National Astronomical Observatory of Japan

Billions of Starless Planets Haunt Dark Cloud Cradles

| Science

Artist’s impression of a Free Floating Planet lost in deep space. (Credit: Univ. of Bordeaux) Original size (12MB)

In Lovecraftian horror, the Universe is filled with “dark planets” ungraced by the light of a host star. New research shows that reality might be even scarier. An international team composed of French, Japanese, and Spanish astronomers has found about 100 planets floating freely in space rather than orbiting stars. Extrapolating this sample to the rest of the Milky Way Galaxy suggests that there are billions of undiscovered starless planets tumbling aimlessly through space.

Free Floating Planets (FFPs) have been known for about 20 years, but their origins have been shrouded in mystery. Are they born naturally in the cold cradle of an interstellar dark cloud, or do they form around stars like other planets, only to be exiled into eternal darkness?

The small number of known FFPs has limited chances to investigate them. In this research, the team compiled and analyzed around 100 TB of data taken over the course of 20 years, including data from new deep wide-field observations obtained with the best infrared and optical telescopes in the world (like the powerful Subaru Telescope’s mosaic cameras, HSC and Suprime-Cam), to search for FFPs in the Upper Scorpius OB young stellar association. After rejecting background stars and galaxies, they ended up with a catalog of 70-170 FFPs, depending on the selection criteria used, as well as more than 3000 more massive associated members. This almost doubles the number of known FFPs.

The sheer number of FFPs found in this sample cannot be explained by the process of planets forming naturally from the contraction of small gas clouds in interstellar space. This indicates that planets formed around stars and then banished to the blackness must be an important contribution.

Assuming that other star forming regions are similar to Upper Scorpius, these results suggest that billions of undiscovered FFP lurk in the darkness between the stars. So the next time you look up at the sky and wonder if the planets are in an evil alignment, take time to think about the billions of planets you can’t see.

I have seen the dark universe yawning,
Where the black planets roll without aim;
Where they roll in their horror unheeded, without knowledge or lustre or name.

- Nemesis, H.P. Lovecraft 1918

These results appeared as Núria Miret-Roig et al. “A rich population of free-floating planets in the Upper Scorpius young stellar association” in Nature Astronomy on December 22, 2021.

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