Organic Molecules in Martian Meteorite Not Biological in Origin

Body in space glowing as it heads through Earth's atmosphere.

They found evidence of water-rock interactions similar to those that happen on Earth. (Image: via Pixabay)

Organic molecules found in a Martian meteorite that hurtled to Earth from Mars were synthesized during interactions between water and rocks that occurred on the Red Planet about 4 billion years ago, according to a new analysis led by Carnegie’s Andrew Steele and published by Science.  

The meteorite, called Allan Hills (ALH) 84001, was discovered in the Antarctic in 1984 and is considered one of the oldest known projectiles to reach Earth from Mars. Steele, who has done extensive research on organic material in Martian meteorites and is a member of both the Perseverance and Curiosity rovers’ science teams, explained:  

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“Analyzing the origin of the meteorite’s minerals can serve as a window to reveal both the geochemical processes occurring early in Earth’s history and Mars’ potential for habitability.”

Organic molecules contain carbon and hydrogen, and sometimes include oxygen, nitrogen, sulfur, and other elements. Organic compounds are commonly associated with life, although they can be created by non-biological processes as well, which are referred to as abiotic organic chemistry. 

The Allan Hills 84001 meteorite.
The Allan Hills 84001 meteorite. (Image: JSC Stanford University via NASA)

For years, scientists have debated the origin story for the organic carbon found in the Allan Hills 84001 meteorite, with possibilities including various abiotic processes related to volcanic activity, impact events on Mars, or hydrological exposure, as well as potentially being the remnants of ancient life forms on Mars or contamination from its crash landing on Earth.  

The Steele-led team, which also included Carnegie’s Larry Nittler, Jianhua Wang, Pamela Conrad, Suzy Vitale, and Vincent Riggi, as well as researchers from GFZ German Research Centre for Geosciences, the Free University of Berlin, the NASA Johnson Space Center, the NASA Ames Research Center, and the Rensselaer Polytechnic Institute, used a variety of sophisticated sample preparation and analysis techniques — including co-located nanoscale imaging, isotopic analysis, and spectroscopy — to reveal the origin of organic molecules in the Allan Hills 84001 meteorite.

ALH84001 meteor.
Organic molecules contain carbon and hydrogen, and sometimes include oxygen, nitrogen, sulfur, and other elements. Organic compounds are commonly associated with life, although they can be created by non-biological processes as well, which are referred to as abiotic organic chemistry. (Image: via NASA)

They found evidence of water-rock interactions similar to those that happen on Earth. The samples indicate that the Martian rocks experienced two important geochemical processes. One, called serpentinization, occurs when iron- or magnesium-rich igneous rocks chemically interact with circulating water, changing their mineralogy and producing hydrogen in the process.  The other, called carbonization, involves interaction between rocks and slightly acidic water containing dissolved carbon dioxide and results in the formation of carbonate minerals.

It is unclear whether these processes were induced by surrounding aqueous conditions simultaneously or sequentially, but the evidence indicates that the interactions between water and rocks did not occur over a prolonged period. What is evident, however, is that the reactions produced organic material from the reduction of carbon dioxide.

Electron microscopy revealed chain structures resembling living organisms in Martian meteorite fragment ALH84001.
Electron microscopy revealed chain structures resembling living organisms in meteorite fragment ALH84001. (Image: via NASA)

Organic molecules found in other martian meteorite samples

These mineralogical features are rare in Martian meteorites, and while carbonation and serpentinization have been shown in orbital surveys of Mars and carbonation has been found in other less-ancient Martian meteorites, this is the first instance of these processes occurring in samples from ancient Mars. Organic molecules have been detected by Steele in other Martian meteorite samples and from his work with the Sample Analysis at Mars (SAM) team on the Curiosity rover, indicating that abiotic synthesis of organic molecules has been a part of Martian geochemistry for much of the planet’s history. Steele concluded:

“These kinds of non-biological, geological reactions are responsible for a pool of organic carbon compounds from which life could have evolved and represent a background signal that must be taken into consideration when searching for evidence of past life on Mars.

“Furthermore, if these reactions happened on ancient Mars, they must have happened on ancient Earth, and could possibly explain the results we’ve seen from Saturn’s moon Enceladus as well. All that is required for this type of organic synthesis is for a brine that contains dissolved carbon dioxide to percolate through igneous rocks. The search for life on Mars is not just an attempt to answer the question ‘are we alone?’ It also relates to early Earth environments and addresses the question of ‘where did we come from?’”

Provided by Carnegie Institution for Science [Note: Materials may be edited for content and length.]

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