Brian Cox's 'Solar System'

Professor Brian Cox has got a new TV show coming out. It’s called ‘Solar System’, and James Tytko went to meet him at BBC Broadcasting House to find out why, in his view, it’s the right time to revisit our cosmic back garden...

Brian - It felt like it was time to make a series really focused on the data that's coming in. Now, for example, in this series, you'll see data from Juno around Jupiter of eruptions on Io. That's data from this year, 2024. So we see Io is the most volcanically active object in the solar system. And the reason is because of what's called the orbital resonance, so the way that the other Galilean satellites interact with Io, which means that it is in an elliptical orbit around Jupiter, which means there are tidal forces on it, which heats it up. And so I like the sense that this is a snapshot of what's happening now and what we are observing now in the solar system.

James - Why are volcanoes so interesting to people studying the solar system? What are the big clues they provide to the big questions we want to answer?

Brian - So if we start on Earth, they're a central and essential part of our geology. And as I say right at the start of the first episode, you might say, well, why are we interested in geology? I mean, it's an interesting science in its own right, but one of the reasons we are very interested in it, if you think about what the origin of life must be, it has to be a transition from geochemistry to biochemistry. Because of course you start with a load of things, the solar system, in this case that formed four and a half billion years ago and there was no life. And then you get geologically active worlds and it's in what we might call out of equilibrium conditions, chemical and thermodynamic, that complex carbon chemistry emerges. So volcanoes and associated with the volcanoes actually on earth plate tectonics are central to the Earth's climate and also to those chemical processes that would've led to the origin of life here in this case around 4 billion years ago on Earth.

James - That's actually an interesting question that I think bears some description, which is where the Earth's heat comes from in the centre of it in the core to drive the volcanic activity that we see on it.

Brian - So about half, at the moment, about half the energy that's there in the Earth core is essentially from the formation. So it's like dropping a rock, basically. You drop a rock to the ground and it gives up its gravitational potential energy, and it's a thing we all do at school. And you hear a bang and it hits the ground and it heats the ground when it hits it. And so part of the earth's store of energy is coming from that, the formation four and a half billion years ago, which is gravity ultimately. And the other half is from radioactive decay of nuclei. Uranium, and radioactive elements like that in the core. And so when you look out into the solar system, one of the first questions you would ask is, well, are there other places which have similar geological activity? So you see it on the surface of Mars. So it's obvious, you just look at Mars, you see things like Olympus Mons, the biggest volcano in the solar system. But those volcanoes are extinct. It's smaller than Earth, so it lost its heat more quickly. And so it's essentially an inactive world ish. So, the point about Io is that it's interesting because it's a very small world where the origin of the energy, so the origin of ultimately the energy that dries the volcanoes is coming from the orbits. And so we did do it, I hope we did it justice. What we ended up filming was the way that I explained it to the director <laugh>, the way that I found of explaining it, because it's quite interesting. It's about the way that Io is tidally locked and the face of Io is locked to the empty focus of the ellipse and not to Jupiter, but the tides are raised obviously on a line going to the planet and so on. So it's quite a complicated story actually.

James - I wonder if we could fill in a little bit of the picture as to why geothermal energy and volcanic activity might be the place to look when we are thinking about origins of life on Earth. And then why are we looking at that further afield in the solar system?

Brian - If you think about chemistry getting complicated, by which I mean very complicated, which is it becomes biology. What we know is that to drive chemical reactions like that, you need differences in temperature, differences in chemical composition and so on. Where does that come from on a planet? Ultimately those conditions are geological conditions. One of the weird things about life on Earth, you have to imagine these imbalances in protons, across membranes in the cells. And that's one of the things, one of the chemical properties, that all life shares and exploits. And it's a bit odd really, because we tend to think of life as being electrons moving around, right? So photosynthesis, we learn about that. It's all about the electrons moving, but actually underpinning that is this proton stage and it's chemistry that's shared by all living things on Earth. So as you infer, therefore it must have been something to do with the origin of life, at least the population of things to which we are all related, which is often called Luca, the last universal common ancestor, it must have had that property. But there's a hint of geology about it, geochemistry. So you have a candidate then for the cradle of life on Earth based on observations of the properties, the chemical properties of life today and geochemistry that exist today on Earth. And so we go to look for those places. If you want to look for life beyond Earth in the solar system, it makes sense to look for places where those conditions are present and those conditions are present. We think on Europa, Jupiter's Moon, Europa, we're not entirely sure. So that's why we've got a couple of missions on the way now. And also Saturn's moon, Enceladus. Is another one. But again, we are not entirely sure. So we need a mission there. That's one of the ways that we steer solar system exploration in terms of the hunt for biology, is to look for those conditions.