A meteorite is a natural object from space, typically a fragment of an asteroid, that survives passage through Earth’s atmosphere and lands on the surface. The question of whether these extraterrestrial rocks are magnetic is a frequent inquiry. While it is a common assumption that all meteorites possess this property, the true answer is nuanced. The magnetic attraction observed in a space rock is a direct consequence of its cosmic origin and internal composition. For the vast majority of recovered specimens, the presence of metal makes them responsive to a magnet.
The Role of Iron and Nickel in Meteorite Magnetism
The powerful attraction demonstrated by most meteorites is fundamentally due to the presence of metallic iron and nickel alloys. These elements are ferromagnetic, meaning they are strongly attracted to a magnetic field. This metallic content is a relic of the formation of their parent bodies, ancient asteroids in the early solar system.
The metallic iron is alloyed with nickel, forming two distinct mineral phases: kamacite and taenite. These alloys are virtually absent in naturally occurring terrestrial rocks. On Earth, nearly all iron has either sunk to the core or oxidized into non-metallic minerals like rust. The metal within a meteorite survived in its primordial, unoxidized state because it formed in the vacuum of space.
Some iron meteorites also retain a remnant magnetization, a subtle, permanent magnetic field imprinted when their parent asteroid was cooling. This ancient magnetic signature was generated by a dynamo effect within the asteroid’s molten core.
Magnetic Variation Across Meteorite Types
The strength of a meteorite’s magnetic attraction varies significantly depending on its classification, which is determined by its ratio of metal to silicate minerals. The three main groups—iron, stony, and stony-iron—display different levels of responsiveness to a magnet. Iron meteorites, for example, are composed of nearly solid iron-nickel metal, making them intensely magnetic and easily attracted to even a weak magnet.
Stony meteorites, known as chondrites, are the most common type and show a noticeable but generally weaker attraction. They are composed primarily of silicates, but contain small, scattered flecks of iron-nickel metal embedded throughout the rocky matrix. This dispersed metallic content is sufficient to generate a magnetic response, though weaker than a solid iron specimen.
In contrast, a small fraction of meteorites, such as achondrites, lunar meteorites, and Martian meteorites, often show little to no attraction. These rocky fragments underwent intense geological processing on their parent bodies, resulting in the separation or removal of metallic iron. Consequently, their composition is closer to terrestrial rock and they are effectively non-magnetic to a standard field test.
Magnetism as an Identification Tool
The magnetic test is a practical and quick initial step for identifying a suspected space rock. An inexpensive ceramic or ferrite magnet, such as a common refrigerator magnet, is the recommended tool. If the rock does not attract a ceramic magnet, it is highly unlikely to be one of the most common meteorite types.
Magnetism is a necessary condition for most meteorites, but it is not sufficient for positive identification. Several common terrestrial rocks and human-made materials also show magnetic attraction, leading to false positives. For instance, the iron oxide mineral magnetite is abundant in some Earth rocks, and industrial slag can contain metallic inclusions that make it magnetic.
Using an overly powerful neodymium magnet is discouraged because its strong pull can attract many weakly magnetic terrestrial rocks, providing misleading results. Furthermore, strong magnets can permanently alter or erase the delicate, ancient magnetic history stored within a meteorite. Therefore, a magnetic test should always be followed up with other observations, such as checking for a dark, melted fusion crust or the rock’s unusually high density.