The fact that iron meteorites are frequently magnetic is one of their outstanding characteristics. Although the magnetism is weak, it contains information about their origin.
This is why astronomers advise against using hand magnets to remove a meteorite’s magnetic history, which is a crucial piece of scientific data for separating meteorites from the surrounding rock.
Because they develop in the presence of a magnetic field, magnetic meteorites do exist. The meteorite has its own magnetism because the iron grains inside it are aligned with the earth’s magnetic field.
For instance, the magnetism of the Martian meteorite Black Beauty was derived from the robust magnetic field of young Mars.
While some meteorites should not have originated in a strong magnetic field, they are magnetic. Usually, the chemical makeup of iron meteorites—such as the proportion of nickel to iron—is used to classify them.
IVAs are one type that are recognized as being made up of pieces of smaller asteroids. IVA meteorites shouldn’t be magnetic as small asteroids don’t have powerful magnetic fields, but many of them are. A recent study demonstrates how that is feasible.
The so-called “rubble pile method” is the process through which small asteroids develop. Over time, little iron-rich rock fragments accumulate and grow into asteroids.
Small asteroids can’t have magnetic fields because they don’t have enough liquid iron to produce a dynamo effect, which is required for a body to have a strong magnetic field. But can they?
Over time, asteroids are also vulnerable to collisions. These impacts cause bits to break off and create the meteorites that we encounter on Earth. However, the authors demonstrate that impacts can cause an asteroid to develop a magnetic dynamo.
A series of events may happen if a colliding body is large enough to melt a layer of material close to the surface but not huge enough to break the asteroid.
The core is heated when a molten layer surrounds a cold rubble core. Convection is created by the churning of the strata caused by lighter components evaporating from the core and moving toward the surface.
Iron convection creates a magnetic field that leaves its mark on some of the asteroid. After a second collision, magnetic pieces are produced, some of which reach Earth.
Thus, the magnetism of IVA meteorites was stirred up by later collisions rather than being created when their parent asteroid was first formed.
With this knowledge, scientists can better comprehend the evolution of our solar system and how planetary drift may have led to an increase in the frequency of asteroid crashes.
Yet another excuse not to use hand magnets when searching for meteorites. A meteorite’s discovery itself might also obliterate the records of its encounters.