Life on other planets

That was a cool film! I wish I could meet a friendly alien like that. Do you think aliens exist, Kim? You’re not the first to wonder, Philip! Books and films have long explored the thrilling idea of life on other planets.

But if you want to find out if aliens really exist – where do you start? What do you look for? Scientists believe planets and moons with conditions similar to those on Earth are more likely to harbour life, to be habitable. Life on Earth probably originated in the ocean. All living organisms on our planet require liquid water for their biological processes.

So, finding water or signs of it on other planets is a potential indicator of life outside Earth — extraterrestrial life. Temperature is another important factor. A planet is more likely to harbour life, if its temperature allows liquid water to exist. A planet’s temperature is mostly determined by its distance from a star, and by the gases that surround it – what’s called its atmosphere. Studying the chemical composition of a planet’s atmosphere gives scientists clues about if it’s habitable.

On Earth, all life consists of molecules containing carbon atoms – organic molecules. So finding certain organic molecules in a planet’s atmosphere, or on its surface, could be an indication of past or present life – a biosignature. Other types of biosignatures include chemicals that — at least as far as we know right now — are produced only by living things and biological processes. One example is the chemical phosphine, which has been detected in Venus' atmosphere. Before everyone gets too excited, – this could be a sign of life, but it could also be a product of a different, unknown process.

Scientists also scan for unusual radio signals. These could be a sign of alien technology. Scientists have actively sent messages out into space, hoping to make contact with potential intelligent life. Surely if aliens existed, scientists would have found them by now! Well Philip, distances in space are enormous.

So far, scientists have only managed to explore the moon and planets closest to Earth. Beyond these is the rest of our solar system, the galaxy, then the observable universe — all of which we know very little about. Also remember, the universe has existed for 13.8 billion years. Earth formed only about four and a half billion years ago. Life has existed here for about three and a half billion years.

Billions and billions of stars, planets, and moons formed before Earth did, and many continue forming now. So, it’s possible there was life somewhere before, but it has disappeared. Also, life might only start in some distant future, long after our solar system is gone. We might also just be looking for the wrong thing. There is a chance that life in other parts of the universe is very different to life on Earth.

Life might not need the conditions we consider habitable, or use the same chemical processes as on Earth. There is one thing we know for sure – it’s unlikely that aliens look and behave like in science-fiction films. Scientists have made some interesting findings, identified planets and moons that could potentially harbour life. But it’s not enough to draw definite conclusions yet. To be able to tell for sure whether there is, or was ever, some sort of extraterrestrial life, we need to collect much more data — from our galaxy and the trillions of other galaxies out there!