Micrometeoroids flux on the Moon

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, via Marzolo 8, 35131 Padova, Italy
e-mail: marzari@pd.infn.it
³ Department of Mineralogical and Petrological Science, via Valperga Caluso 35, 10125 Torino, Italy
e-mail: marco.bruno@unito.it

Received: 11 October 2012
Accepted: 24 December 2012

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 photo-stimulated desorption at the subsolar point, becoming similar in the dawn and dusk regions and dominant on the night side.