COMETARY ORIGIN OF THE ZODIACAL CLOUD AND CARBONACEOUS MICROMETEORITES. IMPLICATIONS FOR HOT DEBRIS DISKS

The zodiacal cloud is a thick circumsolar disk of small debris particles produced by asteroid collisions and comets. Their relative contribution and how particles of different sizes dynamically evolve to produce the observed phenomena of light scattering, thermal emission, and meteoroid impacts are unknown. Until now, zodiacal cloud models have been phenomenological in nature, composed of ad hoc components with properties not understood from basic physical processes. Here, we present a zodiacal cloud model based on the orbital properties and lifetimes of comets and asteroids, and on the dynamical evolution of dust after ejection. The model is quantitatively constrained by Infrared Astronomical Satellite (IRAS) observations of thermal emission, but also qualitatively consistent with other zodiacal cloud observations, with meteor observations, with spacecraft impact experiments, and with properties of recovered micrometeorites (MMs). We find that particles produced by Jupiterfamily comets (JFCs) are scattered by Jupiter before they are able to orbitally decouple from the planet and drift down to 1 AU. Therefore, the inclination distribution of JFC particles is broader than that of their source comets and leads to good fits to the broad latitudinal distribution of fluxes observed by IRAS. We find that 85%–95% of the observed mid-infrared emission is produced by particles from JFCs and 100 μm undergo a further collisional cascade with smaller fragments being progressively more affected by Poynting–Robertson (PR) drag. Upon reaching D 10 4 times brighter during the Late Heavy Bombardment (LHB) epoch ≈3.8 Gyr ago, when the outer planets scattered numerous comets into the inner solar system. The bright debris disks with a large 24 μm excess observed around mature stars may be an indication of massive cometary populations existing in those systems. We estimate that at least ∼10 22 , ∼2 × 10 21 , and ∼2 × 10 20 go f