Which of these is smaller than an asteroid and considerably larger than an atom?
A meteoroid is a small rocky or metallic body in outer space.
Meteoroids are significantly smaller than asteroids and range in size from small grains to one-meter-wide objects. Objects smaller than this are classified as micrometeoroids or space dust. Most are fragments from comets or asteroids, whereas others are collision impact debris ejected from bodies such as the Moon or Mars.
In 1961, the International Astronomical Union (IAU) defined a meteoroid as "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom".
Almost all meteoroids contain extraterrestrial nickel and iron. They have three main classifications: iron, stone, and stony-iron. Some stone meteoroids contain grain-like inclusions known as chondrules and are called chondrites.