A Second Earth

Somewhere out there are worlds that can support life.

For life as we know it to exist, we must have a nice, solid hunk of planet we can plant our feet on. We need lots of water and other friendly chemistry, some of it forming a quilt of atmosphere to keep out the cold. And we need to be just the right distance from just the right star – not too close, not too far; not too hot, not too cold. A terrarium like that incubating for, say, a billion years, might have a fair chance of cooking up something living. Those just right conditions don’t occur often, which explains why it’s been so hard to find life on the tiny handful of worlds we have even a remote chance of visiting: the moons and planets in our solar system. For a long time, scientists didn’t know much about planets elsewhere, so the rest of the cosmos looked like a biological washout.

That has changed. In the past 15 years or so, astronomers have discovered more than 4,200 potential exoplanets – planets orbiting distant stars – and confirmed the existence of more than 1,050 of them. In a galaxy with 300 billion stars, there are surely untold billions of other planets out there. Is anyone home on any of them? Because telescopes cannot yet allow us to view exoplanets, their existence and nature are inferred mostly by how they cause their parent stars to wobble and by the amount of starlight they block as they pass in front of them.

In 2017, NASA will launch the Transiting Exoplanet Survey Satellite, specifically looking for exoplanet atmospheres. Other important tools are NASA’s James Webb Telescope and the European Extremely Large Telescope in the Chilean desert.

One astronomer says, “With billions of rocky worlds available, life would have to be extremely picky not to be able to evolve out there.”