Let's listen out for alien life – and remember we might not understand it

As the Breakthrough Initiative starts scanning far galaxies for radio waves, it is important to remember intelligent life may take a very different form from us

Space probes have explored the main bodies of our solar system, revealing varied and distinctive worlds - but worlds unpropitious for life. There may once have been living organisms on Mars (and there may be life on the moons of Jupiter and Saturn) but there are no "Martians" of the kind familiar from science fiction.

Within our solar system, Earth is the only Goldilocks planet - not too hot and not too cold for water to exist. But the prospects of finding advanced life brighten a billion-fold when we extend our horizons to the other stars - far beyond the range of any probe we can construct today. The most exciting recent breakthrough in astronomy has been the realisation that most stars are orbited by retinues of planets, just like our sun is. And that there are literally billions of Earth-like planets in our Milky Way galaxy.