Frank Drake wrote the Drake Equation in 1961, proposing that the likely number of intelligent civilizations in the universe capable of communicating their existence to others can be extrapolated by factoring in such quantities as the number of stars with planets, the fraction of such planets that support life, the fraction of "earths" where intelligence evolves, and so on.
At the time, the Drake Equation was highly speculative, since no planets outside our solar system had yet been seen. But in recent years, with the help of space shuttles and the Hubble Space telescope, numerous new planets have been discovered, orbiting many different stars. And many of them show evidence of liquid methane and even water.
Last month, NASA started re-examining photos of the surface of Mars taken by the Mars Global Surveyor spacecraft in 1997, and comparing them to recent photos. The images showed one place where the surface topography was distinctly changed, seemingly due to the action of water - providing the most compelling evidence yet for the presence of liquid water on Mars, buried beneath the surface.
The more evidence we obtain, the less likely it seems that we are alone.