With this equation, you can estimate the number of communicating, intelligent civilizations that currently exist in the Milky Way. The individual terms are:
Scientists expect that, if we discover life on Mars, it will most likely be simple bacterial life and not humanoid aliens like most of the martians you have seen in movies. This does not mean that scientists have completely ruled out the possibility of intelligent life in the Milky Way Galaxy, though. One of the tools that you can use ...