When astronauts came back with lunar soil samples after the Apollo missions on the moon, scientists were stumped when they found amino acids in the sample. Why did this caused so much bewilderment? Because amino acid is an organic compounds which makes up protein and this means, it comes from a biological source. Hence, it cannot originate from the moon because it is inhospitable to life.

So where did it come from?

Scientists in 1970s tried their best to answer the question but they were limited by the analytical capabilities of the time. It wasn’t until today, with the technology we have, that researchers have managed to track down the source of the contamination.

NASA initially narrowed it down to four possible sources; the astronauts himself, the lunar module’s exhaust fumes, solar winds or meteorites. After determining that the amino acids have high level of Carbon-13 isotopes, they were able to eliminate the lunar module’s exhaust fumes. The amino acids were also organic ones, and not non-biological ones. This means it’s likely to have come from Earth.

The astronauts may have contaminated the sample accidentally. NASA researchers hope to learn from this experience to apply to future surveys and outer space missions. If you’d like to read more details about NASA’s findings, go here.