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Water in polar craters is less invincible than expected



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Inside Dark, Polar Moon Craters

A permanently shadowed lunar crater. Credit: NASA's Goddard Space Center

The area of ​​the southern pole of the Moon is home to some of the most extreme environments in the solar system: it is inconceivably cold, massively cratered and has areas that are constantly bathing in sunlight or in darkness. That's why NASA wants to send in 2024 astronauts under the Artemis program.

Due to a permanent theme, the NASA Lunar Reconnaissance Orbiter (LRO) measured the lowest temperatures in the solar system in these craters, which have become known as the perfect environment for conserving materials such as water for eons. That's what we thought.

It turned out that, despite the temperature dropping to -388 degrees Fahrenheit (-233 Celsius) and presumably retaining the frost sealed in the ground almost forever, water slowly escapes from the highest, super thin layer (thinner than the red blood cell width) surface of the Moon. NASA scientists recently reported this finding in the Geophysical Research Letters.

Polar fragile craters

This animation shows evidence of high concentrations of hydrogen in the southern half of the Moon. In 1998, NASA's Lunar Prospector mission identified hydrogen on the Moon, which was an early demonstration of potential ice deposits. As you can see in this video, Prospector data showed significantly more hydrogen (shown in blue) on the southern half of the Moon.
Credits: NASA's Center for Scientific Visualization Goddard Space Flight Center

"People think that some areas in these polar craters are catching 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 study of frost. "There are sunny particles and meteoroids that hit the surface and can trigger reactions that usually occur at warm surface temperatures. This is something that has not been highlighted. "

Water is not as unbearable as expected, according to scientists

A high-resolution gravity free-air chart based on data returned from the NASA's Gravity Recovery mission and an internal laboratory covered with field-based viscometer and camera data. The view is up south, with a south pole near the left horizon. Terminator crosses the eastern edge of the Schrödinger basin. Gravity is painted in areas that are in the night or near it. Red corresponds to massive excesses and blue to massive deficits. Credits: NASA's Studio for Scientific Visualization

Unlike Earth, with its plush atmosphere, Moon has no atmosphere to protect its surface. So, when the Sun is sprayed into the solar system by the charged particles, known as the sun, some of them bombard the surface of the moon and lift up aquatic molecules that reflect on new sites.

Likewise, frostbite meteoroids are continually broken into the surface and dig out the soil mixed with frozen pieces of water. Meteoroids can make these soil particles – which are several times smaller than the width of the human hair – crash up to 30 miles from the impact site, depending on the size of the meteoride. The particles can travel so far, because the Moon has low gravity and there is no air that slows down things: "So every time you have one of these effects, a very thin layer of ice grains spread out over the surface, exposed to heat the Sun and the space environment and eventually sublimed or lost to other environmental processes, "said Dana Hurley, a planetary scientist at the Johns Hopkins University of Applied Physics at Laurel, Maryland.

Although it is important to note that even in shady craters, water slowly evaporates, it is possible that water is added, the authors find. Ice comets that run into the moon, next to the sun, could restore it as part of a global water cycle; scientists are trying to figure out. In addition, it is not clear how much water it is. Are they sitting only in the upper layer of the surface of the moon or reaching deep into the moon's crust, do scientists wonder?

However, the highest layers of the soil of polar craters have been transformed for thousands of years, according to Farrelle, Hurley and their teams. Therefore, weak stains, which scientists have detected on poles with instruments such as the LAMP's Lyman Alpha Mapping Project (LAMP), can only be 2,000 years old, rather than millions or billions of years, than they could expect, Farrell's team estimated. . "We can not think of these craters as an iceberg," he warned.

To confirm his team's calculations, Farrell said, a future instrument to detect water vapor would have to find an area of ​​1 to 10 aquatic molecules per cubic centimeter, released from impacts, above the lunar surface.

Good news for the future exploration of the Moon

For future science and research, dispersion of water particles could be great news. This means that the astronauts may not have to expose themselves to the harsh environments of shady craters by themselves and with their instruments to find water rich in land – they could only be found in sunny regions nearby.

"This study tells us that meteoroids work a bit for us and transport materials from the coldest places to some of the border regions, where astronauts can access it with a rover to solar energy," Hurley said. "It also tells us that we have to come to the surface of one of these regions and get first-hand information about what's going on."

If we get to the surface of the moon, it would be much easier to estimate how much water is on the Moon. Because the recognition of water from afar, especially in permanently shaded craters, is a difficult task. The main way in which scientists find water is by means of remote sensing instruments that can recognize which chemical elements are made on the basis of light that they refuse or absorb. "But you need a source of light for that," said Hurley. "And by definition, these permanently shaded regions do not have a strong one."

Understanding the aquatic environment on the Moon

As NASA's astronauts do not return to the moon to dig some soil, or the agency sends new instruments near the surface that can squeeze floating water molecules, the research group theory on the impact of meteoroids on the environment in shady craters could help to break away. in some of the secrets surrounding the moon. Scientists have already helped to understand whether the highest surface water is new or old, or how it can move around the Moon. Another thing that can be explained by meteoroid effects on the soil in the crater is why scientists are looking for a patch of soft frost diluted in the regolithic or moonland instead of pure water ice blocks.

Although there are questions about water, it's important to remember, Farrell said, that scientists have found that the moon is not a dry, dead rock, as many have long suspected. LRO, with its thousands of orbits and 1 petabytes of scientific data returned (equivalent to approximately 200,000 high-definition feature films that are played online), was crucial. This is also the observation of the LCROSS, which detected frozen water after deliberately falling into Cabeus crater in 2009 and dropping the coat of canned material from the bottom of the crater, which included water.

"We suspected the water is in the water and it's certainly learned from LCROSS, but now we have evidence that the water is in the middle latitudes," Farrell said. "We also have evidence that water comes from micrometeorological effects and that we have frost measurements. The question is, how are all these water resources connected? "

This is the question with which Farrell and his colleagues are closer than ever.

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