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An Earth-sized rogue planet is roaming the galaxy without a star

An illustration of a blue fictional planet

Dan Collier/Alamy

A planet that is about the same mass as Earth appears to be floating on its own through space. It is the smallest such rogue planet we have ever spotted, but there are probably many more in the galaxy.

Usually, we find planets beyond our solar system using observations of the light from the planet’s host star. Rogue, or free-floating, planets have no host star, making them difficult to spot. Astronomers have only found a handful, and most are far more massive than Jupiter.

These were mainly spotted using gravitational …