A team of scientists from the United Kingdom and Greece led by Dr Elias Chatzitheodoridis of the National Technical University of Athens has found a mysterious oval structure embedded deep within a famous Martian meteorite called Nakhla.
Two fragments of the Nakhla meteorite. Image credit: NASA.
Multiple fragments of the Nakhla meteorite fell to Earth on June 28, 1911 near the village of El-Nakhla in Egypt. Its crystallization age has been determined to be 1.38 billion years.
About 11 million years ago, an impact event ejected this rock from the Martian surface, after which it traveled through space and crashed into our planet in 1911.
While investigating a polished thin section prepared from the Nakhla sample # BM1911, 369, Dr Chatzitheodoridis and his colleagues found an unusual ‘cell-like’ oval structure with a concentric wall.
“In many ways it resembled a fossilized biological cell from Earth but it was intriguing because it was undoubtedly from Mars,” said Prof Ian Lyon of the University of Manchester, a team member and the senior author of the paper published in the journal Astrobiology.
Transmitted light photomicrographs of the cell-like structure in Nakhla. Left: overview photomicrograph; the oval structure is situated inside a small late-forming pocket of mesostasis materials that is interstitial to two clinopyroxene crystals (Cpx); in detail, the oval exhibits a sharp contact with the adjacent amorphous mesostasis phase (M), which is identified as rhyolitic glass; the opaque phases are Ti magnetite (Mt) and rhoenite (Rho). Right: close-up photomicrographs; black arrows indicate conspicuous, orange-stained microchannel features in clinopyroxene rims; white arrows indicate fractures in the mesostasis M that are stained with iron oxide/hydroxide material (orange to yellow hues) and that extend up to the oval structure. Image credit: Chatzitheodoridis Elias et al.
To determine its nature, the scientists carried out a series of chemical and structural investigations at the micrometer and nanometer scales, employing a wide range of imaging and analytical techniques.
“There is strong textural and chemical evidence that the ovoid structure is indigenous to Nakhla and originated on Mars,” the scientists wrote in the paper.
“The petrographic context of this highly elliptical ovoid structure within late-forming mesostasis glass, coupled with its relatively large size, distinct chemical composition, and complex microtextures, supports this idea and effectively rules out the possibility of an origin by contamination.”
Prof Lyon said: “our research found that it probably wasn’t a cell but that it did once hold water – water that had been heated, probably as a result of an asteroid impact.”
The finding is significant because it adds to increasing evidence that beneath the surface, the Red Planet does provide all the conditions for life to have formed and evolved.
SEM images of the surface of a polished thin section of Nakhla, highlighting the petrographic context of the cell-like structure. Top: overview image. Bottom: close-up image, highlighting the structure and some of the surrounding phases. Abbreviations: Ap – apatite; Cpx – clinopyroxene, separated from the Al-rich Cpx with a dotted line; M – amorphous mesostasis phase (rhyolitic glass); Ol – olivine; Rho – rhoenite; S – sulfide. Image credit: Chatzitheodoridis Elias et al.
It also adds to a body of evidence suggesting that large asteroids hit Mars in the past and produce long-lasting hydrothermal fields that could sustain life on the planet, even in later epochs, if life ever emerged there.
“We have been able to show the setting is there to provide life,” Prof Lyon said.
“It’s not too cold, it’s not too harsh. Life as we know it, in the form of bacteria, for example, could be there, although we haven’t found it yet. It’s about piecing together the case for life on Mars – it may have existed and in some form could exist still.”
Now the scientists are using state-of-the-art techniques to investigate secondary materials in Nakhla and search for possible bio signatures which provide scientific evidence of life, past or present.
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Chatzitheodoridis Elias et al. 2014. A Conspicuous Clay Ovoid in Nakhla: Evidence for Subsurface Hydrothermal Alteration on Mars with Implications for Astrobiology. Astrobiology 14 (8); doi: 10.1089/ast.2013.1069
