Around 100 million years after the Earth’s formation, the celestial body was floating in the vacuum when another planetary body smashed into it. In a computer simulation of the event, the other planetary body clips the top, sending a variety of debris hurdling into the surrounding space. The debris whirl and rotate around the Earth.
Scientists have long known about the 4.5 billion-year-old collision. Initially, it was believed that the second planetary body, Theia, collided with the Earth at an angle of 45 degrees or more. However, scientists from the University of California, Los Angeles (UCLA) are proposing the collision was more head-on than previously postulated.
The research was published in Science.
In their study, the researchers analyzed and compared seven moon rocks brought back from the Apollo 12, 15 and 17 missions, and six volcanic rock from Earth’s mantle, the majority coming from Hawaii. The researchers examined the rocks’ chemical signature, specifically focusing on the oxygen atoms. According to UCLA, a rock’s volume is comprised of 90% oxygen, and oxygen also accounts for 50% of a rock’s weight.
On Earth, 99.9% of the oxygen is dubbed O-16, because each atom is comprised of eight protons and eight neutrons. However, O-17 and O-18 populate the oxygen mixture. The ratio of O-17 to O-16, according to the researchers, is wholly unique to Earth. Mars and other planetary bodies each have a different ratio, making it a unique marker.
In 2014, a team of German scientists reported in Science that the moon and Earth did have different ratios, with moon rocks having a measurably higher ratio of O-17 over O-16 compared to Earth.
However, the UCLA researchers were unable to identify any difference between the moon’s and the Earth’s oxygen isotopes. According to Space.com, the researchers found that the oxygen isotope ratios were within 5 parts per million for O-17, as compared to differing by about 12 parts per million, which is what the German researchers initially reported.
The research presents “high-quality data along with a sound explanation for the surprising similarity of Earth and the moon. There is nothing for me to criticize,” Andreas Pack told Space.com. Pack was part of the research group from the 2014 German study.
Such a sideswipe collision, as initially proposed, would have resulted in the moon being made mainly of Theia. But “Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them,” said Edward Young, the lead author of the new study, and a professor of geochemistry and cosmochemistry at UCLA.
Young believes Theia was the same size as the Earth when the two nascent planetary bodies collided.