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Astronomers have found out what the shadows on the moon hide

A new study conducted by employees of the American space agency NASA has helped to reveal one of the most intriguing secrets of the Moon. Scientists have found that on the surface of this satellite of the Earth, even in the most abnormal conditions, water can remain in the form of ice or frost.

The study is published in the journal Monthly Notices of the Royal Astronomical Society, and it is briefly described on the website of the NASA Jet Propulsion Laboratory.

One of the most exciting mysteries of the Moon for many years is the question: is there water on the surface of this satellite? Recent studies have shown that this option is not excluded. At least, the radar signals clearly indicate this.

At the same time, scientists note that the conditions on the surface of the Moon are too extreme for water. If it is very cold there at night, then it is extremely hot during the day. Therefore, water can freeze during the period when it is on the dark side of the Moon, but it must necessarily evaporate very quickly under the influence of hot sunlight, once on the illuminated side.

A new study provides an explanation for this phenomenon. Its authors paid attention to the surface shadows. The moon is densely covered with craters and rocks, which creates a certain “roughness” of the surface, casting shadows. As an example, NASA showed a photo taken by the Apollo 17 mission in 1972. The shadows are clearly visible in the picture.

Astrophysicists believe that it is these cold shadows that can allow water ice to accumulate in the form of frost even during the daytime when the heat should destroy it.

“More than a decade ago, the spacecraft detected the possible presence of water on the Moon's daytime surface, and this was confirmed by the SOFIA Stratospheric Observatory for Infrared Astronomy in 2020,” says Bjorn Davidsson from the Jet Propulsion Laboratory in Southern California. “These observations were initially illogical: water should not “survive” in such harsh conditions.”

In a new study, Davidsson and his team suggest that the shadows created by the ”roughness“ of the lunar surface serve as a shelter for water ice. And the exosphere of the Moon also helps to preserve its appearance — rarefied gases that function as a thin atmosphere.

Until now, it was believed that water molecules could be captured by a stone or so-called impact glass, which are formed when meteorites hit the surface at extremely high temperatures and pressures. The water fused into these materials can remain on the surface even when heated by the Sun and will reflect a radar signal similar to that recorded by the SOFIA device.

However, recent observations have shown that the amount of water on the surface of the Moon decreases before noon and increases in the afternoon. This indicates that it is able to move from one place to another during the lunar day. And this is not possible if the water is trapped inside a moonstone or impact glass.

In a new study, this computer model was revised. It took into account the “roughness” of the surface, and the simulation showed that frost can form in small shadows, due to which the distribution of water on the surface can also change during the day.

And since there is no dense atmosphere on the Moon to distribute heat over the surface, extremely cold, shaded areas with temperatures up to minus 210 degrees Celsius can safely coexist with areas heated by the Sun to 120 degrees Celsius.

As the Sun moves during the lunar day, surface frost, which can accumulate in cold shaded areas, is slowly exposed to sunlight and circulates in the exosphere of the Moon. Then the water molecules freeze again on the surface, accumulating in the form of frost in other shaded places.

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