Campus: Cal Poly, San Luis Obispo -- November 20, 2001

Life on Mars Still Unproven, Cal Poly Professor and Colleagues Say in Journal Article

Life on Mars still remains in the realm of science fiction, not solid science, according to Cal Poly Physics Professor Richard Frankel and his co-authors in an article to be published Wednesday (Nov. 21) in The Proceedings of the National Academy of Sciences.

Frankel and other members of his research team challenge NASA scientists' much-publicized announcement in 1996 that a Martian meteorite found in Antarctica contains evidence of fossil bacteria - and thus life on Mars at some point in the planet's history.

That 1996 NASA announcement brought a storm of excitement, publicity and controversy. In the five years since, other scientists have shown that nonbacterial contamination could explain many of the "bacterium-shaped objects" and supposedly organic chemicals found in the meteorite and cited by NASA as evidence.

Now Frankel and the other members of his research team have assailed the final NASA contention: that the magnetite crystals found in the Martian meteorite have three-dimensional shapes identical to certain bacteria here on Earth, and different from any of those produced by any inorganic (nonbiological) forces.
Frankel and team members argue that the assumed match between the Martian meteorite's crystals and bacteria on Earth is at best ambiguous and at worst, mistaken.

In their paper, "Magnetite Morphology and Life on Mars," Frankel and his co-authors argue that the evidence for bacterial magnetite crystals on the Martian meteorite is inadequate, and they used comparisons with bacterial magnetite crystals from Morro Bay to help explain why.

The magnetite crystals in the NASA Martian meteorite are tiny, even by the standards of an electron microscope, Frankel explains. They are only 40 to 100 billionths of a meter wide.
"And there's the rub," says Frankel. "The technology necessary to accurately describe the Cal Poly News three-dimensional shape of such small crystals has become available only in the last few years." The magnetite crystals in the Martian meteorite have not yet been subjected to the new viewing techniques. So, Frankel says, "it's still too early to say for sure what the exact shapes of the meteoritic crystals are, let alone whether they match those in bacteria."

The only kind of microscope powerful enough to produce clear images of the magnetite crystals found in the meteorite is a relatively new piece of equipment called a transmission electron microscope, or TEM. By using a beam of electrons rather than a beam of light to view the sample, a TEM allows researchers to see objects smaller than one billionth of a meter wide. But a TEM sees only in two dimensions. It generates a silhouette image of a sample, but conveys little about its thickness, according to Frankel.
An accurate description of the crystals contained in the Martian meteorite and their complex three-dimensional shapes requires that they be examined from a variety of perspectives, Frankel and his colleagues explain. Distinguishing between the crystals' flat facets and tapered tips is a challenge. Only by tilting each crystal at dozens of angles can scientists unequivocally identify their three-dimensional shapes, according to Frankel and his colleagues.

At the time of the NASA study, the tilting experiments could be done only by hand, and with great difficulty. The NASA group used this approach to create images of the magnetite crystals from both the meteorite and from one strain of bacteria found on Earth.

Recently, scientists have coupled TEM technology with computer imaging to make experiments more precise.

This new technology is available at Arizona State University and the University of Cambridge in England. Frankel and his team of co-authors used it to reexamine the evidence in the NASA study and contrast it with biological magnetite crystals from Earth - some collected in Morro Bay.

Their results call into question whether the shapes of all crystals originating in the Martian meteorite found in Antarctica are accurately known. In their research, Frankel and his team demonstrate that the shapes of bacterial magnetite grains found on Earth vary more than previously thought. According to their research, the shapes and sizes differ among bacterial strains, and even within individual bacteria. That expanded variety makes it more likely that bacterial and meteoritic magnetite grains could match by simple chance, Frankel's team concluded.

However, the team did not eliminate the possibility that the Martian crystals could have a biological origin. With the advanced TEM technology now on hand, Frankel and his team members plan more conclusive studies of the magnetite crystals from the Martian meteor and several more strains of terrestrial bacteria.
Frankel's co-authors on the paper are Peter Busek and Martha McCartney of Arizona State University; Rafal Dunin-Borkowski, Paul Midgley and Matthew Weyland of Cambridge University; Bertrand Devouard of Blaise Pascal University in France; and Mihalay Posfai of the University of Veszprem, Hungary.


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