Exoplanets

Exoplanets (AKA Extrasolar planets) are planets outside our Solar System that orbit around a celestial body other than our Sun. It is estimated that billions of exoplanets probably exist in our very own galaxy, the Milky Way. Scientists try to find planets in the Habitable Zone (or Goldilocks Zone) of their star, which means it's not too far away, which would make it too cold for liquid water to exist, and not too close, which would make it too hot for liquid water to exist.

There are a couple of ways to detect an exoplanet.

1) The Doppler Shift
When a planet orbits a star, its gravity tugs very slightly on the star, making the star move a little bit. We can detect this movement to see whether there are planets orbiting the star. The more the star is moved by the planet, the bigger the planet is.

2) The Transit Method
When a planet passes in front of its star, the light coming from the star gets a bit fainter. The size of the planet can be determined by how much dimmer the star gets.

There are some other ways, but these are the two main ways of detecting exoplanets.

Who knows, maybe one day we'll find an exoplanet with liquid water on it, or maybe even life.