Modeling early meteorite impacts on the moon

July 10, 2019

As our solar system was forming nearly four and a half billion years ago, a planet-sized object struck the early Earth, leading to the formation of the moon, possibly from a hot, spinning cloud of rock vapor called a synestia. But after the Earth and moon had condensed from the vapor, there was another phase of growth as meteorites crashed into both bodies.

Despite their common origin there are curious differences between the Earth and moon. Elements such as gold, iridium, platinum and palladium (known as highly siderophile or 'iron-loving' elements) are relatively scarce on the moon compared to Earth. Because these elements were delivered by meteorites, explanations for the difference put limits on how growth by meteorite bombardment unfolded over hundreds of millions of years. Understanding this problem is crucial to figuring out exactly what happened as the Earth and moon grew into the bodies we know today.

"This has been a major problem in terms of how we understand the Moon's accretion history," said Qing-zhu Yin, professor of earth and planetary sciences at UC Davis.

Yin and an international group of collaborators have now carried out a detailed reconstruction that resolves the highly siderophile element problem and gives new insight into the late accretion history of the moon. Their results are published July 11 in the journal Nature.

Less retention of meteorite material

The researchers modeled the millions of meteor impacts that would have brought material to the Earth and moon. They validated their model by comparing the number of predicted impacts with the number of actual craters on the moon.

They found that because of the moon's smaller size, and because some impacts would be at a shallow angle to the surface, relatively less material was left behind by meteorites that hit the moon than by those hitting the Earth.

Yin and colleagues calculated that the siderophile elements would have been retained in the lunar crust and mantle only from about 4.35 billion years ago, later than previously thought and about the time that the magma ocean covering the moon solidified. Siderophile elements arriving before that time would have been absorbed into the moon's iron core.

Taken together, these factors account for the discrepancy in highly siderophile elements between Earth and moon.

"The beauty of this work is such that all of these things are now coming together nicely. We may have solved this problem, at least until someone find new discrepancies!" Yin said.
Other authors on the study are: Meng-Hua Zhu, Macau University of Science and Technology, Macau, China; Natalia Artemieva, Planetary Science Institute, Tucson, Arizona; Alessandro Morbidelli, University of Nice-Sophia Antipolis, Nice, France; Harry Becker and Kai Wünnemann, Free University of Berlin, Germany. The work was supported by the Science and Technology Development Fund of Macau, NASA and the Deutsche Forschungsgeimenschaft.

University of California - Davis

Related Meteorites Articles from Brightsurf:

Meteorites show transport of material in early solar system
New studies of a rare type of meteorite show that material from close to the Sun reached the outer solar system even as the planet Jupiter cleared a gap in the disk of dust and gas from which the planets formed.

Unexpected abundance of hydrogen in meteorites reveals the origin of Earth's water
Meteorite material presumed to be devoid of water because it formed in the dry inner Solar System appears to have contained sufficient hydrogen to have delivered to Earth at least three times the mass of water in its oceans, a new study shows.

Earth may always have been wet
The Earth is the only planet known to have liquid water on its surface, a fundamental characteristic when it comes to explaining the emergence of life.

Surrey academics develop a new method to determine the origin of stardust in meteorites
Scientists have made a key discovery thanks to stardust found in meteorites, shedding light on the origin of crucial chemical elements.

Iron-rich meteorites show record of core crystallization in system's oldest planetesimals
New work uncovers new details about our Solar System's oldest planetary objects, which broke apart in long-ago collisions to form iron-rich meteorites.

How stony-iron meteorites form
Meteorites give us insight into the early development of the solar system.

X-rays recount origin of oddball meteorites
X-ray experiments at Berkeley Lab played a key role in resolving the origin of rare, odd meteorites that have puzzled scientists since their discovery a half-century ago.

An origin story for a family of oddball meteorites
Study suggests a family of rare meteorites likely came from an early planetesimal with a magnetic core.

Ancient asteroid impacts created the ingredients of life on Earth and Mars
A new study reveals that asteroid impact sites in the ocean may possess a crucial link in explaining the formation of the essential molecules for life.

4-billion-year-old nitrogen-containing organic molecules discovered in Martian meteorites
Scientists exploring Mars and analysing Martian meteorite samples have found organic compounds essential for life: nitrogen-bearing organics in a 4-billion-year-old Martian meteorite.

Read More: Meteorites News and Meteorites Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to