Are we alone in this universe?
NASA scientists are trying to find the answer for
this question. They have a clue, and that clue is exoplanets.
Exoplanets are planets that orbit a different star than our sun. For example, there is an exoplanet named 55 Cancri E, that is made out of diamonds! That would be a good planet for people who like jewelry!
There is also a specific group of exoplanets that are in a "habitable zone", or as I like to call it, a "Goldilocks zone", because it is not too hot or too cold for water to exist, meaning the planet is one step closer to being able to support life.
NASA states that there are at least 100 billion stars in our Milky Way Galaxy, and there are at least two planets for each star in the galaxy. In addition, NASA states that 1 out of 5 of these exoplanets are in the "habitable zone".That means that there are at least 40 billion exoplanets in our galaxy that are in the habitable zone!
An earth-like exoplanet would have to be roughly the size of earth (for similar gravity), must be in the habitable zone, must have water vapor, oxygen, nitrogen, methane and other life-creating chemical compounds and must have an atmosphere to hold these together.
NASA's Kepler mission is still looking for more and more exoplanets and has already found over 2,300 exoplanets and sends pictures of them on Twitter! (@NASAKepler). For example, Proxima Centauri B has almost all of the characteristics of the earth, and was very recently discovered, and is the closest to earth exoplanet ever discovered. It orbits around Alpha Centauri A and Alpha Centauri B (it is a complicated astronomical family - it has two suns who also a third sibling that this exoplanet does not orbit!)