Over the past 30 years the Vatican Observatory in Castel Gandolfo has been hosting a biennial summer school, where we invite young scholars from around the world to spend four weeks with us, exploring in depth some topic in astrophysics. This year’s school is centred on water in the solar system and beyond. It’s an area I have worked in since I was a young scholar myself; my master’s thesis, now 41 years old, was all about Jupiter and Saturn’s icy moons.

All of my work on the topic, of course, is long obsolete. Just four years after I had made my computer models to predict what we would see at those moons, the Voyager spacecraft actually visited Jupiter and revealed its moons to be worlds far more elaborate than anything I could have proposed. Still, the basic science has not changed; at our school we taught how to use properties such as density and surface colours – things we can observe – to infer the things we cannot observe about a world’s interior and history.