Micrometeoroids flux on the Moon

Abstract

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.

Meteoroids at the Moon: Orbital Properties, Surface Vaporization, and Impact Ejecta Production

“…Similar to previous calculations (e.g., Bruno et al, ; Cremonese et al, ), our model confirms that impact vaporization is an important source of neutrals for the lunar exosphere. In particular, the peak production of Na vapor at dawn over the one lunation shown in Figure is estimated to be 1.5 × 10 5 cm −2 /s if the fraction of sodium in the soil is assumed to be 0.0031 (Wurz et al, ).…”

“…The history of meteoroid models of Earth's closest neighbor is surprisingly short (Borin et al, ; Cremonese et al, ). While many authors developed a suite of analytic, engineering, and dynamical models for the Earth (Fentzke & Janches, ; McNamara et al, ; Nesvorný et al, ; Nesvorný, Janches, et al, ; Nesvorný, Vokrouhlický, et al, ; Pokorný et al, ), the Moon itself has not yet been discussed in detail.…”

“…With the advent of new ground‐based and space‐borne observations of the Moon there exists new interest in understanding the differences between the lunar and terrestrial meteoroid environments. Like for the case of Mercury (Pokorný et al, , ), modeling the meteoroid flux on the Moon is critical for understanding the importance of impact vaporization as a source for the lunar exosphere (Bruno et al, ; Cremonese et al, ; Morgan et al, ; Morgan & Killen, ; Sarantos et al, ), as meteoroids in the size range of 5–200 μm are considered relevant to the daily resupply of the lunar atmosphere. The importance of impacts for the exosphere was demonstrated by the brightening of its sodium and potassium component during meteor showers (Barbieri et al, ; Colaprete et al, ; Smith et al, ; Szalay et al, ).…”

“…However, the density of the dust cloud predicted by this model is thousands of times higher than what was inferred from the measurement. On the other hand, our model provides realistic numbers for the mass of particles delivered daily to the Moon and for the exosphere density, resulting in a disagreement that is yet to be understood.The history of meteoroid models of Earth's closest neighbor is surprisingly short (Borin et al, 2017;Cremonese et al, 2013). While many authors developed a suite of analytic, engineering, and dynam-…”

Experimental shock metamorphism of terrestrial basalts: Agglutinate‐like particle formation, petrology, and magnetism

“…The calculated average micrometeoroid impact velocity on the Moon is 15.3 km s −1 (Cremonese et al. ) and the root‐mean‐square impact velocity of crater‐forming bodies is 19.2 km s −1 (Stuart and Binzel ). Hence, if the flux of micrometeoroids on the Moon is roughly equal to the flux of crater‐forming bodies ranging in size from ~10 m to ~2 km (as on Earth), and the micrometeoroid velocity distribution spectrum for micrometeoroids is similar to the spectrum for crater‐forming objects, then we could expect that these two suites of projectiles contribute an equal amount of impact energy to the Moon's surface.…”