The formation of the moon remains a mystery, but a new study may provide answers. They lie hidden inside the celestial body.
Tucson - About 4.5 billion years ago, the moon was formed when a small planet called Theia collided with the young Earth and broke a piece out of it. The resulting debris bonded, cooled, and solidified, resulting in the formation of the moon. There is widespread agreement among scientists about this process. But what happened after that? How did the moon evolve into the celestial body we know today? There are different views on these questions in the research community.
Research teams from the Lunar and Planetary Laboratory at the University of Arizona are trying to shed light on the matter with a study. The study, published in the journal
Nature Geoscience
, argues that the moon formed quickly and hot and was therefore likely covered by a magma ocean. This molten rock cooled and solidified, forming the lunar mantle and the bright crust we see in the sky during a full moon. The research team's models suggest that the last remnants of the magma ocean crystallized into dense minerals, including the titanium- and iron-bearing mineral ilmenite.
“Apollo” astronauts found high concentrations of titanium in moon rocks
"Because these heavy minerals are denser than the underlying mantle, gravitational instability arises and one would expect this layer to sink deeper into the moon's interior," said Weigang Liang, who led the research. But how does this relate to the high concentrations of titanium found in the lunar rock samples that the Apollo astronauts brought to Earth in the 1970s?
The research team offers an explanation: Over millennia, the dense material sank into the moon's interior, mixed with the lunar mantle, melted and returned to the surface as titanium-rich lava flows. Jeff Andrews-Hanna, a co-author of the study, puts it succinctly in a statement: "Our moon has literally turned inside out." However, there is little physical evidence for the exact order of these events, so there is disagreement the details.
How was the moon formed? “Without proof you can choose your favorite model”
“Without evidence, you can choose your favorite model. Each model has profound implications for the geological evolution of our moon,” said co-author Adrien Broquet. However, using data from NASA's previous Grail mission, the research team was able to uncover further details: "Ilmenite materials migrated to the Earth-facing side and sank into the interior in sheet-like cascades, leaving a trail that causes anomalies in the moon's gravity field, such as "They were observed by 'Grail'," summarizes Liang.
Andrews-Hanna, another co-author, is excited: “For the first time we have physical evidence that shows us what happened inside the Moon during this critical period of its evolution, and that's really exciting. It turns out that the Moon’s earliest history was written beneath the surface, and it just took the right combination of models and data to reveal that history.”
When the next humans set foot on the moon, researchers will know more
The research team hopes that future lunar missions will install a seismic network to allow better study of the structures' geometry. But one thing is already certain, as Liang emphasizes: “When the 'Artemis' astronauts finally land on the moon to usher in a new era of human exploration, we will understand our neighbor very differently than we did when the 'Apollo 'astronauts set foot on it for the first time."
The violent impact of the planet Theia on Earth also had consequences for our planet: A research team claims to have tracked down remnants of Theia inside the Earth. Another research group suggests that the collision may have triggered plate tectonics on Earth.
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