The Milky Way May Have Trillions of Rogue Planets

Scientists estimate the Milky Way may contain trillions of rogue planets drifting without a star, including many around Earth mass.

Astronomy

Details

Rogue planets are worlds that travel through space without being gravitationally bound to a star. Research using gravitational microlensing suggests they may be far more common in the Milky Way than once expected. One influential estimate puts the number at roughly 20 rogue or very wide orbit planets for every star, which would mean trillions across a galaxy containing hundreds of billions of stars. This is a population estimate, not a direct count of trillions of observed worlds. The method works because gravity can briefly magnify the light from a distant background star when a foreground planet passes almost directly in front of it. That short brightening can reveal a planet that would otherwise be extremely difficult to see because it produces little or no visible light of its own. The same research suggests that many of these wandering worlds could be around Earth mass or smaller. Future space telescopes designed for microlensing surveys are expected to improve the search and could identify hundreds of Earth mass rogue planets in suitable survey regions. Rogue planets may form around stars and later be thrown out by gravitational interactions, while some free floating planetary mass objects may have other origins. The large population estimate remains uncertain because astronomers can observe only a small fraction of these faint and distant objects directly.

More videos

Up nextSaturn Is the Solar System’s Only Planet Less Dense Than Water