The Milky Way is full of planets, and it’s very likely that they are plentiful in other galaxies as well.
But there’s a big difference between it being likely that planets exist outside of our galaxy and having evidence that they do. And the methods that have allowed us to spot planets in the Milky Way simply won’t work at such vast distances. But this week, researchers announced that a technique they proposed may have turned up the first indication of a planet in another galaxy. The data was sitting in the archives of a couple of X-ray telescopes.
Almost every planet we know about was identified by one of two methods: either by watching a planet’s gravitational influence on the wavelengths of light produced by a star or by watching the reduction in light as it passes between us and its host star. At the moment, we don’t have hardware with the resolution needed for these techniques to work well with other galaxies, which generally appear as collections of stars so dense that distinguishing one star from another is nearly impossible.