Jeremy Bellucci from the Swedish Museum of Natural History and his colleagues have found something extraordinary in a rock collected from the Moon’s surface by Apollo astronauts almost half a century ago.
In the most recent issue of Earth and Planetary Science Letters, the scientists report on their study of a clast (fragment) of Apollo sample 14321, collected during the Apollo 14 mission in 1971. After a thorough geochemical analysis, they determined that this piece of rock most likely originated on Earth, where it was excavated by a meteorite impact about 4 billion years ago, then ejected into space to land eventually on the Moon. If so, it would be the first meteorite from Earth recovered on another planetary body, as well as one of the oldest terrestrial rocks found to date.
The authors conclude that this event took place during the Late Heavy Bombardment period, during which, according to many scientists, an extraordinarily high number of large asteroid impacts occurred on Earth. They acknowledge that the fragment of 14321 could also have originated on the Moon. But no other lunar rock has been found that formed at such low temperatures and with such high oxygen content. If the clast indeed formed on the Moon, it would mean that the Moon, or at least one location on the Moon, was once more Earthlike and water-rich than previously thought.
Both of these possibilities support the hypothesis advanced by Ian Crawford and me that there might have been an early habitability window on the Moon, and perhaps even temporary microbial life. If sample 14321 really is from Earth, it proves that the exchange of lunar and terrestrial material is not only theoretically possible, but that it indeed occurred—probably many times and involving a lot of material—at a time when the Moon was three times closer to Earth than it is now. It also would have happened after life originated on Earth, meaning that the Moon may hold clues that would help us answer the greatest mystery of astrobiology: when and where did life begin on our own planet?
If, on the other hand, it turns out that the clast actually formed on the Moon (which seems unlikely given the results from Bellucci et al.) it would improve the chances of habitable conditions having existed on the early Moon. Puddles of water on the lunar surface, potentially with microbes growing and reproducing there, would become a real possibility.
One thing is clear, either way. We don’t know the Moon as well as we might have thought. There are still many questions to be resolved, some of which could have huge impacts (pun intended) on our understanding of life in the universe. Its time to go back to the Moon and retrieve more samples.