Ask Space
HUNT FOR LIFE
Why haven’t we detected other civilisations?
It’s a puzzle; we do expect these civilisations to exist. After all, there could be a trillion planets in the galaxy. But there are barriers that need to be cleared if a planet is to host a communicative civilisation. The first is habitability – we need a terrestrial planet in that ‘Goldilocks zone’ where water flows as a liquid. Abiogenesis – the creation of life from non-life – that’s the second barrier. The basic building blocks of life aren’t unique to Earth: amino acids have been found in comets, complex organic molecules in interstellar dust clouds, water in exoplanetary systems. The development of technological civilisation is a third barrier. Some say we already share our planet with alien intelligences.