This scanning electron microscope image shows spheroidal features embedded in a layer of iddingsite, a mineral formed by action of water, in the Yamato 000593 meteorite. An area with the spheres, circled in red, was found to have about twice as much carbon present as an area (circled in blue) without the spheres. The measure at left is one micron (.001 mm) or about the size of some bacteria. Credit: NASA
A team of scientists at NASA’s Johnson Space Center in Houston and the Jet Propulsion Laboratory in Pasadena, Calif., has found evidence of past water movement and tiny carbon-rich spherules in Martian meteorite Yamato 000593.
The 30-pound (13.7 kg) chunk of Mars was collected on the Yamato Glacier in Antarctica by the Japanese Antarctic Research Expedition in 2000. It was once part of a 1.3 billion year old Martian lava flow but was ejected by a meteorite impact 12 million years ago and landed near the south pole some 50,000 years ago.
Scientists distinguish Mars rocks from Earth’s by the atmospheric gases trapped inside (these are compared to measurements of the planet’s atmosphere made in situ by our Mars landers) and the distinctive composition of oxygen in the minerals making up the rock. Martian rocks contain a greater proportion of oxygen’s heavier forms, called isotopes, compared to Earth rocks.
This scanning electron microscope image of a polished thin section of a meteorite from Mars shows tunnels and curved micro-tunnels deep within Yamato 000593. Iddingsite is a clay mineral indicating that water once flowed through cracks in the rock. The scale bar at lower left is 2 microns. Credit: NASA
The team made two fascinating discoveries when they peered closely into the interior of the meteorite:
* Micro-tunnel structures with curved, undulating shapes that thread their way through the rock and resemble similar textures reported by other researchers in terrestrial basaltic glasses created by bacteria.
* Distinct nanometer- to-micrometer-sized spherules resembling bacteria that are sandwiched between layers within the rock and enriched in carbon compared to their surroundings.
Similar bacteria-like structures are found inside the Martian Nakhla meteorite that fell in Egypt in 1911. Credit: NASA / ARES / JSC
Similar spherical features were previously seen in the Martian meteorite Nakhla that fell in Egypt in 1911. Everett Gibson, who led the new study, was also involved in the 1996 study of Allan Hills 84001, the first Martian meteorite thought to be touched by life’s imprint. I’ll never forget the excitement and controversy at the time when it was announced that possible evidence of life in the form of worm-like structures and organic molecules were found within the meteorite.
Bacteria-like structures in the Martian Allan Hills 84001 (ALH 84001) meteorite discovered in Antarctica in 1984. Credit: NASA
We know now that virtually all potential “signs of life” found by the 1996 researchers could have been created by chemical and other inorganic processes, making the team’s results inconclusive at best.
Likewise, Gibson and Lauren White, lead author of the recent paper on Yamato 000593 in the International Journal of Astrobiology, allow that non-living processes could have cooked up the carbon-rich structures and micro-tunnels. Still, the similarities between structures in basaltic Earth rocks and Yamato 000593 might also imply life’s handiwork on a planet other than our own.
Rock-eating bacteria – called endoliths – inside a basaltic rock found 3,900 feet (1,200 meters) beneath the Indian Ocean floor. Credit: NOAA Ocean Explorer
“As more Martian meteorites are discovered, continued research focusing on these samples collectively will offer deeper insight into attributes which are indigenous to ancient Mars,” said White. “As these meteorite studies are compared to present day robotic observations on Mars, the mysteries of the planet’s seemingly wetter past will be revealed.”
Knowing how scientists relish testing any new claim, especially one hypothesizing early life on Mars, the story of Yamato 000593 can’t help but be revised and expanded in the months and years ahead.