Over the last few decades, astronomers have found approximately 5,000 different “exoplanets”, planets that are not from our own solar system. All of them have been from our own galaxy, the milky way, however.

Now, astronomers may have spotted the first exoplanet that is neither from our solar system nor our galaxy but is located in the spiral galaxy Messier 51 (M51), sometimes called Whirlpool galaxy for its distinctive appearance.

Finding exoplanets in deep space is a difficult feat, especially from other galaxies. For comparison, almost all the other exoplanets previously discovered have been less than 3000 light-years away from Earth. On the other hand, the new planet in M51 is approximately 28 million light-years away.

The results of the study which led to the discovery of the exoplanet were published in a new paper in the journal Nature Astronomy. Researchers from the Center for Astrophysics at the Harvard & Smithsonian in Cambridge (CfA), Massachusetts, conducted the study using NASA’s powerful 22-year-old Chandra X-ray observatory.

Location of the exoplanet within the spiral galaxy Messier 51. Credit: Center for Astrophysics at the Harvard & Smithsonian in Cambridge (CfA)

“We are trying to open up a whole new arena for finding other worlds by searching for planet candidates at X-ray wavelengths, a strategy that makes it possible to discover them in other galaxies,” Rosanne Di Stefano, lead author of the study, and an astrophysicist at the Center for Astrophysics at the Harvard & Smithsonian in Cambridge (CfA) said in a statement.

Researchers from Harvard used the same technique that has been used to detect thousands of other exoplanets, called transits. When a planet passes in front of its star while orbiting, the brightness of the star briefly dips, allowing astronomers to detect it.

However, due to the inherent flaw in the technique, researchers will need to wait for the planet to pass in front of the star again to confirm their observation. Considering the distance of the planet from Earth, that could take a long time.

“Unfortunately to confirm that we’re seeing a planet we would likely have to wait decades to see another transit,” Nia Imara, co-author of the paper and a researcher from the University of California at Santa Cruz said in a statement. “And because of the uncertainties about how long it takes to orbit, we wouldn’t know exactly when to look.”

Cover Image: Center for Astrophysics at the Harvard & Smithsonian in Cambridge (CfA)