"We are not claiming that NASA scientists are wrong or that there cannot be life on Mars, but that there is enough uncertainty to call their claim into question," the researchers wrote.
The meteorite, based on the findings discovered in it, NASA scientists hypothesized that life existed on Mars in the past.
A study that examined the structure of tiny crystals produced by bacteria casts renewed doubt on NASA scientists' claim that a Martian meteorite provides evidence that life once existed on the surface of the Red Planet. The researchers, led by scientists from Arizona State University, used new techniques based on A computerized electron microscope to reveal in greater detail than before the three-dimensional shapes of the crystals, which are composed of from a mineral called magnetite.
The crystals can be formed by inorganic processes or biologically by living bacteria.
In 1996, NASA researchers published the amazing discovery that the magnetite crystals found in the meteorite are similar in size and shape to those produced by a certain species of bacteria from Earth, and therefore could only have been produced by a bacterium that probably lived on Mars billions of years ago. But after a detailed discovery More of the bacterial crystal structure of the magnetite, the researchers from the University of Arizona claim that the analysis of NASA, which relies on older techniques based on electron microscopy, is not necessarily accurate.
"We would not have reached the conclusions they reached," said Peter Bosk of the University of Arizona, one of the lead scientists in the study, which was published this week in the journal "Proceedings" of the National Academy of Sciences. Our article does not claim that they are wrong or that there cannot be life on Mars , but there is enough uncertainty to cast doubt on their claim. Normally, the differences between the two groups' findings are not that important. But in this case, we are talking about the only evidence for life outside For the planet, it's quite important."
The magnetite crystals are very difficult to study, since their length is on the order of 100 nanometers, that is, 100 billionths of a meter, and their shape is complex. A transmission electron microscope (TEM) can produce the general shape of the crystal, but to determine the three-dimensional shape on all its sides and edges the crystal must be tilted precisely at different angles.
The University of Arizona researchers improved the ability to tilt the crystals, and used computers running sophisticated algorithms to interpret the data to discover the three-dimensional shapes. The scientists studied crystals produced by three strains of bacteria, including MV-1, the one studied by NASA scientists, and found that the structural differences between them are greater than NASA researchers thought.
In addition, the structure of the MV-1 crystals that they arrived at using the newer method was different from the structure that the NASA team arrived at.
But Kathy Thomas-Caperta, a senior scientist at NASA, said the researchers have an interesting technique, but "they haven't looked at our meteorite. They must do this and then make a comparison."
