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Water and life

The question of the presence of liquid water on Mars is important because all known life forms require liquid water.

Liquid water transports chemicals in and out of the cells, and it is needed for proteins to function. It also remains liquid over a wide range of temperatures providing a stable environment for life.

Like almost no other molecule, the density of water is less in the solid state than in the liquid state, meaning that ice floats and hence the possibility exists for a sheltered aqueous environment underneath a cover of ice to sustain life.

Finally the water molecule is polar. This means that polar substances such as sugars and salts, that are important to known life forms, are easily soluble in water, while nonpolar substances like the lipids that make up cell membranes will not dissolve in water. This close link between water and life is the reason why NASAs strategy for the exploration of Mars is simply called “Follow the water”.

While the study of Mars can teach us many things about for example the evolution of our own planet and the climate changes we observe, the strongest urge that drives the exploration of Mars is probably the urge to make what would surely be one of the greatest discoveries in the history of mankind: extraterrestrial life. Mars is one of the locations in the Solar System where the discovery of such life, extant or extinct, seems least improbable.

If life is or was present on Mars, several possibilities for the origin of such life exist. Life could have originated on Mars and on Earth independently, the origin of life on Mars would then be what is called a second genesis, or it could have originated on either planet, or in a third place, and then spread by meteorites, a scenario which has been named transspermia.