Trillions of free-floating planets may be roaming the universe, according to a new study by scientists at NASA and Osaka University in Japan. These dark, isolated orbs do not have a host star and are believed to form in the same way as other planets, within the swirling disk of gas and dust surrounding an infant star. However, unlike their planetary siblings, these worlds are violently ejected from their celestial neighborhoods.
Previous estimates had suggested that billions of planets had gone rogue in the Milky Way, but the new research increases that estimate to trillions. The scientists also identified the second Earth-size free-floating planet ever detected. Published in The Astronomical Journal, the researchers used nine years of data from the Microlensing Observations in Astrophysics telescope to indirectly detect exoplanets by measuring how their gravity warped and magnified the light from distant stars behind them.
The team concluded that free-floating planets are six times more abundant than planets orbiting their own suns. They estimate that there are about 20 times more free-floating worlds in our Milky Way than stars, with Earth-mass planets being 180 times more common than rogue Jupiters. This challenges the previous belief that most rogue planets were the size of Jupiter.
The researchers believe that smaller planets are more likely to go rogue as they can be knocked out of their star systems by larger objects. The abundance of these free-floating planets suggests that planet-size objects colliding during the formation process are more common than previously thought.
While it is unclear whether these planets are truly unleashed or just cast out to wide enough orbits that they cannot be linked to a host star, the astronomers are eagerly awaiting data from the Nancy Grace Roman Space Telescope, set to launch in 2027. This data, combined with observations from other telescopes, will provide a better understanding of these mysterious wandering planets.
The possibility of habitability on these free-floating planets is not ruled out. While they would be dark without a host star, hydrogen in their atmosphere could act as a greenhouse and sustain microbial life. However, the search for life on these planets is currently beyond our reach.
Although the study focused on the Milky Way, the researchers believe that these rogue planets may be scattered throughout the entire universe, as other galaxies are expected to be similar. The findings open up new possibilities for understanding the formation and diversity of planets beyond our solar system.