Beschreibung:    Nature of the photometric phase curves of the regolith like surfaces (like those of the asteroids) are believed to be dependent on the single particle characteristics like particle size, shape, composition etc. and physical characteristics of the surface like porosity and roughness. Most of the phase curves have a rapid surge of intensity at small phase angles (typically below 5 ° ) known as opposition effect, followed by a linear less decreasing trend at larger phase angles. Average intensity of the linear region has been found to be mostly dependent on the average particle size and its composition, in many laboratory observations. Generally, it is difficult to explain the nature of light scattering by an ensemble of irregular shaped inhomogeneous particles with a theoretical model, just by studying the phase curves. In the present work, we have investigated whether the theoretically expected variation of the scattered light intensity (at a given phase angle) with the average particle size of the grains constituting regoliths, for a given material of the particle is in agreement with the experimental results or not? If yes, this can be a simpler but efficient way to study light scattering by regolith like surfaces. For theoretical analysis, Hapke formula has been used with Mie theory for single particle phase function, where we have neglected the influence of porosity and roughness presently. The data are also fitted with an empirical formula. It has been found that this empirical formula may also be used to estimate the unknown average particle size of a real regolith with known composition. Content Type Journal Article Pages 1-9 DOI 10.1007/s11038-011-9384-5 Authors D. Deb, Department of Physics, Assam University, Silchar, 788011 Assam, India A. K. Sen, Department of Physics, Assam University, Silchar, 788011 Assam, India Journal Earth, Moon, and Planets Online ISSN 1573-0794 Print ISSN 0167-9295

Beschreibung: Aspect Sensitivity Considerations in Interpreting Radar Meteor Range-Spread Trail Echo Durations Content Type Journal Article Pages 1-1 DOI 10.1007/s11038-007-9211-1 Authors Akshay Malhotra, The Pennsylvania State University Communications and Space Sciences Laboratory University Park PA 16802-2707 USA John D. Mathews, The Pennsylvania State University Communications and Space Sciences Laboratory University Park PA 16802-2707 USA Julio Urbina, The Pennsylvania State University Communications and Space Sciences Laboratory University Park PA 16802-2707 USA Journal Earth, Moon, and Planets Online ISSN 1573-0794 Print ISSN 0167-9295

Beschreibung:    The Theory of Alfven drag (Drell et al. in J Geophys Res 70: 3131–3145 1965 ; Anselmo and Farinella in Icarus, 58, 182–185 1983 ) is applied here to show that the existence of a possible solar ring structure at a radial distance of 0.02 AU (~4R ⊙ , R ⊙  = radius of the sun) predicted by earlier authors (Brecher et al. in Nature 282, 50–52 1979 ; Rawal in Bull. Astr. Soc. India 6, 92–95 1978 , Moon Planets 24, 407–414 1981 , Moon Planets 31, 175–182 1984 , J Astrophys Astr 10, 257–259 1989 ) may not survive Alfven drag produced during even moderate solar magnetic storms which take place from time to time through the age of the sun, but a possible solar ring structure at a radial distance of 0.13 AU (~27R ⊙ ) (Brecher et al. in Nature 282, 50–52 1979 ; Rawal in Bull. Astr. Soc. India 6, 92–95 1978 , Moon Planets 24, 407–414 1981 , Moon Planets 31, 175–182 1984 , J Astrophys Astr 10, 257–259 1989 ) may survive intense Alfven drag produced during even strong magnetic storms of magnetic field value up to 1,000 G. Content Type Journal Article Pages 1-5 DOI 10.1007/s11038-011-9383-6 Authors J. J. Rawal, The Indian Planetary Society, B-201, Vishnu Apartment, Lokmanya Tilak Road, Borivali (West), Mumbai 400 092, India S. Ramadurai, The Indian Planetary Society, B-201, Vishnu Apartment, Lokmanya Tilak Road, Borivali (West), Mumbai 400 092, India Journal Earth, Moon, and Planets Online ISSN 1573-0794 Print ISSN 0167-9295