A new study could have finally unlocked one of the mysteries of Earth’s moon: why the “dark side” we never see is such a strange shape.
Our moon is ‘tidal blocked’ to Earth, which means it rotates at the same speed as our planet orbits, so one side is never visible.
The far side, facing us, has a paler surface, with fewer black spots, than astronomers used to believe were “seas” on the surface.
It also has a thicker crust.
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One study suggests that differences on the “other” side of the moon may be due to radioactivity in rocks on the near side of the moon.
Scientists believe that the Earth-Moon system was formed when a Mars-sized body called Theia crashed into the young Earth, and the moon formed from debris.
In the 1950s and 1960s, space probes returned ‘far side’ images showing that it had no ‘maria’ (seas), with only 1% covered in maria compared to around 30% on the near side.
Researchers believe that lack of maria is associated with a particular form of rock signature known as KREEP, which is short for potassium-enriched rock (chemical symbol K), rare earth elements (REEs, including cerium, dysprosium, erbium, europium, and other elements that are rare on Earth) and phosphorus (chemical symbol P).
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Researchers from the Earth-Life Science Institute at the Tokyo Institute of Technology and the University of Florida analyzed KREEP in the laboratory.
This study shows that, in addition to improved heating, the inclusion of a KREEP component in rocks also reduces their melting temperature.
The find hints at ancient volcanic activity and could also offer important information about the history of the moon and Earth.
ELSI co-author Matthieu Laneuville said: “Due to the relative lack of erosion processes, the Moon’s surface records geological events from the early history of the solar system.
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“In particular, the regions on the near side of the moon have concentrations of radioactive elements like U and Th, unlike anywhere else on the Moon.
“Understanding the origin of these local U and Th enrichments can help explain the early stages of the moon’s formation and, as a consequence, conditions on early Earth.”
The results of this study suggest that the moon’s KREEP-enriched maria has influenced lunar evolution since the moon formed.
Laneuville believes that evidence for these types of self-amplifying, non-symmetrical processes could be found on other moons in our solar system, and may be ubiquitous on rocky bodies throughout the universe.