Asteroids vs Comets vs Meteoroids: Sorting Them Out

A common question is which one is this? The answer is usually in the orbit, not in the object.

By composition and behaviour

• Asteroid - rocky or metallic, no active gas/dust tail. Orbits are often near the ecliptic with moderate eccentricity.
• Comet - volatile-rich, develops a coma and tail near perihelion. Eccentricity often high; the orbit can reach all the way out past the planets.
• Meteoroid - a small fragment of an asteroid or comet. Technically not in the catalogue as a separate “kind”; it is an asteroid that has already broken up.

By the orbital signature

The cometary tell is a very high eccentricity plus a large semi-major axis - the kind of data you’ll see on the comets page. The asteroidal tell is a modest eccentricity and a period in the belt. The kind column in the SpaceAtlas data reflects exactly this split, and it is what drives the object into the asteroid vs. comet category on the category pages.

There is also a middle. Damocloid comets are on asteroid-like orbits but show cometary activity, and a handful of “comet-like asteroids” are the reverse. The label is a working definition, not a hard wall.