Statistical analysis of the flux of micrometeoroids at Mercury from both cometary and asteroidal components

¹ INAF-Astronomical Observatory of Padova, Vicolo dell’Osservatorio 5, 35131 Padova, Italy
e-mail: patrizia.borin@oapd.inaf.it; gabriele.cremonese@oapd.inaf.it
² Department of Physics and Astronomy, University of Padova, via Marzolo 8, 35131 Padova, Italy
e-mail: marzari@pd.infn.it

Received: 17 June 2015
Accepted: 21 October 2015

Abstract

Context. Meteoroid impacts are an important source of neutral atoms for the exosphere of Mercury. We previously estimated the contribution of meteoroids originating in the asteroid belt for vapor release. In this paper, we concentrate on the cometary component of particles impacting the planet. Comets and asteroids are considered to be the two major sources of interplanetary dust particles in the solar system. The debate about which source contributes most to dust populating the solar system is still ongoing.

Aims. In this work, we compute the orbital evolution of dust particles produced by Jupiter-family comets (JFC) via N-body numerical integrations. From our numerical simulations, we compute the fraction of particles hitting Earth and Mercury’s surface and the corresponding distribution of impact velocities. According to some authors more than 80% of all the incoming mass of meteoroids entering the Earth’s atmosphere is concentrated in the mass range 10^-7−10^-3 g. In our model, we considered a slightly different range, 10^-9 to 10^-6 g, to include possible uncertainty.

Methods. The orbital evolution of dust particles of different sizes is computed with a numerical integration code, which includes the effects of Poynting-Robertson drag, solar wind drag, and planetary perturbations.

Results. By comparing the impact frequency of grains evolving either from main belt asteroids or JFC we find that the cometary component is significantly less efficient in releasing dust particles on Mercury than on the Earth. The opposite occurs in the case of dust coming from the main belt with a flux higher at Mercury than on the Earth. This is mostly due to the different dynamical histories of the grains from their release until impact. This may have important implications for the vapor production rate on Mercury. We compare our results with previous estimates given by different authors.