Context. Meteoroid impacts are an important source of neutral atoms in the exosphere of Mercury. Impacting particles of size smaller than 1 cm have been proposed to be the major contribution to exospheric gases. However, our knowledge of the fluxes and impact velocities of different sizes is based on old extrapolations of similar quantities on Earth. Aims. We compute by means of N-body numerical integrations the orbital evolution of a large number of dust particles supposedly produced in the Main Belt. They migrate inward under the effect of drag forces until they encounter a terrestrial planet or eventually fall into the Sun. From our numerical simulations, we compute the flux of particles hitting Mercury's surface and the corresponding distribution of impact velocities. Methods. The orbital evolution of dust particles of different sizes is computed with a numerical code based on a physical model developed previously by Marzari & Vanzani (1994, A&A, 283, 275). It includes the effects of Poynting-Robertson drag, solar wind drag, and planetary perturbations. A precise calibration of the particle flux on Mercury has been performed by comparing our model predictions for dust infall on to Earth with observational data. Results. We provide predictions of the flux to different size particles impacting Mercury and their collisional velocity distribution. We compare our results with previous estimates and we find that these collisional velocities are lower but that the fluxes are significantly higher.

Mass accretion rate on Earth is an important tool to discriminate the extraterrestrial nature of particles or isotopes found in different environments on the ground. In this context, the knowledge of the micrometeoroid flux arriving in our atmosphere is a key parameter and it needs to be calibrated. We provide a new calibration of the flux of submillimeter particles impacting the Earth in the mass range from 10 −9 to 10 −4 g, derived by computing a specific scaling law for impact craters on the Long Duration Exposure Facility (LDEF). We use the hydrocode iSALE to calculate the outcome of impacts on LDEF, adopting realistic impact velocities for dust particles derived from the numerical integration of their trajectories assuming either asteroidal or cometary origin. We estimate a particle mass accretion rate of (7.4 ± 1.0) × 10 6 kg yr −1 if the Main Belt is assumed as the major source of dust, while it reduces to (4.2 ± 0.5) × 10 6 kg yr −1 if cometary dust dominates. These values agree with the estimates provided by independent measurements made on ice core and ocean sediments and based on the abundance of some elements in the samples.

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.

Context. The Moon has a tenuous exosphere consisting of atoms that are ejected from the surface by energetic processes, including hypervelocity micrometeoritic impacts, photon-stimulated desorption by UV radiation, and ion sputtering. Aims. We calculate the vapor and neutral Na production rates on the Moon caused by impacts of meteoroids in the radius range of 5−100 μm. We considered a previously published dynamical model to compute the flux of meteoroids at the heliocentric distance of the Moon. Methods. The orbital evolution of dust particles of different sizes is computed with an N-body numerical code. It includes the effects of Poynting-Robertson drag, solar wind drag, and planetary perturbations. The vapor production rate and the number of neutral atoms released in the exosphere of the Moon are computed with a well-established formulation. Results. The result shows that the neutral Na production rate computed following our model is higher than previous estimates. This difference can be due to the dynamical evolution model that we used to compute the flux and also to the mean velocity, which is 15.3 km s −1 instead of 12.75 km s −1 as reported in literature. Conclusions. Until now, the micrometeoritic impacts have been considered a negligible source for the release of neutral sodium atoms into the exosphere compared to other mechanisms, but according to our calculations, the contribution may be 8% of the photostimulated desorption at the subsolar point, becoming similar in the dawn and dusk regions and dominant on the night side.

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.

The SIMBIO-SYS (Spectrometer and Imaging for MPO BepiColombo Integrated Observatory SYStem) is a complex instrument suite part of the scientific payload of the Mercury Planetary Orbiter for the BepiColombo mission, the last of the cornerstone missions of the European Space Agency (ESA) Horizon + science program. The SIMBIO-SYS instrument will provide all the science imaging capability of the Bepi-Colombo MPO spacecraft. It consists of three channels: the STereo imaging Channel (STC), with a broad spectral band in the 400-950 nm range and medium spatial resolution (at best 58 m/px), that will provide Digital Terrain Model of the entire surface of the planet with an accuracy better than 80 m; the High Resolution Imaging Channel (HRIC), with broad spectral bands in the 400-900 nm range and high spatial resolution (at best 6 m/px), that will pro-The BepiColombo mission to Mercury Edited by Johannes Benkhoff, Go Murakami and Ayako Matsuoka B G. Cremonese

Context. The planet Mercury has an extended and tenuous exosphere made up of atoms that are ejected from the surface by energetic processes, including hypervelocity micrometeoritic impacts, photon-stimulated desorption by UV radiation, and ion sputtering. The well known constituents of the Hermean exosphere are H, He, O, Na, K, and Ca but, from the new MESSENGER data from flybys, many others elements are expected, as for instance Mg. Aims. Meteoroid impacts are an important source of neutral atoms in the exosphere of Mercury. We estimate the vapor and neutral atom production rates on Mercury caused by impacts of micrometeoroids of sizes between 5-100 μm. The micrometeoritic flux is derived from a new statistical approach based on direct numerical integrations of dust particle trajectories under the action of the Poynting-Robertson drag and the gravitational attraction of all planets. Methods. We included two different calibration sources for the meteoroid flux in our calculations of the vapor and neutral atoms and also considered both asteroidal and cometary sources for the dust. Three different surface compositions, which might be found on the planet, have been adopted, each with a different mass fraction of atoms in the regolith of the planet. Results. We derive different values of neutral atom vapor production rates assuming different calibration sources for the meteoroid flux. The three simple mineralogical surface compositions show significant differences in the related production rates, and they are all greater than those reported in the previous papers assuming other dominant source mechanisms. Our neutral atom production rates are about one order of magnitude higher than the previous estimates. This implies that the impact vaporization has a much higher contribution than previously assumed.

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