Did this planet collide with earth to form the moon?

FRIDAY 06 JUNE 2014

Rocks brought back from the moon more than 40 years ago contain evidence of a Mars-sized planet that scientists believe crashed into earth and created the moon.

Above: new evidence indicates that the moon was created when a Mars-sized planet slammed into the earth

German scientists using a new technique said they detected a slight chemical difference between earth rocks and moon rocks.

Scientists said more study would be needed to confirm this elusive piece of evidence that material from another body besides earth contributed to the moon's formation some 4.5 billion years ago.

Scientists believe the moon formed from a cloud of debris launched into space after a Mars-sized body called Theia crashed into young earth. Different planets in the solar system have slightly different chemical make-ups.

Therefore, scientists believed moon rocks might hold tell-tale chemical fingerprints of whatever body smashed into earth. Until now, evidence was elusive.

Above: after Theia collided with the primordial earth, the material ejected began to reform into a body orbiting the earth

Scientists have developed a technique that guarantees perfect separation of oxygen isotopes from other trace gases.

"The differences are small and difficult to detect, but they are there," says Daniel Herwartz, from Germany's University of Cologne, lead author of a paper on the discovery published in this week's issue of the journal Science.

The results indicate that composition of the moon is about 50 per cent Theia and 50 per cent earth, the scientists said, although more work is needed to confirm that estimate.

Apollo missions

The team analysed rocks brought back to earth by Nasa astronauts during the Apollo 11, Apollo 12 and Apollo 16 missions to the moon, which took place in 1969 and 1972.

"This work is the first to claim to see such a difference in the isotopes of oxygen," said Robin Canup, a planetary scientist with the Southwest Research Institute in Boulder, Colorado, who was not involved in the research.

"The reported difference between the earth and moon is extremely small - small enough that I think there will be debate as to whether the difference is real or an artifact of how one interprets the data," she added.

Meanwhile, other teams of scientists have been looking at titanium, silicon, chromium, tungsten and other chemical elements, but so far the lunar samples show no detectable differences from earth samples.