Rogue Planet Found Floating Through Our Galaxy With No Sun

Researchers have discovered a ‘free floating’ planet travelling through our galaxy, untethered to any sun. 

Scientists discovered the planet with a technique called gravitational microlensing, which is only possible when a telescope lies in almost perfect alignment with the observed object and the source star. When the objects are aligned, the foreground object amplifies the light of the background star.

Microlensing was first used to find black holes, but scientists were able to identify the floating planet due to the way it bent the light of more distant stars.

In the study, published today in Astrophysical Journal Letters, astronomers said the planet is the smallest rogue world ever discovered. It is believed to have a mass somewhere between Earth and Mars and emitted a measurable signal for just 42 minutes.

Przemek Mroz, a postdoctoral scholar at the California Institute of Technology and a lead author of the study, commented:

Chances of observing microlensing are extremely slim because three objects – source, lens and observer – must be nearly perfectly aligned.

This is the shortest microlensing event ever found, so the lowest mass planet ever found by microlensing. This is really exciting because it’s such a tiny piece of rock.

The Optical Gravitational Lensing Experiment (OGLE) in Poland has observed a number of free-roaming planets, but because the chances of spotting one are so rare Mróz said they might actually be as common as stars throughout our galaxy.

The data containing information about the floating planet was obtained in 2016, however Mróz and his colleagues did not spot it until they decided to look through archival data during the COVID-19 pandemic.

Per The Independent, Radoslaw Poleski, co-author on the study, said:

When we first spotted this event, it was clear that it must have been caused by an extremely tiny object.

We can rule out the planet having a star within about eight astronomical units.

For reference, Saturn is 9.5 astronomical units from our sun. It is possible that the new planet could be attached to a star, but it would require years more observation to determine if that’s the case – long enough for any potential parent star to shift its position so its light could be separated from that of the background star.

Free-floating planets are thought to come into existence when clouds of gas collapse inward, or through being ejected from orbiting a star. Studying untethered planets could help astronomers to learn more about the history of planetary systems like the solar system.

NASA’s Nancy Grace Roman Space Telescope, which is set to launch in the mid-2020s, is expected to help identify free-floating planets.

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