New evidence of the presence of water ice in the polar regions of the Moon

Distribution of water ice on the Moon's polar areas
Distribution of water ice on the Moon’s polar areas

An article published in the journal “Proceedings of the National Academy of Sciences” describes three specific traces of the presence of water ice on the surface of the Moon. A team led by Shuai Li of the University of Hawaii and Brown University used data collected by the Chandrayaan-1 space probe’s Moon Mineralogy Mapper spectrometer to find traces of that ice concentrated in lunar craters at the south pole and spread in an wider area at the north pole.

The question of the presence of water on the Moon has become a source of discussion during the last decade thanks to new analyzes of rocks brought to Earth during some Apollo missions and to the surveys of some space probes. As for the south pole of the Moon, in 2009 NASA announced that its Lunar CRater Observation and Sensing Satellite (LCROSS) probe had detected the presence of water in the Cabeo crater region.

The Moon Mineralogy Mapper (M3) instrument was used by the Chandrayaan-1 space probe, a mission of the ISRO Indian space agency conducted between 2008 and 2009, but M3 was a contribution from NASA. For this reason the data collected were already analyzed in the USA and Shuai Li, together with Ralph E. Milliken, another member of the team that conducted this research, already announced evidence of the existence of large amounts of water in ancient lunar volcanic deposits in an article published in the journal “Nature Geoscience” in July 2017.

This time, the analysis of the data collected by M3 focused on the Moon’s polar areas and according to the researchers there’s water ice on the surface or at least no more than a few millimeters deep in 3.5% of the so-called cold traps, where temperatures never exceed -157° Celsius (-250° Fahrenheit) due to the fact that they’re in a perennial shadow. M3 not only could detect the reflective properties of ice but also directly measure the way in which water absorbs infrared light, which is different depending on whether it’s in the form of ice, liquid or vapor.

The image (NASA) shows the distribution of ice detected by the M3 instrument at the Moon’s south pole (on the left) and at the north pole (on the right). The blue color represents the areas where ice was localized on the surface, where the gray scale corresponds to the temperature with darker tones representing cooler areas and lighter tones representing warmer areas. Ice is concentrated in the coldest areas.

One of the questions researchers have been asking themselves since the first signs of the presence of water on the Moon was announced is about its origin. A theory that doesn’t concern our satellite only is that it was brought there by asteroids or comets, according to a more specific hypothesis instead water particles that exist in the lunar atmosphere, which exists even if it’s extremely thin, froze and in the course of a time that could be very long they accumulated in cold traps.

According to a research published in July 2018 in the journal “Astrobiology”, about 3.5 billion years ago on the Moon there was a volcanic activity that released various gases and water vapor on the surface so the hypothesis of an accumulation in cold traps could be plausible. In this case, those deposits could be mostly very old as the Moon’s atmosphere has become more rarefied with the passage of time.

This new announcement revamps the idea of ​​using the water existing on the Moon for manned missions and even by possible colonies. There are several new projects to send astronauts to the Moon not only by NASA but also from the Chinese, who are making big steps forward in their space program, and from the Russians, who keep on announcing possible missions but are accumulating delays all the time. The ice on the surface would be relatively easy to pick up and therefore very useful so more than ever we can expect new studies.

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