What’s in the moon’s core? There may be sulfur.

In addition to iron and nickel, the Earth’s metal cores are known to contain considerable light elements such as carbon, sulfur and silicon. But the composition of the moon’s metal core has been unknown, and even the moon’s denuclearination is a matter of constant controversy.

Recently, professor Huang Fang’s team from the University of Science and Technology of China, in collaboration with his counterparts in the United Kingdom and Ireland, combined with the results of stable isotopes and experimental rock, speculated that the moon’s metal cores may contain sulfur, but not much carbon.

Isotope geochemistry, which provides valuable information for the study of the formation of the Earth and the Moon

The moon’s formation is thought to be related to a huge asteroid hitting The Earth, a process known as a “big collision of the moon.” Asteroids hit the Earth with high energy, causing the splashing material to become gasified, so the volatile elements of these materials escape into the vast cosmic deep space and out of the Earth’s lunar system.

In this volatile element escape process, for a certain element, the light isotope runs fast and the heavy isotope runs slowly, so the light isotope gravity isotope of the moon is more likely to be lost. The Earth is not, although there has been a violent impact, but because of the mass of the earth, more gravity, volatile elements escape less, basically retain the pre-impact isotope composition. Therefore, isotope geochemistry provides valuable information for the study of the formation of the Earth and the Moon.

There are differences in isotope composition between the Earth and the moon.

The moon is similar to Earth, with silicate shells and crusts and metal cores. Geochemical studies have found that the volatile elements (the elements that are easy to gasify escape) in the silicate portion of the moon (bulk silicate moon, hereafter referred to as BSM) are much lower than the silicate portion of the Earth (the bulk silicate earth is called BSE). Moreover, the isotope composition of these volatile elements in BSM is heavier than that of BSE.

As shown in the figure below, the horizontal axis represents the semi-condensed temperature of the element, and the lower the temperature, the more volatile the element is; It can be seen that the semicondensation temperature of different elements is different, but the difference in isotope composition is not consistent with the semi-condensation temperature, for example, copper (Cu) semi-condensation temperature is higher than potassium (K), niobium (Ga) and niobium (Rb), but the difference in Cu isotope composition between BSM and BSE is greater than that of K, Ga and Rb.

What's in the moon's core? There may be sulfur.

How exactly did this difference come about? What is the implication of the formation and evolution of the moon?

Impact-coagulation-gasification models are commonly used to explain the moon’s chemical composition, but it ignores the moon’s metal-core formation process. Moon nuclei may explain the abnormality of the Cu isotope: because Cu and Zn are both pro-iron pro-sulfur elements, easy to enter the metal core, and K, Ga and Rb are pro-stone elements that do not enter the metal core, but it is not known the size of isotope fractionation when the metal melt is separated from the moon magma ocean.

The difference in isotope composition between earth and the moon can be explained when the nucleus contains sulfur that month.

Based on such thinking, Huang’s team and its international partners conducted experimental studies on the effects of lunar nuclear formation on isotopes, hoping to further restrict the presence of substances in the moon’s nucleus.

They accurately measured the Cu and Zn isotope fractional coefficients between metal melts (representing the moon’s core) and silicate melts (representing moons). They found that when the nucleus contained sulfur in the month, the formation of the moon’s nucleus could make BSM’s Cu isotope composition more weighted, a result that is a good explanation for the differences in isotope composition between the Earth and the moon.

The paper entitled “The effect of the matter of the core on the cu and Zn isotope sors of the thete Moon” was published recently by Geochemical, an international geochemistry journal Perspective Letters on (Geochem.) Persp. Let. 12, 12–17)。

What's in the moon's core? There may be sulfur.

The study of isotope geochemistry predicts that the moon nucleus contains light elements such as sulfur. Another recent study, published in Nature-Geoscience, suggests that the difference between the sulfur-containing moon core and the moon’s bollbes can explain the content of the platinum element in the lunar sample (Brenan et al). 2019 Nature, which also predicted that the moon’s core might contain sulfur, confirms new understandings among TheRUs. This understanding has important scientific value.

The moon may have had a very short magnetic field, too.

The Earth has a huge magnetic field that protects life from solar activity, and the maintenance of the Earth’s magnetic field is related to light elements in the earth’s core. In general, the more light elements, the more likely the magnetic field may be sustained for long periods of time. But people have been unsure whether the moon has had a global magnetic field. The study of isotope geochemistry supports the possibility that the moon may have had a very short magnetic field, which is important for understanding the environment in which the inner solar system planets gave birth to life.

This work also points to the effect of lunar nuclear formation on lunar components, indicating that in studying the chemical composition of the moon, the collision-gasification process should not only be considered, but also the process of the moon’s nuclear separation.

It should be emphasized that the above understanding of China’s lunar research also has a very good enlightenment. Much of the study of the moon is based on lunar samples brought back by the U.S. Apollo program, but the Location of the Apollo Program is very limited, from the moon to the Earth side, never reached the moon on the back of the Earth side.

Therefore, it is possible that with the implementation of China’s plan, it will change the understanding of important scientific issues such as lunar formation and the evolution of the Earth’s lunar system. The sampling return of China’s lunar engineering is very important, especially for isotope studies from the lunar back samples, which can provide key information for lunar formation.

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