Ancient meteorites' magnetic fields contain records of early histories of planets

Washington, Oct 31 : A new research has determined that ancient meteorites that are among the oldest rocks ever found, still contain magnetic records about the very early history of planets.

MIT planetary scientist Benjamin P. Weiss did the research.

Weiss and his five co-authors examined pieces of three meteorites called angrites, which are among the most ancient rocks known.

The analysis showed that surprisingly, during the formation of the solar system, when dust and rubble in a disk around the sun collided and stuck together to form ever-larger rocks and eventually the planets we know today, even objects much smaller than planets - just 160 kilometers across or so - were large enough to melt almost completely.

This total melting of the planet-forming chunks of rock, called planetesimals, caused their constituents to separate out, with lighter materials including silicates floating to the surface and eventually forming a crust, while heavier iron-rich material sank down to the core, where it began swirling around to produce a magnetic dynamo.

The researchers were able to study traces of the magnetic fields produced by that dynamo, now recorded in the meteorites that fell to Earth.

"The magnetism in meteorites has been a longstanding mystery," Weiss said, and the realization that such small bodies could have melted and formed magnetic dynamos is a major step toward solving that riddle.

Until relatively recently, it was commonly thought that the planetesimals - similar to the asteroids seen in the solar system today - that came together to build planets were "just homogenous, unmelted rocky material, with no large-scale structure," Weiss said.

"Now, we're realizing that many of the things that were forming planets were mini-planets themselves, with crusts and mantles and cores," he added.

That could change theorists' picture of how the planets themselves took shape.

If the smaller bodies were already molten as they slammed together to build up larger planet-sized bodies, that could "significantly change our understanding" of the processes that took place in the early years of the nascent planets, as their internal structures were forming, according to Weiss.

This could have implications for how different minerals are distributed in the Earth's crust, mantle and core today.

ANI