Dr Chris Messenger from the University of Glasgow was on hand to help me with Michael’s question…

• The moon’s gravity is 16% of that on Earth, which means the pee will travel in a straighter arc and about 2.5 times further
• In a uniform gravitational field objects travel in a parabolic arc – sort of a ‘u-shape’
• On the moon, the atmosphere is so thin that the pee would follow a very accurate parabola, as can be seen with the dust thrown up by the lunar rover
• The low atmospheric pressure on the moon would immediately boil the pee which would then fall to the surface as steam
• Despite the low temperature of the moon (as low as -170 degrees Celsius), the pressure reduces the boiling point of water so dramatically that your pee would boil way below body temperature of 37 degrees Celsius, which is why it immediately turns to steam
• The freezing temperature of water on the moon also occurs in the same range as the boiling point, which means that the steam molecules will then freeze into yellow ice crystals

You can listen to the full version of Question of the Week with the Naked Scientists here.