Diamond helps look back over 3.5 billion years into the history of Mars

The Allan Hills 84001 meteorite courtesy of NASA/JSC/Stanford University.

A team of scientists led by Andrew Steele at the Carnegie Institution for Science has used a variety of sophisticated sample preparation and analysis techniques to reveal the origin of organic molecules in a Martian meteorite.  

The meteorite, called Allan Hills (ALH) 84001, was discovered in Antarctica in 1984 and is considered one of the oldest known rocks to reach Earth from Mars.   

The team’s analysis showed that organic molecules found in the Allan Hills meteorite were synthesised during interactions between water and rocks that occurred on the Red Planet about 3.6 – 4 billion years ago. Their findings were recently published in the journal Science.   

Andrew 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:

The study 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 serpentinisation, 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 carbonisation, involves interaction between rocks and dissolved carbon dioxide and results in the formation of carbonate minerals. 

A key part of this research was the investigation into the carbon within the meteorite. The team brought samples of the meteorite to Diamond to study them in extremely fine detail. X-rays were channelled into the I08 beamline and focused onto the tiny samples to measure and map out the carbon within the meteorite.  

Liane G. Benning, a co-author of the work, is Head of Interface Geochemistry at the German Research Centre for Geosciences, GFZ in Potsdam, and an experienced user of Diamond. She said,

The I08 beamline at Diamond Light Source, where the team studied the carbon inside the Martian meteorite.

The team needed to work on the nanoscale at extremely high resolution to be able to map the carbon in the Allan Hills meteorite, so they applied for beamtime at the Diamond synchrotron. 

Liane G. Benning comments, 

The mineralogical features uncovered by this research are rare in Martian meteorites, and while carbonation and serpentinisation 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 Andrew Steele and team in other Martian meteorites 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. 

Andrew Steele comments:

The following institutions were also part of this study: NASA Johnson Space Center, NASA Ames Research Center, Rensselaer Polytechnic Institute and University of Glasgow.