How can we estimate the number of Earth-like planets in the Galaxy? (Intermediate)

I'm doing a science project and i had to read a science fiction book and find the facts in it and it said that 100 billion stars in our galaxy and 10 percent of those starts have planets and maybe one percent of them have Earth-like conditions. Is that true? And how can you estimate the number of stars with planets with earth-like conditions?


Although our exoplanet search is VERY far from being complete, astronomers currently estimate that there is AT LEAST one planet for every star in the galaxy, which is a lot of planets!  

Getting an idea of what percentage of those planets are Earth-like is much more difficult, but we can start to make educated guesses. Your guess that 1 percent of all planets being Earth-like sounds reasonable, but for all we know it could be a much smaller or larger percentage than that!  Until we are able to accurately determine the compositions of exoplanets on a large scale, we won't be able to get a better idea of the actual number.



Page last updated on July 18, 2015

About the Author

Karen Masters

Karen Masters

Karen was a graduate student at Cornell from 2000-2005. She went on to work as a researcher in galaxy redshift surveys at Harvard University, and is now on the Faculty at the University of Portsmouth back in her home country of the UK. Her research lately has focused on using the morphology of galaxies to give clues to their formation and evolution. She is the Project Scientist for the Galaxy Zoo project.

Twitter:  @KarenLMasters

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