The Milky Way Galaxy is home to our solar system, along with an estimated 100-billion other stars. Within our galaxy alone, astronomers have confirmed the existence of over 5,000 planets orbiting stars other than our sun. That may seem like a lot of planets, yet that number only represents a tiny fraction of what is out there. How many planets are there in the Milky Way?

　　

Planets And Stars

Our solar system contains eight planets and one star It would take far too long to observe every star in the Milky Way and confirm the existence of every individual planet. A task such as this would simply be impossible, and so astronomers rely on estimates based on what is currently known. For example, astronomers can calculate the average number of planets per star for all the stars known to have planets. By doing this, astronomers can then apply that average to the entire galaxy, giving us a rough estimate of how many planets there are in the Milky Way. Data from planet-hunting telescopes, such as the Kepler telescope, suggest that on average, every star is orbited by at least one planet. Since the Milky Way has an estimated 100-billion stars, that translates to 100-billion planets. However, it is important to note that this average is based on only a few thousand stars, and when the galaxy contains many billions, the true average number of planets could be significantly different. 

　　

Are There More Planets Than Stars?

The Milky Way contains an estimated 100-billion stars. Image credit: NASA/ESA Our solar system contains one star and eight planets. The number of planets in our solar system significantly outnumbers the number of stars. If every solar system contained more planets than stars, then the number of planets in our galaxy would vastly outnumber the stars. The estimate of 100-billion planets is likely the least possible number of planets. If every star is orbited by the same number of planets in our solar system, then there would be 800-billion planets, or eight times the number of planets than stars. Even if every star were orbited by only two planets, the number of planets would still be twice as high as the number of stars. 

　　

Beyond The Milky Way

Planets are a natural part of star-formation, and so most stars beyond the Milky Way likely also have planets. Image credit: NASA/ESA The vast majority of known exoplanets have been found within the Milky Way. However, astronomers have confirmed the existence of a small number of exoplanets within other galaxies. The sheer number of known planets within our galaxy suggests that planets are a natural part of star-formation, and this likely applies to other galaxies as well since the laws of physics apply to the entire universe. This means that the universe contains trillions upon trillions of individual planets. In fact, there are so many planets in the universe that any planet you can think of, so long as it obeys the laws of physics, probably exists somewhere out there. It is fascinating to know that these are all individual worlds with their own history and evolution. Countless worlds in a seemingly endless cosmos.