What Is Odd Cell-Like Structure in Mars Nakhla Meteorite?

Scanning electron microscope image of a mysterious oval structure in the Nakhla Mars meteorite.

Credit: Elias Chatzitheodoridis, Sarah Haigh and Ian Lyon

Scientists have found a strange structure resembling a microbial cell inside a Martian meteorite, but they're not claiming that it's evidence of Red Planet life.

The researchers discovered the microscopic oval object within the Nakhla Mars meteorite, which fell to Earth in Egypt in 1911.

While the structure's appearance is intriguing, it most likely formed as a result of geological rather than biological processes, team members said.

"The consideration of possible biotic scenarios for the origin of the ovoid structure in Nakhla currently lacks any sort of compelling evidence," the scientists write in a new study published this month in the journal Astrobiology.

"Therefore, based on the available data that we have obtained on the nature of this conspicuous ovoid structure in Nakhla, we conclude that the most reasonable explanation for its origin is that it formed through abiotic processes."

Cell-Like Structure
The hollow ovoid is about 80 microns long by 60 microns wide, researchers said, far larger than most terrestrial bacteria but in the normal size range for eukaryotic Earth microbes (single-celled organisms that possess nuclei and other membrane-bound interior "organelles").

The study team is confident that the object is native to the sample and not the result of terrestrial contamination.

The scientists studied the structure using a number of different techniques, including electron microscopy, X-ray analysis and mass spectrometry.

This work revealed that the ovoid is composed of iron-rich clay and contains a number of other minerals.

The researchers run through a number of possible formation scenarios in the new study, eventually concluding that the ovoid most likely formed when materials partially filled in a pre-existing vesicle, a vapour bubble, for example, in the rock.

Transmitted light photomicrograph of an oval structure (center) in the Mars meteorite known as Nakhla. 

There is no evidence that the ovoid is a sign of Martian life, researchers say.

Credit: Elias Chatzitheodoridis, Sarah Haigh and Ian Lyon

But this supposition doesn't rule out the possibility that Martian lifeforms had something to do with the structure, team members said.

"Despite the extremely biomorphic overall shape of the ovoid, it is highly unlikely that it itself was an organism," said lead author Elias Chatzitheodoridis, of the National Technical University (NTUA) of Athens in Greece.

"However, it could have been formed directly by micro-organisms, or it could trap organic material that came from elsewhere," Chatzitheodoridis told reporters.

"That the ovoid is hollow means that there is enough space to accommodate colonies of microorganisms."

Making a firm link to Mars life would require further study and further discoveries, he added.