The ionization-type cosmic dust detector METEOR-L is being developed for the lunar orbiter Luna-26 and is designed to study the distribution of meteoric bodies in space by mass and velocity, and for long-term monitoring of the dynamic evolution of the dust component in the lunar exosphere. Recent studies of dust clouds around the Moon show a close relationship between the constant and dynamic evolution of the components of the lunar exosphere, the geological history of the formation of the lunar regolith, the processes of formation and accumulation of volatiles in the lunar regolith with the constant impact of such components of the interplanetary medium as interplanetary dust of predominantly cometary origin and meteoroids from the belt asteroids. The cosmic dust detector is capable of registering meteoric particles 0.1-3 mu m in size with a mass of 10(-14)-10(-9) g and speeds from 3 to 35 km s(-1). Tests and calibration at a particle accelerator have confirmed the declared functionality of the detector for detecting cosmic dust particles with parameters characteristic of the lunar exosphere.

The column densities of impact-produced metal atoms in the exosphere during the peaks of activity of the main meteor showers - Geminids, Quadrantids and Perseids - and during quiet periods are estimated. The Na supply rate is estimated to be 2 x 10(4), 3 x 10(3), 10(4), and 2 x 10(4) atoms cm(-2) s(-1) for sporadic meteoroids, Perseid, Geminid, and Quadrantid meteor showers, respectively. A low upper limit on Ca in the lunar exosphere is explained by the condensation of Ca into dust grains during expansion of the cooling impact-produced vapor cloud. The chemical composition of gas-phase species released to the lunar exosphere during meteoroid impacts has been estimated. Most impact-produced molecules that contain metals are destroyed by solar photons while on ballistic trajectories. Energies of Na, K, Ca, and Mg atoms produced via photolysis of the respective monoxides are estimated to be 0.4, 0.35, 0.6, and 0.45 eV, respectively. The relative content of impact-produced Na and K atoms is maximal at altitudes of about 1000-2000 km and during the main meteor showers, lunar eclipses, and passages of the Moon through the Earth's magnetosphere. (C) 2009 COSPAR. Published by Elsevier Ltd. All rights reserved.

The first successful observations of resonant scattering emission from the lunar sodium exosphere were made from the lunar orbiter SELENE (Kaguya) using TVIS instruments during the period 17-19 December, 2008. The emission intensity of the NaD-line decreased by 12 +/- 6%, with an average value of 5.4 kR (kilorayleighs) in this period, which was preceded, by I day, by enhancement of the solar proton flux associated with a corotating interaction region. The results suggest that solar wind particles foster the diffusion of sodium atoms or ions in the lunar regolith up to the surface and that the time scale of the diffusion is a few tens of hours. The declining activity of the Geminid meteor shower is also one possible explanation for the decreasing sodium exosphere.