COMMENT

Can we really call this new object a moon? Something the size of Neptune certainly doesn’t look like any satellite in our Solar System.

In fact, the relative masses of this new exomoon and its planet are about the same as the difference between Earth and the Moon. Granted, our Moon is unusually large – large enough that in the absence of official rules as to what qualifies as a moon some argue we really inhabit a double planet system. But knowing this makes the new system seem more familiar.

Even if that’s true, though, those who study planet formation have a struggle on their hands to explain how two such large bodies could have ended up in orbit around one another.

And things might be more complicated still; astronomers have pointed out that there’s the possibility of satellites in orbit around this new body too. Delightfully, these would be known as ‘moonmoons’.