The world's most famous plumber ventured into space with the release of Super Mario Galaxy. The 3D game used a physics system to endow celestial objects with their own gravity so our hero could circumnavigate tiny worlds without falling off. But to maintain surface gravity, how dense would these planets have to be?

Fortunately, a group of physics students at the University of Leicester decided to tackle this conundrum, with the publication of their research paper, "It's a-me, Density!"

The students deduce that the planets, which are approximately 100 meters (328 feet) in diameter, have the same surface gravity as Earth, based upon observations of Mario's moving and jumping abilities.

After calculating the mass and then the density of the small worlds, the researchers concluded that white dwarf stars have a density that is close to that of the theoretical planets and therefore a candidate for their construction.

However:

Under these conditions, super-compression of the material needs to be considered. If confined in too small a space, elementary particles are not only affected by electric repulsion, but also by a quantum repulsion between electrons. If this quantum force is larger than electric repulsion, electrons become degenerate and exert an additional degeneracy pressure against the gravitational pressure. In white dwarfs this pressure is balanced by gravity to produce a stable body, however the baby planets would not have enough mass to have this stability.

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Further calculations revealed that the degeneracy pressure would outstrip the gravitational pressure by eleven orders of magnitude. "The outcome of this discrepancy is that if constructed, the planet would survive for only a very brief moment before violently destroying itself and any short plumbers who happen to be running about on its surface."