The discovery of tiny burrows found in martian meteorites on Earth adds intrigue to the search for life beyond this planet.
Researchers studying a meteorite that originated from Mars found a series of microscopic tunnels that mimic the size, shape and distribution to tracks left on Earth rocks by the feeding frenzy of bacteria.
Martin Fisk, a professor of marine geology in the College of Oceanic and Atmospheric Sciences at Oregon State University (OSU) in Corvallis, is lead author of a study team’s research findings, published in the February issue of the bimonthly journal Astrobiology and announced March 23 .
Fisk’s research team was unable to extract any DNA from the meteorite, so whether the tunnels are of biological origin remains unknown. Though the scientists said the lack of DNA also does not derail the prospect.
The focus of this study — the Nakhla meteorite — fell from the sky in 1911 near Nakhla in Egypt. The object was later identified as belonging to an exclusive group of objects known as SNC meteorites — of which the nakhlites is a subgroup — considered to come from the martian surface.
Scientists have dated the Nakhla igneous rock fragment at 1.3 billion years in age. They believe the rock was exposed to water about 600 million years ago, based on the age of clay found inside the rocks.
“Virtually all of the tunnel marks on Earth rocks that we have examined were the result of bacterial invasion,” Fisk explained in an OSU press statement. “In every instance, we’ve been able to extract DNA from these Earth rocks, but we have not yet been able to do that with the martian samples.”
That being the case, there are two likely scenarios.
“One is that there is an abiotic [nonliving] way to create those tunnels in rock on Earth, and we just haven’t found it yet,” Fisk said. “The second possibility is that the tunnels on martian rocks are indeed biological in nature, but the conditions are such on Mars that the DNA was not preserved.”
Fisk said it is commonly believed that water is an essential ingredient for life. “So if bacteria laid down the tunnels in the rock when the rock was wet, they may have died 600 million years ago. That may explain why we can’t find DNA — it is an organic compound that can break down.”
Handful of environments
How do scientists know that the meteorite came from the red planet in the first place? Nakhla is one of more than 30 meteorites identified as coming from Mars, hurled off that planet due to asteroid or comet impacts long ago. Eventually, after tumbling through space, a few crossed Earth’s orbit and came to a full-stop on the planet’s surface.
The SNC meteorites contain gas trapped in their interiors. The composition of this gas has been found to be nearly identical to that of the atmosphere on the red planet, as measured by NASA’s twin Viking Mars landers in 1976.
The igneous rocks from Mars are similar to many of those found on Earth, and virtually identical to those found in a handful of environments, including a volcanic field in Canada.
Scientists have come across rock-eating microbes on Earth in a wide assortment of places — below the ocean floor, in desert settings and on dry mountaintops, Fisk and his colleagues pointed out.
A follow-on question that the OSU researchers hope to answer is whether bacteria begin to devour the rock as soon as they are introduced. Such a discovery might help estimate when water — and possibly life — might have been introduced on Mars.
Along with Fisk, other authors on the Astrobiology paper include Olivia Mason, an OSU graduate student; Radu Popa of Portland State University; Michael Storrie-Lombardi of the Kinohi Institute in Pasadena, Calif.; and Edward Vicenzi from the Smithsonian Institution.
Old claim, new data
In other Mars meteorite research, an international team of scientists will fuel more debate about the 1996 NASA-led assertion that another martian meteorite — Allan Hills 84001, or ALH 84001 — contained tell-tale signs of past biological activity on Mars.
The claim centered on whether organic compounds and tiny globules of carbonate minerals imbedded in that meteorite may have been processed by martian biology. Indeed, the tiny carbonate globules from the meteorite seem to resemble minerals that arise from microbial activity on Earth.
But a fresh take on this issue will show that such carbon complexes in ALH 84001 likely formed by nonbiological processing on Mars, according to Andrew Steele of Carnegie Institution’s Geophysical Laboratory in Washington.
The new ALH 84001 research is to be presented at NASA’s Astrobiology Science Conference 2006 being held March 26-30 in Washington.