There is a great deal of evidence for aliens, both in our solar system and beyond. In our solar system, there is strong evidence for the existence of aliens on Mars and Europa. On Mars, there is evidence of past water activity, and on Europa, there is evidence of a subsurface ocean. Beyond our solar system, there is evidence for billions of planets in the Milky Way galaxy, and for billions of galaxies in the universe. There is also evidence for the Big Bang, which is the event that created the universe.