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Well what did we produce? This is what we produced – one floppy disk. This is the entire data take from my instrument – the Surface Science Package – the Penetrometer and eight other sensors. So there we were on the evening of January 14th with our figures. What did it all mean? We had foolishly promised that we would appear – all the science teams would appear – in front of the world’s press. We were going to tell them exactly what Titan was all about. So we had to come up with a story. Well, the data that we thought was the most reliable was actually the data from this instrument – the Penetrometer. There it is. What is it? A graph (we do like graphs, as you might have noticed) of force against depth as we push into the surface.
We were looking at this thinking what we were going to say to the Press. What had we done? What was Titan like? And somebody, we still argue about who it was, piped up from our team: We have landed on crème brûlée – look. We have hit something hard. There is a high force as if we have hit a crust. We have pushed through that crust and then there is something soft, thicker, beneath it. So half an hour later I and my colleagues faced the world’s Press. And what did I say?
So ähnlich wie crème brûlée according to the Berliner Zeitung. Similar to crème brûlée, I think it means. Well, maybe it was a quiet day for news but crème brûlée and Titan was picked up all over the world. There we are on the front page of the Independent. We even made the Sun. It was all over the place.
But of course there were six instruments. Ours was just one of six. What did we learn from the other instruments? Well, there was a camera taking visible images. About a hundred pictures as we descended through the atmosphere. I am just going to show you one or two of them. The first image is from about a hundred and fifty kilometres. You can see the height there showed absolutely nothing. We were peering into that cloud. All we are seeing is cloud. And many of the first images were like that. It wasn't until we got to about twenty-five kilometres above the surface where we started to get a glimpse of that surface. We weren't sure what it was but there was something there. A bit further down, fifteen kilometres or so, this is in fact a composite and we saw a remarkable sight. We were seeing what looked like river channels with tributaries feeding larger channels. And what was this? Was this a coastline? Were we in fact descending towards a sea or a lake of methane? The scale of this, by the way, is about five kilometres across. And then finally we landed and this is what we saw – an absolutely remarkable image. Looks like a desert but the camera at this point is very low down, just a few inches above the surface, so these pebbles, the largest one there is about six inches across. When I say pebbles, remember that Titan is an icy world, so these are pebbles made of ice. So that’s the picture but what could we say about this scene? Well let’s take a look then again at our data. How do we interpret this? How would we relate this to the surface of Titan?
Well, it's obvious isn't it? You go to B&Q in Bletchley and you buy some of this. Now you probably think that this is material that you buy to make your garden look beautiful. But you are wrong. This is material that B&Q sells so that planetary scientists can make planetary surfaces. Either pebbles like these – these are sharp, angular pebbles. Maybe like the sort of material that you would get on a planetary surface if it was bombarded by meteorites and the surface was broken up. Or material like this. This is much smoother, much rounder pieces.
On Earth, of course, these are produced by the action of water flowing over rock, breaking, chipping off bits of rock and gradually smoothing them and rounding them off. Maybe the same thing is happening on Titan, not with water and rock but with liquid methane flowing down those channels that we see and taking off bits of ice and rounding and smoothing them off. So we ran lots of tests – literally hundreds of tests in the laboratory with material like this, lots of other materials to try to understand these graphs. Well, to cut a long story short, what we think has happened is that, despite what the picture shows you we think that this little bit of trace here tells us that this whole surface is coated with a thin veneer of something soft. Maybe material, which has been raining down out of the atmosphere, sort of hydrocarbon coating on the surface. This peak here probably occurred when we hit one of these icy pebbles. We hit it at a very high resistance. We pushed it aside and then we pushed down into this material between the pebbles, which is granular material but it's icy. So it's icy chips, probably of this sort of size and consistency. But what I can tell you for sure is that we didn’t land on crème brûlée! What do we learn from all of this? Well one thing that I learnt is that pictures are great. They are wonderful. They tell you a lot. But go for the graphs as well. As scientists we love graphs and there is so much more information in them.
With thanks to:
- Planetary and Space Science Research Institute
The Open University Lecture 2007
This is part 9 of 10