They don’t call Hafþór Júlíus Björnsson ‘The Mountain’ for nothing.

In 2015, the strong man and Game of Thrones actor broke a millennium-old record by taking – or more accurately, staggering – five steps with a 650 kilogram (1,430 pound) log on his back.

To most of us, this was simply an extraordinary example of heroic strength. To scientists, this feat marked a crushing limit to the gravitational pull any mortal could ever hope to endure, setting a boundary on the mass of planets we might expect to colonise.