Director of Alien: Covenant Ridley Scott has told the press that he believes extraterrestrial beings are out there right now, and that the science backs him up. He told the Guardian: ‘The experts have now put a number on it, having assessed what is out there. They say that there are between 100 and 200 entities that could be having a similar evolution to us right now.’ This was surprising news to RISING, so we asked Professor Lewis Dartnell, at the University of Westminster if we should be watching the skies for armadas of xenomorph invaders – or even little green men haunting the woods?
RISING Your job as an astrobiologist is to search for evidence of extraterrestrial life – could you say that there are 100-200 alien lifeforms that have evolved to a similar level to us?
PROFESSOR LEWIS DARTNELL ‘Any estimate on the number of planets in our galaxy with complex life is no more than wild guesswork. If there are intelligent species out there, in our galaxy, there are good reasons to suppose that their motivations for voyaging across the vast distances between the stars to visit the Earth would be more out of curiosity as anthropologists or biologists, rather than war-crazed armies or hungry predators.’
RISING So, the million-dollar question: could aliens already be here, living among us?
PLD ‘Yes, it is possible, but we see no evidence for that. We have got very good at finding life in a variety of different environments on Earth under very extreme conditions. All of the organisms that we have found so far all fall into the same genetic tree of life as we do, so we’re all related to each other. So, there’s no reason to think that there are alien cells here among us.’
RISING Crikey – you’re one step ahead of us here – where have biologists on Earth been looking to learn about possible alien life forms?
PLD ‘Astrobiologists like myself go to a lot of ‘analogue’ sites – places here on Earth that are similar in important ways to extraterrestrial locations. I’ve done field work in the Atacama desert in Chile, the oldest, driest desert on Earth, yet you still find bacterial life there clinging on by its fingertips. The Atacama is a lot like Mars, life there is water-limited. The cold, dry valleys of Antarctica are also similar. There are also super-acidic places like the Rio Tinto in Spain, which has conditions thought to be similar to ancient rivers and lakes on Mars, and bacteria manage to survive here. In Lake Vostok in Antarctica, liquid water under great pressure is trapped under 4000m of ice – this could be similar to Europa one of the icy moons of Jupiter; or Enceladus, one of Saturn’s moons. If we can understand how life might survive in Lake Vostok, it can help us imagine how life might exist on the icy moons, and answer the question about how life in such extreme environments might make its living.’
‘There are more planets in the universe than grains of sand on Earth’
RISING Once you’ve scoped out these analogues, where in the universe are scientists looking for alien life, and why?
PLD ‘The main focus of our search for life is our next-door neighbour, Mars – it’s a habitable place, or at least has been in the past. We’re sending fleets of robotic explorers and probes to work out where the water might have been, using our experience of the Atacama, and to find out what signs of life might still be there. We also want to check out Europa and Enceladus, those icy worlds in our own solar system, and looking further afield beyond our own back garden, at the other stars in our galaxy: the Milky Way. I think that there’s a good chance of life on one of the Earth-like planets that the NASA Kepler telescope has found. Kepler is coming up with a shopping list of planets in this spiral arm of the galaxy, ranked by the length of their year and how hot they are likely to be. Later missions will target the most promising exoplanets, analysing their atmospheres for oxygen. The early exploration of these planets will first be done from space-mounted telescopes. We don’t yet have the technology to send probes that far.’
RISING We’ve heard about the Goldilocks Zone out in space – what has alien life got to do with porridge?
PLD ‘It’s named after the fairy tale about Goldilocks tasting the bears’ porridge and looking for the perfect bowl. It’s the region around a star where a planet orbiting it would be neither too close and hot; nor too far away and cold, where liquid water could persist on the surface for long enough for life to get started. We also call it the Habitable Zone.’
RISING Before Ridley Scott got his hands on aliens, turning them into steroid-abusing preying mantises, they were little green men – but could aliens that have evolved on different planets look anything like us?
PLD ‘The vast majority of life in the galaxy would be microbial, the same way that the great majority of life on Earth are microbes, single cells and microscopic life forms because that is the first life to form – it’s hardier than multi-cellular beings like us. Most life in the galaxy will probably look a lot like terrestrial bacteria. Their genetics and their energy metabolism might be different from us, they might be built out of different organic elements, but they are not likely to be that different in shape and form.’
RISING So, could an alien planet look much like, you know, Earth?
PLD ‘If there’s a sufficiently Earth-like planet out there where evolution had a chance to progress beyond single-celled life over billions of years, to alien plants or animals, some of the features of these plants or animals would be recognisable to us, even familiar. An alien tree would have to solve the same problems that a tree on earth does. It would probably have a trunk and branches, the leaves might be a different colour, tuned to make energy from a different wavelength of light from a different sun.’
RISING What about the critters – xenomorph, much?
PLD ‘If complex animals could have evolved, at the most basic level they’d have to have a gut tube to absorb their food, with a mouth at one end and an anus at the other. A higher life form might have limbs and muscles to move around; they’d put their sense organs at the front of their body on their head, so that they could see which way they were going. Here on Earth, eyes have evolved independently scores of times. So you’d expect to recognise a lot of features on the alien animal. But if it was an intelligent alien, there is no reason to think that it might be humanoid in appearance. Having five fingers, say, may just be a quirk of our own evolution, but they would still have things like hearts and lungs, guts, brains and eyes.’
RISING If it was an intelligent alien, would we even be able to communicate with it?
PLD ‘Humans throughout history have met each other in remote wildernesses with no common language, and quickly worked out how to communicate – I don’t see any reason why an intelligent alien and a human couldn’t do the same. We’d have shared experiences and reference points, given that we live in the same galaxy. The stars, planets, and chemistry are universal, you’d start there at the basics and build up to more complex concepts such as love and emotions once you understood each other’s psychology. That’s important because language is obviously linked to our brains, and how we perceive the world around us.’
‘If it was an intelligent alien, there is no reason to think that it might be humanoid’
RISING The other day we looked at the cosmic clock, compared to Earth’s geological time, and then to humanity’s lifespan, and our brains almost fell out of our ears – what are the odds another alien life-form could have evolved to the same point, at the same time, as us?
PLD ‘I think that the very reason you do science is to try and answer questions like that. It’s impossible to answer that question before we have found life elsewhere in our galaxy. We just don’t know how likely it is that life gets started on an Earth-like planet. Terrestrial life could be a cosmological fluke, or a near inevitability. Our best bet is to explore Mars, and the icy moons of Europa and Enceladus, looking for life. If those other worlds in our solar system developed life independently then that will give us a better handle on how likely we are to find life elsewhere in the galaxy.’
RISING Is it possible that we are alone in the universe?
PLD ‘Yes of course it’s possible. Searching only the local neighbourhood of our own galaxy, the Milky Way, Nasa’s Kepler telescope has identified over 3600 new planets outside our solar system. Astronomers have narrowed those down to twenty that lie in the Goldilocks or Habitable Zone. Nasa estimates that there are 2000 billion galaxies in the universe. Each might be teeming with planets and moons where life could potentially exist. There are more planets in the universe than grains of sand on Earth, that adds up to at least 100 billion possibly habitable worlds.’
RISING So, what are the chances of being able to search outside the Milky Way?
PLD ‘The distances to even the nearest galaxies to the Milky Way are so impossibly vast that it would take a radio signal millions of years to travel there. Yes, there might be life out there, but it’s essentially irrelevant because of the great distances involved. Astrobiologists limit our research to the local part of our own Milky Way galaxy where we can feasibly study these things and have a reasonable chance of discovering a civilisation, and then communicating with it. We have a lot more searching to do before we can truly say that we are alone in the universe.’
WHAT NEXT? If you’ve been inspired to apply some science to fiction and make your own mind up about aliens, why not follow @SETIInstitute on Twitter to track the search for extraterrestrial life?