New 'Apollo lunar samples' find solves decades-old mystery

A recent NASA study has solved an enduring mystery from the Apollo missions to the moon - the origin of organic matter found in lunar samples returned to Earth.

Samples of the lunar soil brought back by the Apollo astronauts contain low levels of organic matter in the form of amino acids. Certain amino acids are the building blocks of proteins, essential molecules used by life to build structures like hair and skin and to regulate chemical reactions.

Since the lunar surface is completely inhospitable for known forms of life, scientists don't think the organic matter came from life on the moon. Instead, they think the amino acids could have come from four possible sources. First, since traces of life are everywhere on Earth, the amino acids could be simply contamination from terrestrial sources, either from material brought to the moon by the missions, or from contamination introduced while the samples were being handled back on Earth.

Second, rocket exhaust from the lunar modules contains precursor molecules used to build amino acids (such as hydrogen cyanide or HCN). This contamination could produce amino acids during lunar sample analysis in the lab.

Third, the solar wind, a thin stream of electrically conducting gas continuously blown off the surface of the Sun, contains the elements used to make amino acids, such as hydrogen, carbon, and nitrogen. Just like contamination from lunar module exhaust, material from the solar wind could produce amino acids during sample workup.

Fourth, chemical reactions inside asteroids make amino acids. Fragments from asteroid collisions occasionally fall to Earth as meteorites, bringing their extraterrestrial amino acids with them. The lunar surface is frequently bombarded by meteorites and could have amino acids from asteroids as well.

Lead author Jamie Elsila of NASA's Goddard Space Flight Center in Greenbelt, Maryland said that with all the technologies, they have determined that most of the amino acids came from terrestrial contamination, with perhaps a small contribution from meteorite impacts.

The study appears online in Geochimica et Cosmochimica Acta.