(Includes the new definition of "planet")

The following definitions for meteorite, meteoroid, micrometeorite, micrometeoroid, and interplanetary dust particle (IDP) have been proposed by Alan Rubin (UCLA) and Jeffrey Grossman (U.S. Geological Survey); excerpted from Meteoritics and Planetary Science 45, #1, 114–122 (2010).


A natural solid object larger than 10 µm in size, derived from a celestial body that was transported by natural means from the body on which it formed to a region outside the dominant gravitational influence of that body, and that later collided with a natural or artificial body larger than itself (even if it is the same body from which it was launched). Weathering processes do not affect an object's status as a meteorite as long as something recognizable remains of its original minerals or structure. An object loses its status as a meteorite if it is incorporated into a larger rock that becomes a meteorite itself.


A 10 µm to 1-m-sized natural solid object moving in interplanetary space. Meteoroids might be primary objects or derived by the fragmentation of larger celestial bodies, not limited to asteroids.


A meteorite between 10 µm and 2 mm in size.


A meteoroid between 10 µm and 2 mm in size.

Interplanetary Dust Particle (IDP)

A particle smaller than 10 µm in size moving in interplanetary space. If such particles susequently accrete to larger natural or artificial bodies, they are still called IDPs.

The following improved definition for planet has been proposed by Runyon et al., #1448 (2017), and currently describes ~110 known planets in the Solar System; this supersedes the flawed definition adopted by the IAU in 2006.


A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters.

See also the paper by Lineweaver and Norman, 'The Potato Radius: a Lower Minimum Size for Dwarf Planets', which imposes some sound mathematical reasoning to the arbitrary parameters used by the IAU—based on an arbitrary mass and diameter in the initial draft, and ultimately based on absolute magnitude—in their definition of "dwarf planet".