Scientists Take Alien Census

Some researchers are so convinced that there are alien civilizations, they aren't asking "Is there life on other planets?" anymore. Instead they are asking, "How much extraterrestrial life is out there?"

In a recent paper published online by the International Journal of Astrobiology, a graduate student from the Royal Observatory, Edinburgh, in Scotland estimated there should be 361 advanced, stable civilizations in the Milky Way.

He based his theory on current observational knowledge of stars and planetary systems, as well as the assumption that life can only arise under a narrow set of initial conditions, according to Scientific American .

Not everyone in the field is buying the theory. "We have to admit that we're hugely ignorant of many of the pieces of information that we would need to know before we could realistically estimate the prevalence of intelligent life elsewhere in the galaxy," planetary scientist Ian Crawford of Birkbeck College at the University of London, told Scientific American.