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Expert Voices

What planets need for life

Our expert voices conversation on "How to look for alien life."

We find ourselves in a universe that appears, at first glance, ripe for life. Liquid water, abundant even in our own solar system (though most of it is hiding underneath thick icy crusts), amino acids hitching rides on comets, simple proteins found in young systems, millions upon millions of stars exactly like our sun in just the Milky Way galaxy.

By all appearances we should not be alone, and yet we don't see a single sign of anybody else, anywhere.

The chances of life appearing in the universe are obviously greater than 0 (otherwise I wouldn't be writing this and you wouldn't be reading this), but seem far, far less than 1.

What Earth got right: We can understand why planets like Mars and Venus wound up dead — too small to sustain a protective magnetic field and choking on its own oppressive atmosphere, respectively — even though they had a decent shot. But we don't fully understand the special sauce that makes life possible. So we're playing a numbers game. How many planets are out there? How many have liquid water? How many have a stable star and the right cocktail for life? It's only by obsessive, detailed observations will we crack it.

The other voices in the conversation: