Dark flight
As darkness flight is called the phase in which a meteoroid without luminosity the atmosphere traversed.
General
If a meteoroid enters the earth's atmosphere , it becomes noticeable as a luminous phenomenon from a mass of around one milligram , which is known as a meteor or, in popular parlance, a falling star. As a rule, these particles are only a few tenths of a millimeter in size .
With such small particles, the perceptible luminous phenomenon is weak and only lasts a few tenths of a second. From a size of about 1 cm, the meteoroid becomes a rather conspicuous ball of fire that can be observed for hundreds of kilometers. From a brightness of about −4 mag (Venus brightness), the meteor is called a bolide .
If such a piece of rock or iron does not completely dissolve while flying through the atmosphere, a small residue reaches the earth's surface and can sometimes be recovered as a meteorite .
Flight phases of a meteor
Illuminated flight phase
Depending on its size, a meteor (which can become a meteorite when it reaches the surface of the earth ) lights up at heights of approx. 80 to 85 kilometers ( mesosphere ). The speed of entry into the atmosphere can vary greatly between 11.2 km / s and 72 km / s. The probability that a meteor survives atmospheric flight, however, is higher, the lower its entry speed (relative to the earth's surface) and the greater its mass. The actual glow (contrary to popular opinion) is not generated by the glowing of the meteor as a result of air friction , but the high kinetic energy of the meteor tears the electrons from the atoms of the surrounding air particles , the air is ionized . The resulting plasma ball can reach a diameter of several hundred meters in bright bolides. When the electrons recombine (reunite) with the atomic nuclei , light is emitted. This process is therefore also referred to as recombination lighting . This flight phase usually only lasts a few seconds. The air friction removes material ( ablation process ) from the surface of the meteoroid. Whether a meteorite residue is ultimately left over after the ablation process depends on the one hand on the initial mass of the meteoroid, but also on its entry speed and entry angle into the earth's atmosphere.
Dark flight phase
As a rule, a meteor goes out at a height of at least 30 kilometers if its material has been completely worn away by the ablation process. However, no residual material reaches the ground. A larger particle can, however, penetrate further into the deeper atmosphere and is slowed down even more strongly to a speed of about 4 to 2 km / s by air friction in the atmospheric layers with greater air density. At this speed, however, no recombination lights can take place, making the meteorite (residual body) invisible to the naked eye. The ablation process, i.e. the loss of material on the meteorite, can, however, continue for a short time due to air friction, but usually remains invisible to the human eye. The dark flight phase begins (depending on the size of the original body) at an altitude of about 20 kilometers above the earth's surface. The meteorite is slowed down further and finally goes into free fall . The further trajectory of the meteorite can be decisively influenced by wind drift . It is noteworthy that the dark flight of a meteorite can take several minutes. In the equilibrium between weight and air friction, the meteorite has a falling speed of approx. 80 to 60 m / s, with which it finally hits the earth's surface. As a rule, however, no crater is torn. At most, it penetrates several centimeters into the ground.