Patrick Short, Sanger Institute
Studying exoplanets and their transits has yeilded lots of interesting information on what their atmosphere is made of. But they're so far away, so whatís the point? Why do we care whatís circulating in their atmospheres? Graihagh Jackson put this to Patrick Short...
Patrick - Itís important because these gases, and elements, and these sorts of things give us an idea of whether a planet might support life to begin with
Graihagh - Thatís Patrick Short who is a PhD student based at the Sanger Institute. I met him because he competed in a science communication competition called FameLab where applicants have to get up on stage and give a talk about something they feel passionate about. Patrickís topic? The quest to find ET.
Patrick - And then also it could provide clues of whether life actually exists. So methane, for instance, is produced by most living things here on earth so if we see a planet with a huge methane signature then itís probably a pretty good place to search.
Graihagh - What are the chances there is actually life out there? I know thousands of exoplanets have been discovered but really, is it likely that thereís life out there in the first place?
Patrick - Yes, itís an important question. Actually, one that has vexed a lot of people for a long time so there have been some attempts to quantify this. One of the big distractions or criticisms is, I guess, that there are just so many unknowns that itís really hard to put a firm yes or no or even a probability of life in our galaxy or in other galaxies somewhere else in the universe but there have been quite a few pretty valiant stabs at it. So the most famous one was by Dr Frank Drake and he actually didnít intend it to really be his legacy or to be the thing that he was remembered for. It was basically intended to drum up conversation at a conference and the idea was basically to put a rough, back of the envelope calculation on what is the probability that we find life somewhere in our galaxy.
Graihagh - At this stage I think it would be a really good idea to go through Drakeís equation to understand a bit more about what these limitation are. So what is the first item in the equation?
Patrick - So the first item is the rate of star formation in the galaxy. So they express this in terms of number of stars per year. So the Milky Way is about 13 billion years old and Drake puts his first estimate at 1 star per year. So thatís a first step.
Graihagh - So 13 billion - letís write that down.
Patrick - So this would be n and star I guessÖ
Graihagh - OK. What next?
Patrick - So next is what proportion of these stars have planets around them. So not all stars have planets and Drake put this at somewhere between ⅕ and Ĺ . And then weíve also got the number of planets per star. So given that itís got a planet, how many does it have in general and he puts this at between one and five. Given that youíve got a star thatís got planets weíll assume conservatively that itís got one planet and weíll assume aggressively that itís got five habitable planets per star.
Graihagh - And when weíre talking habitable we mean the right sort of temperature, that itís got an atmosphere, and it doesnít spin too fast, it doesnít spin too slowly. All these types of things that are needed for life.
Patrick - Yes, exactly.
Graihagh - So weíve got number and stars and then how many habitable planets around those stars. So whatís next after that?
Patrick - Then weíve got the probability that a habitable planet will result in life. So, I guess, you can consider it the probability that given all the right conditions to find that habitable planet that life will arise on that planet and Drake puts that at one. So heís quite an optimist - he says if weíve got a star with a habitable planet then life will arise on that planet. And then this follows quite closely by the second term which is the probability that that life will turn into intelligent life, which Drake also puts at one. So he thinks that itís inevitable that if life is created it follows to intelligent life.
Graihagh - After this, thereís still more is there?
Patrick - Yes. So then thereís the probability that they donít develop communication skills so Drake was specifically interested in looking for civilisations that would have made contact with us or that we could make contact with. And he puts their probability of developing communication at between 1/10 and ⅕, so 0.1 and 0.2.
Graihagh - OK - communication. Surely thatís the final one?
Patrick - No - weíve actually got one more. So Drake has factored in exactly how long these communications will last. We weíve been doing our search for extraterrestrial intelligence listening not broadcasting but only for a few decades so he places his lower bound and upper bound between somewhere between 1,000 and 100 million years.
Graihagh - OK. So if we take this equation and we do the conservative estimate, what do we get?
Patrick - So the conservative estimate which is: 13 billion stars, ⅕ of which planets, one of which is habitable and which we develop life 100% of the time, intelligent life another 100% of the time, 10% of the time they develop communication tools and they only use these communication tools for 1,000 years. Then Drake estimates that we would have actually only have about 20 habitable planets in our galaxy, which is the Milky Way.
Graihagh - That doesnít seem like very many. What about on the other end of the spectrum?
Patrick - On the other end of the spectrum if you want to go with Drakeís most optimistic estimates, then Drake arrives at a maximum of 50 million intelligent species within our galaxy and again, thatís just within the Milky Way. So weíve got another hundred billion of these galaxies out there so, even if we pick Drakeís lowest estimate which is 20, then weíve got in the order of 2 trillion intelligent species that we could get in contact with.
Graihagh - I mean that sounds incredibly high so why the heck have we not been able to make contact with any of these civilisations or, indeed, they make contact with us?
Patrick - Yes, so that opens up a whole other famous chapter of physics history. So this question was asked by Enrico Fermi, heís a physicist and, I think the exact terminology he used is ďif this is the case then where is everybody.Ē And his point being that if we accept that somewhere between this conservative and aggressive estimate of the amount of life out there that surely either we should have heard somebody, detected something or had somebody get in contact with us. And especially the extra layer of evidence is that weíre actually somewhat young in terms of the history of the universe. So, if we can imagine our society fast forwarding just a few hundred million years, then we should most certainly be able to colonise the galaxy and do all these intergalactic travels and certainly communication but, the fact of the matter is, we havenít heard from anybody. So the paradox here is if we can accept that the universe is teeming with life and one of the possible explanations for why we havenít heard from anybody and thereís quite a few interesting ones, I think.
Graihagh - Like what?
Patrick - One of my favourites is this idea that if we consider ourselves young in terms of the intelligent life spectrum, then any other intelligent life out there that was older than us may be so incredibly advanced and more developed than us that they donít actually consider us to be intelligent life. Think of our relationship with ants; they communicate with scent and we really donít spend a lot of time trying to device scent systems to try and communicate with the ants. And then thereís other more practical considerations that it may be that some of these estimates are of,f and there is life out there but itís so far spread out that the physical limitations of the universe make it impossible for us to communicate with one another in practical amount of time. And maybe theyíve tried to communicate with us but itís still on itís way so itís just being sent across the universe at light speed and maybe some day weíll hear it.
Graihagh - We could speculate all day on the possibilities but Fermiís problem still stands. Where is everybody? And then that sorta makes me ask, well why are we bothering anywayÖ Sat in the sun with Patrick in a park, with kids mucking about on the swings, I realised that one of the things we enjoy the most (and I suppose makes us fundamentally human) is that interaction with others. And that combine with our curiosity, well, then the search for life elsewhere in the universe, despite all it improbabilities, is still worth it.
Patrick - Yes, Iím very optimistic. I would be thrilled if we found life somewhere else. I think it would be super exciting. I donít know, I guess weíll just have to wait and see butÖ who knows?