A meteoroid is a small body travelling through space. These bodies typically originate from comets and asteroids. There is no well defined size range for a meteoroid. However, we usually refer to a meteoroid as a piece of matter, which when it strikes the Earth's atmosphere, produces the visual phenomenon called a meteor. However, if the meteoroid is small enough, it will not produce a meteor, but will decelerate slowly enough to remain intact, and then float gently to the Earth's surface.

Further, if the meteoroid is large enough, some fraction of it will survive the ablative entry through the atmosphere, and land on the surface. This part of the meteoroid is then termed a meteoroid. For bodies even larger in size, the atmosphere proves an ineffective deceleration mechanism, and most of the meteoroid arrives descends intact and hits the surface with the (hyper) velocity it had in space. The impact energy is often sufficient to totally vapourise the impactor, as well as some of the Earth's regolith, and form a crater. There may only be condensed vapour left to indicate the nature of the impacting body.

Size or mass is thus a very important characteristic of a meteoroid, and in the table below we propose a meteoroid classification based on size.

Meteoroid ClassMeteoroid Mass/Size Primary OriginPhenomenon Descriptor Visual MagnitudeComments
<100μComets MicrometeoritesNone Survive entry without vapourisation. No detectable meteor. Add 30,000-40,000 tons to Earth mass / year. Interplanetary dust.
100μ - 1mmComets Submeteors10 to 5 Can be detected by radio/radar. Do not survive atmospheric entry.
1mm - 3cmComets Meteors5 to -4 Visible. Do not survive ablative re-entry process.
3cm - 30cmCmts/Ast Fireballs-4 to -12 Bright meteor. IAU current designation.
10cm - 1mAsteroids Bolides-12 to -20 Very bright meteor. Old IAU designation of a fireball. At this size the meteoroid penetrates below 50km and often produces sounds.
0.4m - 4m
Asteroids Meteorites-16 to -23 Meteor must generally by brighter than mag -18 and body has to penetrate below 20 km altitude. Impacts at about 100m/s. Possible pit if large.
4m - 20m
Asteroids Impactors< -22 Meteoroid is so large that the column of air it encounters is insufficient to reduce its speed. Vapourises on impact making crater.
20m - 1km
Asteroids Disasters< -30 Impact releases enormous energy. Tidal wave, earthquake, dustcloud.
> 1km
> 1010ton
Asteroid Catastrophe?? Global hazard. > 25% global deaths. If >4km then mass extinction.