LET’S get one thing out of the way: aliens are almost definitely out there. On average, every star in the Milky Way has a planet orbiting it. Fully one-fifth of those stars have a planet that could be temperate and conducive to life as we imagine it. That’s 50 billion potentially habitable planets just in our own galaxy – which is one of billions in the universe.
“If you’re going to say that there’s no chance we’re going to find any life elsewhere, you must think there’s something really miraculous about Earth,” says at the SETI Institute in Mountain View, California. “And that’s a suspicious point of view, that we’re just miraculously better than all the other planets.”
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That doesn’t mean intelligent life is close by. We have been exploring our solar system for a long time, so if it contained intelligent life forms we would probably know about it by now. With simple, microbial life, it is a different story. The best places to look are the icy outer solar system moons Europa, Enceladus and Titan because we know they have liquids that could support life, says , director of the Carl Sagan Institute at Cornell University in New York.
“Our most basic assumptions about life are from a sample of one planet”
For anything bigger, we must peer further afield – and, as yet, our technology for spying life at a distance is rudimentary. Our best bet is to study the atmospheres of alien planets for signatures of gases like oxygen and methane that only coexist if some thermodynamically implausible process – call it life – is constantly replenishing them. We can’t do that quite yet, but with the imminent launch of the James Webb Space Telescope and construction of the Extremely Large Telescope in Chile, we should soon be able to.
I don’t want to be alone
Remotely sensing just one other world with alien life would tell us that we aren’t alone in the universe, and that life is probably widespread. But it won’t tell us what that life is like. We naturally tend to think of any advanced life as human-like, but we don’t even know what future humans will be like. “If someone had written this article 100 million years ago and asked what aliens would be like, they probably would have heard from a triceratops or a brontosaurus that aliens are probably small at one end, big in the middle, and small again at the other end,” says Shostak.
Even assumptions such as life being carbon-based and requiring liquid water are based on a sample of one planet. Life on Titan could use liquid hydrocarbons in the way we use water. Some scientists have speculated that life could be silicon-based. Given computing’s rapid progress, advanced alien life could even consist of artificially intelligent machines, says Shostak.
It is probably just as well not to think of life as one thing. “When I look around the Earth, I see so many forms of life that I could never have imagined,” says Kaltenegger. “I think whatever we can imagine, the diversity of life if it exists out there is going to just blow our minds.”
Cutting-edge science throws up all sorts of controversial, nebulous and mind-bending concepts. Here’s your guide to how to think about some of the fiddliest of them:
- In the quantum world, uncertainty reigns – or is it all in the mind?
- Think you understand how evolution works? You’re probably wrong
- Why information could be our route to the universe’s deepest secrets
- Who do you think you are? Why your sense of self is an illusion
- Homo sapiens? Genetic insights suggest we may not really be a species
- Big bang retold: The weird twists in the story of the universe’s birth
- Firms and governments use the internet to spy on us. Should we care?
- D’oh! Why human beings aren’t as intelligent as we think
- Extinction is a fact of life. Could we stop it – or even reverse it?
- No more goody two shoes: Why true altruism can’t exist
- Why it’s time to call time on the ‘nature vs nurture’ debate
- Dark energy: Understanding the mystery force that rules the universe
