How the moon was formed: Mars-sized planet collided directly with Earth ages ago, new study says

Artist's depiction of a collision between two planetary bodies similar to the hypothesised collision between Earth and a smaller, Mars-sized object—Theia. (NASA/JPL-Caltech)

Ever wondered how the Earth's moon was formed?

A new study strongly points to quite a violent origin: It was a by-product of a direct collision between a planet about the size of Mars called Theia and our own planet when it was still at a young age.

A team of researchers recently reached this conclusion after analysing materials from the moon brought to Earth by the Apollo 12, 15, and 17 missions.

According to the study published on Thursday in the "Science" journal, the striking similarities in the composition of materials from the moon from those in our environment here on Earth strongly suggest that Theia smashed right smack onto our planet.

Edward Donald Young, lead author of the paper and a professor of Department of Earth, Planetary, and Space Sciences at the UCLA, said his team's findings are enough to disprove the current belief that Theia only sideswiped, and did not completely collide with Earth.

"My view is that the issue of Theia content is more or less settled," Young said, as quote by Popular Mechanics.

"The collision was so vigorous, so powerful, so rich in energy that it probably mixed the whole system very thoroughly," Young further explained.

The researchers were particularly convinced after they found out that the Moon shares the same oxygen and some tungsten isotopes in the same ratios as Earth—strong indications that our planet and its lone satellite are composed of the same materials.

Salt-heavy lunar rocks and soil also matched the materials usually found at the bottom of the Earth's oceans.

These could only be possible if Theia completely and directly struck the Earth. The Moon would primarily have contained material from Theia and only a little material from Earth if these two planetary bodies just side-swiped each other.

Despite these findings, Young said more mysteries about the Earth and the moon still need to be answered, including how they established their present rotations and orbits.

related articles
Mars mystery unravelled: NASA finds reason why Red Planet can\'t support life
Mars mystery unravelled: NASA finds reason why Red Planet can't support life

Mars mystery unravelled: NASA finds reason why Red Planet can't support life

NASA postpones Mars exploration mission next year to 2018 due to leaky instrument
NASA postpones Mars exploration mission next year to 2018 due to leaky instrument

NASA postpones Mars exploration mission next year to 2018 due to leaky instrument

News
Marriage is the safest relationship, latest figures suggest
Marriage is the safest relationship, latest figures suggest

Of the eight children murdered during lockdown, 7 were killed thanks to the actions of a step parent or new partner.

Abortion rises in Northern Ireland for fourth year running
Abortion rises in Northern Ireland for fourth year running

Abortion was legalised in Northern Ireland in 2019.

Churches helping millions of Brits get by as living costs remain high
Churches helping millions of Brits get by as living costs remain high

Across the country, people are looking to the church for help.

Isaiah 41:10 is YouVersion's Bible verse of the year
Isaiah 41:10 is YouVersion's Bible verse of the year

Isaiah 41:10 had the highest international engagement on YouVersion during 2025, while in the UK it was Jeremiah 29:11 that topped the list.