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Register a new userLaboratory light scattering from regolith surface and simulation of data by Hapke model
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The small atmosphereless objects of our solar system, such as asteroids, the moon are covered by layer of dust particles known as regolith, formed by meteoritic impact. The light scattering studies of such dust layer by laboratory experiment and numerical simulation are two important tools to investigate their physical properties. In the present work, the light scattered from a layer of dust particles, containing 0.3{mu}m Al2O3 at wavelength 632.8 nm is analysed. This work has been performed by using a light scattering instrument ellipsometer, at the Department of Physics, Assam Universiy, Silchar, India. Through this experiment, we generated in laboratory the photometric and polarimetric phase curves of light scattered from such a layer. In order to numerically simulate this data, we used Hapkes model combined with Mies single particle scattering properties. The perpendicular and parallel components of single particle albedo and the phase function were derived from Mie theory. By using the Hapkes model combined with Mie theory, the physical properties of the dust grain such as grain size, optical constant (n,k) and wavelength can be studied through this scheme. In literature, till today no theoretical model to represent polarisation caused due to scattering from rough surface is available, which can successfully explain the scattering process. So the main objective of this work is to develop a model which can theoretically estimate polarisation as caused due to scattering from rough surface and also to validate our model with the laboratory data generated in the present work.
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On July 14th 2015, NASAs New Horizons mission gave us an unprecedented detailed view of the Pluto system. The complex compositional diversity of Plutos encounter hemisphere was revealed by the Ralph/LEISA infrared spectrometer on board of New Horizons. We present compositional maps of Pluto defining the spatial distribution of the abundance and textural properties of the volatiles methane and nitrogen ices and non-volatiles water ice and tholin. These results are obtained by applying a pixel-by-pixel Hapke radiative transfer model to the LEISA scans. Our analysis focuses mainly on the large scale latitudinal variations of methane and nitrogen ices and aims at setting observational constraints to volatile transport models. Specifically, we find three latitudinal bands: the first, enriched in methane, extends from the pole to 55deg N, the second dominated by nitrogen, continues south to 35deg N, and the third, composed again mainly of methane, reaches 20deg N. We demonstrate that the distribution of volatiles across these surface units can be explained by differences in insolation over the past few decades. The latitudinal pattern is broken by Sputnik Planitia, a large reservoir of volatiles, with nitrogen playing the most important role. The physical properties of methane and nitrogen in this region are suggestive of the presence of a cold trap or possible volatile stratification. Furthermore our modeling results point to a possible sublimation transport of nitrogen from the northwest edge of Sputnik Planitia toward the south.
While the Earth and Moon are generally similar in composition, a notable difference between the two is the apparent depletion in moderately volatile elements in lunar samples. This is often attributed to the formation process of the Moon and demonstrates the importance of these elements as evolutionary tracers. Here we show that paleo space weather may have driven the loss of a significant portion of moderate volatiles, such as sodium and potassium from the surface of the Moon. The remaining sodium and potassium in the regolith is dependent on the primordial rotation state of the Sun. Notably, given the joint constraints shown in the observed degree of depletion of sodium and potassium in lunar samples and the evolution of activity of solar analogues over time, the Sun is highly likely to have been a slow rotator. Since the young Suns activity was important in affecting the evolution of planetary surfaces, atmospheres, and habitability in the early Solar System, this is an important constraint on the solar activity environment at that time. Finally, since solar activity was strongest in the first billion years of the Solar System, when the Moon was most heavily bombarded by impactors, evolution of the Suns activity may also be recorded in lunar crust and would be an important well-preserved and relatively accessible record of past Solar System processes.
When creating asteroid regolith simulant, it is necessary to have a model of asteroid regolith to guide and to evaluate the simulant. We created a model through evaluation and synthesis of the available data sets including (1) the returned sample from Itokawa by the Hayabusa spacecraft, (2) imagery from the Hayabusa and NEAR spacecraft visiting Itokawa and Eros, respectively, (3) thermal infrared observations from asteroids, (4) the texture of meteorite regolith breccias, and (5) observations and modeling of the ejecta clouds from disrupted asteroids. Comparison of the Hayabusa returned sample with other data sets suggest the surficial material in the smooth regions of asteroids is dissimilar to the bulk regolith, probably due to removal of fines by photoionization and solar wind interaction or by preferential migration of mid-sized particles into the smooth terrain. We found deep challenges interpreting and applying the thermal infrared data so we were unable to use those observations in the model. Texture of regolith breccias do not agree with other data sets, suggesting the source regolith on Vesta was coarser than typical asteroid regolith. The observations of disrupted asteroids present a coherent picture of asteroid bulk regolith in collisional equilibrium, unlike lunar regolith, HED textures, and the Itokawa returned sample. The model we adopt consists of power laws for the bulk regolith in unspecified terrain (differential power index -3.5, representing equilibrium), and the surficial regolith in smooth terrain (differential power index -2.5, representing disequilibrium). Available data do not provide adequate constraints on maximum and minimum particle sizes for these power laws, so the model treats them as user-selectable parameters for the simulant.
(16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Discovery-class Psyche mission. Despite gaining considerable interest in the scientific community, Psyches composition and formation remain unconstrained. Originally, Psyche was considered to be almost entirely composed of metal due to its high radar albedo and spectral similarities to iron meteorites. More recent telescopic observations suggest the additional presence of low-Fe pyroxene and exogenic carbonaceous chondrites on the asteroids surface. To better understand the abundances of these additional materials, we investigated visible near-infrared (0.35 - 2.5 micron) spectral properties of three-component laboratory mixtures of metal, low-Fe pyroxene, and carbonaceous chondrite. We compared the band depths and spectral slopes of these mixtures to the telescopic spectrum of (16) Psyche to constrain material abundances. We find that the best matching mixture to Psyche consists of 82.5% metal, 7% low-Fe pyroxene, and 10.5% carbonaceous by weight, suggesting that the asteroid is less metallic than originally estimated (~94%). The relatively high abundance of carbonaceous chondrite material estimated from our laboratory experiments implies the delivery of this exogenic material through low velocity collisions to Psyches surface. Assuming that Psyches surface is representative of its bulk material content, our results suggest a porosity of 35% to match recent density estimates.
Photometric observations of exoplanet transits can be used to derive the orbital and physical parameters of an exoplanet. We analyzed several transit light curves of exoplanets that are suitable for ground-based observations whose complete information is available on the Exoplanet Transit Database (ETD). We analyzed transit data of planets including HAT-P-8 b, HAT-P-16 b, HAT-P-21 b, HAT-P-22 b, HAT-P-28 b and HAT-P-30 b using the AstroImageJ (AIJ) software package. In this paper, we investigated 82 transit light curves from ETD, deriving their physical parameters as well as computing their mid-transit times for future Transit Timing Variation (TTV) analyses. The Precise values of the parameters show that using AIJ as a fitting tool for follow-up observations can lead to results comparable to the values at the NASA Exoplanet Archive (the NEA). Such information will be invaluable considering the numbers of future discoveries from the ground and space-based exoplanet surveys.
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