The greatest mystery for humankind is whether and where there is life elsewhere in the universe. Given the vastness of space and the relative brevity of both a human life and humanity's time on Earth, the odds of answering those questions in the affirmative are long. Still, the odds have been appreciably diminished, and we can thank NASA's Kepler spacecraft for that.

The Kepler spacecraft was launched in 2009 to try to determine how many Earth-like planets can be found in the Milky Way galaxy. It travels through space using a telescope to see changes in a star's brightness that occur when a planet crosses the face of the star as seen from the Kepler's frame. This "transit method" typically requires several passes before a planet can be observed, which means that the investigation is still in its early days, even though the spacecraft has been traveling for nearly six years. Once a candidate planet has been identified, scientists use other methods — followup observations using other instruments or they dig deeper into the Kepler data — to confirm the existence of the planet.

The study of planets beyond our solar system is called Exoplanet science, and it is a young field. While human beings have pondered for thousands of years the existence of life elsewhere in the universe, the first world beyond our solar system was not confirmed until 1992, and astronomers first found alien planets around a sunlike star in 1995.