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            Throughout human history, the physical universe has often presented dangers to explorers. For example, when primitive humans left their tribal villages to search for food and water, they risked death or injury from dangerous animals. Later, when people sailed the oceans in search of new lands for settlement or trade, many died in terrible storms.  Similarly, the ocean of outer space has many dangers.  However, it also has several unique challenges for explorers including its vacuum environment, countless high-speed meteors, and few known sources of water. 

            One of the challenges that is unique to space

is the fact that space is a vacuum, which is a risk for

various reasons. First, in a vacuum there is no

atmosphere and therefore no air pressure. Without air

pressure, the human body has no oxygen to sustain

itself. After too many minutes without oxygen, a

person would lose consciousness and eventually die.

Also, in a vacuum a person's blood will gradually begin

to boil. Finally, without an atmosphere, the rays of the

Sun can cause radiation poisoning.  With current

technology, the dangers of the outer space vacuum are

too overwhelming for prolonged space travel.

            Another difficulty that is unique to outer space is the presence of meteors and micrometeors. These are pieces of rock and metal that are left over from the formation of the solar system. Many of these objects travel at very high speeds. Under the Earth's blanket of air, people are usually protected from meteor impacts. However, in space, people and spaceships are vulnerable to collisions with meteors. It is true that the chance of meteor impacts is relatively small, but if even a small micrometeor happens to collide with a spacecraft, it could cause serious damage.

            A third special challenge involved with the environment of space involves the fact that it is very difficult to find life-sustaining water off the Earth. For example, the planet Mercury, which is closest to the Sun, is too hot to have water, so space travelers must take water from Earth if they want to visit Mercury. A similar situation exists on the planet Venus, second from the Sun. This planet is likewise too hot for water to exist. Similarly, the fourth planet, Mars, is too cold and dry, although there may be some water frozen at the north and south poles of the planet.  Although astronauts are able to recycle their own waste into drinkable water, the fact that no additional usable water exists in our solar system makes long-distance space travel very risky.

            There are other difficulties involved with space exploration, but these are three of the most important ones. In summary, without adequate air pressure, the unprotected human body may be seriously harmed in a vacuum. In addition, meteors can threaten human life and damage spacecraft. Finally, the lack of water in space means that human life may have a difficult time surviving on other planets. As one can see, the challenges of space travel are rather different from terrestrial dangers.