Skip to main content

Mother Earth’s Sisters: More Than 100 Billion Planets in Milky Way

As many as 100 billion planets may exist in the Milky Way, more than one for every star.
  • Author:
  • Updated:

There may be at least one planet per star in the Milky Way, which means that Mother Earth could have as many as a 100 billion sisters.

A study published in the January 12 issue of the journal Nature has found that the most comprehensive census of the Milky Way’s stars to date indicates that at least one planet is orbiting each of the galaxy’s 100 billion stars. Though most of them are uninhabitable rock, it sets the notion that our solar system is an anomaly on its ear.

"This statistical study tells us that planets around stars are the rule, rather than the exception," said study lead author Arnaud Cassan of the Paris Institute of Astrophysics, according to The Christian Science Monitor. "From now on, we should see our galaxy populated not only with billions of bright stars, but imagine them surrounded by as many hidden extrasolar worlds."

Moreover, the team of scientists at the Paris Institute of Astrophysics revealed, many of those planets may orbit two stars, much like the fictional planet Tatooine in Star Wars.

"We used to think that the Earth might be unique in our galaxy," said Daniel Kubas, another scientist from the institute and a co-author of the study, in a statement. "But now it seems that there are literally billions of planets with masses similar to Earth orbiting stars in the Milky Way."

The planets were discovered, or intuited, via a process called gravitational microlensing, as described by Scientific American.

Below, Wall Street Journal senior science correspondent Robert Lee Hotz explains the discovery and puts it in perspective.