A major factor that affects astronauts’ mental well-being is time. To date, astronauts have only spent a few months in space at a time, but longer expeditions would require astronauts to spend significantly more time inside a spaceship. For example, a round-trip expedition to Mars could take about three years. Being confined in a small space for such a long period of time is not healthy. Research has shown that travelers on such long journeys—such as sailors or explorers in the Arctic—have an above-average chance of suffering from depression.