Scientists Measure Mass of a Rogue Exoplanet for the First Time

For the first time, an international team of researchers has measured the mass and distance of a rogue exoplanet. The discovery marks a breakthrough in studying planets that drift freely through space, untethered to any star. Their findings have now been published in the journal Science.

The planet, located roughly 9,800 light-years away, was analysed using a technique called microlensing. This method allowed scientists to determine its mass—about 0.219 times that of Jupiter—without needing multiple images. The measurements were made possible by a rare microlensing event, observed simultaneously by ground-based and space telescopes.

Unlike most planets, this one did not remain in its original star system. Instead, it was ejected into interstellar space at some point after forming. Its mass places it in a range similar to Saturn, making it one of the few rogue planets with such precise data.

The success of this study follows decades of microlensing surveys, such as OGLE and MOA, which have detected around 100 rogue exoplanets since the 1990s. Many of these isolated worlds were found in the Milky Way's bulge and disk. Researchers now see simultaneous microlensing observations as a key tool for uncovering more about these drifting planets.

The findings provide the most accurate measurements yet of a rogue exoplanet's properties. With this method, scientists can now study similar free-floating planets in greater detail. The discovery also reinforces the potential of microlensing in future astronomical research.