Shadow mechanism and opposition effect of light for atmosphereless celestial bodies

1Morozhenko, OV, 1Vidmachenko, AP
1Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
Section: Dynamics and Physics of Solar System Bodies
Language: Russian

In the modified Irwin — Yanovitskij — Hapke shadow model of formation of opposition brightness effect the relationship between the single scattering albedo ωand transparency coefficient of particles κ is used in the form κ = (1 - ω) ;)n. This reduces the number of unknowns to two parameters (the packing density of particles g and ю) and the scattering function χ(α). Our analysis of spectrophotometric measurements of the Moon and Mars shows that a good agreement between the observed data on opposition effect and some change of color index with the phase angle а for the Moon and Mars can be obtained for n = 0.25, g = 0.4 (the Moon) and 0.6 (Mars). Applying this method to some of asteroid types also gave satisfactory agreement: the E-type (g = 0.6, ω = 0.6, Ag = 0.21, q = 0.83 or g = 0.3, ю = 0.4, Ag = 0.15, q = 0.71) for the Martian indicatrix; M-type (g = 0.4, ω ≤0.1, Ag ≤ 0.075, q g ≤ 0.075, q = 0.43) for a modified lunar indicatrix. Polarization measurements of T. Gehrels and others revealed that when а = 1.6° for the bright feature Copernicus (L = -20°08', φ = +10°11') of the lunar surface the plane polarization position in the G, I filters differed by 22° and 12° from one typical for the negative branch, whereas in the U filter and for the dark feature Plato (L = -10°32', φ= +51°25') the deviation was within the error limits (±3°). It is probable that this fact is a result of the coherent mechanism of thepolariza- tion peak forma tion.

Keywords: atmosphereless celestial bodies, opposition effect of light