Planetary rings in my pocket like grains of sand: public lecture on granular mechanics

Posted by mjs76 at Feb 11, 2011 09:55 AM |
In our weekly inaugural lecture on 15 February 2011, one of our Professors of Mathematics will show how the rings of Saturn actually behave very much like a fluid.
Planetary rings in my pocket like grains of sand: public lecture on granular mechanics

Ice plumes on Enceladus (image: NASA)

A public lecture entitled ‘Statistical mechanics of granular matter: simple concepts and complex phenomena’ is, for many people, not an enticing prospect. It sounds like a talk about calculating how long cement takes to set, which would only be marginally more interesting than sitting and timing it yourself.

But don’t worry, because when you actually investigate what Professor Nikolai Brilliantov* researches in our Department of Mathematics and what he will be talking about, it turns out to be massively interesting. And nothing to do with cement.

Well, actually a bag of dry cement is a granular system, as is a bowl of sugar or – and this is where it gets exciting – any of the rings around Saturn. The fascinating thing about granular systems is that they can behave like a solid, a liquid or even a gas. Think of a sandy beach. Dry sand is solid enough to support your weight but scoop some up and it runs through your fingers like a fluid. (There is also an amazingly cool lizard, the Florida sand skink, which can actually swim through sand at a depth of about 10cm.)

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‘Statistical mechanics of granular matter’ is a relatively new field because, although it’s not too difficult to calculate the interaction of a few particles, a whole load of them is a different matter. Nikolai, who graduated from Moscow State University in 1980, has published three books on the subject: two in English and one in Russian. His particular area of expertise is granular gasses, like the Saturnian rings, in which particles move freely, occasionally colliding.

Nikolai’s lecture will look at the current state of research into granular mechanics in general, then concentrate on granular gasses. He will show how the particles in granular gasses violate the principle of energy equipartition, which says that, in a system at thermal equilibrium, a particle’s energy is equal for all degrees of freedom. He will also explain how shocks, vortices and clusters can form spontaneously from the chaotic interaction of particles. It all sounds amazing.

Finally, Nikolai will discuss how these mathematical theories of grain movement can be applied in the real world; the world in question being Saturn (which is recognised by most astronomical organisations as the way coolest planet).

A couple of years ago, Nikolai published a few papers about Saturn’s moon Enceladus - which is  embedded in the planet’s rings – and this work attracted quite a bit of media attention. Enceladus is special because it is one of only three non-terrestrial bodies in the Solar System which could conceivably have liquid water (the other two are Mars and Europa).

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Professor Nikolai Brilliantov

When the Cassini probe passed by Enceladus the images returned knocked everyone sideways because they showed a vast plume of water vapour and microscopic ice crystals blasting out continuously from near the moon’s South Pole. This made for some great images, but it is research into the mechanics of granular gasses by Nikolai Brilliantov and his colleagues which has enabled us to understand how this expelled material spreads out from Enceladus and has, over time, formed Saturn’s E ring, the widest and outermost of the planet’s rings. In his most recent work Nikolai has shown that the present distribution of particle sizes in the rings can help us to understand the history of the rings’ formation. 

Which is a long, long way from watching cement dry.

This free public lecture, part of our Inaugural Lectures series, takes place on Tuesday 15 February 2011 at 5.30pm in the Ken Edwards Building, Lecture Theatre 1.

*Nikolai Brilliantov has won the University’s coveted ‘Best Academic Surname’ award for the past two years.