Meteorite's magnetic memory gives clues to Earth's future

Scientists have studied the magnetic memory contained in ancient meteorites, offering a tantalising glimpse of what may happen to the Earth's magnetic core billions of years from now.
Using a detailed imaging technique, the researchers were able to read the magnetic memory contained in ancient meteorites, formed in the early solar system over 4.5 billion years ago.
The readings taken from these tiny 'space magnets' may give a sneak preview of the fate of the Earth's magnetic core as it continues to freeze.
Using an intense beam of X-rays to image the nanoscale magnetisation of the meteoritic metal, researchers led by the University of Cambridge, UK, were able to capture the precise moment when the core of the meteorite's parent asteroid froze, killing its magnetic field.

These 'nano-paleomagnetic' measurements, the highest-resolution paleomagnetic measurements ever made, were performed at the BESSY II synchrotron in Berlin.
The researchers found that the magnetic fields generated by asteroids were much longer-lived than previously thought, lasting for as long as several hundred million years after the asteroid formed, and were created by a similar mechanism to the one that generates the Earth's own magnetic field.

The results help to answer many of the questions surrounding the longevity and stability of magnetic activity on small bodies, such as asteroids and moons.
The particular meteorites used for the study are known as pallasites, which are primarily composed of iron and nickel, studded with gem-quality silicate crystals.

Contained within these chunks of iron however, are tiny particles just 100 nanometres across - about one thousandth the width of a human hair - of a unique magnetic mineral called tetrataenite, which is magnetically much more stable than the rest of the meteorite, and holds within it a magnetic memory going back billions of years.
The researchers' magnetic measurements, supported by computer simulations, demonstrated that the magnetic fields of these asteroids were created by compositional, rather than thermal, convection - meaning that the field was long-lasting, intense and widespread.
These meteorites came from asteroids formed in the first few million years after the formation of the Solar System. At that time, planetary bodies were heated by radioactive decay to temperatures hot enough to cause them to melt and segregate into a liquid metal core surrounded by a rocky mantle.

As their cores cooled and began to freeze, the swirling motions of liquid metal, driven by the expulsion of sulphur from the growing inner core, generated a magnetic field, just as the Earth does today.
"In our meteorites we've been able to capture both the beginning and the end of core freezing, which will help us understand how these processes affected the Earth in the past and provide a possible glimpse of what might happen in the future," said Dr Richard Harrison of Cambridge's Department of Earth Sciences, who led the research.