of the rings are generated by gravitational interactions with Saturn’s many moons, these are known as shepherd moons which by their gravity help to keep the rings in shape by ‘kicking’ material into the rings or out into space. However many details remain unexplained.

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A Cassini image looking across Saturn’s rings showing where the B-ring lies.

The spacecraft’s ring-grazing orbits began last November, and will continue until late April, when the mission enters its ‘grand finale’ phase. During 22 final orbits Cassini will repeatedly dive through the gap between the rings and Saturn before plunging into the planet’s atmosphere in mid-September to conclude its incredible 13-year odyssey around the Saturn system.

If you want to see Saturn and its rings this is a good time to do it; Saturn rises about 2:15 in the morning in mid-March and an hour earlier by mid-April and lies in the constellation Sagittarius. That means for us that it is quite low in the sky. It gets to its highest point in the sky a little before sunrise, so you have a good chance of seeing it. (Sagittarius is a lovely constellation full of objects as when you look at it you are looking in the direction of the centre of our galaxy the Milky Way.)

You will need to look towards the East and South to see it but it will be the brightest object in that part of the sky.

To help you find it the moon will be either side of Saturn on the 16th and 17th of April.

Binoculars will show that it has a funny shape, almost like a rugby ball, and a small telescope will begin to show the rings. The rings are currently tilted towards us and will make for a lovely sight.

The Cassini-Huygens mission is a joint venture between NASA, ESA (the European Space Agency) and the Italian space agency ASI. It was launched from Cape Canaveral on the 15th. October 1997 aboard a Titan IV-B which is the NASA’s largest and most powerful rocket.

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Published in: on March 26, 2017 at 12:14  Leave a Comment  
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Oh My!

The solar system is full of amazing sights; from aurora on Earth, to giant solar flares, to the great red spot there are countless objects to fascinate us. every now and then comes along something you just don’t expect. Often these are from objects you just wouldn’t imagine to be interesting (which just proves the old adage; ‘never judge a book by its cover.’)

The Cassini mission to Saturn (launched on October 15th. 1997 and arrived seven years later) is starting to wind down (sadly) and will soon be sent on a course that will see it fly through Saturn’s rings and eventually into the planet’s atmosphere to be destroyed. Despite that it is still providing us with surprises; the most recent being its images of the little shepherd moon Pan.

759Raw image of Pan. NASA. The grey lines either side of Pan are rings of Saturn!!

Looking through a telescope at Saturn from Earth the rings look quite simple; there

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appear to be two sets separated by  black gaps or ‘divisions’. the Encke division is very difficult to see and cuts around the A ring. The second gap is the Cassini division and is much easier to see, lying between the A and B ring. The image below also shows the C ring or crepe ring which is very difficult to see in amateur telescopes and is only hinted at in the above Nordic telescope image.

post-6974-0-24780700-1405571735Stargazer’s lounge image. (Just for clarity and because you can never have too many pictures of Saturn!)

This begs the question: how are the rings able to stay so neat? could it be gravity and that he material that makes up the rings be in just the right place that they don’t change?

Pioneer 11  became the first spacecraft to visit Saturn. It was launched from Cape Canaveral  on the 5th. April 1973. Pioneer 11’s path through Saturn’s outer rings took it within 21,000 km of the planet, where it discovered two new moons (almost colliding with one of them in September 1979) and a new “F” ring. Saturn from Pioneer looked very similar to Saturn through a telescope.

739508main_739460main_AC79-9107_3-full_full Pioneer 11 image of Saturn.

It wasn’t until the Voyager spacecraft flew past Saturn ( Voyager 1 in November 1980 and Voyager 2 in August 1981) that we began to realise what a complicated and far more extensive system the rings formed.

8bg                       Saturn’s rings with “spoke” features in B-ring. Aug. 22, 1981. Distance 2.5 million miles.

The spokes created much excitement and discussion and were endlessly replayed in a video sequence on TV…and to be honest I did and still could watch them happily for hours.

10bg The F-ring (discovered by Pioneer 11.) Two braided but separate orbit rings. Nov. 12, 1980. Range 750,000 km.

A clue to the structure of the rings was found by Voyager 1 when  it discovered three new moons, Prometheus, Pandora, and Atlas. Prometheus and Pandora are shepherding moons of the F-rings, and Atlas is a shepherd of the A-rings. After a lot of analysis and some careful thinking it was realised that these moons are able to control the movement (or shepherd) of material making up the rings by either pushing the material into place in the rings or ejecting stray material from the system all together. All this is done by the gravitational force of the much larger satellites on the smaller material that makes the rings. Pan creates stripes called “wakes” ( which are places where ring material has collected in an orderly manner) in the ring material on either side of it. Since ring particles closer to Saturn than Pan move faster in their orbits, these particles pass the moon and receive a gravitational “kick”. This kick causes waves to develop in the gap and also throughout the ring, extending hundreds of miles into the rings. These waves intersect downstream to create the wakes.

Pan has a similar shape to Atlas and that unusual shape may be the result of fine material from the rings aggregating on the surface of the moon.

A little more about Pan before we go: it was discovered on the 16th. July 1990 by Mark Showalter who was working on Voyager data. It is approximately 35 kilometres across and 23 km wide. It lies within the Encke Gap in Saturn’s A Ring. It orbits Saturn every 13.8 hours, at a distance of 134,000 kilometres and is responsible for keeping the 325 kilometre wide Encke Gap open.

There are many fascinating worlds around Saturn – have a look for Daphnis another shepherd moon as well as the ones mentioned above.

To give you an idea of the complexity of the ring system here is another image from Cassini:

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THE INTRIGUING WORLD OF ENCELADUS.

Enceladus is one of Saturn’s most interesting moons. It had long been suspected that there may have been a small ocean lying under the icy crust of the satellites south pole: images of geysers shooting jets ice and dust have often been imaged by the Cassini probe orbiting Saturn.

NASA have now discovered (15th. September 2016) that there is a global ocean hidden beneath the ice covering the whole moon. The finding implies the fine spray of water vapor, icy particles and simple organic molecules Cassini has observed coming from fractures near the moon’s south pole is being fed by this vast liquid water reservoir.

Cassini scientists analysed more than seven years’ worth of images of Enceladus taken by the spacecraft, which has been orbiting Saturn since 2004. They carefully mapped the positions of features on Enceladus — mostly craters — across hundreds of images, in order to measure changes in the moon’s rotation with extreme precision.

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The icy surface of Enceladus.

As a result, they found Enceladus has a tiny, but measurable wobble as it orbits Saturn. Because the icy moon is not perfectly spherical — and because it goes slightly faster and slower during different portions of its orbit around Saturn — the giant planet subtly rocks Enceladus back and forth as it rotates.

Using computers to measure this wobble, or libration, scientists have worked out that there the ocean must be moon-wide as anything smaller would result in a much smaller libration.

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How Enceladus’ may look.

Saturn lies 1.4 billion kilometres from the Sun (that’s eight times further away than Earth is from the Sun) a year on Saturn is 29.5 earth years long. Because it is so far away the Sun is not as powerful as it is on Earth and so temperatures are much lower, so much lower that liquid water shouldn’t exist on any body that far away and yet it does.

How is that possible? Well that is a mystery although some astronomers think possibility that tidal forces due to Saturn’s gravity could be generating much more heat within Enceladus than previously thought. Saturn is much bigger than Enceladus and as the moon orbits the planet its surface is gently pulled in and out of shape by Saturn’s gravitational force possibly generating heat that allows water to flow. This pulling on a smaller a body is what is meant by a tidal force.

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Cassini’s image of jets.

Scientists first detected signs of the moon’s icy plume in early 2005, further discoveries have been made: in 2015 they shared results that suggest hydrothermal activity is taking place on the ocean floor. On Earth hydrothermal vents are found on the floors of oceans, raising the temperature of the water nearby by many degrees, this in turn allows for all kinds of unusual and unexpected creatures to be found in regions where it had been thought there could be no life.

The material ejected from Enceladus may also help keep Saturn’s magnificent rings topped up with material. How the rings have survived for so long under the tidal forces of the gas giant’s gravity has long been a mystery but this may go some way to solving that puzzle.

All these findings raise the inevitable but intriguing question; could there be some form of life lurking in the Ocean of Enceladus? Cassini will continue to examine the plumes of material ejected from the moon to try and detect signs that something even more amazing may be waiting to be found.

In fact Cassini is scheduled to make a close flyby of Enceladus on the 28th. October, in the mission’s deepest ever dive through the moon’s active plume of icy material. The spacecraft will pass just 30 miles (49 kilometers) above the moon’s surface. there is a lot more to learn about this and the other amazing moon of Saturn.

Published in: on September 27, 2016 at 09:53  Leave a Comment  
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