An international group of scientists emerged on Sunday after a year of near isolation in a research station set up in Hawaii to simulate conditions on Mars.
Greeted with a cry of "welcome back to Earth," the six scientists - three men and three women - emerged from a small white dome on Hawaii's Mauna Loa volcano, which has a landscape resembling the one found on Mars.
The dome sits at an elevation of 2,500 metres above sea level where no plants grow, and the six scientists who participated in the experiment were only allowed to leave the dome if they were wearing a space suit.
Part of a long-term goal to send humans to Mars, the Hawaii Space Exploration Analog and Simulation (HI-SEAS) experiment was designed to explore whether a crew could live together in close quarters over an extended period of time and under adverse conditions.
"Bring something you can work on," German scientist Christiane Heinicke said after her year-long stay atop the volcano.
"One of your biggest enemies is boredom," she said. "You have to be willing and able to adapt to the others and make compromises, and if you're unable to do that, you shouldn't be here."
Each scientist worked on research projects during their stay and learned how to get by with limited resources while avoiding personal conflicts within the confines of the dome. Communications with the outside world were delayed by 20 minutes, the same amount of time it would take to relay messages to and from Mars.
Putting three men and three women in a small dome for a year might sound like a crude Big Brother experiment, but it was expected to provide valuable knowledge for space research. If the dream of many space-faring countries of sending humans to the Red Planet becomes reality, the trip alone would take up to a year.
Another hurdle is cooperation among the crew while they live on Earth's neighbouring planet, which on average is 228 million kilometres away. They must be able to endure in an inhospitable environment until the planets align favourably for the return trip.
The group became the first to complete a year-long Mars simulation in the United States.
Kim Binsted, principal investigator for the HI-SEAS, told the Hawaii Tribune Herald newspaper that the only longer Mars simulation was held in Russia and lasted 520 days.
Three other shorter simulations have been held in the Hawaii dome, she said, and two more simulations are planned, each eight-months long.
Upon emerging the crew was to be given fresh fruit and other food that was not available during the simulation, the Tribune Herald said.