Credit NASA Hubble Space Telescope
Over the last twenty years or so, astronomers have detected over 4,000 planets orbiting other star systems. Our Milky Way galaxy may have billions of planets orbiting other stars. It’s a goal to find earth-sized planets orbiting their stars in what is called the habitable zone, or that distance from their parent star where any water on the planet is liquid.
SETI is a project that searches for radio waves coming from these types of planets. The discovery of such radio emitting planets would be strong evidence of intelligent life on that planet.
The Parkes observatory has detected a possible radio wave from a planet orbiting Proxima Centauri, the closest star to our Sun. Proxima Centauri is only 4.2 light years away and has two confirmed planets, one orbits its parent star in the star's habitable zone.