Given a text passage, come up with an appropriate title for it. The title should accurately represent what the main focus of the passage is. The title of a passage may be present in the first few sentences of the passage and/or be referred to multiple times in the passage. The title should be 1-5 words long.
Q: The Drake equation is a probabilistic argument used to estimate the number of active , communicative extraterrestrial civilizations in the Milky Way galaxy .
A: 
Drake equation