You’re never really sure until you have evidence…If you go back to this question of are we alone, there's a very famous equation called the Drake Equation that looks at that potential. The Drake Equation is used to estimate the number of communicating civilizations in the cosmos, or more simply put, the odds of finding intelligent life in the universe. N = The number of civilizations in the Milky Way galaxy whose electromagnetic emissions are detectable. While we certainly knew there were billions of stars in our galaxy, billions of stars in the universe, and suspected many of them would have planets around them, we couldn’t confirm it until the Kepler telescope. You can have a hypothesis, but until you have evidence you're not really sure. Kepler has confirmed just how common planets are out there. It has detected three planet systems, five planet systems, and seven planet systems. Given his higher resolution capacity, Kepler has the ability to detect planets between the size of Earth and Neptune. Previously, we could only detect larger planets the size of Jupiter or Saturn. These large planets are gas giants and not likely to be habitable. Kepler discloses to us “earth-size” planets that could be “habitable.”It found huge numbers of planets in that size category. Prior to Kepler, we had no idea how common Earth size planets were in the universe. Planet size is important because in order to sustain life planets need to be large enough to sustain an atmosphere conducive to life. The findings from Kepler have informed and revolutionized our views on the potential for there being habitable planets out there.