We can now know why the moon has so much less bling than the Earth.
Gold, platinum and other metals known as highly siderophile ("iron magnet") elements are much more abundant in the Earth's crust than in that of its natural satellite.
This may seem strange, given the common (and violent) history of both worlds. About 4.5 billion years ago, a Mars-sized planet, dubbed Theia, struck the proto-Earth, throwing large quantities of material from both bodies into the space. Part of this liberated substance was incorporated into the bruised and bruised Earth, and some fused to form the moon.
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But scientists do not think that highly siderophilic elements (HSE) were really part of this mix. These metals were probably delivered later by asteroid impacts; we still do not know why the Earth has had a bigger share. For example, has Earth just been invaded by some huge rocks rich in HSE, while the Moon has managed to escape these catastrophic impacts? Or has a relatively constant flow of small impactors carrying HSE preferentially touched the Earth a long time ago, driven by the stronger gravity of our planet?
"This has been a major problem in understanding the history of the accretion of the moon," said Qing-zhu Yin, professor of Earth Sciences and Planets at the University of California to Davis, in a statement.
Yin is a member of a research team that has looked into this issue. The scientists – led by Meng-Hua Zhu, of the Macau University of Science and Technology in China – used computer simulations to model millions of impacts on the moon.
The results suggest that the Moon, with its much lower gravity compared to the attraction of the Earth, simply has not been very successful at hooking to the material provided by the impactor , Including HSE; many things are lost in space. In fact, the "impact / retention ratio" of the moon is about three times lower than previously thought, the team said.
Scientists further calculated that the retention of HSE in the lunar crust and mantle had probably started later than expected – 4.35 billion years ago, at about the same time as the ocean Magma covering the moon has cooled and solidified. HSEs that arrived before that date probably sank and were integrated into the moon's core, the researchers said.
These two factors may explain the relative poverty of HSE in the lunar crust and mantle, according to the team, which details the results in a study published online today (July 10) in the journal Nature.
"The beauty of this work is such that all these things are now going well together," Yin said. "We may have solved this problem, at least until someone finds new gaps!"
Original article on Space.com.