The existence of water has always been a crucial standard used to judge whether there will be creatures in a place. Especially, the missions to Mars always take the discovery of the evidence which can demonstrate the existence of water as one of their most important tasks, making efforts to prove the existence of creatures on Mars through the discovery of water. After all, as is firmly believed by a lot of astrobiologists, liquid water is the most important requirement for life. Actually, water plays the role of guaranteeing the normal operation of creatures’ body, for which it is believed that there are creatures on Mars after the scientists found a high possibility of the existence of water there. In the following paper, the significance of liquid water to life and the existence of liquid water on Mars will be analyzed in detail.

Above all, water is an indispensable factor for life. In the first place, liquid water is an important part of life. For instance, the main component of human body is water, which accounts for 70% of human body weight. Water in human body is distributed everywhere in the form of blood, saliva, digestive juice, urine, tissue fluid, intracellular fluid and other body fluids, playing an important physiological role. Water is not only a component of cells and body fluids, but also participates in metabolism and plays a key role in digestion, absorption, recycling and excretion. Water also plays a role in regulating body temperature and lubrication to protect the eyeball, joints, respiratory tract, gastrointestinal tract and thoracic cavity, abdominal cavity, pelvic cavity and so on (Brack, 1993).

If a person does not take a certain vitamin or mineral, he may be able to live for several weeks or years with illness. But if he does not have water, he can only live for several days. Adequate water in the human body can enhance physical strength, vitality and immunity, for which drinking plenty of water makes people feel energetic. All in all, without water, there is no possibilities for human beings to live on the earth like the conditions now. Secondly, as the direct or indirect source of energy, photosynthesis of plants requires liquid water. It can be seen from the process of photosynthesis of plants that water as a raw material plays a significant role in the source of energy in the world.

All in all, photosynthesis of plants can be said to be the foundation of the life of creatures on the earth. In addition, water transpiration can regulate plant temperature and enable enzymes to have good activity. Therefore, water is also a significant requirement for the life of plants, which can directly or indirectly influence all the lives through photosynthesis of plants. Moreover, liquid water constitute the living environment of hydrobionts, which plays a basic role in their life as well.

On the evening of September 28, 2015, NASA released the blockbuster news that the Mars Mystery had been solved. According to the information provided by it, spectral evidence suggests that there is now liquid water on Mars (Wilson, 2015). Long before the press conference, many people had guessed with great accuracy what the “big discovery” was about to be announced from NASA’s list of people who had announced that they would attend the conference. Because Lujendra Ojha, a doctoral student, was among the participants in the conference, and his appearance gave people a strong signal. After all, it was him that discovered Recurring Slope Lineae on Mars, suggesting that liquid water might be found on Mars.

In 2011, when he was an undergraduate at the University of Arizona, dark stripes were found on the walls of some craters from high-definition images taken by the Mars Reconnaissance Orbiter (Nikolakakos, & Whiteway, 2015). Lujendra Ojha named these stripes Recurring Slope Lineae and suggested that they might be related to water flow. Recurring Slope Lineae (RSL) are long stripes of darker color with lower reflectivity that are quite active on the surface of Mars. When the temperature rises, RSL begins to form and grow.

When the temperature drops and the weather is cold, it disappears again. That is to say, this kind of slope generally starts to appear in spring, becomes more and more obvious in the whole summer, and gradually disappears in autumn and winter. It had been observed for many years that RSL usually appeared repeatedly in the same place. It was speculated that this mysterious geological phenomenon might be related to flowing water, which was directly related to the important proposition of whether there was water on Mars (Wilson, 2016). Lujendra Ojha and his colleagues had been using remote sensing data from scientific instruments mounted on multiple Mars orbiters to study the geological or hydrological processes of the formation of these slopes and explain their origins.

This time, they finally found evidence. The main achievement of this discovery was to use the data obtained by HiRISE and CRISM on Mars Reconnaissance Orbiter to discover the spectral evidence of hydrated salts on Mars. Spectral analysis has always been a common method in satellite remote sensing. Since each element has its own characteristic spectral line, the target substance can be identified according to the spectral characteristics. First, Lujendra Ojha used HiRISE’s high-resolution photographs to identify the locations of seasonal slopes. Then, he extracted the spectra of these locations and their surrounding areas from CRISM’s detection data. Because the spectrum of RSL had the same absorption characteristics as that of hydrated salts, it was speculated that there were hydrated salts in RSL. Finally, according to the change of hydrated salts content monitored by the spectrum of RSL, it could be determined that these slopes were formed by the action of water flow.

The average distance between Mars and the sun is about 227.9 billion kilometers. The surface is dry, cold and the atmosphere is thin. The surface temperature of Mars varies with geographical location, time of day and surface properties. The temperature is lowest before dawn, then rises rapidly, reaching its highest level just after noon, then drops rapidly in the afternoon, and then slowly drops to its lowest level at dawn. Because of the eccentricity of Mars orbit, the highest temperature in summer in the southern hemisphere of Mars is about 30K higher than that in the northern hemisphere, exceeding 273K in a wide latitude range. The highest temperature is recorded at noon in midsummer, and at 25 degrees south latitude, which refers to the maximum of 295K.

The lowest temperature means that in mid-winter, the temperature of the Antarctic crown can be reduced to 140 K. At depths of several centimeters below the surface, the average daily temperature is 210-220 K; in the winter polar region, the temperature drops to 150 K. Surface temperature varies greatly with day, season and latitude. The highest temperature in summer can reach 17 C, but the average daily temperature does not exceed – 33 C. Because the atmosphere is very thin, it is very common for daily temperature to change by 100 degrees Celsius. In the polar region above 50 degrees north-south latitude, the whole winter temperature is very low (below – 123 C), which makes the main component of the atmosphere CO2 freeze into white sediment, forming the polar cap.

Due to the seasonal cycle of the polar cap, the surface total pressure fluctuation reaches 30% (Edwards, & Piqueux, 2016). Because the surface temperature of Mars is often lower than the freezing point of pure water, it is difficult for pure liquid water to exist on Mars, and the presence of perchlorate reduces the freezing point of aqueous solution. Generally, the freezing point of the aqueous solution after adding ammonium salt can be reduced to about minus 40 degrees Celsius. The optimized formula in the laboratory can reduce the freezing point of the aqueous solution to about minus 80 degrees Celsius.

So even at temperatures far below zero degrees Celsius, the brine on Mars has some mobility. In addition, because of the high content and density of perchlorate in the aqueous solution, the low temperature on Mars makes the aqueous solution viscous. So even if it’s liquid, the viscosity of the aqueous solution can rise by 2 – 3 orders of magnitude, just like the glue with poor fluidity. This is why, despite the large number of RSL observed on Mars, no liquid flow has been found so far. However, the current research has proved the theoretical possibilities of the existence of water, and the practical discovery of water still requires a period of time and further research. Therefore, it can still be believed that there is still liquid water on Mars today, although it has not been found.

To conclude, on account of the significant role of water in maintaining the basic physiological activities of creatures, it has always been regarded as a crucial standard to judge whether there is life in some places, especially in some planets. For instance, the question whether there exists life on the Mars has always been a hot topic concerned by a lot of people including many excellent scholars, and the development of the question changes with the discovery of the evidence which can prove the existence of water on the Mars. Although no one has succeeded in getting water from the Mars, it can still be firmly believed that water actually exists on the Mars, because it has been proved theoretically. Maybe it is “locked” in some covert regions on the Mars and will eventually be found by people, which may even result in the discovery of creatures on the planet.