Graph showing the maximum number of ETIs presently existing in the Milky Way. (IMAGE)
Caption
This graph shows the maximum number of ETIs presently existing in the Milky Way. The solid orange line describes the scenario of planets with nitrogen–oxygen atmospheres with 10 per cent carbon dioxide. In this case the average lifetime of a civilization must be at least 280,000 years for a second civilization to exist in the Milky Way. Changing the amount of atmospheric carbon dioxide produces different results.
Credit
Manuel Scherf and Helmut Lammer.
Usage Restrictions
Credit must be given to the creator. Only noncommercial uses of the work are permitted. Adaptations must be shared under the same terms.
License
CC BY-NC-SA