Water. It is found everywhere on Earth, from polar ice caps to steam geysers. And where they find water, they find life, almost without exception. “When we find water here on Earth - be it ice-covered lakes, deep-sea hydrothermal vents, arid deserts - if there is any water, we find microbes that manage to live in it,” says Brian Glaser, an oceanographer at University of Hawaii at Manoa, studying astrobiology.
Therefore, NASA's unusual motto in the hunt for extraterrestrial life was "follow the water."
Recently, NASA scientists announced a find on Mars: the dark streams that scientists have seen during the summer months on Mars for more than ten years, turned out to be evidence of flowing water. While salt streams may be too oversaturated in chloride salts to support life, they increase the likelihood of life on Mars at this time.
But why exactly is water such an important molecule for life? Could there be other ingredients that provide the perfect recipe for life on other planets?
It turns out that several chemical properties of water make it indispensable for living things. Not only does water dissolve almost everything, but it is also one of the few materials that can be solid, liquid and gaseous in a relatively narrow temperature range.
Current life
Almost all life on Earth uses a membrane that separates the body from the environment. To stay alive, the body takes on important materials to produce energy, filtering out toxic substances like waste. In this regard, water is necessary because it remains liquid at earth temperatures. As it flows, it provides an efficient way of transferring substances from the cell to the cell's environment. Releasing energy from solids is much more difficult (although there are microbes that eat rock), Glazer says.
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The other part of the equation - besides the fact that water can carry substances into and out of the cell - is related to a unique chemical configuration. The humble water molecule consists of two hydrogen atoms bonded to an oxygen atom.
“The way they are combined makes water a wonderful universal solvent,” which allows it to dissolve just about any substance, Glaser says.
This is primarily due to the fact that the molecule has polarity, hydrogen atoms cluster on one side of the molecule, forming a positive region, and oxygen at the other end forms a negative charge. The positive hydrogen end attracts negative ions (or atoms with an extra electron in the outer shell), while the negative end attracts positive ions (which lack one of their electrons).
Water's remarkable dissolving properties make it ideal for transferring substances like phosphates or calcium ions into and out of the cell.
Water phases
Another unusual feature of water is that it can be solid, liquid, and gaseous within the temperature range found on Earth. Other molecules that have been identified as good candidates for supporting life tend to remain liquid at temperatures or pressures that would be inhospitable to most famous life forms.
“Water is actually a sweet spot,” Glazer says.
The fact that water can be in all three phases in a relatively narrow pressure range creates many opportunities for life to flourish, he adds.
“All three conditions of water available on our planet create a pleasant variety of habitats and microclimate,” says Glazer. For example, frozen ice can be found in mountain glaciers, while water vapor helps to warm the atmosphere.
Water cradle of life
Water can be more than a liquid that makes life easier - it can be the protective cradle that brought the building blocks of life to Earth, says Ralph Kaiser, a physicist and chemist at the University of Hawaii who studies astrochemistry.
According to one of the theories of the origin of life on Earth, the theory of panspermia, ice comets crashed into the Earth, carrying tiny organic molecules that became the basis for life. But traveling through space is an ordeal, primarily because of the powerful levels of radiation that can destroy delicate organic molecules.
However, water in its solid form can protect molecules from radiation. "Perhaps because the building bricks were frozen in the water, it became their protective mantle."
In search of substitutes
Of course, while water is essential to life on our own planet, there may be life forms that do not live by the rules of earthlings.
Scientists are also looking for other fluids that could play a similar role as a universal solvent and transport medium. Top contenders include ammonia and methane, says Chris McKay, an astrobiologist at NASA's Ames Research Center in Moffett Field, California. Ammonia, like water, is a polar molecule relatively common in the universe, but scientists have not yet found large bodies with ammonia in the solar system.
Methane is not polar, but it can dissolve many other substances. However, unlike water, methane becomes liquid only at very cold temperatures - at minus 182 degrees Celsius.
“We know Titan has large lakes of liquid methane and ethane,” this is one of Saturn's moons, McKay says. "So the very interesting question is whether life can use liquid methane or ethane."
Ilya Khel