Comet dust

These are typically 20-100 micrometers, a size not arbitrary but observed[9] as the porous aggregates tend to fracture[10] or compact.

Meteoroids are 30 micrometers to 1 meter, dust is smaller, and the term "micrometeoroid" is discouraged (though not micrometeorite).

[40][41][42] Though organics are cosmically abundant, and were widely predicted to exist in comets, they are spectrally indistinct in most telescopes.

For example, the isotopic ratios of comet and of interstellar dust are very similar, indicating a common origin.

The 1) interstellar model says that ices formed on dust grains in the dense cloud that preceded the Sun.

[50][51] In the 2) Solar System model, the ices that formed in the interstellar cloud first vaporized as part of the accretion disk of gas and dust around the protosun.

For long period comets, most of the time it will be so far from the Sun that it will be too cold for evaporation of ices to occur.

If a comet has an accumulation of thick dust layers, it may have frequent perihelion passages that don't approach the Sun too closely.

The accumulation of dust layers over time would change the physical character of the short-period comet.

Dust particles, aided by ices and organics, form "aggregates" [27][38][53] (less often, "agglomerates"[54]) of 30 to hundreds of micrometers.

These are rarely seen in the coma, as gas pressure is often insufficient to lift them to significant altitude or escape velocity.

Whether the actual cometesimals/planetesimals were pebble-scale,[67] boulder-scale,[68] or otherwise has been a key topic in Solar System and exoplanet research.

ISO measured no infrared evidence of a classical cometary dust tail due to small particles.