Which Planets Outside Our Solar System Have Aliens?

Two decades ago, astronomers weren’t sure if any planets existed outside of our own solar system.

Now they’ve identified more than 1,000 all over the galaxy.

But in order to support liquid water and therefore life as we know it, a planet must be small enough, rocky, have an atmosphere that’s dense but not crushing, and sit just the right distance from its star: Too close and water would evaporate, too far and it would be a frozen wasteland.

which planets outside our solar system have aliens

So of the 1,000 known exoplanets, just 12 might boast the Goldilocks-like conditions necessary for aliens, says astronomer Abel Méndez of the Planetary Habitability Laboratory at the University of Puerto Rico. But how likely is that?

Méndez used size and orbital distance to calculate an Earth Similarity Index for each. The closer the planet is to 1.0, the better the chance of ET.