Astronomers estimate there are approximately 100 quintillion planets in the universe based on the assumption that each star has one planet orbiting it.
The Milky Way alone contains about 100 billion stars and there are trillions of galaxies in the universe. Astronomers have discovered 5,502 planets orbiting other stars (known as exoplanets) within the Milky Way. Adding the 8 planets in our Solar System, the total comes to 5,510 known planets. Counting the number of planets is a challenging task, and the astronomical community is certain that there are many more planets yet to be discovered.
Research has only discovered 5,510 planets in the Milky Way. (Image: NASA)
“Even though we currently know of over 5,000 planets, we can estimate that there is one planet around each star,” said Mark Popinchalk, an astronomer at the American Museum of Natural History in New York. The Milky Way has 100 billion stars, so the number of planets is approximately that too. We can’t provide an exact figure.”
Popinchalk likened determining the total number of exoplanets to guessing how many people live in a city without searching online. To get an accurate number, one could try to meet each person and count them one by one, but that is entirely impractical. Instead, it would be much easier to make an estimate based on the number of people living in a household and the number of households in the city.
Astronomers estimate that each star has roughly one planet based on observations. Scientists employ two different techniques to search for exoplanets, including the transit method used by the Kepler Space Telescope and the radial velocity method, which led to a Nobel Prize discovery (the exoplanet 51 Pegasi b). With both methods, astronomers focus on the star rather than the planet, looking for small signs indicating the planet’s presence, such as a dimming of the star’s light when a planet passes in front of it or the star’s wobble due to gravitational influence from the planet.
All planets discovered so far are within the Milky Way. No one knows for sure if an exoplanet can be found outside our galaxy, simply because they are too far away and difficult to observe. A technique called gravitational microlensing reveals a few potential planets outside the galaxy.
Using Popinchalk’s analogy, counting the number of planets in the universe is like figuring out how many people live in every city on Earth. “If the Milky Way has about 100 billion planets, and there are a thousand billion other galaxies, each having many such planets, we can multiply and conclude that there are 100 quintillion planets in the universe,” Popinchalk stated.
With such a vast number of planets, people often speculate that there is almost certainly at least one planet with life in the universe. We will have to wait at least a few more decades for the next generation of space telescopes, specialized in observing exoplanets like the James Webb Space Telescope, to begin searching for life in the galaxy.
