The Nakhla meteorite originated from Mars and fell to Earth in Egypt in 1911. It has been studied extensively over the years, and is one of the first indicators humans had about past water and mineral content on Mars. A biomorphic ovoid structure was recently discovered, which strongly resembles some sort of microorganism. Scientists studying the formation ultimately determined it was caused by geological forces and was not formed by a living organism. However, the analyses did reveal an incredible amount of information regarding the composition of Mars and its potential habitability. The research was led by Elias Chatzitheodoridis of National Technical University of Athens and the paper was published in an open access format in the journal Astrobiology.
It was not immediately clear how the structure formed. Several hypotheses were kicked around, including that it was formed by ancient Martian microorganisms. In order to investigate the structure’s origins, the meteorite was subjected to a barrage of tests including x-ray analyses, mass spectrometry, electron microscopy, and atomic force microscope topographic mapping.
The researchers are confident that the structure was indigenous to the sample, and not the result of any contamination once it got to Earth. The ovoid structure itself is about 80 microns long, 60 microns wide. The average E. coli bacterium is about 2 microns long, so if prokaryotes were involved, it would have taken an entire colony to create a space that large. Eukaryotic microorganisms can easily be as large as the structure. However, they ultimately decided that it wasn’t likely that they were looking at the imprint of alien life.
Instead, the data revealed that the structure was likely formed due to geological processes. It appears that the rock from which the meteorite originated had been struck by another object. The shock produced heat and pressure which melted the permafrost and mixed fluids and minerals on and below the surface. It looks most likely that vaporized liquid formed a bubble, which was then filled with the organic material.
"This study illustrates the importance of correlating different types of datasets when attempting to discern whether something in rock is a biosignature indicative of life," Astrobiology’s Editor-Sherry L. Cady said in a press release. "Though the authors couldn't prove definitively that the object of focus was evidence of life, their research strategy revealed a significant amount of information about the potential for life to inhabit the subsurface of Mars.”
While they didn’t find direct evidence of microbial life, they also didn’t find anything that completely ruled it out either. They discovered minerals that are essential for life, which backs up findings from the Curiosity rover that Mars could have been habitable in the past. The paper states that “although compelling evidence for a biotic origin is lacking, it is evident that the Martian subsurface contains niche environments where life could develop.”