Scientists think that Mars was far away from today's desert. Watercarved canyons, lakes filled craters, and a magnetic field may have protected them from space radiation. The atmosphere was left undefended when the magnetic field of the martian interior died out. Researchers can't agree on when that happened
It has been found that the planet's field persisted until 3.8 billion years ago, hundreds of millions of years longer than previously thought. The clues in the meteorite, a Mars rock that ended up on Earth after an impact blasted it from its home planet, could help reconcile differing timelines of the planet's early history. The findings were discussed last week at a meeting of the American Geophysical Union.
A paleomagnetist who was not involved in the study says that they were able to paint a pretty good picture of what might have happened. It wasn't possible with the technology before.
The internal fields of iron-bearing minerals are aligned with the planet's field, preserving a stamp of its orientation. A magnetic palimpsest can be created when parts of a rock are heated up by impact events.
Magnetic signatures can be found in rocks on the surface of Mars. The Hellas, Argyre, and Isidis asteroid impact basins don't seem to have any magnets at all. The craters were formed about 4.1 billion years ago. Magnetic signatures from other parts of Mars suggest the field has survived longer than the basins let on.
Sarah Steele is a graduate student in Earth and planetary sciences at Harvard University.
Steele wondered if Allan Hills 84001 had something to say on the question. At 4.1 billion years old, the only known pristine sample to record this critical era of Mars's history is the 2-Kilogram rock, which wasbunked in the 1990s but is still studied today.
Steele and Fu used a state-of-the-art quantum diamond microscope to image the Allan Hills sample. It uses diamond's sensitivity to tiny changes in magnetic fields to map the changes across grains as small as a human hair. There are three distinct populations of iron-sulfide minerals. Two were magnetized in different ways.
Steele and Fu propose that the groupings reflect three impact events that were recorded by the meteorite. Fu says the global magnetic field must have been present at least 3.8 billion years ago because the two older mineral populations are magnets. About 17 microtesla is the average strength of Earth's field.
Ben Weiss is a planetary scientist at the Massachusetts Institute of Technology. The atmosphere could be protected from the solar wind, a stream of particles that can accelerate the loss of water vapor and other components to space. It is possible to have a period on Mars where it is possible to live.
Rob is more cautious about that line of reasoning. He says a field could speed up atmospheric losses by sending more solar wind to the poles.
The two populations record fields point in opposite directions, which is a clue to the planet's internal workings. The researchers don't think there's a chance of the rock rotating. Earth flips its poles every few hundred million years. The simulations show that the martian reversals could help constrain the history and nature of the dynamo.
Many large basins don't have a magnetic signal. Steele used computer simulations to show layers of alternating magnetic fields canceling out the net magnetic field of the basins. Steele says that the reversals could allow us to tie all the strings together.
Magnetic reversals can provide a time marker for rocks from different places. Weiss is excited to hear that there is evidence for a reversal in a meteorite. The plan we have in mind here is a lot more feasible ifMars's dynamo reverses.
The Allan Hills meteorite sparked Fu's interest in science when he first saw it on television. Fu says that early Mars is a dark box. It is cool that we can still get new information out of a rock that has been analyzed to death.
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