One of the most shocking things about meteorites is that they have a magnetism of their own. It is not strong, but it contains the information about the origin of these “fallen from the sky” rocks, which is especially important for scientists. That’s why astronomers discourage “meteor hunters” from using magnets to search for them, because the magnets used can destroy the magnetic history of meteorites.
Why are meteorites magnetic?
The magnetism of meteorites occurs because they form in the presence of magnetic fields. The iron “grains” inside a meteorite are aligned along the external magnetic field, which gives it its own magnetism.
For example, the Martian meteorite named “Black Beauty” acquired its own magnetism from the strong magnetic field of Mars early in its existence.
Some meteorites exhibit magnetism, but this is not necessarily due to strong magnetic fields.
This is usually the case with metallic meteorites, with a special chemical composition characterized by high levels of nickel and iron. One particular type, called IVA, is known to be fragments of smaller asteroids.
They do not have strong magnetic fields, so these meteorites should not exhibit magnetic properties. However, many do. A recent study shows how this is possible.
The fascinating discovery of scientists
Small asteroids are formed by what is called the “debris heap method”. Small pieces of iron-rich rock coalesce over time to create a small asteroid.
For a celestial body to generate a strong magnetic field, the existence of liquid iron is needed to create a “dynamo effect”, but since small asteroids do not have such a thing, they cannot have a magnetic field either. Or can I, in fact?
Asteroids are subject to collisions over time. These collisions that shatter them into small pieces are the fragments we find on Earth. But the authors of the study published in Universe Today showed that this impact can create a “dynamo effect” inside the asteroid.
If another body is not large enough to shatter an asteroid, but can melt the layer of material on its surface, then a chain of events occurs.
When the cold core of a “debris pile” is surrounded by a molten layer of material, the core heats up. Lighter elements evaporate from the core and migrate to the surface, allowing the outer layers to generate the convection effect.
The iron convection generates a magnetic field, which is “imprinted” in certain parts of the asteroid. Subsequent collisions create fragments with their own magnetism, some of which reach Earth.
Therefore, the magnetism of Type IVA meteorites does not come from their initial formation from their “parent” asteroids, but rather from subsequent collisions that transform their cores.
Knowing this, researchers can now better understand the history of the Solar System and how phenomena for celestial bodies wandering through space can trigger more frequent asteroid collisions.
