NASA Shares Evidence for Planet Collision Forming the Moon

NASA has announced the results of a lunar rock study the space agency conducted. The study looked into the Moon’s past. The findings, according to NASA, support the so-called Giant Impact theory describing how the Moon first developed. That means the likelihood that a collision between Earth and another planet created the Moon has just gone up.

The scientists behind the lunar rock study recently published their findings in the journal Proceedings of the National Academy of Sciences. NASA planetary scientist Justin Simon and graduate fellow Tony Gargano, both at the agency’s Johnson Space Center, led the research.

“There’s a huge difference between the modern elemental makeup of the Earth and Moon and we wanted to know why,” Simon said in a NASA press release. “Now, we know that the Moon was very different from the start, and it’s probably because of the ‘Giant Impact’ theory,” the planetary scientist added.

Planetary collision forming the Moon


The Giant Impact theory, or Big Splash, speculates that ejecta from a collision between the proto-Earth and a Mars-sized planetesimal (a minute planet) called Theia clumped into what is now the Moon. The theory suggests this collision would have occurred roughly 4.5 billion years ago. Back then the solar system was only about 100 million years old.

Simon, Gargano, et al. focused on the amount and types of chlorine in the lunar rocks. The researchers chose chlorine because it’s a volatile element, meaning it vaporizes at a relatively low temperature.

When the researchers quantified the amount of the light chlorine in the lunar rocks’ composition, they found a depleted supply of the element relative to what they find in Earth rocks. On top of that, the lunar rocks’ composition also had a relatively high amount of heavy chlorine. The light and heavy designations are references to the two isotopes’ different atomic masses.

“The chlorine loss from the Moon likely happened during a high energy and heat event, which points to the Giant Impact theory,” said Gargano. The theory predicted this lunar composition because Earth would’ve attracted light chlorine after its collision with Theia, while the less massive Moon would’ve retained the less easily vaporized heavy chlorine. Immediately above is a visualization—unrelated to this work—showing what the astronomical collision may have looked like.

Featured Image: NASA