“When most people think of cyanide, they think of spy movies — a guy swallowing a pill, foaming at the mouth and dying,“ said lead author Karen Smith, senior research scientist at Boise. “But cyanide was probably an essential compound for building molecules necessary for life.”
Life seeded by meteorites
According to the scientists, the extraterrestrial compounds found in the meteorites resemble the active sites of hydrogenases, which are enzymes that provide energy to microorganisms like bacteria by breaking down hydrogen gas. Based on the results of the study, these compounds were also present on early Earth, before the emergence of life, during a time where the planet was constantly bombarded by meteorites and the atmosphere was more hydrogen-rich.
Smith and co-author Mike Callahan, assistant professor at Boise, developed new analytical methods to extract and measure ancient traces of cyanide in meteorites. The researchers found that the meteorites containing cyanide belong to a group of carbon-rich meteorites called CM chondrites. No cyanide was found in any other meteorites that they tested, including Martian ones.
Scientists have found cyanide in meteorites before. However, in their study, Smith and Callahan were surprised to find that the cyanide, along with carbon monoxide, were binding with iron to form stable compounds in the meteorites. Using high-resolution liquid chromatography-mass spectrometry, they identified two different iron cyano-carbonyl complexes in the meteorites. These iron cyano-carbonyl complexes resembled portions of the active sites of hydrogenases.
Hydrogenases are large proteins present in almost all modern bacteria and archaea that are widely believed to be be ancient in origin. The active sites of hydrogenases -- the region where the chemical reactions take place -- are actually much smaller metal-organic compounds contained within the protein. According to Callahan, these are what that the cyanide-bearing compounds in the meteorites resemble.
Testing rocks in space
One of the biggest mysteries surrounding the origin of life is how it could have arisen from non-biological chemical processes. The similarities between the cyanide compounds found by the researchers and the active sites of hydrogenase enzymes suggest that non-biological processes in the parent asteroids of meteorites that struck the Earth in prehistoric times could have produced the molecules needed for life. (Related: Mars may have developed habitable conditions as early as 4.2 billion years ago.)
However, to be able to test this, the team must get samples from an actual asteroid in space. To this end, they have enlisted the help of NASA's Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx), which is currently at the near-Earth asteroid 101955 Bennu.
“Data collected by NASA’s OSIRIS-REx spacecraft of asteroid Bennu indicate that it is related to CM chondrites,” said Jason Dworkin of NASA’s Goddard Space Flight Center, who co-authored the study.
“OSIRIS-REx will deliver a sample from Bennu to study on Earth in 2023. We will search for these very compounds to try to connect Bennu to known meteorites and to understand the potential delivery of prebiotic compounds such as cyanide, which may have helped start life on the early Earth or other bodies in the solar system.”
If the cyanide compounds are found in 101955 Bennu, then it could go a long way to proving that meteorites helped in the emergence of life on Earth.
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