by Tanja Schumann (TU Berlin), March 2025
Rogue planets are planets that wander lonely through space without a star. In recent years, scientists have discovered more and more of these strange and fascinating objects. But where do they come from? Did these planets originally form in the same way as ours? What event uprooted them from their home?
And what is particularly exciting: can life exist on such planets without starlight?
Artist’s depiction of a rogue planet not orbiting a star. Credit: ESO/M. Kornmesser/S. Guisard under CC BY 4.0.
In 2021, the team led by Núria Miret-Roig from Laboratoire d’Astrophysique in Bordeaux (France) published a study in which they report the discovery of no fewer than 70 of these vagabond planets. They analysed 80,000 images taken over a period of 20 years.
Without their host star to illuminate them, these planets are very difficult to detect. Only in the first ten million years after their formation are planets of the mass of Jupiter and up to 13 times its mass still hot enough to glow. This is why they can be located with the help of large telescopes.
There are several theories about the origin of such wandering exoplanets. Based on the statistical analysis of the objects found, the researchers estimate that two mechanisms are most likely: either a gravitational interaction within the star system that led to the loner being catapulted out. Or the collapse of a gas cloud that was too small to lead to the formation of a star. But astronomers are not ruling out other mechanisms either.
Future observational data will hopefully soon provide new insights.