Traces of ancient planet that collided with Earth found in lunar rocks!

ALBUQUERQUE, New Mexico (PNN) - March 10, 2020 - Traces of the ancient Mars-sized wandering planet Theia that nearly destroyed Earth and formed the Moon 4.5 billion years ago have been found in lunar rocks.

This goes some way to proving a long-held theory that the Moon was formed out of material expelled after Theia collided with the Earth billions of years ago.

Researchers from the University of New Mexico examined the oxygen isotopes in Moon rocks brought back to Earth by Apollo astronauts.

They discovered the oxygen isotopes - an indicator of the origin of the material - were slightly different to those found in Earth rocks, suggesting they came from Theia.

The team haven't predicted exactly how the Moon formed or how the impact happened but say their findings can help others create a more detailed theory.

Previous studies of the lunar rocks returned to Earth by Apollo astronauts found they were almost completely identical to those on Earth - but the New Mexico team found that wasn't the case.

They examined samples of rocks gathered from a number of different lunar sites and with both high and low titanium basalts.

They modified a standard isotope analysis technique in order to get a higher-than-usual precision measurement of the oxygen isotope.

Previous studies averaged together the measurements of all the samples but the New Mexico team took a different approach and got surprising results.

“While the Earth rocks occupy a very narrow range of oxygen isotope compositions, the lunar samples demonstrated nearly three times that variability,” said Erick Cano from the University of New Mexico.

“Typically, all the lunar samples are lumped together as a whole and the average value of all the lunar samples measured in the study is taken as the value for the moon,” he said.

“We show that the method of averaging together lunar isotope data while ignoring lithological differences does not give an accurate picture of the differences between the Earth and Moon,” they wrote in their paper.

The team found that the deeper into the Moon from which the samples were taken, the greater the difference between them and oxygen isotopes on Earth.

They discovered that the distinct oxygen isotope composition on Theia was not completely lost through the impact with Earth, and lives on in the Moon.

Lead author Erick Cano said, “The research is important because it eliminates the need for giant-impact models that include a complete oxygen isotope homogenization between the Earth and the Moon. It provides a foundation for future modelling of the impact and lunar formation.”

They say it could also suggest that Theia formed further out in the Solar System and then moved in before colliding with the Earth - rather than forming near the Earth.

The giant impact theory is the most pervasive idea for explaining both the formation of the Earth and our relatively large moon compared to other rocky planets.

The theory goes that about 4.45 billion years ago, 150 million years after the solar system formed, Earth was hit by a Mars-size object called Theia.

Exactly how this happened is hotly debated, in part because previous studies suggested the oxygen isotopes on Earth and the Moon were nearly identical.

The new research shows the two celestial bodies are not similar at all and become less similar the deeper into the Moon you go, and the study authors say large parts of Theia could still be inside the core of the Moon.

“Since the giant impact hypothesis was formulated there have been various challenges doubting it,” said Simon Kelley at the University of Edinburgh. “These findings are different because they appear to support and validate it.”

The research has been published in the journal Nature Geoscience.