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The search for water on Mars
The search for water on Mars

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2 Why search for water?

As you have seen in Figure 1, two-thirds of the Earth’s surface is covered in water; however, it is not evenly distributed across the globe. For those living in humid climates (such as at The Open University’s campus in Milton Keynes, UK), water can be easily taken for granted until there is a spell of hot weather! When this happens, plants dry up and some may die, but others are remarkably resilient and will spring back to health as soon as rain arrives.

On Earth, there are also regions that are much drier than the UK. Look at photographs in Figure 6 and Figure 7. Both were taken in January and show differences in the availability of water depending on geography and climate.

This is a photograph of a wood. In the foreground, the ground is covered in brown leaves with a few small green plants growing in it. In the middle ground a small body of standing water can be seen, with rings forming on the surface of the water from drops that fall into the pond. Behind and to the right of the pond are large trees, extending out to a wood.
Figure 6 A photograph taken in a small wood near the OU campus in Milton Keynes, UK, after some rain. Image: Susanne Schwenzer.

Life is obvious in Figure 6, with green leaves and even a small insect causing the ripples on the puddle. Figure 7, a photograph taken at the same time of year as Figure 6 but in the Atacama desert, shows no obvious signs of life in this picture, but studies have shown that microbial life is possible even with the extreme lack of water here. Occasionally you can find a tiny burrow or footprints of animals that have adapted to the harsh conditions.

This is a photograph of the Atacama desert. The image is filled with a barren, brown ground surface that has very little structure apart from some polygonal patterns made from cracks in the middle ground. Around the cracked area there are large rocks, casting their shadows in the bright sunlight. The rocks are of various sizes and most have sharp edges and are of angular forms. One area in the foreground is covered in very small, dark brown nodules.
Figure 7 The Atacama desert. Image: Susanne Schwenzer.

What is clear, therefore, is that even where water is scarce, life can be found. For this reason, the search for life beyond Earth has been intimately linked with the search for water. Indeed, ‘follow the water’ has been NASA’s guiding motto for many years.

But if we’re looking for evidence of water on another planet, what might we be looking for?

  • List as many places as you can think of where water can be found outdoors on Earth?

  • Although most of the Earth’s water is in oceans, you might have also thought of rivers and lakes, puddles, rain, snow, ice, frost, fog, and steam.

  • In your answer, you may have listed forms of water that are liquid, some that are solid, and others are gaseous. Can you organise your list into these three states of matter?

  • Liquid: rivers and lakes, puddles, rain

    Solid: ice, snow, frost

    Gaseous: steam

    Fog cannot easily be organised because it consists of tiny droplets of water or ice that float in the air. For this reason, it may be best described as a ‘suspension’.

There are many forms of water on Earth but, so far, you’ve only heard about ice on Mars. In the next section you will learn more about the properties of water and why it is specifically liquid water that is important for life.