Through the experiences of the intrepid character Lucy Leavitt, we are taken on a fulldome journey to examine the question “When is a planet not a planet?”

This question is posed by Lucy, who, along with her scientist mother Lillian, is on board a research craft heading to the outer limits of the Solar System. This trip is to gain data to silence recent debates questioning Pluto’s status as a planet.

We examine some of the new information about our Solar System and discuss how Pluto is different to the other planets in the Solar System. We investigate where Pluto belongs in the overall structure of the Solar System and highlight the difficulties of defining what makes a planet.