What is dark flight?
Dark flight is the final stage of a meteorite's fall, after it has slowed so much that it stops glowing. It then drops unseen for several minutes, pushed around by the wind.
A fireball's dramatic part, the bright streak, lasts only a few seconds. During that time the meteoroid is being slowed and burned away by the atmosphere. Once its speed falls to around 2 to 4 km/s, the air no longer heats it enough to glow. The light goes out, typically somewhere around 15 to 35 km above the ground. From that moment the rock is in dark flight: it carries on falling but is now invisible.
In dark flight a meteorite behaves much like any heavy object dropped from a great height. Gravity pulls it down, air resistance pushes back, and it soon reaches its terminal velocity, the constant speed at which those two forces balance. For a typical stone that is a few hundred kilometres per hour. Because the fall starts so high, it often takes several minutes to reach the ground, and the stones cool on the way.
Dark flight is the headache in predicting where meteorites land. Without any light, cameras cannot follow the pieces, so scientists must calculate their paths using the speed and direction measured at the end of the bright phase. Winds at different heights, especially fast jet-stream winds, can carry stones sideways by several kilometres, and small ones drift more than heavy ones. Researchers therefore feed weather data into computer models and run many versions for different possible masses and shapes, producing a map of likely landing zones.
Sometimes weather radar picks up the falling fragments in dark flight, helping to pin down the search area. Witnesses near the landing zone may also hear the stones whistling or buzzing in the last moments before impact.