Now we can know why the moon has much less brightness than Earth.
Gold, platinum and other metals known as highly siderophile elements ("iron lovers") are much more abundant in the earth's crust than in its natural satellite.
That may seem strange, given the shared (and violent) history of the two worlds. About 4.5 billion years ago, a planet the size of Mars called Theia crashed into the prototype-Earth, throwing huge amounts of material from both bodies into space. Some of these liberated things were incorporated into the bruised and battered Earth, and some joined to form the moon.
Related: How the moon evolved: a timeline of photos
But scientists do not believe that highly siderophile elements (HSE) were actually part of that mixture. These metals were probably released later by asteroid attacks; It has not been clear why Earth gained more participation. For example, has the Earth just been hit by a few huge, HSE-rich rocks, while the moon managed to escape these catastrophic impacts? Or did a relatively constant flow of smaller impactors with HSE strike the Earth preferentially long ago, attracted by the strongest gravity of our planet?
"This has been a big problem in terms of how we understand the moon's accretion history," said Qing-zhu Yin, a professor of earth sciences and planetariums at the University of California, Davis, in a statement.
Yin is a member of a research team that analyzed this question. The scientists, led by Meng-Hua Zhu of the Macao 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 weaker gravity compared to the Earth's attraction, simply has not been very good at holding on to the material delivered by the impactor, including the HSE; Many of the things are lost in space. In fact, the "impactor retention index" of the moon is about three times lower than previously believed, the team found.
The scientists also calculated that the retention of HSE in the crust and lunar mantle probably started later than previously estimated, 4.35 billion years ago, approximately when the magma ocean that covers the moon cooled and solidified . The HSEs that arrived before that time probably sank and joined the moon's core, the researchers said.
These two factors may explain the relative scarcity of HSE in the lunar cortex and mantle, according to the team, which details the findings in a study published online today (July 10) in the journal Nature.
"The beauty of this work is such that all these things now combine very well," Yin said. "We may have solved this problem, at least until someone finds new discrepancies!"
Original article on Space.com.