A few minutes after taking the first step on the moon, Neil Armstrong took the time to describe the surroundings, noting that the surrounding landscape is very reminiscent of the high desert in the United States – a nickname for the mountainous region of the Mojave Desert, Northern California and neighboring states. Even today, more than 50 years after the first visit of humans to the moon and countless studies and observations, there is no doubt that the moon is a completely desert body. But two new studies released tonight (Monday) show another similarity between the moon and the deserts on Earth. Even there, it turns out, there is more water than you see at first glance.
The search for water on the moon is not new. In 2008, the Indian spacecraft Chandrayaan-1 launched a projectile into the lunar soil near the South Pole, sampled the soil that rose from the explosion and identified a small amount of water molecules in it. About a year later, the American spacecraft LCROSS carried out a similar operation with a more intense explosion, which confirmed the findings and even discovered more impressive amounts of water in another area near the South Pole. In these studies, the composition of the materials was based on infrared radiation with a wavelength of three microns (0.003 millimeters), which makes it possible to identify the chemical signature of a hydroxyl ion (-OH). Hydroxyl is part of the water molecule, H2O, however hydroxyl ions also exist separately from water molecules, as part of the minerals that make up the rocks of the moon.
Because of this, the researchers could not determine with certainty that these were indeed water molecules in the lunar soil, nor could they accurately assess which part of the OH bonds they identified were water and which part are ions that make up the minerals and are not related to water. In recent years, the search for water on the moon has gained momentum, especially in light of plans to re-launch humans to the moon, and perhaps even establish a permanent base there. Both studies now published have used a variety of observational and data analysis methods, and both reinforce the hypothesis that not only is there surface water of the moon in the polar regions, they are also present there in greater quantity than previously thought, and may also be more available.
The telescope hovers far above the atmospheric water vapor. SOFIA plane with the open telescope door near the tail
The first study Based on observations in the flying telescope of the US space agency, NASA, and the German space agency, DLR. The telescope, known as the SOFIA (SOFIA) stands for a dedicated Boeing 747, which allows the sky to be photographed from a height of about 12 kilometers, far above the water vapor in the atmosphere, which scatter the sub-radiation. -Red and do not allow such observations from the ground.
In the airborne observation, the researchers used infrared radiation with a wavelength of six microns, which allows the distinction between a hydroxyl ion and a water molecule. The research team was led by Casey Honniball, who is pursuing her postdoctoral fellowship at the US Space Agency’s research center.
Honibol and colleagues scanned several areas of the moon in the 2018 flying plane telescope, comparing the observation results to those obtained from measuring rocks and minerals in the laboratory, when their water content is known. After more than two years of analyzing the data, it was concluded that the water concentration in the sampled areas is between 200 and 400 parts per million. That is, given the density of lunar soil in this region, out of every kilogram of lunar soil in this region, at least 200 milligrams are water molecules. The researchers estimate that in the areas near the South Pole the water content may be even higher, up to 1.3 grams per kilogram, compared to a concentration ten times lower in the samples brought by the astronauts in the Apollo missions, from areas much closer to the moon’s equator.
Distinguish between water and sand. Honibol (left) while flying to photograph the moon with a SOFIA telescope
The water on the surface of the moon cannot be in a liquid state and not even as ice. In the absence of an atmosphere, every drop of water on the moon evaporates or immediately takes off into space. Even individual water molecules that are fixed to the surface and cannot evaporate, are prone to decomposition due to the intense radiation that constantly hits the moon. Honibol and colleagues estimate that most of the water they identified is trapped within glass crystals that are formed when tiny meteorites hit the moon’s soil and cause local melting of the sand into glass. A smaller portion of the water molecules are probably trapped between the moon’s sand grains in a way that protects them from exposure to environmental conditions. About 30 percent of the sand on the moon’s surface is made up of such glass grains, so there is a lot of water that may be trapped inside them. However, it is not clear how much of this water is available for use by humans who will establish a colony on the moon. Extracting them from glass or sand crystals can be complex, require complex technology and consume a lot of energy.
The second study It is the result of a long-running collaboration between three researchers: Paul Hayne of the University of Colorado, Oded Aaronson of the Weizmann Institute of Science, and Norbert Schörghofer of the Planetary Institute in Arizona. In this study, the researchers examined the “cold traps” – areas cold enough to “capture” and freeze water molecules before they evaporate into space. These are the only places on the moon where the water molecules are protected from the sun and do not evaporate from the surface. They found that these cold traps are more common in the polar regions of the moon than previously thought, indicating the possibility that these regions have relatively much water, and in the case of this study – this also means that they are much more accessible and available.
Because the moon has no atmosphere, its face is littered with craters in a variety of sizes, scars from meteorites and asteroids for billions of years. Because the inclination of the moon on its axis is very small, there are craters in the areas near the poles that the sunlight never penetrates. These craters are called “permanent shadow regions” or PSR for short. While in other regions of the moon the temperature reaches more than 120 degrees Celsius at the peak of the lunar “day” and less than 150 degrees Celsius below zero at the peak of the “night” (each lasting about two weeks ours), within these craters the temperature remains low. In the coolest craters, temperatures of only 15 degrees were measured above absolute zero, that is, about 258 degrees below zero degrees Celsius.
When the sun is less than above the horizon, the shadow can be seen in the many craters near the North Pole. Photo of the LRO satellite
The three researchers analyzed more than 5,000 photos of craters in the lunar poles taken by the American satellite LRO that has been orbiting the moon since 2009. They analyzed the topographic data like the depth of the crater by the length of the shadows at different shooting times, and cross-referenced the data with geological data. Of the rocks, and with temperature measurements in selected craters performed in an infrared LRO instrument. Based on a weighting of all the data, they developed a model that allows to calculate the probability that a particular crater is a cold trap – that is, its inner part is very cold and it may trap water molecules and accumulate ice gradually. “Until now it was known that ice accumulates mainly in the largest craters. In this work we were able to calculate the stability of the ice as a function of the size of the crater, and we show that there are many small craters that have frozen water,” Aaronson explained to the Davidson Institute. “We estimate that about 20-10 percent of all cold traps on the moon are small-scale craters, from a few kilometers to meters and even tens of centimeters.”
The researchers examined the dispersal and density of such craters in the region of the two poles of the moon, and estimate that the area of cold traps on the moon is about 40,000 square kilometers – more than double the estimate in a previous study, which also included Scherghoff and wine. About 60 percent of this area is in the circle of the moon’s south, although researchers in the Arctic found a higher rate of small craters. The researchers also showed that many PSR craters are not cold traps because the temperature in them is not cold enough, and these are mostly PSR craters that are relatively far from the poles.
Another important finding is the accessibility of water in these craters, if and when humans come to explore them, as planned for example in the American “Artemis” program, which plans to land humans on the moon in the coming years. “Because there are a lot more small craters than large craters, the chances are much higher to land close enough to a small crater that is a cold trap,” Aaronson explains. “Also, the ice in these craters is much more accessible, because the large craters often have very steep sides, which are not suitable for crossing on foot or in an SUV, while the smaller craters are usually characterized by a milder slope.”
Where did the water come from to the moon? Researchers estimate that the water now on the moon’s surface has accumulated in slow processes over its more than 4 billion years of existence. One possible source of water is a collision of comets in the moon. Comets are mostly made of ice, and when they collide with the moon, most of the water evaporates into space, although small amounts may be trapped on the surface, and even reach the poles and get caught in the cold traps. Another possibility is the formation of water molecules with the help of radiation: the solar wind contains protons, and each proton is actually a nucleus of a hydrogen atom. Minerals on the moon contain hydroxyl ions (-OH), some of which are even formed from the impact of a proton on an oxygen atom. Injury of a proton from the sun to a hydroxyl ion under the right conditions can form a molecule of H2O, i.e. water. The probability of such a single event is very low, but for billions of years quite a few such events probably occur. Another possibility is the release of water molecules trapped in rocks deep in the moon, for example in volcanic events. Here, too, most of the molecules are lost to space, but some may be trapped in the surface and in the cold traps.
The findings of both studies align well with the theories of very slow and gradual water accumulation. So that they can determine which model, or which models are better suited to water formation, the researchers hope that manned or robotic missions can bring samples from the water to Earth. This will make it possible to analyze, for example, their isotopic composition, understand their origin and perhaps even shed new light on the question of how the moon was formed.
If we wanted to use the water on the moon to produce drinking water, oxygen and fuel for the benefit of a manned colony, it would seem inevitable to have access to the ice deposits in the great craters. However at least in the first stage the main need of access to water is for research. Frozen water in the cold traps in craters may be much more available than the water observed in the Honibol study, which is probably trapped in glass or between sand grains. As mentioned, landing in the crater area of the South Pole is one of the planned missions of the Artemis program. “Thanks to our research, we will be able to help choose a landing site near accessible small craters that contain ice, without having to risk access to a deep crater,” Aaronson concludes.
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Moon, Tucson, Lunar water, Ice
World news – GB – Water on the Moon: Researchers have found encouraging findings