Magnetic Martians

kw: astrobiology, musings

Fourteen years have passed since images like these were proclaimed as possible fossils from Mars. The controversy has quieted down, but not gone away. It took me a while to locate an image with a scale bar on it. The first objection to these was, if they are remnants of cells, they are much too small.

During the hot part of the public discussion, every article that mentioned these "worms" implied that they are composed of calcite. I was not paying enough attention at the time to look further into it. Recently, I happened to read a more detailed analysis that stated they are a mix of iron oxides, including magnetite. Now that got my attention. Then an even better article showed up: "Chains of magnetite crystals in the meteorite ALH84001: Evidence of biological origin" by E. Imre Friedmann, Jacek Wierzchos, Carmen Ascaso, and Michael Winklhofer; PNAS, January 2001. I don't know how I missed it at the time.

If the apparent lumpiness of these chains represents cells, they are roughly 150nm in diameter, which is small even for nanobacteria, and apparently too small for protein synthesis machinery to function (assuming Martian bacteria used proteins). But if each of these items was a chain of mineral grains in a single cell, the size problem vanishes.

Most of this image is taken up by a single bacterial cell. Within it is a chain of magnetite particles, which it uses to detect and orient with the Earth's magnetic field. Allowing for the differing scales of the two images, this chain is the same size as the chains of grains from Mars.

But, it is objected, Mars has no magnetic field. That doesn't mean it never had one. Its core is frozen now, but must have been molten at an earlier time, simply from the cosmology of planet formation. Early in Mars's history, it did have a magnetic field, it is likely to have had an atmosphere and liquid water; lots of physiographic features on its surface show this.

If life got a start on Mars as soon as it did on Earth, there may have been a period as long as a billion years for it to evolve and flourish, before the loss of water and atmosphere made everything extinct. In the late 1990s, the trend of the debate was decidedly anti-Martian life. Now, the pendulum is back the other way.