So there _could_ be an exoplanet, a planet behind our galaxy.
Twenty years ago researchers were already arguing this fact, now there is discussion of around 300 exoplanets and maybe even the detection of the first planet in an Andromeda galaxy. The tirtheenth planet?

Jetzer’s team first conducted a simulation of microlensing events in the Andromeda galaxy, which is more than 2 million light years away from Earth. Once they had determined the clues that a planet in Andromeda would show, they returned to a survey completed in 2004 … that showed an unusual light curve. That event, the group says, matches up to its theory and can be attributed to a companion of a mass about six times that of Jupiter. That suggests either a planet, or a small companion star such as a brown dwarf…. “The interesting thing is that the technology is in place to truly see planets of Jupiter’s mass and even less in other galaxies…. It’s an exceptional thing”, says study coauthor Francesco De Paolis.

Source: Discover Magazine.