A soon-to-be-launched NASA telescope may be able to detect over 400 Earth-sized rogue planets wandering through the Milky Way galaxy.
These rogue planets are believed to have begun their lives in a planetary system, similar to our Solar System, but were subsequently ejected for some reason. Despite the familiar image of planets orbiting orderly around a host star, new research indicates that there could be more of these “orphaned” planets than there are stars in the Milky Way, at a ratio of 20:1. This suggests that the number of wandering planets in our galaxy is six times greater than the planets orbiting host stars.
A lonely ice planet in the universe. (Image: NASA).
“We estimate that our galaxy is home to rogue planets at a concentration 20 times greater than that of stars – meaning there are trillions of planets wandering out there,” said David Bennett, the study’s author and a senior scientist at NASA.
Essentially, planets outside our Solar System, also known as exoplanets, are detected by their influence on their host stars. However, rogue planets are often too far from any host star to be easily detected. One of the primary goals of NASA’s Nancy Grace Roman Telescope is to discover these solitary worlds. Previous estimates suggested that the Roman Telescope, set to become operational in May 2027, could detect about 50 Earth-sized rogue planets, but new figures indicate that this number could be closer to 400.
Since the discovery of the first exoplanet orbiting a Sun-like star in 1995, the number of discovered exoplanets has reached 5,000, with most of these being massive objects orbiting their host stars.
Meanwhile, the research team revealed that rogue planets are typically smaller than or equal to Earth in size.
“We found that Earth-sized rogue planets are more common than larger planets. The difference in average mass between planets orbiting a star and free-floating planets is key to understanding the mechanisms of planet formation,” said Takahiro Sumi, a study author and currently a professor at Osaka University.
The chaotic nature of the planet formation process likely explains how these rogue planets began to wander through the galaxy. Smaller mass planets often have weaker gravitational forces to cling to their host stars, making them more susceptible to being ejected and drifting alone in the universe.
