Question: How many solar systems are in our galaxy and do you think there could be another planet like Earth in a different solar system?

Colin Johnston answered on 17 Nov 2014:

Based on discoveries of planets orbiting other stars (exoplanets), especially the surveys of large numbers of stars with planets by NASA’s Kepler mission, we are sure here is at least one planet on average per star in the Milky Way.

This suggests that there are 100 billion or more planetary systems in our galaxy alone.

Around 1 in 5 Sun-like stars (similar brightness and temperature to the Sun) have a roughly Earth-sized (usually larger) planet in their habitable zone.

Finding a planet exactly like Earth would be hard with today’s technology. It will be easier with larger telescopes which are on the way. I am sure in the next twenty years we will find a planet the same size as Earth at a similar temperature. Next thing will be to check its atmosphere for oxygen, if there is a significant quantity we will have proved there is life elsewhere in the Universe.