Astronomers may have detected a moon from outside of our solar system for the first time. Either way, they’ve definitely come up with a terrible pun.

The ‘candidate moon’ is formerly known as Kepler-1625b but has been nicknamed a “Nep-moon” because it’s a similar size and mass to Neptune. That would give it a radius around ten times bigger than any moon in our solar system.

While most of the emphasis of work with the Hubble telescope has been on finding exoplanets, a parallel project also hunts for exomoons. The first potential exomoon comes after more than 3,000 exoplanets have been found.

As is usually the case with such potential discoveries, the astronomers haven’t literally seen the candidate moon through the telescope. Instead its existence and size has been deduced based on dips in the light coming from the star at the centre of the solar system. The theory is that the exomoon explains why the light sometimes dips by more than usually happens when the relevant planet passes ‘in front’ of the star.

Dr David Kipping, who co-authored a paper on the finding, was unwilling to put a figure on how unlikely the discovery is to indeed be an exomoon. Formally it’s recorded as a four sigma confidence level: put another way, the chances that it isn’t an exomoon are the same as a coin coming up heads 15 times in a row. However, Kipping notes that the analysis is based on only three observations, so says any statistics could be misleading.