Laboratory photometry of regolith analogues: Effect of porosity-II

1A.Kar,1A.K.Sen,2R.Gupta
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114211]
1Department of Physics, Assam University, Silchar 788011, India
2IUCAA, Ganeshkhind, Pune 411007, India
Copyright Elsevier

Context:
Numerous minor bodies of our solar system are covered by loosely bound dust particles; these layers are called regolith. Light scattered by regolith surfaces is a function of their bulk porosity, of the sizes, shapes, structures and compositions of the constituent particles.

Aims:
To increase our data base, the present work is an extension of our previous work by Kar et al. (2016), where we reported light scattering data for regolith surfaces with different porosities, sizes, and composition of the particles (from very low to moderate absorption). The new samples have larger particles with moderate to high absorption, three originate from industry, and three are natural (among them a mixture of two previously studied samples).

Methods:
The samples were prepared with different bulk porosities. Photometric phase curves were built for two different geometrical configurations. The light source was a He-Ne laser at 632.8 nm. The phase angle () covered for the first configuration is from 45 to 126° and for the second configuration it is from 45 to 108°, in steps of 9 and 4.5° respectively. We maintained incident angle ()= emergent angle () for the first configuration and , while varying for the second configuration. The experimental data were fitted successfully to the semi-empirical model proposed by Hapke (2008) and interpreted in terms of the porosities and sizes of the particles. The albedo values obtained from the model for two samples are compared to those calculated directly from Mie theory.

Results:
The successful fit by the model is confirmed just as the increase of reflectivity with the decrease of porosities for a given composition and particle size. Further, it was observed that reflectivity increases with the decrease in particle size for a given composition.

Finally, we have tested that for corundum and silicon carbide samples with a and particle sizes ( respectively), the best fitted albedo () values that can be obtained from Hapke model, match very well with those calculated directly by Mie Theory. This also re-validated our approach adopted in the present work.

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