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.