They’ve spent the last eight months living alone on a remote Hawaii volcano, and now they’re heading home. Six NASA research subjects will leave their Mars-like habitat on Sunday and return to the world, and will once again be able to enjoy fresh fruits and meat.

The four men and two women were part of a project to recreate living conditions on the surface of Mars by going to one of the most unforgiving places on the world: a remote volcano in Hawaii. Everything about it was meant to imitate a human colony on Mars, including a self-imposed 20-minute delay on communications with the outside world, which is how long it would take to send a signal to the surface of the Red Planet.

Scientists are trying to better understand what kind of psychological effects humans who go to Mars will have to endure. This experiment will help NASA pick crews that have the traits needed to survive on a two to three years Mars expedition.

“A team of six volunteer scientists completed one of the most extensive studies of the demands of life on a distant world by closing themselves off to the rest of the world for eight months in an effort known as HI-SEAS,” NASA said in a 2015 statement on a similar previous mission. “Their chore wasn’t so much to stay alive, but to see how isolation and the lack of privacy in a small group affects social aspects of would-be explorers.

“The research is expected to bear directly on NASA’s decisions when composing crews for future missions to Mars. The group also experimented with many budding technologies future Mars explorers could employ during real expeditions to the Red Planet. It was the third and longest of the simulation missions. The next simulation is planned to last a year. A mission to Mars may take two and a half to three years, with approximately half of that time on the planetary surface.”