arXiv subjects

Megha Bhatt

Publications and source records attributed to Megha Bhatt.

4 recordsLinked to original sources

arXiv2026

Morphological and mineralogical characterization of the Freundlich-Sharonov Basin: Implications for the lunar farside magmatism

Volcanism on the Moon is highly asymmetric, with the nearside having extensive mare emplacements and the farside exhibiting only sparse, localized volcanism. The Freundlich-Sharonov Basin (FS Basin), a preNectarian/Nectarian impact basin located on the central farside of the Moon (18.35N, 175.2E), hosts a limited volume of spatially restricted and isolated volcanic patches, which provide an ideal geological setting to investigate controls on the lunar magmatism in a thick, KREEP poor farside crust. In this study, detailed geological characterization of the FS Basin is provided for the first time, incorporating insights from morphological, chronological, and compositional analyses using high resolution datasets from missions such as Chandrayaan1 (Moon Mineralogy Mapper), Kaguya, and Lunar Reconnaissance Orbiter. The results of this study reveal a previously undetected ~192 km diameter inner depression ring, along with spatially aligned subsurface magmatic intrusions, and exposures of PAN and orthopyroxenes along the basin rings. Compositional analyses indicate that the FS Basin experienced at least two volcanic eruptions dominated by exceptionally high-alumina basalts (~16 to 24 wt% Al2O3) around ~3.4 Ga and ~2.1 Ga. This is the highest reported alumina content in the lunar maria, also expanding the period of known high alumina volcanism on the Moon to the late phase. We propose that the limited extent of volcanic eruptions in the FS Basin is a result of the combined effects of composition-dependent magma buoyancy, reduced magma production, and impact modified crustal structures determining the magma extrusion sites.

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arXiv2026

Wide-field Polarization Imaging and Numerical Modeling of the Coma and Tail of Comet C/2023 A3 (Tsuchinshan-ATLAS)

Imaging polarimetry enables the spatially resolved investigation of cometary dust properties across different morphological structures. While cometary comae have been studied thoroughly in the pertinent literature, cometary tails have remained less explored. Comparing these regions can reveal differences in the size, structure, and composition of their dust. The goal of this study is to examine the size, structure and composition of the dust particles in the coma and in particular in the tail of the bright comet C/2023 A3 (Tsuchinshan-ATLAS) and to infer possible differences. For this purpose, we rely on the method of telescopic wide-field polarimetric imaging of the comet in the visible to near-infrared domain in order to obtain the dependence of the degree of linear polarization (DoLP) of the coma and tail on the phase angle across a broad range. An off-the-shelf industrial grade polarization camera was used in combination with a telescope of short aperture ratio. These observations are complemented by T-matrix and Discrete Dipole Approximation modeling using the MSTM5 and DDSCAT software framework, respectively, for simulation of light scattering by dust particles of fractal agglomerate and agglomerate debris morphology. Our observations indicate that the coma exhibits a high maximum DoLP of 0.34, which is further exceeded by a factor of about two by the DoLP of the comet's tail. Our modeling results suggest a 50:50 olivine-carbon composition. The fraction of agglomerate debris was found to be 50% in the coma and possibly higher in the tail. The differences between coma and tail in the observed maximum DoLP and the phase angle at which it occurs can be explained by a predominance of particles with radii larger than 0.6 micrometer in the coma vs. smaller sub-micrometer particles close to the Rayleigh limit in the tail [...]

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arXiv2023

Chandrayaan-3 Alternate Landing Site: Pre-Landing Characterisation

India's third Moon mission Chandrayaan 3 will deploy a lander and a rover at a high latitude location of the Moon enabling us to carry out first ever in-situ science investigations of such a pristine location that will potentially improve our understanding on primary crust formation and subsequent modification processes. The primary landing site (PLS), is situated at 69.367621 degS, 32.348126 degE. As a contingency, an alternate landing site (ALS) was also selected at nearly the same latitude but nearly 450 km west to PLS. In this work, a detailed study of the geomorphology, composition, and temperature characteristics of ALS has been carried out using the best-ever high resolution Chandrayaan 2 OHRC DEMs and Ortho images, datasets obtained from Chandrayaan 1 and on-going Lunar Reconnaissance Orbiter. For understanding the thermophysical behaviour, we used a well-established thermophysical model. We found that the Chandrayaan 3 ALS is characterised by a smooth topography with an elevated central part. The ALS is a scientifically interesting site with a high possibility of sampling ejecta materials from Tycho and Moretus. Based on the spectral and elemental analysis of the site, Fe is found to be near approx. 4.8 wt.%, with Mg approx. 5 wt.%, and Ca approx. 11 wt.%. Compositionally, ALS is similar to PLS with a highland soil composition. Spatial and diurnal variability of around 40 K and 175 K has been observed in the surface temperatures at ALS. Although belonging to similar location like PLS, ALS showed reduced daytime temperatures and enhanced night-time temperatures compared to PLS, indicating a terrain of distinctive thermophysical characteristics. Like PLS, ALS is also seems to be an interesting site for science investigations and Chandrayaan 3 is expected to provide new insights into the understanding of lunar science even if it happens to land in the alternate landing site.

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arXiv2015

Spectral calibration for deriving surface mineralogy of Asteroid (25143) Itokawa from Hayabusa Near-Infrared Spectrometer (NIRS) Data

We present spectral calibration equations for determining mafic silicate composition of near-Earth asteroid (25143) Itokawa from visible/near-infrared spectra measured using the Near Infrared Spectrometer (NIRS), on board the Japanese Hayabusa spacecraft. Itokawa was the target of the Hayabusa sample return mission and has a surface composition similar to LL-type ordinary chondrites. Existing laboratory spectral calibrations use a spectral wavelength range that is wider (0.75-2.5 microns) than that of the NIRS instrument (0.85-2.1 microns) making them unfit for interpreting the Hayabusa spectral data currently archived in the Planetary Data System. We used laboratory measured near-infrared reflectance spectra of ordinary (H, L and LL) chondrites from the study of Dunn et al. (2010), which we resampled to the NIRS wavelength range. Using spectral parameters extracted from these resampled spectra we established a relationship between band parameters and their mafic silicate composition (olivine and low-Ca pyroxene). We found a correlation >90% between mafic silicate composition (fayalite and forsterite mol. %) estimated by our spectral method and X-ray diffraction (XRD) measured values. To test the validity of the newly derived equations we blind tested them using nine laboratory-measured spectra of L and LL type chondrites with known composition. We found that the absolute difference between the measured and computed values is in the range 0.1 to 1.6 mol. %. Our study suggests that the derived calibration is robust and can be applied to Hayabusa NIRS data despite its limited spectral range. We applied the derived equations to a subset of uncalibrated NIRS spectra and the derived fayalite and ferrosilite values are consistent with Itokawa having a LL chondrite type surface composition.

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