A 13,000 year old meteorite from Mars, found in 1984 in the Allan Hills Region of Antarctica, is back in the news. The rock caused quite a stir when NASA announced during an August 1996 press conference that it contained evidence of past life on Mars.
The first paper in Science described micrometer-sized carbonate deposits, shaped like pancakes, along tiny cracks and crevices in the meteorite, known as ALH84001. Researchers theorized that the carbonates were deposited from carbon dioxide-saturated fluids that were no more than 100 degrees Celsius -- the temperature around which microorganisms on Earth flourish.
They also found nanometer-sized iron sulfide and iron oxide grains (which they theorized were produced by bacteria) and organic compounds known at polyaromatic hydrocarbons, or PHAs, which they suggested were the organic remains of Martian organisms.
The clincher, however, was the discovery of “worm-shaped objects” within the meteorite’s fractures, which scientists proposed were the fossilized remains of the organisms themselves.
The results were controversial from the start and were quickly followed by a flurry of papers that refuted every leg of the argument including the life-friendly temperature of the water; the biological origin of the iron grains; and the prospect that the organic PAHs actually came from Antarctica, not Mars.
"A quiet consensus has emerged that the ALH84001 meteorite contains no evidence of past Martian life," wrote Georgia Tech’s John Bradley.
This month, NASA scientists responded with a fresh volley of research that used a new analysis technique, called ion beam milling, to study the iron grains. They conclude that there is "considerable evidence" that the nanocrystal iron grains were not the result of geology, which leaves biology as the only other alternative.
In advance of scientists deciding what this latest research means, some members of the (British) press have decided that life (once again) has been found on Mars, or at least inside this one Martian rock.
They may be right, of course. Or, quite possibly, given a couple of weeks or even days, scientists may trump the results once again. That is the nature of the scientific process.
We'll have more on this story next week.
(ALH84001: A space crypt for Martian bugs? Credit: NASA)
COMMENTS (0)