The night sky frequently offers a “shooting star,” a bright streak of light. These celestial visitors embark on a fiery journey as they encounter Earth’s atmospheric layers, transforming into the glowing objects we witness from the ground.
What Are Meteors?
Space contains rocky or metallic fragments, from dust grains to small asteroids, known as meteoroids. These objects originate primarily as debris from comets or asteroids, with some coming from the Moon or other planets. When a meteoroid enters Earth’s atmosphere at high speed, it becomes visible as a streak of light, called a meteor. If a portion of this space rock survives its atmospheric passage and reaches Earth’s surface, it is then called a meteorite.
The Atmospheric Layer Where Meteors Burn Up
Most meteors begin to burn up within the mesosphere, Earth’s third atmospheric layer. This layer extends from about 50 to 85 kilometers (31 to 53 miles) above the Earth’s surface. While the air in the exosphere and thermosphere is too thin, the mesosphere contains enough gases to cause friction and generate heat. This makes it the primary region where meteoroids encounter sufficient atmospheric density to ignite and become visible.
Temperatures in the mesosphere generally decrease with increasing altitude, reaching extreme lows of around -90°C (-130°F) near its top boundary, the mesopause. Despite these cold temperatures, the increasing density of air molecules as one descends through this layer creates the conditions necessary for meteoroids to heat up. The mesosphere’s air density, though thin compared to lower layers, is sufficient to slow down incoming meteoroids, leading to their fiery disintegration.
Why Meteors Burn Up in the Atmosphere
Meteors do not burn in the conventional sense of combustion, which requires oxygen. Instead, their intense heat and light arise from atmospheric compression and friction. As a meteoroid hurtles into Earth’s atmosphere at speeds often tens of thousands of miles per hour, the air molecules in front of it are compressed rapidly. This sudden compression causes the air to heat up dramatically, reaching temperatures hotter than the surface of the sun. This heat then transfers to the meteoroid’s surface.
The extreme heat from this compression and friction causes the meteoroid’s outer layers to vaporize and erode in a process known as ablation. Ablation involves the removal of material from the meteoroid’s surface through mechanisms like sublimation, vaporization, or melting. This process converts the meteoroid’s kinetic energy into heat, light, and ionization energy, creating the brilliant streak seen in the night sky. The visible trail is composed of hot, glowing gases and vaporized material from the meteoroid itself.
What Happens After Burning?
Most meteors completely disintegrate in the atmosphere due to intense heat and forces. The vast majority never reach the ground, turning into fine dust or vapor. This ablated material, sometimes referred to as meteoric smoke, eventually settles onto Earth’s surface.
Rare, larger meteoroids that survive the atmospheric journey are called meteorites. These objects have enough mass and structural integrity to withstand the ablation process, though they often slow down significantly before impact. Such meteorites provide scientists with valuable physical samples of extraterrestrial material, offering insights into the formation and composition of our solar system.