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Some scientists believe that one day we may be able to colonise Mars. That move may even be necessary: one day Earth might become uninhabitable and Mars would be our next best option. Although we have not yet managed to send a manned mission to Mars, Martian projects are moving to the top of the space exploration agenda. Within the next 20 years people may be walking on Mars.
In the 1960s, at the height of the Cold War space race, many people believed that one day humans could visit another planet. TV programmes and films predicted that cruises in the Caribbean would be replaced by trips to Mars. But scientists soon discovered that space travel is bad for human health.
The problems
Spending any length of time in space is hugely problematic for humans, largely due to the lack of gravity. At first, weightlessness gives you a feeling of motion sickness. But, after a few days of space travel, the problems become more serious. Muscles waste away because they have no body mass to support. The bones in the legs, pelvis and spine become brittle as the body reabsorbs calcium, which seems no longer to be needed because there is no stress on the bones.
The heart - a muscle like any other - shrinks and beats irregularly, blood pressure drops and aerobic capacity falls. After a few months in space, super-fit astronauts return to Earth so weakened they have to spend months in rehabilitation.
The way that weightlessness affects perception is also a problem. Once gravity is removed, our whole spatial map changes. Floors can be ceilings and vice versa. This is very disorienting for astronauts who sometimes feel as though they are permanently upside down: no matter which way they turn, they feel uncomfortable. It is also very easy for astronauts to lose their sense of direction, which can be extremely dangerous when navigating or manoeuvring a spaceship.
Are there any solutions?
These are problems which we will have to overcome if we intend to travel to Mars: the 300 million mile round trip would take about three years.
To combat the problems of weightlessness, scientists have come up with rudimentary treatments - such as expandable bungee cords, which enable astronauts to have something for their muscles to pull on - to counteract zero gravity. In addition, astronauts have to do around four hours of vigorous exercise every day to prevent muscle wastage.
However, neither of these methods is a proper long-term solution. Science will probably need to come up with drug treatments and gene therapy if humans are ever going to spend years in space.
Another alternative is to build spinning space crafts. Using centrifugal force, spinning space stations could create an artificial gravity which may prevent us suffering some of the problems caused by weightlessness.
To combat the problems of perception in a zero gravity environment, scientists have developed virtual reality programmes which astronauts can use to train them to see rooms in terms of six 'equal' surfaces, rather than a floor, a ceiling and four walls.
Visiting Mars
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