Uranus, the seventh planet from the sun, has the poetic name of the Greek god of the heavens. In the English language, it is, unfortunately, the literal butt of every astronomy joke. And last year the new discovery about the seventh planet’s odour – or, more precisely, the chemical composition of its atmosphere – has not helped the comic element. In this week’s Big Questions podcast we visited Professor Patrick Irwin from the Atmospheric, Oceanic and Planetary Physics, from the University of Oxford to ask: Why does Uranus smell like farts?