Ahmadābād, India
Ahmadābād, India

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Basu Sarbadhikari A.,University of Tennessee at Knoxville | Basu Sarbadhikari A.,Planex Inc. | Goodrich C.A.,Planetary Science Institute | Liu Y.,University of Tennessee at Knoxville | And 3 more authors.
Geochimica et Cosmochimica Acta | Year: 2011

Larkman Nunatak (LAR) 06319 is an olivine-phyric shergottite whose olivine crystals contain abundant crystallized melt inclusions. In this study, three types of melt inclusion were distinguished, based on their occurrence and the composition of their olivine host: Type-I inclusions occur in phenocryst cores (Fo77-73); Type-II inclusions occur in phenocryst mantles (Fo71-66); Type-III inclusions occur in phenocryst rims (Fo61-51) and within groundmass olivine. The sizes of the melt inclusions decrease significantly from Type-I (∼150-250μm diameter) to Type-II (∼100μm diameter) to Type-III (∼25-75μm diameter). Present bulk compositions (PBC) of the crystallized melt inclusions were calculated for each of the three melt inclusion types based on average modal abundances and analyzed compositions of constituent phases. Primary trapped liquid compositions were then reconstructed by addition of olivine and adjustment of the Fe/Mg ratio to equilibrium with the host olivine (to account for crystallization of wall olivine and the effects of Fe/Mg re-equilibration). The present bulk composition of Type-I inclusions (PBC1) plots on a tie-line that passes through olivine and the LAR 06319 whole-rock composition. The parent magma composition can be reconstructed by addition of 29mol% olivine to PBC1, and adjustment of Fe/Mg for equilibrium with olivine of Fo77 composition. The resulting parent magma composition has a predicted crystallization sequence that is consistent with that determined from petrographic observations, and differs significantly from the whole-rock only in an accumulated olivine component (∼10wt%). This is consistent with a calculation indicating that ∼10wt% magnesian (Fo77-73) olivine must be subtracted from the whole-rock to yield a melt in equilibrium with Fo77. Thus, two independent estimates indicate that LAR 06319 contains ∼10wt% cumulate olivine. The rare earth element (REE) patterns of Type-I melt inclusions are similar to that of the LAR 06319 whole-rock. The REE patterns of Type-II and Type-III melt inclusions are also broadly parallel to that of the whole-rock, but at higher absolute abundances. These results are consistent with an LAR 06319 parent magma that crystallized as a closed-system, with its incompatible-element enrichment being inherited from its mantle source region. However, fractional crystallization of the reconstructed LAR 06319 parent magma cannot reproduce the major and trace element characteristics of all enriched basaltic shergottites, indicating local-to-large scale major- and trace-element variations in the mantle source of enriched shergottites. Therefore, LAR 06319 cannot be parental to the enriched basaltic shergottites. © 2011 Elsevier Ltd.

Acharyya K.,University of Virginia | Acharyya K.,Planex Inc. | Herbst E.,University of Virginia
Astrophysical Journal | Year: 2016

The Large (LMC) and Small (SMC) Magellanic Clouds are irregular satellite galaxies of the Milky Way. Both are metal- and dust-poor, although the SMC is significantly poorer in both. We have recently simulated the chemistry in cold dense regions of the LMC and found that a rich chemistry exists in the gas-phase. In this paper, we report a companion study of the chemistry of dense regions of the SMC, confining our attention to cold regions of dense clouds with a variety of densities, visual extinctions, and grain temperatures, and a fixed gas-phase temperature. With a gas-to-dust ratio and elemental abundances based on observations and scaling, we found that for molecules like CO and N2, which are predominantly formed in the gas phase, their abundances are consistent with the reduced elemental abundances of their constituent elements above 25 K; however, for species that are produced fully (e.g., CH3OH) or partially on the grain surface (e.g., H2CO, NH3), the dependence on metallicity can be complex. Most of the major gas-phase species observed in our Galaxy are produced in the SMC although in lower quantities. With our simulations, we are able to explain observed gas-phase abundances reasonably well in the dense sources N27 and LIRS 36. We have also compared our calculated abundances of selected ices with limited observations in dense regions in front of young stellar objects. © 2016. The American Astronomical Society. All rights reserved.

Kusuma K.N.,Planex Inc. | Sebastian N.,Planex Inc. | Murty S.V.S.,Planex Inc.
Planetary and Space Science | Year: 2012

Spectral information from the Moon Mineralogy Mapper (M3) onboard Chandrayaan-1 and DIVINER Lunar Radiometer onboard LRO have been used for geochemical and mineralogical characterisation of the Gruithuisen region on Moon along with morphometrical information from LOLA Digital elevation model. The apparent reflectance of M3 on global mode is used for (1) spectral characterisation (2) estimating the abundance of Ti and Fe using Luceys method and (3) discriminating non-mare region from mare regions by means of Minimum Noise Fraction (MNF) transform and Integrated Band Depth (IBD) parameters. Christensen frequency (CF) value derived from DIVINER data is used to delineate the silica saturated lithology from the undersaturated rocks as well as to delineate their spatial spread. Low values of FeO, TiO 2, and IBD indicate non-mare nature of the domes and highland material, also supplemented by CF values. The highland rocks represent signatures of sodic plagioclase, the end result of plagioclase crystallisation from Lunar Magma Ocean. Compositional variations are observed among the domes. NW dome has highest silica concentration than the other two domes and in turn higher viscosity. It is most likely that the three domes tapped residual liquid from different locations of the residual magma chamber which is in constant mixing. The extrusion is probably a localised phenomenon, where urKREEP welled out along the zone of crustal weakness formed by Imbrium Impact. It is likely that δ dome has extruded over a larger time span than other two features. © 2012 Elsevier Ltd. All rights reserved.

Morphologic characteristics of ice-rich landforms in the martian mid-latitudes record evidence for significant modification of the landscape in response to spin-axis/orbital parameter-driven shifts in the Late Amazonian climate. These landforms are spatially distributed across the mid-latitudes and their co-existing presence has so far not been observed from a single crater to infer how exactly a terrain has been modified while Mars was undergoing major-moderate-minor shifts in its Late Amazonian climate. We have therefore carried out an in-depth investigation of Moreux crater (~135. km, centered at 41.66°N, 44.44°E in the Protonilus Mensae region) for identification of features associated with recent and episodic glacial events and for emphasizing the role played by these glacial events in the modification of the crater. Evidence for extensive modification of the surfaces over crater rim/wall and around central peak by emplacement of multiple scales of ice-rich landforms that represents large history of glacial activities was found. From our results we document phases of major-moderate-minor glacial activities within the crater as: (1) piedmont lobes/lobate debris aprons/linear valley fills (~1. Ga-100. Ma), (2) viscous flow features (~30-0.1. Ma) and (3) gullies/thermal contraction crack polygons (~2.1-0.4. Ma). The form and distribution of the random valleys observed within Moreux suggests their formation by pressure-induced melting and flow occurring beneath an extensive layer of ice. We also suggest that central peak of Moreux probably acted as the locus for accumulation of ice/snow and the diversity of glacial/periglacial features within the crater was possibly controlled by differences in the amount of accumulated ice/snow and the rate at which the terrain responded to the shifts in climate during subsequent periods of obliquity changes. Taken together, these ice-rich deposits within Moreux suggest that sequential modification of the crater surfaces over the rim/wall and around central peak has occurred over the last tens of millions of years of martian history. This new evidence thus adds another well-documented case to rapidly accumulating evidences for widespread glacial activity in the middle latitudes of Mars in recent martian history. © 2014 Elsevier Inc.

Sinha R.K.,Planex Inc. | Murty S.V.S.,Planex Inc.
Planetary and Space Science | Year: 2013

In this study, we examine the existence of multiple episodes of glacial activities in Deuteronilus Mensae region on Mars from the analysis of high-resolution remote sensing images acquired by Mars Reconnaissance Orbiter (MRO) ConText Camera (CTX) and High resolution imaging science experiment (HiRISE). The investigated portion from northern mid-latitude of Mars is centered at 44.6 N and 28.8 E and lies ~200 km to south of the largest crater (Lyot) of northern plains. We have critically examined the features on the surface of regional aprons and suggested a possible process by which these formations would have resulted. The entire morphology of the surface was mapped using CTX data sets for developing a general idea about the class of landforms and their extent. The topographic characteristics of the region were derived from Mars Orbiter Laser Altimeter (MOLA) data sets to assess the down-slope flow of ice-debris mixture and the local slope-variations were determined to interpret the flow of small-scale features. The degradational extent of craters lying on the surface of linear valley fill (LVF) flow and the formation of layered pit units in the low-lying region of plateau 2 were systematically explained to account for the presence of ice in the near surface beneath the debris apron. The examined flow-features on the apron surface were compared with their terrestrial glacial analogues for deducing the possible explanation for the variation in pattern of LVF flow. Processes resulting in similar type of glacial landforms as in Himalaya, Antarctica, and parts of Alaska on Earth were widely identified and attributed to be the major cause that has led to shape the fretted terrain on Mars. We have also attempted to classify the different stages of Martian glacial activity, based on the nature of landforms observed in the study region. The morphological evidences and comparisons between the features on Earth and Mars ascertained that Mars has experienced extensive glaciation during the past, and has preserved the landforms on its surface resulting from multiple glacial epochs. © 2013 Elsevier Ltd.

He J.,Syracuse University | Acharyya K.,Planex Inc. | Vidali G.,Syracuse University
Astrophysical Journal | Year: 2016

We measured the binding energy of N2, CO, O2, CH4, and CO2 on non-porous (compact) amorphous solid water (np-ASW), of N2 and CO on porous ASW, and of NH3 on crystalline water ice. We were able to measure binding energies down to a fraction of 1% of a layer, thus making these measurements more appropriate for astrochemistry than the existing values. We found that CO2 forms clusters on the np-ASW surface even at very low coverages. The binding energies of N2, CO, O2, and CH4 decrease with coverage in the submonolayer regime. Their values at the low coverage limit are much higher than what is commonly used in gas-grain models. An empirical formula was used to describe the coverage dependence of the binding energies. We used the newly determined binding energy distributions in a simulation of gas-grain chemistry for cold cloud and hot-core models. We found that owing to the higher value of binding energy in the submonolayer regime, a fraction of all these ices remains for much longer and up to higher temperatures on the grain surface compared to the single value energies currently used in the astrochemical models. © 2016. The American Astronomical Society. All rights reserved.

Sinha R.K.,Planex Inc. | Murty S.V.S.,Planex Inc.
Journal of Geophysical Research E: Planets | Year: 2013

Glacial/periglacial landforms lying within impact craters on Mars have led to the identification of two mechanisms for their formation: (1) intermittent deposition of atmospherically emplaced snow/ice during past spin-axis/orbital conditions and (2) flow of debris-covered ice-rich deposits. The maximum presence of the young ice/snow-rich features (thermal contraction crack polygons, gullies, arcuate ridges, and lobate debris tongues) was observed on the pole-facing slope, indicating that this slope was the preferred site for ice/snow accumulation (during the last 10 Ma). In this study, we investigated 30 craters lying in the Alba Patera volcanic province in the latitudinal bands between 45°N and 32.4°N. Morphological comparison of the younger ice/snow-rich features in these craters led us to conclude that glacial/periglacial features in Alba Patera are mainly present within pole-facing slopes of craters lying within 45°N-39°N. The craters lying within 40.2°N-40°N did not show any glacial/periglacial features. We suggest that the formation of these young ice/snow-rich features follows the same orientation trends as those of other older (>10 Ma) glacial features (debris-covered ice/snow-rich large deposits at the base of the crater wall) in the region. The present work has revealed that the onset of physical processes that result in the formation of glacial/periglacial landforms is also dependent on the changes in elevation ranges of the investigated craters in Alba Patera. Our results confirm past inferences for accumulation of ice/snow on Mars and suggest that the period of ice/snow accumulation activity in Alba Patera occurred throughout the Amazonian and lasted until the recent past, i.e., 2.1-0.4 Ma. © 2013. American Geophysical Union. All Rights Reserved.

Varatharajan I.,Planex Inc. | Srivastava N.,Planex Inc. | Murty S.V.S.,Planex Inc.
Icarus | Year: 2014

A comparative assessment of the mineralogy of young basalts (~1.2Ga to ~2.8Ga) from the western nearside, Moscoviense basin, and the Orientale basin of the Moon has been made using Level 2 Moon Mineralogy Mapper (M3) data from the Chandrayaan-1 mission. Spectral data characteristics of the individual units have been generated from fresh small craters to minimize the complications due to space weathering. Representative spectra for individual units and the derived spectral parameters (band centers and integrated band depth ratio) have been used to study composition of these young basalts. A modified approach of Gaffey et al. (Gaffey, M.J., Cloutis, E.A., Kelley, M.S., Reed, K.L. [2002]. Mineralogy of asteroids. In: Asteroids III. The University of Arizona Press, Tucson, pp. 183-204) (for olivine-pyroxene mixtures) and the methodology of Adams (Adams, J.B. [1974]. J. Geophys. Res. 79, 4829-4836. http://dx.doi.org/10.1029/JB079i032p04829) (for interpreting pyroxene type) have been used to improve our understanding of the spectral behavior of these basalts. Most of the young basalts of Oceanus Procellarum are characterized by abundant olivines and they show complex volcanic history. Vast exposures of olivine concentrated units having higher abundance of olivine content than high-Ca pyroxenes are emplaced in the northern Oceanus Procellarum region. Mostly, they show distinct stratigraphic gradation with the immediately underlying units of relatively lower olivine content. The Moscoviense unit shows signatures of Fe-rich glasses along with clinopyroxenes. The basalts of Orientale basin are typically devoid of olivine and are rich in high-Ca pyroxene. Thus, mineralogy of these mare basalts which erupted during the late stage volcanism vary across the Moon's surface; however, broader observations reveal apparently higher FeO content in the younger basalts of western nearside and Orientale region. © 2014 Elsevier Inc.

Planex Inc. | Date: 2013-02-19

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