SHARON SHANKS | The Cosmos Astrobiologists agog over meteorite crystals

More evidence for ancient life on Mars has some astronomers scrambling for their microscopes, not their telescopes.
Just because some scientists are astronomers doesn't mean they all use telescopes to study the sky. Some use powerful scanning microscopes to look for signs of life inside rocks from space. They are the astrobiologists -- an exciting and growing field within astronomy.
Their microscopes are working furiously right now, thanks to the release last week of two new scientific papers that have reignited the smoldering debate over ancient life on Mars.
Here's the debate: The two papers, published in the journal Proceedings of the National Academy of Sciences, argue that the magnetite found in the Allen Hills meteorite, the piece of Mars rock that started the debate in 1996, and two other younger Martian meteorites could only be biological in origin.
Biological, of course, means life.
A team of researchers found that a quarter of the strings of fossilized magnetic "crystals" found inside ALH840001 (the official designation for the Allen Hills meteorite) were identical to a type of magnetite found on Earth that is created only by a particular type of bacteria.
Organic (living processes) and inorganic (chemical processes) can make magnetite crystals. The crystals deep inside the meteorite, however, are pure and free of defects, a sign of organic formation, the researchers stated. Chemical processes don't produce such pure crystals.
Explanation: What the researchers are studying are basically tiny magnets -- little bar magnets one millionth of an inch in size. They can only be studied by scanning electron microscopes.
Here on Earth, microbiologists have been studying magnetotactic ("magnetic sensing") bacteria for only the past two decades or so. Most bacteria don't care what kind of magnetic field surrounds them.
Some others do care, and produce tiny magnetic crystals in chains that resemble a string of peals that serve to orient the bacteria with magnetic forces, such as the Earth's magnetic field.
The magnetite, a form of iron and oxygen, forms in dense little bodies enclosed by membranes. They don't touch each other -- another clue that the strings of magnetic crystals found in the Mars meteorites are biological in nature. They are clearly very close together, but don't touch.
If the magnetite wasn't enclosed in structures within the bacteria, their magnetic attraction to each other would cause them to form into clumps, not a line, according to other researchers.
About those bacteria: Magnetic microbes on Earth have been a curiosity, but not much research has been done with them (a situation that may change, thanks to the recent discoveries). Most microbacterial research is within the medical field -- finding and identifying bacteria that make us sick or can make us well.
The magnet-feeling bacteria on Earth have been found deep within rocks; some thrive in low oxygen levels and others don't need oxygen at all.
The reason why these tiny bits of primitive life have adapted magnetic pointers is a mystery, however. There doesn't seem to be any obvious reasons why a bacteria needs to move to the north or south.
Bacteria and other microorganisms are the most abundant living things on Earth. They thrive in the soil, rocks, water, your intestines, and plants.
They have adapted to fill niches in every sort of environment you can think of: at the bottoms of frozen lakes, at the tops of mountains, in your eyelashes, miles below the surface, and in the complete dark at the bottom of the oceans.
Some bacteria are harmful, of course, but most are benign or beneficial -- without bacteria in our intestines, for example, we wouldn't be able to absorb and digest our food.
Another team of researchers also examined two other Martian meteorites named Nakhla and Shergotty (from the locations where they were found). They found similar lines of spheres embedded in or coated by Martian clays.
Significance: Like the announcement last summer about compelling evidence for recent water activity on Mars, the new papers are smoking guns for the scientific community.
They present a theory and the evidence, and now it's up to others to either support or refute their claims. So far, strong arguments have been made on both side of the "organic/chemical" debate surrounding ALH80001, but the question is far from being answered. It will take a mission to Mars by robots or humans to collect non-random samples and return them to Earth.
The pieces of Mars we do have on Earth came here completely by accident. Large, catastrophic impacts on the surface of Mars knock away part of the planet's crust with so much force that the rocks were blasted into space.
There they floated for millions and billions of years until they traveled close enough to Earth to be caught up by our planet's gravity. The Allen Hills meteorite was found in Antarctica; others have been found in deserts. Both areas help preserve the meteorites.
Some scientists are already refuting the biological nature of the magnetic strings within the meteorites.
Just because the authors of the papers couldn't find a chemical, inorganic process to explain the formation of the magnetites doesn't mean one doesn't exist. More research on inorganic processes will certainly be conducted in the near future.
The team of scientists involved in both papers include those who originally published the ALH84001 paper in 1996: Kathie Thomas-Keprta and David McKay at NASA's Johnson Space Center.
Others include Imre Friedmann of NASA's Ames Research Center, who is also known for discovering microorganisms living inside desert rocks.