Meteoroids are small rocks or metal objects in outer space.

Meteoroids are much smaller than asteroids, ranging in size from small particles to a meter wide object. Objects smaller than this size are classified as microfluidics or space dust. Most are debris from comets or asteroids, while others are impact debris ejected from objects such as the moon or Mars.

When a meteoroid, comet or asteroid enters the earth's atmosphere at a speed usually exceeding 20 km / S (72000 km / h; 45000 mph), the aerodynamic heating of the object will produce streaks from luminous objects and objects. Traces of glowing particles left in the wake. This phenomenon is called meteor or "meteor". A series of meteors appear at intervals of seconds or minutes, which seems to originate from the same fixed point in the sky, called meteor shower. If the object withstands the erosion of the atmosphere as a meteor and hits the ground, it is called a meteorite.

An estimated 15000 tons of meteoroids, microfluidics and different forms of space dust enter the earth's atmosphere every year.

Almost all meteoroids contain extraterrestrial nickel and iron. They have three main categories: iron, stone and stone iron. Some stone meteoroids contain granular inclusions, which are called chondrites and chondrites. Stony meteoroids without these characteristics are called achondrites and are usually formed by extraterrestrial Mars activities. They contain little or no extraterrestrial iron. The composition of meteoroids passing through the earth's atmosphere can be inferred from their tracks and spectra. Their effects on radio signals also provide information, especially for daytime meteors, which are otherwise difficult to observe. From these trajectory measurements, it is found that meteoroids have many different orbits. Some clusters (see meteor shower) in the stream are usually related to the mother comet, while others seem to be sporadic. Debris from meteoroids may eventually spread to other orbits. The combination of spectrum with trace and light curve measurement results in a variety of compositions and densities, from fragile snowballs with a density of about a quarter of that of ice to dense rocks rich in ferronickel. The study of meteorites also provides insights into the composition of non transitory meteorites.