Many people gaze at the night sky and observe what appears to be a “falling star,” a fleeting streak of light. These celestial events are not actual stars descending from their positions, but rather small pieces of space rock entering Earth’s atmosphere. While most of these objects vaporize completely before reaching the surface, some do survive the fiery descent. When they make contact with the ground, these space rocks are known by a specific scientific term. This article explores what these objects are and what happens when they land on Earth.
Understanding Falling Stars
The common term “falling star” refers to a scientific phenomenon known as a meteor. A meteor begins its journey as a meteoroid, which is a small, rocky or metallic body orbiting the sun. These meteoroids can range in size from tiny dust grains to objects smaller than an asteroid.
When a meteoroid enters Earth’s atmosphere at high speed, friction with the air causes it to heat up and burn. This burning creates the bright streak of light we observe in the sky. Most meteors burn up entirely during their atmospheric passage, never reaching the ground.
However, if a meteoroid is large enough to survive this fiery journey and successfully lands on Earth’s surface, it is then reclassified as a meteorite. Therefore, a “falling star” is a visual event in the atmosphere, while a meteorite is the physical object that remains after that event.
The Impact Phenomenon
The descent of a meteoroid through Earth’s atmosphere is a significant event. As the object plunges downwards, it often appears as a bright fireball, sometimes rivaling the sun, known as a bolide. This light is generated by heat and friction, causing the object to glow and shed material.
Larger objects can sometimes break apart during entry, creating multiple bright fragments or a shower of smaller pieces. The atmospheric entry and impact can also produce sounds. As the meteoroid travels at supersonic speeds, it can generate sonic booms that may be heard over vast distances.
Rumbling sounds, whistling, or hissing noises have also been reported as the object passes through the air. Upon reaching the ground, the immediate physical impact can vary from a simple thud for smaller objects to forming impact craters for larger ones, depending on their size and speed.
Appearance of a Meteorite
Once a meteorite lands on Earth, it has several characteristics that distinguish it from Earth rocks. A fresh meteorite features a dark, thin outer layer known as a fusion crust. This crust forms as the meteorite’s surface melts and re-solidifies due to heat experienced during its atmospheric flight.
Over time, this fusion crust can weather away, causing the meteorite to appear rusty brown. Many meteorites also display surface indentations called regmaglypts, which resemble thumbprints pressed into clay. These depressions are formed by ablation as hot air currents sculpt the rock during its rapid descent.
Meteorites are heavy for their size, a result of their higher metallic content, particularly iron and nickel, compared to most Earth rocks. Most meteorites are magnetic to some degree, and iron meteorites show a strong attraction to a magnet.
If a meteorite is broken or cut, its internal structure might reveal shiny metal flecks of nickel-iron alloys or small, spherical inclusions called chondrules, which are common in stony meteorites. Their overall shape is irregular, with rounded edges, and they lack the bubbly appearance or quartz crystals found in many terrestrial rocks.
Where to Find and Identify Meteorites
Meteorites can fall anywhere on Earth, but they are most commonly found and recovered in certain environments. Deserts, both hot and cold, are good locations because their dry conditions preserve meteorites from weathering and the lack of vegetation makes dark objects stand out. Dry lakebeds and agricultural fields can also be areas for finding these space rocks.
When attempting to identify a potential meteorite, several non-destructive tests can be performed. The magnet test is useful, as most meteorites contain enough iron to be attracted to a strong magnet. Another indicator is their density; meteorites feel heavier than common Earth rocks of similar size.
A streak test, performed by rubbing the specimen on an unglazed ceramic surface, can also be helpful; most meteorites will leave no streak or a very faint gray one, unlike many terrestrial minerals that leave colored streaks. If a rock contains visible quartz crystals or has a bubbly, porous texture, it is unlikely to be a meteorite. Should a find be made, it is advisable to report it to scientific institutions for analysis rather than attempting to cut or clean the specimen.