New evidence suggests that Mars’s magnetic field persisted until 3.9 billion years ago—hundreds of millions of years longer than many had thought.
Once upon a time, scientists believe, Mars was far from today’s cold, inhospitable desert. Rivers carved canyons, lakes filled craters, and a magnetic field may have fended off space radiation, keeping it from eating away the atmospheric moisture. As the martian interior cooled, leading theories hold, its magnetic field died out, leaving the atmosphere undefended and ending this warm and wet period, when the planet might have hosted life. But researchers can’t agree on when that happened.
When certain kinds of iron-bearing minerals crystallize out of molten rock, their internal fields align with the planet’s field like tiny compasses, preserving a stamp of its orientation. Subsequent impact events can heat up parts of a rock, glazing it with fields from later times and creating a magnetic palimpsest.in rocks on the surface of Mars.
Clues to an ancient magnetic field were found in thin slices of the martian meteorite Allan Hills 84001.Steele and Harvard planetary scientist Roger Fu imaged three paper-thin slices of a 0.6-gram Allan Hills sample with Fu’s state-of-the-art quantum diamond microscope. One of only a handful in the world, it relies on the sensitivity of atomic impurities in diamond to tiny changes in magnetic fields; it can.
Rob Lillis, a planetary geophysicist at the University of California, Berkeley, is more cautious about that line of reasoning. He says a field could also accelerate atmospheric losses by funneling more solar wind to the poles.
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