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Illustration of gravitational microlensing event
courtesy Jan Skowron/Astronomical Observatory, University of Warsaw

A ‘rogue’ planet has been spotted floating through the Milky Way

If confirmed, the planet would be the smallest of its kind, and could tell astronomers more about the planetary systems in our galaxy

Astronomers have spotted a new “rogue” planet floating through our galaxy, seemingly unattached to a star. With a mass somewhere in-between that of the Earth and Mars, the planet is thought to be the smallest of its kind to have been discovered.

The find comes courtesy of researchers using a technique called “gravitational microlensing”, which involves observing foregrounded objects – such as the planet – passing in front of distant stars. The nearer object is revealed as it bends and magnifies the star’s light, a phenomenon that also reveals characteristics such as its mass.

“When we first spotted this event, it was clear that it must have been caused by an extremely tiny object,” says Radoslaw Poleski, a researcher at the Astronomical Observatory of the University of Warsaw, and co-author of a study on the discovery published in Astrophysical Journal Letters. “We can rule out the planet having a star within about eight astronomical units.” (One astronomical unit is the average distance between Earth and the sun, aka around 93 million miles.)

Finds based on gravitational microlensing are rare, since they depend on the astronomer’s telescope being in near-perfect alignment with the object and the star, adds Przemek Mroz, the lead author of the study, and a postdoctoral scholar at the California Institute of Technology. “If we observed only one source star, we would have to wait almost a million years to see the source being microlensed.”

The researchers, who based the study on data collected during microlensing surveys of the Milky Way, also say that studying such free-floating planets could enable astronomers to figure out more about planetary systems in the galaxy, including our own.

Other objects that have been detected floating through space in the past few months include an asteroid calculated to have a small chance to collide with Earth just before the US election, and 24 planets deemed potentially “super habitable“ (which might come in handy after the election, tbh).

Watch a simulated version of a gravitational microlensing event involving a “rogue” planet below.