Cooking a comet

Using party ice, water and charcoal, Rosetta Mission engineer Warwick Holmes and University of Waikato’s John Little create a model of a comet in front of a live audience.

Transcript

WARWICK HOLMES

So now I would like to introduce John Little from the science department here at Waikato who is going to show you today how we’re going to cook a comet.

Now, that’s a bit misleading, because there’s no cooking involved – it’s actually extremely cold. What we’re going to try and show you is, here on Earth, all the science and the measurements that we’ve taken so far with Rosetta and Philae, we’re going to try to create, as close as we can here on Earth, the equivalent of what a comet would look like.

So the primary ingredient that we have is frozen carbon dioxide gas – so we call it party ice – which they use for sometimes delivering cakes. And frozen carbon dioxide gas is one of the most important frozen gases on the comet, together with water ice, which is the majority of the material on the comet. And then we have all this exotic carbon chemistry – we have these amino acids, we have formaldehydes, we have methanes, we have alcohols, we have sugars even as well.

And so today, what I’d like John to try and help you do is to make an analogy – an analogue of the comet. So it’s extremely cold, and we’ll be crushing this ball of ice together, together with charcoal to make it as dark as we possibly can. So in principle, the comet should be completely jet black – as black as we can make it – so that hopefully when we hold it up you shouldn’t even be able to see it, but of course you will.

So it’s cold, it’s dark and it’s evaporating all the time – so you can see the vapour of the carbon dioxide gas coming off. So he’s going to be pouring in the frozen carbon dioxide ice. Already, we’ve put some charcoal inside with some water. As you can see, it’s extremely cold, which is the temperature of the comet.

OK, so that’s the primary ingredient together with water and ice, which is in there as well, and some liquid water. Now we have to try and mix all that up and then crush it into a solid ball to hopefully form a solid mass which we can then hold up in front of you as a steaming cold black comet.

Now we’re going to try and take it out of the plastic bag, if we can, we’ll hold it up for you to show you.

OK, there we are.

Now, I have to say that is the absolute best example I’ve ever seen. So you can see that it’s evaporating in the temperature of the surrounding atmosphere here – and we might get the bowl ready again just to catch it – there we are.

The important thing to see here is it is evaporating, it is volatile and it’s very cold, and these are the frozen gases which are evaporating just in the ambient temperature of our hall here. But as the real comet gets close to the Sun, exactly the same process occurs. The difference is that there’s the solar wind from the Sun actually pushes this evaporation and plasma and gases away and forms the big tail we’re familiar with in normal comets.

But this is an excellent example of how dark and how cold and how eerie a comet really is.

The Science Learning Hub would like to acknowledge the following for their contribution to this resource:
Warwick Holmes
John Little
Seminar video footage courtesy of the University of Waikato