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[escepticos] bacterias en Marte: mas pruebas



> RESEARCHERS PUBLISH LATEST RESULTS
> IN CONTINUING SEARCH FOR ANCIENT MARTIAN LIFE
>
> Dwayne Brown
> Headquarters, Washington August 2, 2002
> (Phone: 202/358-1726)
>
> Catherine E. Watson
> Johnson Space Center, Houston
> (Phone: 281/483-5111)
>
> http://ares.jsc.nasa.gov/astrobiology/biomarkers/recentnews.html
>
> In the latest study of a 4.5 billion-year-old Martian meteorite,
researchers
> have presented new evidence confirming that 25 percent of the magnetic
> material in the meteorite was produced by ancient bacteria on Mars. These
> latest results were published in the journal Applied and Environmental
> Microbiology.
>
> The researchers used six physical properties they refer to as the
Magnetite
> Assay for Biogenicity (MAB) to compare all the magnetic material found in
> the ancient meteorite -- using the MAB as a biosignature. A biosignature
is
> a physical and/or chemical marker of life that does not occur through
random
> processes or human intervention.
>
> "No non-biologic magnetite population, whether produced by nature or in
the
> laboratory, has ever met the MAB criteria," said Kathie Thomas-Keprta, an
> astrobiologist at NASA's Johnson Space Center (JSC) in Houston and the
lead
> researcher on the study. "This means that one-quarter of the magnetite
> crystals embedded in the carbonates in Martian meteorite ALH84001 require
> the intervention of biology to explain their presence."
>
> Magnetotactic bacteria, which occur in aquatic habitats on Earth, arrange
> magnetite crystals in chains within their cells to make compasses, which
> help the bacteria locate sources of food and energy. Magnetite (Fe3O4) is
> produced inorganically on Earth, but the magnetite crystals produced by
> magnetotactic bacteria are very different -- they are chemically pure and
> defect-free, with distinct sizes and shapes.
>
> Four of the MAB biosignature properties relate to the external physical
> structure of the magnetite crystals, while another refers to their
internal
> structure and another to their chemical composition.
>
> In their earlier studies, the researchers found that approximately
> one-quarter of the nanometer-sized magnetite crystals in ALH84001 had
> remarkable physical and chemical similarities to magnetite particles
> produced by a bacteria strain on Earth called MV-1. This is the first
time,
> however, that any researcher has used the full MAB range of biosignature
> properties to compare the proposed bacteria- produced crystals in Mars
> meteorite ALH84001with the bacteria-produced crystals from Earth and with
> the other magnetites in the meteorite.
>
> The comparison between the proposed bacteria-produced crystals in the
> meteorite and crystals known to be produced by Earth-bacteria MV-1 is
> striking and provides strong evidence that these crystals were made by
> bacteria on Mars.
>
> The fact that Mars Global Surveyor data suggest that early Mars had a
> magnetic field is consistent with a reason why Mars would have
magnetotactic
> bacteria. "Our best working hypothesis is that early Mars supported the
> evolution of bacteria that share several traits with magnetotactic
bacteria
> on Earth, most notably the MV-1 group," said Simon Clemett, a coauthor of
> the paper at Johnson.
>
> Mars has long been understood to provide the sources of light and chemical
> energy sufficient to support life, but in 2001 the Mars Global Surveyor
> spacecraft observed magnetized stripes in the crust of Mars, which showed
> that a strong magnetic field existed in the planet's early history, about
> the same time as the carbonate containing the unique magnetites in
ALH84001
> was formed.
>
> In June, researchers using the Mars Odyssey spacecraft announced that they
> had found water ice under the surface of Mars. These attributes, coupled
> with a carbon dioxide-rich atmosphere, would have provided the necessary
> environment for the evolution of microbes similar to the fossils found in
> ALH84001.
>
> "We believe this latest study proves that the magnetites in ALH84001 can
be
> best explained as the products of multiple biogenic and inorganic
processes
> that operated on early Mars," Thomas-Keprta said.
>
> An international team of nine researchers collaborated on the three-year
> study. The team, led by Thomas-Keprta of Lockheed Martin at Johnson Space
> Center, was funded by the NASA Astrobiology Institute. Co-authors of the
> study are Clemett and Susan Wentworth of Lockheed Martin at JSC; Dennis
> Bazylinski of Iowa State University (funded by the National Science
> Foundation); Joseph Kirschvink of the California Institute of Technology
in
> Pasadena; David McKay and Everett Gibson of JSC; Hojatollah Vali of McGill
> University in Canada; and Christopher Romanek of the Savannah River
Ecology
> Laboratory.
>