Meteorites are magnetic because they generally contain ferromagnetic minerals such as magnetite (Fe3O4) or pyrrhotite (Fe1-xS). These minerals became magnetized during the solidification of the meteorite, thus retaining a certain magnetization.
Meteoroids are often magnetic because they contain a lot of metallic minerals, notably a natural alloy of iron and nickel. This alloy is called kamacite or taenite when the proportion of nickel varies slightly. When these rocks form in space, these heavy metals accumulate at their center and give rise to the so-called iron meteorites. The richer a meteoroid is in iron-nickel, the more it will be attracted to a magnet. Stony meteorites, on the other hand, contain less of these metals but can still have some metallic fragments, which explains a sometimes weaker, but always present, attraction.
A meteorite forms by slowly cooling in space after being melted or heated to very high temperatures during collisions or violent cosmic events. During this gradual cooling, if a magnetic field is present in the surroundings, it can influence the arrangement of magnetic minerals inside the meteorite. Minerals containing iron and nickel then act like tiny magnets by aligning according to this initial field, creating a lasting magnetic memory. Essentially, when the meteorite cools and solidifies, it "records" the direction and intensity of this primordial magnetic field in its internal structure. It is this phenomenon that makes it possible to detect residual magnetism when a meteorite is found on Earth.
In space, meteorites continuously traverse solar winds, streams of charged particles coming from the sun. These particles interact with the metals contained in the meteorites, potentially enhancing or slightly altering their magnetism. Some meteorites even experience small cosmic shocks, collisions with other space rocks that modify their internal magnetic properties by realigning the magnetic domains. There is also cosmic radiation, consisting of highly energetic particles coming from far within the galaxy, capable of inducing small magnetic changes as they pass through these space objects over millions of years. All of this contributes to the somewhat special and magnetic nature of the meteorites that eventually arrive here on Earth.
When a meteorite enters the Earth's magnetic field, it undergoes a direct interaction. This encounter can slightly alter its internal magnetic field. During its fall to Earth, the meteorite aligns itself with the magnetic field lines of our planet, sometimes leaving traces of terrestrial magnetism in its minerals. Meteorites found on the ground can therefore exhibit mixed magnetism, combining their own spatial history with the effects of their passage through the Earth's magnetic environment. This phenomenon allows scientists to better understand the trajectory and precise origin of certain meteorites that have fallen to our planet.
The characteristic patterns known as Widmanstätten figures, visible after polishing on certain meteorites, are never found in natural terrestrial rocks, thus proving their extraterrestrial origin!
The Hoba meteorite, discovered in Namibia, is the largest known meteorite on Earth to date. It weighs over 60 tons and is almost entirely composed of iron and nickel!
Some internal parts of meteorites sometimes retain a magnetic imprint from the time when they were still under the influence of an extraterrestrial magnetic field, thus providing us with a valuable insight into the early magnetic history of the solar system!
Although the majority of magnetic meteorites are metallic, some stony meteorites can also exhibit a slight magnetization because they contain iron-rich minerals such as magnetite.
In general, the magnetism of an isolated meteorite is too weak to significantly influence everyday electronic devices. However, if a meteorite is particularly massive or specific, it could slightly disrupt sensitive instruments in its immediate environment.
Often, a meteorite containing iron-nickel will be attracted to a powerful magnet, unlike the majority of terrestrial rocks. In fact, using a magnet is one of the first steps in identifying a potential meteorite.
The natural magnetism of a meteorite can decrease over time, especially if it is exposed to prolonged terrestrial conditions, such as humidity and oxidation. However, the metal contained in the meteorite will generally remain responsive to magnets even after losing some of its initial magnetism.
Metallic meteorites (ferrous meteorites) are primarily composed of iron-nickel alloys and exhibit a strong magnetic property. On the other hand, stony meteorites are mainly made up of silicate minerals and have little to no noticeable magnetism.
Even though iron and nickel are the main players in magnetism within meteorites, some secondary minerals like magnetite can also exhibit magnetic properties. However, these cases are less common, and their magnetism is generally weaker.
No, not all meteorites are necessarily magnetic. Only those containing metals like iron and nickel have noticeable magnetic properties. Stony meteorites or those primarily made of silicate materials generally exhibit little to no magnetism.
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