A group of six recruits are spending a year living without fresh air or food in a small dome near a Hawaiian volcano. This is order to simulate what life might be like for humans on Mars.
The group is made up of four scientists, an architect and a pilot. The experiment began at 1am (3pm Friday local time) on Saturday.
If they want to leave the dome they must wear a spacesuit. Hawaii Space Exploration Analog and Simulation (HI-SEAS) mission will help NASA plan for a human mission to Mars. The HI-SEAS project has already seen recruits carry out four-month and eight-month stays in the dome.
One of the recruits, scientist and journalist Sheyna Gifford, tweeted a photo of her first meal inside the dome, a rehydrated cheese and turkey quesadilla with peas and sweetcorn.