less solar system bodies Janna M Dlugach Main Astronomical Observatory of the National Academy of Sciences of Ukraine Kyiv Ukraine Michael I Mishchenko NASA Goddard Institute for Space Studies New York USA ID: 277731
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Slide1
Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies
Janna M. DlugachMain Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
Michael I. Mishchenko
NASA Goddard Institute for Space Studies, New York, USASlide2
Opposition effects for some solar system bodiesSlide3Slide4
Angular profiles of the enhancement factor and the degree of linear polarization
Angular profiles of the enhancement factor (dotted curves) and the degree of linear polarization (solid curve) for a semi-infinite homogeneous medium composed of sparsely distributed non absorbing Rayleigh scatters, illuminated by normally incident unpolarized light (Mishchenko et al., 2000
)
.Slide5
Main characteristics of the coherent back- scattering peak
HWHM =
The angular widths of the
observed
backscattering intensity
peaks are consistent with the results of theoretical
computations for particle sizes of the
order of the wavelength, packing densities ranging
from several percent to approximately 40%, and particle
compositions ranging from water ice (Europa,
Saturn’s rings) to silicates (44 Nysa and 64 Angelina).
The
observed
amplitudes of the peaks are consistent with
the theory of
coherent backscattering by a regolithic layer composed of submicrometer-sized grains.Slide6
Scattering by a spherical volume randomly filled with small spheresSlide7
Current numerical capability
Computational technique: the numerically exact superposition T-matrix method and the Fortran-90 multiple sphere T-matrix (MSTM) code developed for use on parallel computer clusters.http://www.eng.auburn.edu/users/dmckwski/scatcodes
N
= 1875,
m
= 1.31,
kR
= 31,
kr
= 2,
ρ
= 0.5
(Mackowski and Mishchenko 2011)Slide8
Brightness and polarization opposition effects
m
= 1.31,
kR
= 40,
kr
= 2
(Dlugach, Mishchenko, Liu, Mackowski 2011)Slide9
Opposition effects for Saturn’s rings and Europa
Franklin and Cook 1965
Thompson and Lockwood 1992
Mishchenko et al. 2009
Franklin and Cook 1965
Lyot 1929Slide10
Conclusion
The photometric and polarimetric observational data for several high-albedo solar system objects reveal coexisting brightness and polarization opposition effects of comparable angular widths and with angular profiles consistent with the exact solutions of the Maxwell equations. The results of our theoretical analysis point to the conclusion that both these effects are caused by the coherent backscattering of sunlight by regolithic layers composed of microscopic grains.Slide11
AcknowledgmentsThank you for your attention!
This research was partially sponsored by the NASA Radiation Sciences Program managed by Hal Maring and by the NASA Remote Sensing Theory Program managed by Lucia Tsaoussi.
We acknowledge support from the National Academy of Sciences of Ukraine under the Main Astronomical Observatory GRAPE/GPU/GRID Computer Cluster Project.