• Mars is known as a "self-sterilising" planet. Its surface is saturated by ultra-violet radiation by the Sun. Ultra-violet rays are what can cause skin cancer on Earth although, fortunately, the Earth's atmosphere filters out most of these dangerous rays. The soil is extremely dry on Mars because of the lack of water, and this soil also undergoes an oxidising process, which is what causes the soil to rust (it forms a metal oxide) and appear rusty-coloured. This self-sterilisation of Mars prevents micro-organisms (small and basic but living objects) from forming on or under the surface.

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• Mars does have water in its atmosphere. It may only be a small amount, but could provide life to certain living organisms that need very little water. Also, water in the atmosphere and strong evidence that water once flowed around the planet, suggest that there may be a possibility of liquid water deep under the surface. The picture below shows two 'islands' that may have formed as water flowed around them. We can see examples of this in rivers on sand on Earth.

• Missions to Mars show the planet to be made up of many rocks and pebbles (more evidence of water!) similar to ones on Earth. (Look at the rock below while wearing 3D glasses and watch it leap out of the screen!)

• A face and two hearts have been discovered on Mars. People believed that these could have been created by advanced beings!

• It is known that tiny micro-organisms can exist on Earth in some very extreme conditions. They can live deep below the surface and never be exposed to light or in extremely cold or hot places, in places impossible for the survival of humans or most other creatures. Mars may appear inhospitable for humans, but could have conditions suitable for organisms similar to the ones living in the extreme places on Earth. In fact, Martian conditions are not as extreme as conditions can be on Earth where some forms of life exist.

• If Mars did have water, it will also have had a thicker atmosphere. This thicker atmosphere would have prevented the dangerous rays of the sun from hitting the planet, with its atmosphere filtering them out as happens on Earth. People believe that Mars' temperature was also higher which greatly increases the chances of life on the planet. Below is an artist's impression of what Mars may have looked like when water flowed on its surface billions of years ago.

• A piece of rock from Mars, which landed on Earth when a meteor hit Mars and scattered its rocks, contains signs of life. Small fossils and evidence of a basic once-living micro-organism provided the strongest proof yet that life did once exist on Mars billions of years ago. The picture below shows these tiny bacteria-like micro-organisms, about one thousandth of the size of a human hair!

The search for life continues on Mars with the missions to explore the surface and whatever is below it. One day, humans will walk on the planet. When humans do visit Mars, they will be expected to survive on the planet for about three years. They will have to wait for Earth to be in the correct position to return home. In these three years, they will have to learn to adapt to the hostile conditions on Mars and will have a longer period of time in space to discover the secrets of another planet. Mars will become their new home. Who knows what aliens they might meet there?

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