Four volunteers are learning to breathe in argon – a gas which planet Mars has got in plenty. It's part of a Russian project that, one day, hopes to send a manned crew to the Red Planet. A 10-day experiment is underway to find out if people can

Aleksandr Dyachenko, who's heading the experiment, says argon, combined with the right portion of oxygen, is quite safe for people.

Indeed, three quarters of the air we breathe is nitrogen. Inside the capsule where the volunteers are placed, it is largely replaced by argon while the oxygen levels are being reduced.

Low oxygen is needed because it's more fire-safe onboard. Besides, arriving on the Red Planet the mission won’t be able to receive any supplies from home and will have to switch to self-supply at some point. So they will have to use Martian air mixed with oxygen.

Learning to breathe argon is just one element in the Mars-500 project, which is being led by Russian scientists. The most important event will be the 520-day simulation of a Mars mission which is due next year.

The journey to the planet takes 250 days followed by a month studying life on Mars. Then there's the 240-day journey home, which is ten days shorter because the planet's orbit moves it closer to earth.

This will be the longest-running Mars experiment in history.