Will humans ever live on other planets? The stranding of two astronauts has thrown the spotlight on the conditions that space travellers are forced to deal with.
The smelly truth about life in space
Left behind: Suni Williams and Butch Wilmore (above) said it was hard to watch their malfunctioning craft depart the International Space Station without them after being stranded in space for eight months. Glossary
International Space Station - A joint project between the US, Russia, Japan, Canada and the European Space Agency.
Pong - A bad smell or a two-dimensional table tennis arcade game. Created in 1972, it is one of the earliest video games.
Radiation - Energy given off when radioactive material decays. It can be extremely harmful and sometimes fatal, causing vomiting, skin damage, hair loss and cancer.
GMT - Short for Greenwich Mean Time
Gravity - An invisible force that pulls objects towards each other. Earth's gravity keeps us on the ground and makes things fall. It is less strong on Mars.
Atmosphere - The layer of gases surrounding a planet or moon, held in place by that planet's gravity. Small planets and moons have weak gravitational fields, and therefore only a very thin atmosphere.