The Meteoroid and Orbital Debris Working Group studies meteoroids and orbiting spacecraft debris that poses a hazard to spacecraft, threatens to penetrate habitats and fuel tanks, and cause failure to solar cells and electrical wires.
Meteoroids are natural particles in orbit about the sun.
Their size is considerably smaller than an asteroid and considerably larger than an atom or molecule. Orbital debris is man-made material induced by spacecraft that can be as large as spent rocket motors and as small as the dust particles ejected from the nozzles of maneuvering thrusters. The graphic shows the number of catalogued space objects in orbit as of 27 September 1991. Meteoroids are natural particles that are not individually tracked and catalogued. The vast majority of meteoroids are cometary in nature but some have asteroidal origin as well.