Moon born out of planet collisionA HEAD-ON collision between a young Earth and a “planetary embryo” called Theia spawned our moon about 4.5 billion years ago — contradicting the long-held theory of a glancing blow, according to a new study.
Theia struck our planet when it was 100 million years old, but scientists have been divided on the nature of the impact and how much debris was exchanged between the two bodies, according to space.com.
Evidence now suggests that the debris that eventually formed Earth and our lunar neighbour was thoroughly mixed before they separated.
“The collision that formed the moon was a high-energy impact,” said the study’s lead author, Edward Young, a cosmochemist and geochemist at UCLA.
Previously, scientists believed Theia hit Earth at a side-swipe angle of 45 degrees or more. But in that scenario, the moon’s chemical composition would be markedly different from Earth’s.
But after studying moon rocks brought back to Earth by astronauts in the Apollo 12, 15 and 17 missions, as well as six volcanic rocks from the Earth’s mantle, the researchers discovered that the lunar isotopes were identical to Earth’s.
“We don’t see any difference between the Earth’s and the moon’s oxygen isotopes — they’re indistinguishable,” Young said.
The new findings dispute a 2014 report by German scientists in Science that the moon’s ratio of oxygen isotopes is different from Earth’s.
“Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them,” Young said. “This explains why we don’t see a different signature of Theia in the moon versus the Earth.”
The Mars-sized Theia, which did not survive the cataclysmic collision, likely would have become a planet had the fateful collision not occurred, he added.
The new research was published Friday in the journal Science.
http://science.sciencemag.org/content/351/6272/493http://www.heraldsun.com.au/technology/science/a-headon-collision-created-the-moon/news-story/4e636c38c1c70403c842acb32c817d2a
