When a space rock enters Earth’s atmosphere, it transforms into a meteor, appearing as a streak of light across the sky. These “shooting stars” are a common sight in the night sky, yet they are rarely observed in the lowest part of our atmosphere, the troposphere. The troposphere is the atmospheric layer closest to Earth’s surface, extending up to about 10-20 kilometers (6-12 miles) high, where nearly all weather phenomena occur and where we live and breathe. The minimal presence of meteors in this dense, lower layer highlights the protective capabilities of the upper atmosphere.
The Violent Entry into Earth’s Atmosphere
Space rocks, known as meteoroids, hurtle through space at immense speeds. Upon encountering Earth’s atmosphere, these meteoroids collide with atmospheric gases. This rapid compression of air in front of the meteoroid generates extreme heat. The intense heat causes the meteoroid’s surface to ablate, meaning it vaporizes and melts. This process of superheating and shedding material creates the luminous streak of light we recognize as a meteor.
Where Most Meteors Incinerate
The fiery demise of most meteors occurs high above the Earth’s surface, primarily in the mesosphere and the lower thermosphere. The mesosphere, located approximately 50 to 85 kilometers (31 to 53 miles) above Earth, is where the atmosphere becomes dense enough to cause significant heating and ablation. Even though the air in these layers is still thin compared to sea level, the sheer speed of the incoming meteoroid means that even a small number of gas molecules can generate enough resistance to vaporize most objects. Most meteoroids are quite small, often no larger than a grain of sand or a pea, and are entirely consumed in these upper atmospheric regions.
Why the Troposphere is Largely Unaffected
The upper atmospheric layers act as an effective shield, preventing the vast majority of incoming space debris from reaching the troposphere. By the time any meteoroid descends through the mesosphere and lower thermosphere, it has either completely vaporized into fine dust or has been significantly slowed and reduced in size. Only exceptionally large or robust objects have any chance of surviving to lower altitudes. Visible meteor streaks stop tens of kilometers above the Earth’s surface.
The Rare Survivors: Meteorites
On rare occasions, a meteoroid is massive and durable enough to withstand the intense atmospheric entry and reach Earth’s surface. When this occurs, the surviving fragment is no longer called a meteor but a meteorite. By the time these objects reach the lower atmosphere, they have lost most of their cosmic velocity and no longer produce the bright, fiery streak characteristic of a meteor, instead falling to the ground at a significantly reduced speed.