Collisional balance of the meteoritic complex

Taking into account meteoroid measurements by in situ experiments, zodiacal light observations, and oblique angle hypervelocity impact studies, it is found that the observed size distributions of lunar microcraters usually do not represent the interplanetary meteoroid flux for particles with masses ⪅10−10g. From the steepest observed lunar crater size distribution a “lunar flux” is derived which is up to 2 orders of magnitude higher than the interplanetary flux at the smallest particle masses. New models of the “lunar” and “interplanetary” meteoroid fluxes are presented. The spatial mass density of interplanetary meteoritic material at 1 AU is ∼10−16g/m3. A large fraction of this mass is in particles of 10−6 to 10−4 g. A detailed analysis of the effects of mutual collisions (i.e., destruction of meteoroids and production of fragment particles) and of radiation pressure has been performed which yielded a new picture of the balance of the meteoritic complex. It has been found that the collisional lifetime at 1 AU is shortest (∼104years) for meteoroids of 10−4 to 1 g mass. For particles with masses m > 10−5g, Poynting-Robertson lifetimes are considerably larger than collisional lifetimes. The collisional destruction rate of meteoroids with masses m ⪆ 10−3g is about 10 times larger than the rate of collisional production of fragment particles in the same mass range. About 9 tons/sec of these “meteor-sized” (m > 10−5g) particles are lost inside 1 AU due to collisions and have to be replenished by other sources, e.g., comets. Under steady-state conditions, most of these large particles are “young”; i.e., they have not been fragmented by collisions and their initial orbits are not altered much by radiation pressure drag. Many more micrometeoroids of masses m ⪅ 10−5g are generated by collisions from more massive particles than are destroyed by collisions. The net collisional production rate of intermediate-sized particles 10−10g ⪅ m ⪅ 10−5g is found to be about 16 times larger at 1 AU than the Poynting-Robertson loss rate. The total Poynting-Robertson loss rate inside 1 AU is only about 0.26 tons/sec. The smallest fragment particles (m ⪅ 10−10g) will be largely injected into hyperbolic trajectories under the influence of radiation pressure (β meteoroids). These particles provide the most effecient loss mechanism from the meteoritic complex. When it is assumed that meteoroids fragment similarly to experimental impact studies with basalt, then it is found that interplanetary meteoroids in the mass range 10−10g ⪅ m ⪅ 10−5g cannot be in temporal balance under collisions and Poynting-Robertson drag but their spatial density is presently increasing with time.