Moon's Amino Acids Likely Earthly Contamination: Photos
It's tough to protect the moon from us, as a group of scientists recently found when looking at rocks collected by Apollo astronauts.
Imagine making a science finding from samples collected from another world -- samples collected before you were even born. This is the situation that Jamie Elsia, an astrochemist at the NASA Goddard Space Flight Center, recently encountered when looking at the building blocks of life, called amino acids, that were present on the moon's surface. These were collected in rocks brought back by Apollo astronauts in the 1960s and 1970s.
Elsia's team discovered that it was contamination from Earth that likely put most of the amino acids on the surface. But they went through several hypotheses before coming to that conclusion, such as looking at the lunar module, the sun and even meteorites.
"Because we already knew that amino acids are found in meteorites and should be delivered to the lunar surface, this finding tells us more about survivability of organic compounds on the moon than it does about amino acids generally," Elsia told Discovery News in an email. "We hope that our findings may help as researchers try to understand how the radiation and weathering environment on the moon affect organic molecules."
The solar wind is the constant stream of particles that the sun emits, and which flows through the solar system. Over time, this could allow the sun to plant elements such as hydrogen, carbon and nitrogen atoms on the moon, the researchers theorized. If they combined in certain forms, such as hydrogen cyanide (a combination of all three elements), this would be considered a precursor to amino acids.
But the researchers ruled this out. The proportion of two types or isotopes of carbon -- carbon-13 and carbon-12 -- is different in the solar wind than the amino acids found on the lunar surface, Elsila wrote. "Also, we would have expected higher amino acids in the soils that were more exposed to the surface and the solar wind, and we didn't see that," she said.
All of the moonwalkers flew to and from the lunar surface using a craft called the lunar module, sometimes abbreviated as "the LM." It had a downward-facing engine that peppered the moon with exhaust during the landing and ascent. It turns out the exhaust contained small, volatile molecules like hydrogen cyanide.
This seemed a plausible explanation until the researchers looked at samples taken near the lunar module, and another one picked up about 4 miles (6.5 kilometers) away. The same amount of amino acids was found in both locations. "If the engine exhaust was responsible, we expected to see higher amino acid content in the sample taken next to the lunar module," Elsila wrote.
When space rocks fall on the surface, they can pack quite a punch. On Earth, most signs of old meteorites have eroded over time. On the moon, however, you can see evidence of thousands of craters even with a small telescope. The very largest ones are dozens of miles in diameter.
There are some kinds of meteorites, such as carbonaceous chondrites, that contain amino acids. And it turns out that when the researchers looked at their samples, there were some different types of amino acids present -- some that aren't around on the Earth. However, it appears that meteorites contribute a smaller amount of amino acids than one other source, as discussed in the next slide.
This is the most likely source. On Earth, there are only 20 amino acids that are associated with life. The rest are part of abiotic (non life-forming) chemical reactions. What's more, most amino acids have two forms that are mirror images of each other. Earth's are mostly left-handed. The lunar amino acids matched Earth life both in type and in form.
Researchers also measured the isotopic ratio for three of the amino acids and found another match for similar compounds on Earth. "All of this evidence led us to conclude that terrestrial contamination was a prime contributor of these compounds," Elsila wrote.
"I don't want to criticize those who worked on the Apollo mission or the curators who have managed these samples since their return to Earth, as everybody involved worked diligently to minimize contamination," Elsila added. "This work shows how hard it is to completely eliminate contamination, and that is a lesson that should be taken to heart by future sample return missions, both lunar and to other solar system bodies."
This is something especially in the minds of the OSIRIS-Rex team that is launching for asteroid Bennu in 2016 and coming back to Earth with samples in 2023. According to Elsila, that team is thinking both about how to reduce contamination, and how to understand what contamination might exist, to make sure they get the best science return possible from the samples.
"Contamination knowledge is particularly useful," she said. "OSIRIS-REx uses 'witness' materials that are exposed to the spacecraft environment and can record any potential contamination, so that future scientists can analyze both the witness material and the returned sample to understand what is truly asteroidal and what is the results of contamination. Future sample return missions can also benefit from this strategy."