Space rock terminology depends entirely on its location relative to Earth. A meteoroid is the object itself, a piece of rock or debris traveling through space, ranging from a grain of sand to a small asteroid. When a meteoroid enters the Earth’s atmosphere and becomes a visible streak of light, it is called a meteor, often nicknamed a “shooting star.” If a fragment of the original space rock survives the atmospheric journey and lands on the ground, it is classified as a meteorite. This luminous display is caused by the conversion of kinetic energy into heat, not combustion.
The Cause of Incandescence
The brilliant light produced by a meteor is a result of intense aerodynamic heating, not simple friction. As the meteoroid enters the atmosphere at speeds often exceeding 11 kilometers per second, the air directly in front of the object is rapidly compressed. This extreme compression creates a powerful shockwave and dramatically raises the gas temperature through an adiabatic process. The superheated air can reach up to 10,000 Kelvin, far surpassing the melting point of the meteoroid material.
This intense heat causes the meteoroid’s surface to vaporize, a process known as ablation. The glowing trail observed is a combination of this vaporized material and surrounding air molecules ionized into a plasma state. Smaller meteoroids, often the size of a sand grain, are entirely consumed by ablation, leaving behind no solid remnants.
The Mesosphere: The Primary Burn-Up Zone
Meteors typically become visible when the meteoroid enters the upper atmosphere, usually between 120 and 100 kilometers in altitude. This is the point where the atmospheric density becomes sufficient to initiate the heating and ablation process. The most significant burn-up and peak luminosity occur primarily within the Mesosphere, the layer extending from roughly 50 kilometers up to 85 kilometers above the surface.
The Mesosphere provides the optimal balance of atmospheric density and the meteoroid’s retained speed to cause rapid vaporization. Below this layer, the air is too dense, and above it, the air is too thin to cause significant heating. Most meteors, particularly the small ones that create “shooting stars,” are completely destroyed between 95 kilometers and 50 kilometers. The ionization trails left by these events are sometimes visible in the upper Mesosphere, which is otherwise the coldest layer of the atmosphere.
Fate of Objects That Reach Lower Altitudes
A small percentage of larger, more durable meteoroids—often classified as fireballs or bolides—survive the initial ablation in the Mesosphere and continue into the denser Stratosphere and Troposphere below 50 kilometers. Once the object enters these lower layers, the increased atmospheric resistance causes rapid deceleration. This slowing causes the intense aerodynamic heating to drop significantly, which in turn ends the visible streak of light.
At this point, the surviving fragment enters a phase known as “dark flight,” where it continues to fall but is no longer luminous. The object, now a meteorite, slows from its initial hypersonic speed to a much slower terminal velocity, typically around 100 to 200 miles per hour, before hitting the ground. Because the object has cooled substantially during this subsonic dark flight, it usually impacts the Earth at ambient air temperature.