Space, the final frontier, is a vast, mysterious expanse that has fascinated humanity since time immemorial. As we gaze upon the stars, we often forget that remnants of these celestial bodies sometimes make their way to Earth in the form of spacerocks and meteorites. These celestial remnants provide invaluable insights into the origins of our solar system and the universe at large. This article explores different types of spacerocks and meteorites and their significance.
What Are Spacerocks and Meteorites?
Spacerocks, often referred to as meteoroids, are small, rocky or metallic bodies in outer space. When these spacerocks enter the Earth’s atmosphere and survive the intense heat of entry to reach the surface, they are termed meteorites.
Meteorites should not be confused with meteors (commonly known as shooting stars). Meteors are meteoroids that burn up completely upon entering Earth’s atmosphere, leaving a trail of light but never reaching the ground.
Types of Meteorites
Meteorites are primarily classified into three categories: stony meteorites, iron meteorites, and stony-iron meteorites. Each group provides unique information about the universe’s formation and evolution.
Stony Meteorites
Stony meteorites, also known as “chondrites,” are the most common type of meteorite. They are primarily composed of silicate minerals and are characterised by the presence of chondrules—small, round grains that formed from the solar nebula over 4.5 billion years ago. Chondrites are essentially cosmic time capsules, providing scientists with clues about the early solar system.
Stony meteorites are further classified into ordinary chondrites (the most common type), carbonaceous chondrites (rich in volatile elements and organic compounds), and enstatite chondrites (extremely rare and made of minerals formed in highly reducing conditions).
The second type of stony meteorites are achondrites, which do not contain chondrules. These meteorites are thought to originate from differentiated celestial bodies like the moon, Mars, or the asteroid Vesta.
Iron Meteorites
Iron meteorites, composed primarily of iron-nickel alloys, are fragments of the cores of larger, ancient asteroids that underwent differentiation. They are known for their Widmanstätten patterns—unique geometric designs visible when the meteorite is cut, polished, and etched with acid.
Iron meteorites are further divided into classes based on their metal content and mineralogy, including octahedrites, hexahedrites, and ataxites.
Stony-Iron Meteorites
Stony-iron meteorites are rare specimens that contain nearly equal amounts of metal and silicate minerals. They are further divided into two main types: pallasites and mesosiderites.
Pallasites are thought to originate from the boundary between the core and mantle of differentiated asteroids. They exhibit a mix of metallic iron and olivine crystals, creating a striking visual contrast.
Mesosiderites are a mixture of metal and different types of silicate minerals, likely from the violent collision between two differentiated asteroids.
The Significance of Spacerocks and Meteorites
Meteorites are invaluable to scientists because they provide direct evidence of conditions in outer space, the material composition of asteroids, and the processes that led to the formation and evolution of the solar system. They even provide clues to the potential for life elsewhere in the universe, as some meteorites have been found to contain amino acids, the building blocks of life.
Meanwhile, the study of spacerocks that haven’t yet entered Earth’s atmosphere helps astronomers and scientists understand their composition, origin, and trajectory. This knowledge is crucial for assessing potential risks to Earth from meteor impacts
How to Identify Meteorites
Finding a meteorite can be a thrilling discovery, but how can one differentiate an actual meteorite from a common earth rock? Here are some characteristics to look for:
Fusion Crust
When a meteoroid enters the Earth’s atmosphere, the intense heat causes its surface to melt and form a thin, dark rind known as a fusion crust. This crust is usually black or dark brown and may appear somewhat glossy. However, keep in mind that weathering can alter the appearance of the fusion crust over time.
Density
Meteorites are typically denser than common rocks due to their high iron content. If the rock feels unusually heavy for its size, it could potentially be a meteorite.
Magnetic Properties
Most meteorites contain iron-nickel metal and will therefore be attracted to a magnet. If your rock is magnetic, that’s a good sign, but note that some earth rocks also have magnetic properties.
Regmaglypts
Also known as thumbprints, regmaglypts are small, shallow indentations on the surface of some meteorites, particularly iron meteorites. These depressions are caused by the ablation process as the meteorite descends through the atmosphere.
Interior Appearance
If possible, examine a fresh break or cut surface of the rock. Many stony meteorites contain small, round structures called chondrules. Iron meteorites, on the other hand, will show a pattern of interweaving bands of kamacite and taenite, known as a Widmanstätten pattern, when cut, polished, and etched with acid.
Streak Test
When rubbed on a streak plate (a piece of unglazed porcelain), meteorites usually leave no streak or a weak, grey streak. Many earth rocks, on the other hand, will leave a coloured streak.
While these characteristics can help you identify potential meteorites, confirming a meteorite find often requires laboratory analysis by professionals. If you believe you’ve found a meteorite, consider contacting a local university, museum, or meteorite collector for further analysis.
