by
Mike Wall
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.
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.
"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."
A 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 vapor bubble, for example
— in the rock.
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 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
Space.com via email. "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.
"We would be happy if we could have found more than one ovoid, with
exactly the same texture both in the micro and the nanoscale,"
Chatzitheodoridis said. "However, we require to open up enough sample in
a very careful way. Compelling evidence, though, would be if we could
really find many of the same, clearly in a form of a colony, together
with chemical and mineralogical biosignatures that are common for
terrestrial microbes."
Habitable Martian environments?
Nakhla is a well-studied meteorite — scientists have spotted possible signs of Mars life within it
before —and previous research has mapped out its history in some
detail. Nakhla's parent rock apparently crystallized about 1.3 billion
years ago, Chatzitheodoridis and his colleagues write in the new study,
then experienced two shock events that heated it up considerably.
The first of these shocks likely occurred around 910 million years ago
and the second 620 million years ago. This latter event, which was
triggered by a nearby meteorite strike on Mars,
apparently included the flow of hot water through Nakhla's parent
outcrop, the authors write. Finally, about 10 million years ago, another
impact blasted Nakhla free of Mars, sending it on a looping trip
through space that ended with its arrival at Earth in 1911.
Whether or not the Nakhla ovoid has some connection to Martian life,
study of the meteorite can help researchers better understand the Red
Planet's past (and, perhaps, present) potential to support life, Chatzitheodoridis said.
Martian meteorites contain "important information, and latest work has
shown that now one has to look more carefully at them and in finer
detail," he told
Space.com.
"In our case, it is such work that allowed us to see from a small
volume of sample a big story, i.e., that hydrothermal waters have
actually acted also in the latest periods of Martian history, even if
they were caused by a bolide impact, and that they were capable of
initiating a number of complicated processes that resulted in the
formation of niche environments which can sustain life, if life [ever]
emerged on the planet," Chatzitheodoridis added.
In his column for 
