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Liquid water

Common water

Liquid water (H2O) is commonly used water two O) Is created by hydrogen 、 oxygen Composed of two elements Inorganic , on normal atmospheric temperature Atmospheric pressure The bottom is colorless and odorless transparent liquid.^[1]

Chinese name: Liquid water
Foreign name: H two O
Element composition: Hydrogen and oxygen (H, O)

Smell: Colorless and tasteless
Status: The most important component of organism
Specific heat capacity: 4.2 * 103 J/kg· centigrade

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five Other characteristics
six Origin of liquid water

definition

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Water is one of the most common substances, an important resource for the survival of all life including human beings, and also the most important component of organisms. Water plays an important role in the evolution of life. Human beings have long known about water Material outlook Zhongdu regards water as a basic element, one of the five elements; Ancient western Four element theory There is also water in it.

water properties

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Water is a colorless and odorless transparent liquid under normal temperature and pressure. In nature, pure water It is very rare. Water is usually a solution of acids, alkalis, salts and other substances. It is still traditionally called water. Pure water can be obtained through several distillation with platinum or quartz vessels. Of course, this is also relatively pure water, which can not be absolutely free of impurities Gaseous A substance that is transformed from solid to solid. Solid water is called ice; The gaseous state is called water vapor.

density

The density of water is the largest at 3.98 ℃, which is 1 × 10 ³ kg/m3. When the temperature is higher than 3.98 ℃, the density of water decreases with the increase of temperature. When the temperature is 0~3.98 ℃, the water does not obey Thermal expansion and cold contraction The density increases with the increase of temperature. When water is at 0 ℃, the density is 0.99987 × 10 ³ kg/m3, and when ice is at 0 ℃, the density is 0.9167 × 10 ³ kg/m3. So ice can float on the water.

Specific heat capacity

Watery Specific heat capacity It is 4.2 * 10 ³ J/kg · C, and the specific heat capacity of steam is 2.1 * 10 ³ J/kg · C

Heat of vaporization

Watery Heat of vaporization 40.8 Kilojoule / mole , equivalent to 2260 kJ/kg.

Thermal conductivity

At 20 ℃ Thermal conductivity 0.006 J/s · cm · K, the thermal conductivity of ice is 0.023 J/s · cm · K, and the thermal conductivity of snow is 0.00029 J/s · cm · K when the density of snow is 0.1 × 10 ³ kg/m3.

Freezing point

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0 ℃ (under normal pressure)

boiling point

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100 ℃ (under normal pressure)

Other characteristics

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1、 water When the steam temperature is higher than 374.2 ℃, the gaseous water cannot be converted into liquid water by pressurization.

2. The thermal stability of water is very strong, steam When heated to more than 2000K, there is only a small amount dissociation It is hydrogen and oxygen, but water will dissociate into hydrogen and water under the condition of electricity.

3. Has a large cohesion and surface tension In addition to mercury, water has the largest surface tension and can produce obvious Capillarity And adsorption.

4. Pure water has very weak conductivity, but ordinary water contains a small amount of electrolyte and has conductivity.

5. Water itself is also a good solvent, and most inorganic compounds are soluble in water.

6. At - 213.16 ℃, water molecule will appear Hydrophobicity 。

Origin of liquid water

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Phoenix discovers evidence of liquid water on the surface of Mars for the first time

Tencent Science and Technology News《 New scientist 》According to the magazine, scientists have successfully found evidence that liquid water may exist on the surface of Mars or under its shallow surface. They came to this conclusion after analyzing the photos taken by the Phoenix probe.

It is reported that in“ phoenix ”After the successful landing of Mars, scientists found that some strange and puzzling formations appeared on many parts of the probe, and their size will continue to increase over time. Some researchers speculate that these forms are mainly salt rich (including those later discovered by Phoenix Perchlorate ）"Dirty water".

In the process of research, scientists have collected a lot of evidence for this theory. They found that the condensation point of the mixture of water and perchlorate can be as low as minus 70 degrees Celsius, which means that this liquid mixture may exist on the surface of Mars.

Researchers believe that they have found the answer to why Phoenix has inexplicable "spots": salt mixtures will absorb a large amount of water vapor from the surface of Mars and condense into liquid droplets, which may solidify at night.

not long ago, University of Arizona A similar research result was announced by the scientists of. They are interested in the causes of some new gullies on the surface of Mars. During the research, scientists found that some gullies recently appeared on the surface of Mars may be the result of groundwater.

Scientists have discovered many gullies on the surface of Mars long ago. Since no evidence of the existence of liquid water has been found on Mars so far, many researchers believe that the movement that led to the formation of these gullies stopped long ago. However, the latest data from the Mars Global Surveying Orbiter shows that such gully structures are still in the process of being formed today.

The researchers successfully confirmed that water and ferric sulfate (the latter widely exists in Martian soil) Freezing point It can be as low as minus 68 degrees Celsius. By analyzing the previously obtained analysis data of Martian soil, scientists have successfully mapped out the areas where this mixture may be distributed on the surface of Mars.

Using a computer model, the researchers determined the temperature and pressure values needed to keep the mixture of water and ferric sulfate liquid. Later, they pointed out that similar conditions might have existed on the surface of Mars or its shallow surface. The research results show that these areas where liquid water and ferric sulfate may be distributed are very consistent with those where new gullies are found.

It should be noted that the American Phoenix detector It has finally been confirmed that there is water ice on the surface of Mars. In addition“ Mars Reconnaissance Orbiter ”Evidence of the existence of ice has also been found under the shallow surface of Mars.

First direct evidence of liquid water on Mars

This controversial discovery can also be made by the Phoenix Mars probe Previous findings. Previously, Phoenix was found in Martian soil Perchlorate Perchlorate can maintain the liquid characteristics of water below zero. Scientists believe that this antifreeze The effect makes it possible that liquid water exists widely below the surface of Mars. But they also pointed out that even though liquid water widely exists on Mars, the salinity of this water is too high to sustain life. In the observation photos sent back a few days after the Phoenix lander landed in 2008, scientists found a mysterious spot on one of the probe's feet. Strangely, in the next few weeks, the area of this spot continued to increase. The scientists of the Phoenix project team therefore launched a heated debate on the source of this spot. One possibility that most interests scientists is to guess that these spots are droplets of salt water, which will absorb Water vapor , so it will continue to increase.

For this view, members of the Phoenix project team Nilton Lennon Chief scientist of Phoenix mission Peter Smith 22 other scientists participated in the debate. The results of the scientists' debate will be officially published in March. There are many cave The Grand Canyon and river channels can also provide evidence for the widespread existence of large amounts of liquid water on the surface of Mars. Although the surface of Mars looks dry, the shape of crater changes constantly Gully It also shows that there may be an aquifer below the surface of Mars, and occasionally liquid water flows will erupt. Since Phoenix landed at the North Pole of Mars, the temperature was too cold for pure water to exist in liquid form. However, brine can remain liquid at lower temperatures. Therefore, Leno and other scientists believe that if Perchlorate If it widely exists on Mars in highly concentrated form, liquid water may also exist below the surface of Mars. "According to my calculation, you can find almost anywhere below the surface of Mars Salt solution 。”

Southwest Research Institute Scientist Mark Bullock simulated the environment on the surface of Mars and conducted experiments on saline water. His experimental results strongly verified the views of Leno et al. The researchers used a computer model to simulate the traces of liquid water flowing in the Martian atmosphere, and then compared them with the traces of sand rolling on Mars. They found that under the same atmospheric environment as Mars Mars Reconnaissance Orbiter The traces shown in the photos returned by (MRO) are more consistent

Liquid water drops on the robot arm of Phoenix probe

Mars has all the elements of life

This news has surprised scientists who have been searching for extraterrestrial life for many years. They said that if this discovery is confirmed, all the elements suitable for life on Mars are ready: liquid water and stable heat source. In all its Mars exploration In the task, NASA The strategy of "looking for water" is proposed to determine whether Mars once had life or supported the existence of life. Why are scientists keen on finding life on Mars? In the solar system, Mars is not only the closest planet to the Earth, but also a planet very similar to the Earth. In the first billion years of the formation of the solar system, the environmental conditions of Mars and Earth were very similar. If it can be confirmed that there is water and life on Mars, people will soon move to this red planet. University of Colorado Space biologist Bruce - Czech Republic "There is more than one reason to believe that there was life on Mars, whether in the past or now," Skie said

Before that, scientists had not found any evidence that liquid water existed on the surface of Mars. American astronomer Parsivar Lowell The report said that he found that there were crisscross canals on Mars. Some people think that the canal was excavated by high IQ species for survival in the dry Martian environment. Researchers also found evidence of ice in the Arctic region of Mars. NASA scientists said that there is a mysterious mist on the surface of some parts of Mars, which can be observed by spacecraft in Mars orbit and giant telescopes on Earth“ Martian fog ”。 Further research shows that the main component of the "Mars fog" is methane gas. Experts speculate that these methane gases are formed by“ Alkaniferous organism ”The gas released by Martian life. Scientists believe that these "Martian life" must still be alive, otherwise there will be no continuous methane in the Martian atmosphere.

Liquid water sealed for billions of years hides clues to the origin of life

2.6 billion years ago liquid water

According to foreign media reports, not long ago, a research team composed of British and Canadian scientists found 2.6 billion year old liquid water in a 2 mile deep mine, which was trapped in the same Rock stratum The latest research shows that these liquid waters contain very rich chemicals, known as life sustaining water. The 2.6 billion year old liquid water material may be the oldest water on the planet, and even life may be found in it. Similarly, scientists proposed that we can use the same method to find liquid water on Mars. The discovery of Curiosity and other rovers has proved that ancient Mars had a humid environment. If we can find liquid water in the depths of the Martian stratum, It may also lead to the discovery of Martian life^[2] 。

This research has been published in Nature In the magazine, this discovery may force us to rethink where life may appear on the earth and reveal clues about how microbes evolve. The cave where the earth's ancient liquid water was found is located in Canada Ontario Scientists also found rich gases, such as methane, hydrogen and different forms of isotopes. In fact, this liquid water hydrothermal vent The surrounding conditions are similar. Hydrogen and methane originate from the interaction between ancient liquid water and rocks, Natural radioactive element They also participate in these chemical reactions. The gas produced can provide energy for microorganisms, which also makes Microbial community It can survive for billions of years without solar energy source.

Surrounding liquid water Crystalline rock It is believed to have a history of 2.6 billion to 2.7 billion years, but no one would expect that the liquid water mixed in it also has the same age. university of manchester A technology has been developed that can be used to investigate these long-lived substances. The lower limit of their fluid properties is set at 1.5 billion years. In this regard, the life information in the liquid water has become the focus of scientists' research. How did the microorganisms that existed hundreds of millions of years ago evolve in an extremely short environment? Is the initial state of life on the earth these microorganisms? Some scientists think that although the surface of Mars is desolate, whether there is similar life information hidden in the depth of its rock stratum is undoubtedly a very valuable research topic.

Foreign media: the first liquid water lake found on Mars

The first liquid water lake found on Mars

On July 25, 2018, AFP reported that the first liquid water lake was found on Mars. It is reported that scientists have found a huge underground aquifer on Mars, which increases the expectation of life on Mars.^[1]

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