Atmospheric entry
Atmospheric entry is the fiery plunge of a meteoroid or spacecraft into a planet's air, where it slows and heats up.
Atmospheric entry begins when a meteoroid, travelling at between about 11 and 72 kilometres per second, meets the thin upper atmosphere roughly 100 to 120 kilometres up. As it ploughs through the air, it squeezes the gas in front of it so violently that the air heats to thousands of degrees and glows. The surface of the meteoroid melts and is stripped away, a process called ablation.
Most meteoroids are tiny and vanish completely. Larger ones slow down as they push through denser air. Many break into fragments under the pressure, which can make the fireball flare. If pieces survive until they have slowed to a few kilometres per second, usually at a height of 15 to 30 kilometres, they stop glowing and fall the rest of the way in dark flight.
The whole bright phase lasts only a few seconds. Engineers designing heat shields for returning spacecraft study the same physics, and fireball observations help them test their models.
Related terms
Level: Explorer Ages 10 and up