How will real Mars mission differ from simulation?
Six members of an international crew have come to the end of a gruelling 17-month Mars simulation exercise. But in what ways would a real mission to the Red Planet be different?
After 520 days of isolation, three Russians, two Europeans and a Chinese man have emerged from their sealed capsule.
Their 70-million mile journey within the confines of a warehouse in Moscow is complete, bringing to an end the simulated flight by the European Space Agency that sought to test the physiological and psychological impact of a mission to Mars.
The six men experienced some of the conditions a crew could expect when the real trip takes place, possibly within about 20 years.
The regimented daily routine, the rations and the 20-minute delay in communications with "Earth" were ways in which the intense training exercise hoped to put the men's mental and physical well-being to the test.
So in what ways would a real mission to be Mars be different?
People living on Earth are protected from dangerous radiation particles that come from the Sun because they are deflected by the Earth's magnetic field. No such shield exists for a crew travelling to Mars.
Apollo flights to the moon also had this risk but a trip to Mars is much longer and therefore increases the length of exposure.
Radiation poses the highest health risk for those on a real trip to the Red Planet, says Rupert Gerzer, director of the Institute of Aerospace Medicine in Germany, because these particles can increase the risk of cancer.
Other health risks include nerve damage and digestive problems.
The radiation fluctuates according to solar activity, which can often strike with little warning, says space underwriter David Wade.
For protection from these storms, the crew could seek refuge in a shelter in the spacecraft for one or two days until the storm passes, he says. Water tanks could be an effective barrier.
The six men on the Mars simulation exercise did not experience the weightlessness they would on a real mission.
Living in zero gravity means muscles are prone to deteriorate and cardio reflexes are weakened because they would not be used, says Mr Gerzer.
To combat this, space experts suggest astronauts exercise at least two or three hours a day, even though the body does adapt to being constantly weightless.
Despite that, says Mr Gerzer, an astronaut would not return in the same physical shape as when they left because of not having to use as much strength in space.
Muscles most susceptible to damage are weight-bearing bones such as heels, knees and hips, says Mr Wade, effects similar to osteoporosis.
It takes two to three days for the body to get used to being in space and during that time astronauts often experience "space sickness", a feeling of nausea while the body gets used to being weightless.
They would also have to adapt to Mars's gravity, which is a third of that on Earth, once they land.
In February, three of the crew members made a mock landing on Mars - complete with space suits and assisted by a robot rover. But in fact, they were still in a Moscow suburb.
The mission "tried to make the surface look like Mars" using sand, but it was no comparison to the planet's lack of oxygen or gravity levels, says Christer Fuglesang, head of the Science and Application Division of ESA.
Another important aspect of Martian atmosphere the crew did not experience is sand storms, which in reality could damage equipment, says astronomer and author David Whitehouse.
A real mission to Mars would actually take about three years, almost double the time of the Mars500 experiment, says Mr Wade.
Once there, the crew would spend about 18 months on the planet's surface, carrying out research while Earth and Mars realigned sufficiently for the trip back.
Perhaps the most obvious difference is that the Mars500 simulation went nowhere.
"The people in the Mars simulation know that they're on Earth," says Mr Whitehouse. "If they really needed to, they could open a door and get out."
For that reason, it doesn't provide the same stressful environment of a real mission.
If something goes wrong during a real mission, there may be no turning back.