According to a planetary science paper published by Nature on the 14th, scientists reported the results of detection of internal differences in the front and back hemispheres of the moon. The study is based on gravitational field data from the NASA "Grain Recovery and Internal Laboratory" (GRAIL) mission, which shows that there may be temperature differences deep inside the moon. This means that the moon's "heart" - the interior is asymmetric, which may explain the contrast of the appearance of the moon's surface and the difference between volcanic activities on the front and back of the moon.　　

Conceptual model of internal evolution of the moon

Image source: British "Nature" website

There are obvious differences in geology, volcanic activity, and lunar crust thickness on the front of the moon (i.e. the side facing the earth) and the back of the moon. The front is darker in color and is covered with the moon sea (the basalt plains on the surface of the moon indicate that volcanic activities are more dense); while the back of the moon has a complex terrain and a more rugged terrain. Some researchers have proposed hypotheses that these differences may be explained by differences in the internal structure of the moon, but observational evidence has been lacking.

　　Researchers at NASA's Jet Propulsion Laboratory analyzed data from the GRAIL mission this time, mapping the moon's gravitational response to its orbit, which could reveal the satellite's internal structure. They found that the deformation ability of the front and back lunar mantle was 2%-3%.

　　The researchers then simulated the lunar structure and determined that these figures could be explained by Kelvin's temperature difference of 100-200 in the two hemispheres - the frontal lunar mantle is higher than the backal lunar mantle. They proposed the hypothesis that what maintains this thermal difference may be the radioactive decay of thorium and titanium inside the moon's frontal surface—perhaps the remains of volcanic activity formed on the frontal lunar surface 3 billion to 4 billion years ago.

　　The researchers noted that this method used to explore the interior of the moon could also be used to measure structural differences in other planetary objects, such as Mars, Enceladus, and Io, especially because these methods do not require the probe to land on the surface of the object.

　　The moon actually has "two faces". One side is gentle and quiet, covered with a dark sea of ​​moon; the other side is rugged, like a forgotten wilderness. Scientists have long been speculating whether this surface difference means that there are different "minds" hidden inside the moon. The answer is indeed: the "heart" of the moon is actually asymmetric! Through descriptions of differences and assumptions about causes, scientists unveil the veil of the moon's "double-sided mystery", and at the same time, they also provide a new way to detect the internal structure of celestial bodies. In the future, this approach is expected to be used on Mars, Enceladus and even remote ice satellites, helping us better understand these "silent partners" in the solar system. (Reporter Zhang Mengran)

[Editor in charge: Zhu Jiaqi]