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Chinese lunar Chang E5, the first probe to detect water on the moon during the mission

Using a device that detects water by measuring the reflectance spectrum of the moon and rocks, Changhai 5 was able to find it near its landing point in the storm ocean near the moon.

The definitive detection of water on the moon from orbit, after several uncertain results by telescopes and other missions, was first performed by the Chandrayan-1 mission in India using NASA’s lunar mineralogical mapping tool. The discovery of Chandrayan-1 was announced in September 2009, and since then, water on the moon has been extensively mapped by other orbiters, such as NASA’s Reconnaissance Orbiter, which has been operating since 2009.

Map the abundance of hydrogen at the poles of the moonA map of the abundance of hydrogen (a sign of water) at the moon’s poles; The bright parts, which indicate the greater abundance of hydrogen, do not correspond to the current poles of the moon (black dots), which probably indicate the location of the ancient poles of the moon (white dots).

But before Changhai 5, no other mission was able to detect water during the lunar surface mission. Astronauts on the Apollo missions returned water samples to Earth in the 1970s, but the presence of water in them was not detected until decades later, when laboratory equipment was strengthened.

One of the reasons for the delay in discovering water on the moon was the long distance between surface missions; China’s Changhai 3 mission in 2013 was the first surface-level mission in 37 years. Prior to that, the Soviet Luna 24 mission in 1976 was the last lunar probe.

With the launch of new initiatives such as NASA’s Cargo Merchant Service, which includes several missions scheduled for the coming years, surface missions will accelerate. NASA is also preparing to send an ice-hunting astronaut named Viper in late 2023, which will land west of the Noble Crater near the Moon’s south pole.

Water has a distinctive spectral signal that was expected to be recorded in Changhai 5 mineralogical spectrometer measurements designed to identify water. According to speakers at the mission’s Chinese team’s press conference at the Chinese Academy of Sciences, the main challenge was the extreme heat of the moon, which initially obscured the measurements.

For this purpose, the researchers used a “heat correction model” and were able to detect the spectral signal of water at a wavelength of 2.85 micrometers. The amount of water found is very small, about 120 units per million in soil and 180 units per million in rock.

Chang E 5 spectroscopy of lunar soil Figure A shows the landscape of the sampling range. The magnified section shows a rock that has been sampled spectrally. Figure B shows the exact location of spectral sampling with colored rectangles. Red rectangles have the least water frequency and blue rectangles have the highest water frequency. Images of the three samples D9, D11 and D14 can be seen around the main image.

These results were confirmed using a sample of lunar soil that Changhai 5 returned to Earth in December 2020. This was the first example of lunar material being returned to Earth after the Luna24 mission in 1976.

According to officials at the press conference, the ratio of water in the moon’s soil in the initial review of the returned samples is the same as Changhai 5’s finding at the lunar surface. Surface water on the moon is attributed to solar winds, which are a constant stream of charged particles emitted from the sun. But its origin seems to be more complex in the rocks of the moon and probably has its roots inside the moon.

Examining the composition of the rocks and comparing them with the results of orbital remote sensing shows that the rocks may have been separated from an older basaltic unit and moved to the Changhai 5 landing site.

“The lower water content in the soil compared to lunar rocks could indicate the outflow of gas from the mantle magma reservoir below the Changhai 5 landing site,” the press conference said.

Sample of Chang E 5 from the soil of the moon

The discovery of surface water in the hurricane ocean area may be due to volcanic eruptions, which could have carried water, the researchers said. These volcanic materials contain potassium (K in the periodic table of elements), rare earth elements (REE) and phosphorus (P), abbreviated as “KREEP”.

Changhai 5 tried to determine the age of volcanic activity on the moon using KREEP materials, but no new results were announced at the press conference.

Related article:

China has completed several successful missions to the moon in recent years; For example, Changhai 4, which was the first surface around the moon and spent more than 1,000 days there. It plans to return lunar specimens to Earth by sending Changhai 6 in 2024.

New research on Changhai 5 data has been led by Hongli Lin and Yangtin Lin of the Institute of Geology and Geophysics at the Chinese Academy of Sciences. The study is published in the journal Science Advances.


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