Like HowStuffWorks on Facebook!

What are the odds there is life in outer space?


Odds of Extraterrestrial Life: Cheat Sheet

Stuff You Need to Know:

  • Some astronomers involved with the search for extraterrestrial intelligent life, or SETI, use instruments such as radio telescopes to "listen" for aliens.
  • At the first official SETI conference in 1961, radio astronomer Frank Drake presented the Drake Equation, a formula that estimates the number of potential intelligent civilizations in our galaxy.
  • The Drake Equation produces wildly variable results. Some calculations indicate we may share our galaxy with 12,000 alien civilizations. Carl Sagan suggested that 1 million civilizations might exist in the galaxy.
  • After years of searching and finding no ETs, many astronomers now think the values used in the Drake Equation should be ratcheted down. The implication: We may not be completely alone, but we're in no danger of having our personal space invaded.

Now, test your knowledge with these quizzes!

Check out these image galleries!


More to Explore