Asteroidal and cometary dust flux in the inner solar system

Context. Meteoroids impacting terrestrial planets at high speed may have different effects. On bodies without atmospheres, such as the Moon and Mercury, they form impact craters and contribute to the gardening process through which the surface material is constantly mixed. The interaction of high-speed meteoroids with the atmosphere of Venus, the Earth, and Mars, may lead to the deposition in the ionosphere of species such as neutral Mg or Fe and their ionized atoms, caused by ablation processes during the entry. Aims: In this work we estimate and compare the flux and impact speeds onto the planets of the inner solar system by numerically integrating the orbital evolution of putative dust particles of asteroidal and cometary origin. Methods: The trajectories of dust particles of different sizes are computed with a numerical code that accounts for the gravitational forces due to all planets, the Poynting-Robertson drag and the solar wind drag. The flux of dust grains on each planet is estimated by calibrating the outcome of our model with the flux on the Earth reported previously. Results: We obtain new estimates of the flux and impact velocities for both asteroidal and cometary dust particles on Venus and Mars. For Venus we find that cometary grains enter the planet atmosphere at higher speeds, possibly contributing to the upper layers, while asteroidal grains would be relevant for the lower layers, possibly leading to a compositional gradient. This effect is also present for Mars, but it is less marked. We also find that analytical predictions, not taking radiative forces into account, of both flux and average impact speed are reliable for Mars but fail for Venus because of the complex dynamical evolution of grains in the inner solar system. Conclusions: Our results on the velocity distributions and fluxes of micrometeoroids on the terrestrial planets can be used to put stringent contraints on models that estimate either the superficial material mixing that is due to meteoroid impacts or the formation of ionospheric layers for planets with an atmosphere.