Moon’s origins revealed in rocks’ chemistry

New chemical measurement supports giant impact hypothesis for lunar beginnings

2:07pm, June 5, 2014

BIG HIT  A new analysis of moon and Earth rocks shows that the two bodies have slightly different chemical makeups, supporting the hypothesis that an object the size of Mars slammed into Earth, forming the moon.

The messy details of the moon’s birth just got a bit neater.

Earth and its little lunar sister aren’t actually twins, a new chemical analysis of Earth and moon rocks reveals.

The findings help iron out a big wrinkle in the giant impact hypothesis, the only idea about the moon’s origin that hasn’t been shot down yet, says Harvard University planetary scientist Sarah Stewart, who was not involved with the study.

“When everyone saw this work, we all breathed a huge sigh of relief,” she says. “In my mind, the giant impact hypothesis is still standing.”

According to this hypothesis, about 4.5 billion years ago a Mars-sized body called Theia bashed into the Earth, spitting out debris that mashed together to form the moon. Computer analyses of the collision suggested that the moon should be made mostly of Theia’s remains.

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