Inside the dark, polar craters of the moon, water is not as invincible as expected, scientists argue

Inside the dark, polar craters of the moon, water is not as invincible as expected, scientists argue

A high resolution outdoor gravity map based on data returned by NASA's Gravity and Interior Recovery Laboratory mission, superimposed on the ground based on NASA's Lunar Reconnaissance Orbiter altimeter and camera data . The view is to the south, with the south pole near the horizon in the upper left. The terminator crosses the eastern edge of the Schrödinger basin. Gravity is painted in areas that are on or near the night side. Red corresponds to mbad excesses and blue to mbad deficits. Credit: NASA scientific visualization study.

The region of the south pole of the Moon is home to some of the most extreme environments of the solar system: it is unimaginably cold, mbadively craterized and has areas that are constantly bathed in sunlight or in the dark. This is precisely the reason why NASA wants to send astronauts there in 2024 as part of its Artemis program.

The most attractive feature of this region further south is the craters, some of which never see the light of day reaching their floors. The reason for this is the low angle of sunlight that hits the surface at the poles. For a person standing at the southern lunar pole, the Sun would appear on the horizon, illuminating the surface on its side and, therefore, mainly brushing the edges of some craters, leaving their deep interiors in the shade.

As a result of permanent darkness, NASA's Lunar Reconnaissance Orbiter (LRO) has measured the coldest temperatures in the solar system within these craters, which have been known as perfect environments to conserve material such as water for eons. Or so we believed.

It turns out that although the temperature drops to -388 degrees Fahrenheit (-233 degrees Celsius) and presumably can keep frost trapped in the ground virtually forever, water is slowly leaking from the thinner top layer (thinner than the width of a red blood cell) of the moon's surface. NASA scientists recently reported this finding in a paper in the magazine. Geophysical Research Letters.

"People think that some areas in these polar craters trap water and that's it," said William M. Farrell, a plasma physicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who led the frost investigation. moles. "But there are solar wind particles and meteoroids that hit the surface, and they can cause reactions that normally occur at warmer surface temperatures. That is something that has not been emphasized."

Unlike Earth, with its luxurious atmosphere, the Moon has no atmosphere to protect its surface. Then, when the Sun sprinkles charged particles known as the solar wind in the solar system, some of them bombard the surface of the Moon and lift water molecules that bounce back to new places.

Similarly, rebel meteoroids constantly crash against the surface and tear off the ground mixed with chunks of frozen water. The meteoroids can shed these particles from the ground, which are many times smaller than the width of a human hair, at a distance of 19 miles (30 kilometers) from the place of impact, depending on the size of the meteoroid. The particles can travel so far because the Moon has a low gravity and there is no air to slow things down: "So, every time you have one of these impacts, a very thin layer of ice grains extends across the surface, exposed to heat from the sun and space environment, and eventually sublimated or lost to other environmental processes, "said Dana Hurley, a planetary scientist at the Johns Hopkins University Laboratory of Applied Physics in Laurel, Maryland.

While it is important to keep in mind that even in shaded craters, water is slowly leaking, water may also be added, the authors of the article point out. The icy comets that crash against the Moon, plus the solar wind, could replace it as part of a global water cycle; That is something scientists are trying to figure out. Also, it is not clear how much water there is. Are you sitting alone on the top layer of the Moon's surface or does it extend deep into the Moon's crust, scientists ask?

Either way, the top layer of the polar crater floors will be reworked for thousands of years, according to the calculations of Farrell, Hurley and his team. Therefore, weak patches of frost that scientists have detected at the poles using instruments such as the LAMP instrument of the LRO Alpha Mapping Project (LAMP) of LRO could be only 2,000 years old, instead of millions or billions of years as some might expect, Farrell's team estimated. "We can't think of these craters as ice dead spots," he said.

Inside the dark, polar craters of the moon, water is not as invincible as expected, scientists argue

Crater of permanent shadow on the moon. Credit: NASA's Goddard Space Flight Center.

To confirm the calculations of his team, Farrell said, a future instrument capable of detecting water vapor should find, above the surface of the Moon, one to 10 water molecules per cubic centimeter that have been released by impacts.

The good news for future lunar exploration

For the next science and exploration, the dispersion of water particles could be great news. This means that it is possible that astronauts do not have to submit themselves or their instruments in the harsh environment of crater soils in the shade to find a soil rich in water; They could find it in nearby sunny regions.

"This research tells us that meteoroids are doing part of the work for us and transporting material from the coldest places to some of the border regions that astronauts can access with a solar exploration vehicle," Hurley said. "It also tells us that what we have to do is surface on one of these regions and get first hand information about what is happening."

Reaching the lunar surface would greatly facilitate the evaluation of how much water there is on the Moon. Because identifying water from afar, particularly in shadowy craters, is a sensitive matter. The main way scientists find water is through remote sensing instruments that can identify what chemical elements things are made from according to the light they reflect or absorb. "But for that, you need a light source," Hurley said. "And, by definition, these permanently shaded regions don't have a strong one."

Understanding the water environment on the moon

Until NASA astronauts return to the Moon to dig up some land, or the agency sends new instruments near the surface that can detect floating water molecules, the theory of the research team on the influence of meteoroids on the Environment inside shaded craters could help eliminate them. in some of the mysteries surrounding the water of the moon. It has already helped scientists understand if the upper surface waters are new or old, or how they can migrate around the Moon. Another thing that the impacts of meteoroids on the crater floors could help explain is why scientists are finding patches of thin frost diluted in regolith, or lunar soil, instead of ice blocks of pure water.

Although questions about water abound, it is important to remember, Farrell said, that it was only in the last decade that scientists found evidence that the Moon is not a dry and dead rock, as many had long badumed. The LRO, with its thousands of orbits and 1 petabyte of returned scientific data (equivalent to about 200,000, high-definition movies and feature films broadcast online), has been critical. So has the lunar crater observation and detection satellite (LCROSS), which revealed frozen water after crashing on purpose in the Cabeus crater in 2009 and releasing a tuft of material preserved from the crater floor that included water.

"We suspect that there was water at the poles and we learned safely from LCROSS, but now we have evidence that there is water at mid-latitudes," Farrell said. "We also have evidence that there is water coming from the impacts of micrometeoroids, and we have frost measurements. But the question is, how do all these water sources relate?"

That is a question that Farrell and his colleagues are closer to answering than ever.

Scientists discover one of the mechanisms of water formation on the moon.

More information:
W.M. Farrell et al. The young age of the LAMP observed in polar cold traps, Geophysical Research Letters (2019). DOI: 10.1029 / 2019GL083158

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NASA Goddard Space Flight Center

In the dark, polar craters of the moon, water is not as invincible as expected, scientists argue (2019, July 23)
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