THE question of whether there is extraterrestrial life has fascinated human thinkers throughout history. In recent decades, technology has allowed us to move beyond pure speculation. We have sniffed for the tell-tale signs of water within our solar system, analyzed incoming radio signals for patterns indicating alien communication — and are now searching distant stars in our galaxy for rocky, Earth-like planets. While these experiments have yet to provide a definitive answer, they are generating data telling us more about the probability of other forms of life being out there. Most space scientists agree it is unlikely life has only occurred in our little corner of the universe. Many believe that the existence of extraterrestrial life will be confirmed this year. Alien life is probably not the little green men so beloved of science fiction. Yet, as I explain here as part of the celebration of Science Month on TV channel Eden, I do believe complex intelligent organisms in various forms are out there. This does not mean that we should prepare the alien reception committee just yet. The question often overlooked is how likely is it that we will find them or they us? The Drake equation, devised in 1961 by Frank Drake, Emeritus Professor of Astronomy and Astrophysics at the University of California, is a formula designed to estimate the number of detectable extraterrestrial civilizations in our Milky Way galaxy. Note the important word “detectable”. The answer is the result of multiplying seven variables – the 200 billion stars in our galaxy, the percentage of these that have planets, the average number of life-supporting planets per star, the proportion of these on which life develops and on which intelligent life develops, the percentage with communication technology, and the proportion that release detectable signals in the right time frame for us to pick them up. We can input values into the Drake equation, with some based on solid science and others based more on guesswork. Peering into space is generating a great deal of new knowledge but we still have a lot to learn down here on Earth. In a documentary I am presenting, called Do We Really Need the Moon?, we look at the theory that suggests tides might have triggered the precursors of DNA, the genetic blueprint of life, from the chemical soup that already existed on Earth. The Voyager 1 spacecraft, which is carrying a recording of greetings from Earth, has been travelling through the solar system since the 1970s and has only made it into deep space. To get to our nearest neighbouring star, Proxima Centauri, would take it 76,000 years. If one of our four alien civilisations is on the other side of the galaxy then it would take millions of years just for electromagnetic signals to travel that distance, and by then they may be too weak to be detectable.Until not long ago, most scientists assumed that there was no life at the bottom of the ocean because of the lack of sunlight. While about 500 humans have flown in space, only three have been to the deepest depth of the oceans, the Mariana Trench, which lies at 10,994 metres below sea level in the Pacific. Film director James Cameron was the most recent earlier this year. Discoveries in the murky depths suggest we should think more broadly about the conditions in which life can develop. Some have suggested hydrothermal vents, which bring hot, mineral-rich water gushing through the ocean floor, could have provided the spark that triggered the creation of early life. Conventional wisdom has been that life is carbon-based and needs water, but some researchers are doing exciting work, playing with ideas such as silicon-based life forms. Silicon is just below carbon in the periodic table, has some chemical similarities and is widely available in the universe. Just weeks ago, the go-ahead was given for the construction of the world's largest optical telescope. The European Extremely Large Telescope, to be built on top of a mountain in Chile, will have a main mirror measuring 40 metres in diameter. This compares with the Very Large Telescope, a suite of interconnected optical telescopes with four primary mirrors that measure 8.2 metres across. Then there is the conceptual design for the futuristic Overwhelmingly Large Telescope, with a single mirror of 100 metres in diameter. These telescopes will allow us to probe the chemical make-up of the atmospheres of planets. We may find unusual results such as spikes of chemicals we weren't expecting. Maybe we will see spikes of silicon compounds, indicating life forms. Flowing methane and pools of methane have been identified on Titan, one of Saturn's moons. It makes me wonder whether a form of life could be based on liquid methane. The creatures we have found on the bottom of the ocean floor use thermal energy from the centre of the Earth rather than sunlight. This variant on life and the other possibilities being looked at lead me to believe we may need to extend our notion of where alien life might be found. It might be prudent to consider whether we are talking about friends or foes. Stephen Hawking said we shouldn't send signals out into space because if there are life forms more advanced than us it might not be wise to tell them where we are. I don't believe we should be worried. If they are very intelligent I don't know what we have that they would want enough to attack us. We do have water on Earth but if they are travelling halfway across the galaxy to find us they will bump into plenty of water on the way. They will probably see us as we see ants – oddities perhaps worthy of study. I can't see what their motive to exterminate us would be. Using the Drake equation, it leaves me with an estimate of four intelligent alien civilisations in our galaxy with means to communicate and overlap in time with humans.Nevertheless there remains a big problem. Communicating across the galaxy is challenging.The Voyager 1 spacecraft, which is carrying a recording of greetings from Earth, has been travelling through the solar system since the 1970s and has only made it into deep space. To get to our nearest neighbouring star, Proxima Centauri, would take it 76,000 years. If one of our four alien civilisations is on the other side of the galaxy then it would take millions of years just for electromagnetic signals to travel that distance, and by then they may be too weak to be detectable. The notion we constitute the only little spike of life in the universe is a lonely one. Perhaps we can take comfort from the likelihood that there are all sorts of weird and wonderful life forms out there. — Agencies
