Free-floating Planets Abound in Milky Way

Researchers discovered at least seventy free-floating planets in a region of the Milky Way known as the Upper Scorpius OB stellar association.

IMAGE: An artist’s impression of a free-floating planet. Using observations and archival data from several of NSF’s NOIRLab’s observatories, together with observations from telescopes around the world and in orbit, astronomers have discovered at least 70 new free-floating planets — planets that wander through space without a parent star — in a nearby region of the Milky Way known as Upper Scorpius OB stellar association. CREDIT: NOIRLab/NSF/AURA/J. da Silva

This story was actually released right as we went on hiatus for the holidays, but I have been wanting to write about it ever since. In a paper published in Nature and led by Núria Miret-Roig, researchers detail the discovery of at least seventy free-floating planets in a region of the Milky Way known as the Upper Scorpius OB stellar association. And there could be as many as 170 planets hidden within the twenty years of observations the team analyzed.

Free-floating planets are those planets that are not currently orbiting a star. We used to call them rogue planets, as they had gone rogue from their stellar system of origin, but since we don’t know how true that particular description is, the term was changed to ‘free-floating’. Of course, since these planets are not orbiting a star, they are also not reflecting or blocking a star’s light, nor are they gravitationally influencing a star’s orbit. And dark, cold objects are difficult to detect.

In the past, detecting free-floating planets involved microlensing, using the chance alignment of an exoplanet and a background star and detecting…