70+ Rogue Planets Without a Star Discovered

When we think of planets, we usually think of a rocky or gaseous round ball orbiting a star. In fact, orbiting a star is considered one of the three requirements for an object to be considered a planet. But astronomers have begun to discover planets in our galaxy that don’t seem to orbit a star at all. These rogue planets have been the topic of recent research published in Nature Astronomy last month.

Concept art of an Earth-sized rogue planet covered in ice. Credit: NASA’s Goddard Space Flight Center.

Planets without a star, called free-floating planets (FFPs) have all been discovered using indirect methods, as direct observation of such an object would be impossible with current technology. The researchers behind the discovery of these FFPs estimate they may have found 70–170 of them.

These free-floating planets were detected using both ground and space-based telescopes. These telescopes include the ESA’s Very Large Telescope (VLT) and the space-based Gaia satellite. All of the FFPs are gas giants, like Jupiter, which are easier to detect due to their large masses. This does not necessarily mean that there are more gas giants out there than rocky planets, it just means they are easier to detect. We may one day be able to find more rocky planets, only then could we determine if the galaxy tends to have more gaseous planets or rocky planets. These FFPs are also may be young, as they were primarily found in young stellar clusters.