Why is water so important for finding extraterrestrial life?

Water. On Earth, it is found everywhere, from polar ice caps to steam geysers. And where water is found, life is found, almost without exception. “When we find water here on Earth — be it ice-covered lakes, deep-sea hydrothermal springs, arid deserts — if there is any water, we also find microbes that manage to live in it,” says Brian Glaser, an oceanographer from University of Hawaii in Manoa, studying astrobiology.

Therefore, the NASA motto in the hunt for extraterrestrial life was “follow the water.”

The other day NASA scientists announced the discovery on Mars: dark streams that scientists have seen on Mars over the course of the summer months for more than ten years have proven to be evidence of flowing water. While saline streams may be too saturated with chloride salts to support life, they increase the likelihood of life on Mars at the moment.

But why is water just such an important molecule for life? Can there be other ingredients that provide the perfect recipe for living on other planets?

It turns out several chemical properties of watermake it indispensable for living beings. Water not only dissolves almost everything, but is also one of the few materials that can be in a solid, liquid and gaseous state in a relatively narrow temperature range.

Current life

Virtually all life on Earth usesthe membrane that separates the body from the environment. To stay alive, the body takes important materials for energy production, sifting out toxic substances like waste. Therefore, water is necessary because it remains liquid at terrestrial temperatures. As it flows, it provides an efficient way to transfer substances from the cell to the cell's environment. It is more difficult to release energy from a solid (although there are germs that eat stone), says Glaser.

The other part of the equation is besides the fact that watercan carry substances into and out of the cell - associated with a unique chemical configuration. A modest water molecule consists of two hydrogen atoms linked to an oxygen atom.

“The way they are connected makes water a wonderful universal solvent,” which allows it to dissolve almost any substance, says Glaser.

First of all it is due to the fact thatmolecules are polarity, hydrogen atoms pile up 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 are devoid of one of their electrons).

The amazing dissolution properties of water make it an ideal vehicle for transferring substances, like phosphates or calcium ions, to and from the cell.

Water phases

Another feature of water is thatit can be solid, liquid and gaseous within the temperature range that is observed on Earth. Other molecules that have been identified as good candidates for life support, as a rule, remain liquid at temperatures or pressures that will be inhospitable for the most famous forms of life.

“Water is actually a sweet spot,” says Glaser.

The fact that water can be in all three phases in a relatively narrow range of pressures creates many opportunities for prosperity, he adds.

"All three states of water available on ourthe planet creates a pleasant variety of habitats and microclimates, ”says Glaser. 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 it easier.the flow of life processes - it can be a 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 onEarth, 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 blocks were frozen in the water, it became their protective mantle."

In search of substitutes

Of course, although water is important for life on our own planet, there may be life forms that do not live by earthly rules.

Scientists are also looking for other liquids that couldplay a similar role as a universal solvent and transport medium. The main contenders are ammonia and methane, says Chris McKay, an astrobiologist at the NASA Ames Research Center in Moffet 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 can dissolve many other substances. However, unlike water, methane becomes liquid only at very cold temperatures - at minus 182 degrees Celsius.

"We know that on Titan there are big lakes fromliquid methane and ethane ”is one of Saturn’s moons, says McKay. "So the question is very interesting, whether life can use liquid methane or ethane."