Saturn is one of the most well-known planets in the solar system, perhaps owing to its distinctive set of rings. The largest of these rings, the H-ring, was only discovered as recently as 2009 and cannot be seen from Earth. Now, using images taken by NASA’s WISE spacecraft, scientists at the University of Maryland have given us the first insights into the structure and formation of Saturn’s outermost ring. I spoke to lead researcher, Doug Hamilton, to try to remove the shroud around Saturn’s most mysterious ring…
Doug – We’ve been able to look at the structure of the ring in these images and what we’ve discovered is that the particles are dominated by fairly small dust grains. So, 10 microns in size, a hundredth of a millimetre, very very small.
Tom – The rather catchily named H-ring was discovered in 2009 by the Spitzer space telescope, but what led to its formation?
Doug – This one seems to have come form the satellite Phoebe. So, Phoebe is a distant object of Saturn, its got a tilted orbit around Saturn, which means that it goes up and down and the height that it goes up and down matches the height of our ring. It tells us that Phoebe is the source of the dust particles.
Tom – So how does the material come off Phoebe to actually form this ring?
Doug – Its an impact onto Phoebe. There are collisions form other objects out at Phoebe’s distance, so think of a comet tail and all of the debris that come off of it, all of those bits are hitting the satellites and kicking off debris that form part of the ring. And then where Phoebe is located there are another 50 small satellites and occasionally they collide producing more debris.
Tom – The main rings of Saturn are visible from Earth – you can even see them with your own telescope on a clear night, so why can’t we see this new ring?
Doug – Since the dust particles are black they are really hard to see with visible light. You’ve got black dust particles set against the blackness, the darkness of space. So what we do is we realise that those black dust grains will absorb sunlight quite efficiently and they heat up and they re-emit heat, they re-emit red light. We use telescopes that are sensitive to that light.
Tom – You visualise this using infrared light, what does it look like on these images?
Doug – This is pretty neat aswell. It’s fairly planar, so it’s flat. You want to think of a coin, sort of a coin edge on. It’s a flat, yet extended structure. And we see it just because of how the dynamics of the particles work, we always see this thing edge on from the Earth. So you have your coin and you flip it on its side and you’re looking at it like that. So what we see in the sky is a rectangle.
Tom – What makes this ring particularly interesting?
Doug – It’s turned our whole idea of what rings are on its head, because we always think that rings are formed close to their parent planets and then you get moons and satellites further away. And this has just flipped it around – so we’re as far away from Saturn as you can get and still be in orbit around the planet and there’s satellites out there, but there’s also a ring. And so this teaches us – it makes us think differently about rings and hopefully we’ll open our minds a bitand learn a bit more abut how they form.
Tom – The analysis of these new images from the WISE spacecraft has given us greater insight into the structure of Saturn’s latest ring, but how does this new ring compare to the others?
Doug – We have the massive rings that you see on the telescope images, those have been known for a long time. Those are composed of big house-sized chunks of ice. And then we have Saturn’s E-ring. So that’s a ring that’s bigger than the main rings of Saturn and it’s extremely tenuous and it’s made up only of small dust grains. This large ring that we have at great distances is in-between. So we have big particles like you find close to Saturn, we have the small particles like you would find in Saturn’s E-ring and everything in-between.
Tom – Are there any other applications, any other knowledge you’ve gained from studying this ring?
Doug – We like things that are the biggest, the brightest, the furthest and so on… And this is the largest ring in the Solar System. So that’s kind of nice just on a gee-whizz level. On a deeper level what it teaches us is not to be too bound by our expectations. So nobody expected a ring to be this large and so as we go forth and look at exoplanets, and we’re looking in the data for signals, we’ve been surprised over and over with exoplanets. And back here in the Solar System we’ve been surprised by this ring and what it teaches us is to be open-minded. The universe has a lot of things it can do – it hasn’t shown us all of its secrets.
You can listen to the interview for the Naked Scientists here.