Hitesh Changela - Academia.edu (original) (raw)

Papers by Hitesh Changela

Frontiers in Astronomy and Space Sciences

Meteor plasmas and impact events are complex, dynamic natural phenomena. Simulating these process... more Meteor plasmas and impact events are complex, dynamic natural phenomena. Simulating these processes in the laboratory is, however, a challenge. The technique of laser induced dielectric breakdown was first used for this purpose almost 50 years ago. Since then, laser-based experiments have helped to simulate high energy processes in the Tunguska and Chicxulub impact events, heavy bombardment on the early Earth, prebiotic chemical evolution, space weathering of celestial bodies and meteor plasma. This review summarizes the current level of knowledge and outlines possible paths of future development.

Nitrogen is an important part of any biosphere/organic cycling, but aspects of the nitrogen cycle... more Nitrogen is an important part of any biosphere/organic cycling, but aspects of the nitrogen cycle for Mars are quite unclear. Nitrate and (per)chlorate have been detected in sedimentary rocks and aeolian sediments in Gale crater on Mars as well as in martian meteorites. Their occurrences have implications for global nitrogen/chlorine cycles and the habitability on Mars. However, the origins of nitrate and (per)chlorate, and their possible formation are not well understood. Interaction between the atmosphere and surface of Mars during dust events have cause electrostatic discharge (ESD). By simulating this process in a Mars chamber, nitrate and (per)chlorate can form from halite precursors under martian atmospheric conditions. The obtained nitrate/(per)chlorate ratio (0.28 ± 0.19) is in agreement with Gale crater observations (0.23 ± 0.12), which is much lower than in terrestrial Mars analogues and the products of other pathways proposed for Mars. The electrochemistry during Mars dus...

International Journal of Astrobiology, 2022

The authors apologise that upon publication of this article the author Yangting Lin's name was in... more The authors apologise that upon publication of this article the author Yangting Lin's name was incorrectly spelled. Within the original article the authors name was spelled Yangtin Lin. Additionally, the reference for Hu X, Oberst J and Willner K (2020) was not included in the article. The online version of this article has been updated.

Geochimica et Cosmochimica Acta, 2015

The major form of organic material delivered to Earth from an extraterrestrial origin is Insolubl... more The major form of organic material delivered to Earth from an extraterrestrial origin is Insoluble Organic Matter (IOM). A morphological study of IOM in the CR (Renazzo-type) and CM (Mighei-type) carbonaceous chondrites was performed in order to constrain its origins and processing history. IOM residues from the following CR chondrites: GRO 95577 (CR1), Al Rais (CR1/2), EET 92042 (CR2), QUE 99177 (CR3) and the CM chondrites: MET 01070 (CM2.2), Cold Bokkeveld (CM2.3), Murchison (CM2.4) and QUE 97990 (CM2.5) were studied using Annular Dark Field STEM imaging. Characteristic features of the IOM, organic nanoglobules, were manually identified and measured for their abundances and size distributions. The IOM residues were also compared holistically for their degree of average 'roughness' or 'coarsening' using fractal image analysis. Manually identified nanoglobules have abundances making up less than 10% of the total IOM, which is consistent with previous studies. Their measured abundances do not correlate with petrologic grade. Thus parent body processing did not systematically deplete their abundances. The IOM is however on average 'smoother' or 'coarser' in the more altered chondrites, demonstrated by a lower fractal dimension using fractal box counting (D B). The D B values for the IOM in the CR chondrites are distinctive: QUE 99177 has the largest D B value (average = 1.54 ± 0.004) and GRO 99577 has the lowest (average = 1.45 ± 0.011). Al Rais and EET 92042 have IOM with average D B values within this range (average, 1.46 ± 0.009 and 1.50 ± 0.006). The CMs record a similar but less distinctive trend in D B , with QUE 97990 having the largest value (1.52 ± 0.004), MET 01070 the lowest (1.45 ± 0.019), and Cold Bokkeveld (1.50 ± 0.011) and Murchison (1.49 ± 0.017) equivalent to one another within error. The identified nanoglobules in the IOM of the CM chondrites are on average larger than those in the CR chondrites. The 'coarsening' or 'smoother' texture of the IOM (lower D B) in the more altered chondrites coupled with a tentative increase in the size of large features (identified nanoglobules) demonstrates that the aqueous processes leading to the lower petrologic types also formed the overall IOM morphology. In addition, observations of fluid-like textures more frequently found in the more altered carbonaceous chondrite residues suggests that organic and aqueous fluids determined at least some of these morphologies. The polymerization of organic solutions is consistent with these morphologies. Their formation conditions are more favorable under the containment of carbonaceous chondrite parent bodies.

Meteoritics & Planetary Science, 2020

The ungrouped achondrite Northwest Africa (NWA) 7325 parent body underwent a severe impact after ... more The ungrouped achondrite Northwest Africa (NWA) 7325 parent body underwent a severe impact after primary crystallization, which completely melted plagioclase and partially melted pyroxene, followed by Mg diffusion into the adjacent plagioclase‐melt. The 26Al‐26Mg system was therefore modified, forming a pseudoisochron with an initial δ26Mg* of 0.094 ± 0.005‰ and an age of 4563.12 ± 0.33 Ma between the primary crystallization and subsequent impact event(s). The positive initial δ26Mg* can be interpreted by a model age of ~1.77 Ma after CAIs when a chondritic composition differentiated into a magma/rock with the Al/Mg ratio equivalent to that of NWA 7325 (~1.52). The LREE enrichments and a positive Eu anomaly suggest that the NWA 7325 parent magma formed by the melting of a plagioclase‐rich crustal lithology, which crystallized from a magma ocean. Differentiation of the magma ocean was prior to 1.77 Ma after CAIs. NWA 7325 is also unique by containing many rounded voids (5–6 vol%) interstitial to or enclosed in silicates, suggested to have formed by the leaching/vaporization of pre‐existing Fe‐Ca‐Mg‐Mn sulfides. This is supported by the similar morphology between voids and Cr‐bearing troilites, the discovery of relict oldhamite, and the highly reducing conditions of NWA 7325. The loss of pre‐existing sulfides could explain the unusual subchondritic Mn/Mg ratio of the bulk sample. Furthermore, the enrichment of moderately volatile elements (K/Th ratio ~2600–10,000) in the NWA 7325 parent body may result from the bonding with S2‐ in silicate melts under highly reducing conditions. NWA 7325 therefore provides evidence of sulfur‐rich magmatism in the early solar system.

Introduction: The major form of organic matter (OM) in carbonaceous chondrites (CCs) is submicron... more Introduction: The major form of organic matter (OM) in carbonaceous chondrites (CCs) is submicron, macromolecular material that is mostly insoluble [1]. The nature of the precursor OM that accreted into the CC parent bodies and formed these inclusions is still not understood. Contributions from a variety of sources including OM formed in interstellar [2], nebular [3] and parent body [4] enviroments have all been envisioned. The CR chondrites exhibit a wide range of aqueous alteration [5,6]. We have investigated the variation in the morphology, molecular chemistry and mineral-organic associations of OM across a range of CR petrologic types in an attempt to constrain its origins and understand its evolutionary history on the parent body. We aim to answer the following questions: A. How are different types of OM distributed in the CR chondrite matrices? B. What are the functional chemistry, morphology and surrounding mineralogy of discrete organic particles and are they related? C. Doe...

Conclusions Insoluble organic matter (IOM) is an acid insoluble fraction of organic matter (OM) i... more Conclusions Insoluble organic matter (IOM) is an acid insoluble fraction of organic matter (OM) in extraterrestrial materials. IOM constitutes a major proportion, 70-99%, of total OM found in primitive meteorites.[1] It is present as solid macromolecular organic material that is largely made up of small aromatic moieties with short, highly branched aliphatic moieties that forms side chains on and cross links between the aromatic moieties.[2] Isotopic anomalies in IOM (enrichments in D/H and 15N/14N ratios relative to solar and terrestrial values) point to an origin in cold molecular clouds and/or the cold outskirts of the protoplanetary disk.[3,4] It is however not clear what the carriers of these isotopic enrichments that accreted onto the parent body. One characteristic component of IOM is nanoglobules: solid or hollow, carbonaceous spheres.[5] Using Transmission Electron Microscopy (TEM), we have been performing image analysis on the IOM from the primitive carbonaceous chondrites...

Journal of Geophysical Research: Biogeosciences, 2020

Magnetite produced by magnetotactic bacteria (MTB) provides stable paleomagnetic signals because ... more Magnetite produced by magnetotactic bacteria (MTB) provides stable paleomagnetic signals because it occurs as natural single-domain magnetic nanocrystals. MTB can also provide useful paleoenvironmental information because their crystal morphologies are associated with particular bacterial groups and the environments in which they live. However, identification of the fossil remains of MTB (i.e., magnetofossils) from ancient sediments or rocks is challenging because of their generally small sizes and because the growth, morphology, and chain assembly of magnetite within MTB are not well understood. Nanoscale characterization is, therefore, needed to understand magnetite biomineralization and to develop magnetofossils as biogeochemical proxies for paleoenvironmental reconstructions. Using advanced transmission electron microscopy, we investigated magnetite growth and chain arrangements within magnetotactic Deltaproteobacteria strain WYHR-1, which reveals how the magnetite grows to form elongated, bullet-shaped nanocrystals. Three crystal growth stages are recognized: (i) initial isotropic growth to produce nearly round~20 nm particles, (ii) subsequent anisotropic growth along the [001] crystallographic direction to~75 nm lengths and~30-40 nm widths, and (iii) unidirectional growth along the [001] direction to~180 nm lengths, with some growing to~280 nm. Crystal growth and habit differ from that of magnetite produced by other known MTB strains, which indicates species-specific biomineralization. These findings suggest that magnetite biomineralization might be much more diverse among MTB than previously thought. When characterized adequately at species level, magnetofossil crystallography, and apomorphic features are, therefore, likely to become useful proxies for ancient MTB taxonomic groups or species and for interpreting the environments in which they lived. Plain Language Summary Biomineralization is a widespread process that provides living organisms with mineralized skeletons and organelles. Biominerals are mainly responsible for Earth's fossil record. As a striking example of microbial biomineralization, magnetotactic bacteria form intracellular chains of magnetic nanocrystals that they use to sense Earth's magnetic field. Their fossilized remains (magnetofossils) are being used increasingly to reconstruct paleomagnetic and paleoenvironmental information. However, magnetofossil identification remains challenging because magnetite particle growth and chain assembly processes are poorly understood. We report a species-specific crystal growth and chain arrangement process in a novel magnetotactic strain WYHR-1. Our findings suggest that magnetofossil crystallography could become a proxy for ancient bacterial taxonomic groups or species and for interpreting the environments in which they lived.

Geochimica et Cosmochimica Acta, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Surface and Interface Analysis, 2019

NanoSIMS has been the most widely used analytical technique for measuring the elemental and isoto... more NanoSIMS has been the most widely used analytical technique for measuring the elemental and isotopic ratios of micrometer to sub‐micrometer particles, e.g., pre‐solar grains, soil particles, and fog‐helium aerosol particles. Automated sample stage movement combined with particle recognition algorithm is commonly used to improve analytical efficiency. However, due to the effect of sample topography or variation in ion yield rates, the global thresholding method used in previous studies has a low recognition rate. In order to improve the recognition rate, here we have developed a high‐efficiency sub‐micron particle recognition method. This method searches for the threshold that minimizes the intra‐class variance of the local domain (the radius of the local is set to 10 pixels). The central pixel of this circular ROI is then tested against the threshold found for this region. Presolar grains from the Qingzhen (EH3) meteorite and soil organic particles from Oxisol were analyzed. The analytical efficiency was improved by 120‐200% compared with the global thresholding algorithms. This method can be widely applied in automated studies of large numbers of micrometer to sub‐micrometer particles.

Meteoritics & Planetary Science, 2019

Zircons and apatites in clasts and matrix from the Martian breccia NWA 7034 are well documented, ... more Zircons and apatites in clasts and matrix from the Martian breccia NWA 7034 are well documented, timing ancient geologic events on Mars. Furthermore, in this study, zircon trace elemental content, apatite volatile content, and apatite volatile isotopic compositions measured in situ could constrain the evolution of those geologic events. The U-Pb dates of zircons in basalt, basaltic andesite, trachyandesite igneous clasts, and the matrix are similar (4.4 Ga) suggesting intense volcanism on ancient Mars. However, two metamict zircon grains found in the matrix have an upper intercept date of~4465 Ma in crystalline, whereas amorphous areas have a lower intercept date of 1634 AE 93 Ma. The younger date is consistent with the date of apatites (1530 AE 65 Ma), suggesting a metamorphic event that completely reset the U-Pb system in both the amorphous areas of zircon and all apatites. dD values in all apatites negatively correlate with water content in a two-endmember mixing trend. The D (dD up to 2459&) and 37 Cl heavy core (3.8&) of a large apatite grain suggest a D-, 37 Cl-rich fluid during the metamorphic event~1.6 Ga ago, consistent with the trace elements Y, Hf and Ti and P in zircons. The fluid was also therefore P-rich. The D-, 37 Clpoor H 2 O-rich rim (<313&) suggests the degassing of water from the Martian Cl-poor interior at a later time. This D-, 37 Cl-poor Martian mantle reservoir could have derived from volcanic intrusions postdating the younger metamorphic event recorded in NWA 7034.

We report coordinated XANES, TEM, and nanoSIMS analysis of two large, carbon-rich veins in CR2 ch... more We report coordinated XANES, TEM, and nanoSIMS analysis of two large, carbon-rich veins in CR2 chondrite GRA 95229. The variability in morphological, isotopic, and chemical properties is compared to previous results on C-rich veins in CR3 QUE 99177.