How we could track down ET
It may be light years away but scientists have developed a nifty way to see if planets around other stars could have evolved life. Carole Haswell told Graihagh about how she does it...
Graihagh - It’s the Naked Scientists, with me Graihagh Jackson - the search for extraterrestrials - are we alone in the universe? Now, as Nick has just said, in order to be considered to be alive, you need parasitise your environment to make copies of yourself and then you excrete stuff. So could we track the elements cells excrete, this metabolic activity? A bit like a biosignature? Here’s Jim Al-Khalili, professor of physics at the university of surrey...
Jim - So certain types...only created by living organisms.
Graihagh - That’s all very well but the Andromeda galaxy is far, far away. It’s a nearest neighbour and is still a whopping 2.5 MILLION light years away. So let’s stick to our patch of sky - how are we then looking for biosignatures around stars say, a hundred lightyears from home?
Carole - My name is Carole Haswell. I’m an astrophysicist at the Open University where I do research on exoplanets.
Graihagh - Exoplanets are just planets outside our solar system. Exo being greek for outside.
Carole - As a very young child I knew that I wanted to be an astronomer and, like many young people, I thought that I wanted to do cosmology just because seemed like the ultimate thing to do. And then, I think, as I got older and actually started studying at university, then I realised that actually, cosmology seemed to me to be a little bit abstract and removed from things that I could identify with and so, at that point, I decided that I wanted to work instead on things closer to home. So, I in fact started my research career still doing something that’s quite far out. I was working on accretion around black hole binary star systems and I did enjoy that but in, I think it was about 2003, I saw a paper which had observed an exoplanet using the Hubble space telescope. And when a planet passes in front of a star from our point of view, it blocks say 1% of the light from the star and produces a very subtle dip every time it goes round the orbit. But this particular paper, they had used the Hubble space telescope to look in the ultraviolet and they had seen, instead of a 1% very subtle dip, a 15% diminishing in the light from the star and this told us that the planet was actually surrounded by a huge cloud of hydrogen. And, at that point, I thought this is just too exciting and exoplanets are the way to go.
Graihagh - I mean obviously it had a profound importance for you but what was the importance of that discovery more generally in the scientific community I’m thinking?
Carole - What that paved the way for was the whole field of being able to actually assess the chemical composition of exoplanets. So, here you have a planet orbiting a distant star and because the planet is surrounded by some gas, which is translucent. The gas is made up of atoms and ions which absorb light at particular wavelengths.
Graihagh - I think of it like a looking at a rainbow. Whilst hydrogen may block one frequency of light - red let’s say - methane might block green. So you have a rainbow - or spectrum of light - that goes mm and YELLOW and PINK and mm! PURPLE and ORANGE and BLUE! And by looking at what’s colours are missing you can work out what elements are found in the atmosphere of this extremely, distant planet. Soooooo coool.
Carole - So it really opened the field for being able to actually measure what planets outside our own solar system are made of or at least what their atmospheres and the surround gas cloud is made of.
Graihagh - What I find absolutely insane is that these exoplanets are a long, long, way away. I mean, how far are we talking in light years?
Carole - Well the very, very closest star is about 4 light years away and, obviously, most stars are very much further away than that - hundreds or more light years away. So the transit method has found thousands planets or planet candidates. Not all of them have been completely verified but it’s been extremely successful at finding planets.