Past Events

Abstract: The Martian ionosphere has been a subject of study since the first mission to the red planet. It is the gateway of many atmospheric loss processes and therefore plays an important role in determining the evolution of the climate and habitability of Mars over geological time. The chemistry, dynamics and energetics of the ionosphere of Mars have spatial and temporal variations due to wide variations in solar forcing, atmospheric dynamics and composition, and the magnetic field. Understanding how competing physical processes produce the observed state of the ionosphere is a major unifying theme that underpins the science of the Martian ionosphere and this calls for the thorough understanding of the the variability of Martian ionosphere. There have been several space missions for studying Martian atmosphere/ionosphere. These missions have revolutionized our understanding on Martian atmosphere/ionosphere. While observations are the key stone in our knowledge of the Martian ionosphere, they have inherent limitations in their temporal and geographical coverage. Computational models can help to overcome these limitations and in addition provide further insight into the physical processes that produce the observed structures. The need to determine how the ionospheric peak varies on spatial and temporal scales is the motivation behind developing a photochemical model for Martian ionosphere. Using the observations from NASA’s MAVEN spacecraft as model inputs, we investigated the behaviour of Martian electron and ion density profiles. The sensitivity of the model calculated plasma profiles to the variations in parameters such as neutral atmospheres, plasma temperatures, etc are explored which was used in understanding in observed features in Martian ionosphere.

Abstract:
Stellar systems, like our solar system, are formed within dense molecular clouds in the interstellar medium. In a large-scale (molecular cloud-scale) scenario, several environmental conditions, like hub filament formation, H II regions, and edge-dominated filamentary collapse, can influence the formation of stars or star clusters. Although the dominant mechanisms are not observationally constrained. In a smaller-scale (protostellar core scale) scenario, while a dense molecular core undergoes gravitational collapse, a disk-jet system is formed naturally to conserve angular momentum. The jet appears from the protostellar disk surface and removes excess angular momentum, therefore, playing a vital role in the growth of the central core, the formation and evolution of the circumstellar disk, the chemical composition of the disk and emerging planetesimals within it. However, the jet launching zones and the impact of accretion bursts on the emerging planets are not well studied observationally due to a lack of very high-resolution observations.
In this seminar, I shall present the formation and evolution scenario of the dense core, especially the (1) dominant mechanisms of molecular cloud collapse (2) the launching mechanisms and morphological changes of the protostellar jet (3) the impact of accretion outbursts in the chemical composition of the emerging planetesimals, First, I shall discuss the dominant environmental effects of protostar formation in molecular clouds with our multiwavelength observations. Then I shall talk about our recent results on protostellar jet/outflow from the high spatial resolution and high sensitivity observations with Atacama Large Millimeter/submillimeter Array (ALMA), which is currently the largest radio interferometry array on Earth. In particular, I shall probe the dominant mechanism of jet launching, whether the jet launches from the inner disk (i.e., X-wind) or a more extended disk region (i.e., disk-wind). Finally, I shall describe the possible connection of the jet with the accretion burst and formation of complex organic molecules (COMs) within the disk, which would be the chemical composition of emerging planetesimals.

Abstract:
Internal waves and tides exist in the ocean interior due to differences in fluid densities. Interactions between internal tides generated by tidal flow over bathymetric features and near-inertial waves generated by winds yield a spectrum of internal waves at many frequencies. High-resolution realistic ocean simulations have come a long way and now contain a well-developed spectrum. We present results from some of our most recent works where we suggest improvements to the well-known K-Profile Parameterisation which leads to a better internal wave wavenumber spectrum in regional ocean simulations by comparing it to observational data. Improvement in the vertical wavenumber spectrum of internal waves is crucial for fine-scale parameterization. Breaking of internal waves causes mixing, and it has important effects on the distribution of ocean temperature and nutrients. I will discuss observations of year-long geophysical turbulence in the Bay of Bengal measured with mixing meters called Chipods. We study the role of low-salinity water in modulating subsurface turbulence and elaborate on the seasonal nature and depth penetration of turbulence. This could be of importance to improving our understanding of the role of the Bay in the Indian monsoon. We find a prolonged suppressed phase of turbulence in the post-monsoon season which conditions the Bay for the summer monsoon of the next year. We also provide evidence of an interesting diurnally varying mixing signature in the Bay which, we strongly suspect, is biological in origin. I will briefly describe how the observations of vertical turbulence variability in the Bay inspired our theoretical work on nonlinear optimal perturbations in a viscosity-stratified flow. I will also touch upon an ongoing work where we take up the task of mapping the incoherent tides of the world's oceans using spatiotemporal basis functions.

Abstract:
The Himalaya is one of the most tectonically-active mountain belts of the world and therefore is a hub of recurrent small to medium-magnitude earthquakes. Surprisingly, mega-earthquakes (Mw> 7.5) are very rare in the Himalaya and occurred only a few times in the last 1500 years or till the time recorded by paleo-seismology. The Himalayan earthquakes are caused by periodic/ stochastic release of strain accumulated at the decollement of the orogenic wedge, known as the Main Himalayan Thrust (MHT). During earthquakes, the ‘usually-locked’ MHT slips and often the slip is transpired to the surface by various surface-breaking fault-splays rooted to the MHT. However, not all seismic events could trigger a surface-rupture and often induce ‘blind faults’. Out of the 40 – 50 mm/y intraplate convergence, ~14±2 mm/y is accommodated by various faults and folds of the western Himalaya. The cumulative slip rates are fairly consistent over geodetic to millennial timescales. Despite the high cumulative slip rates anticipated for the western Himalaya, it hardly experienced any complete surface-rupture earthquake in the last 600 – 1000 years. This simply means that at least some parts of the western Himalaya are under high risk of a large seismic event/s in near future. The future earthquake/s will either create a new fault or reactivate older faults of the Himalaya.
In this seminar, I will discuss the potential structures (both surface-breaking faults and blind faults) in the western Himalaya which can get reactivated. For this, two major aspects have to be well-constrained – 1. millennial-scale deformation rates on folds and faults and 2. Time since the last seismic event that triggered the growth of the structure. My work is focused on constraining the Late Pleistocene – Holocene deformation rates from several active structures across the western Himalaya. This involves mapping of tectonically-deformed (folded or offset) fluvial terraces and dating those terraces using Terrestrial Cosmogenic Nuclides (10Be and 26Al) and Optically-Stimulated Luminescence (OSL) dating methods. Mapping is done by both field survey techniques (RTK-DGPS and hand-held GPS) and remote sensing (Digital elevation model analysis). By combining previously-published paleo-seismological records or by dating undeformed terraces, I measure the timing of the last recorded deformation. By multiplying millennial-scale deformation rates with the number of years of seismic quiescence, I calculate the slip deficit on several faults and folds of the western Himalaya. The higher the slip deficit, the higher the chance of earthquakes in the near future. My work underlines the fact that the Jammu sector and the eastern Himachal sector of the western Himalaya are under high seismic risk as in both the cases, one Mw 7.5 seismic event is already due.

Abstract:
High Resolution Cross-Correlation Spectroscopy (HRCCS) has come of age in the last decade with detection of multiple species in hot Jupiter atmospheres now becoming commonplace. However, hot Jupiters are not the most frequently observed exoplanets – those are Super Earths and Sub-Neptunes. Understanding the atmospheres of those objects would go a long way in examining the dichotomy between the more gaseous and/or icy (similar to Neptune and Uranus) and the more terrestrial (rocky or water worlds similar to Earth or Mars) objects, which in turn has the potential to remove the degeneracy in composition that exists for such objects today. Efforts at characterization of atmospheres of such bodies at low resolution are often constrained by the fact that presence of clouds, hazes and aerosols in the atmosphere can result in flat spectra which obscures chemical signatures. HRCCS is expected to still be sensitive to species present above the cloud deck in such atmospheres. In this seminar, I shall talk briefly about the history of the field, and then place my efforts at creating a dedicated pipeline to extend the limit of HRCCS detections to the cloudy Neptune mass limit. I shall also talk about using a novel Bayesian tool for model selection coupled with a new approach towards mitigating the effects of the data processing pipeline on the signal, in order to move towards a more quantitative retrieval-based approach in the future.

Poster

Have you ever wondered how things as tough as rocks deform over scales of millimetres to many hundreds of kilometres?

How the interior of planetary bodies like Earth deform under the convective stresses over million to billion years?

How glaciers and ice sheets are mechanically responding to the rising temperatures?

SEPS, NISER brings you a short course on the physics of rock deformation & experimental techniques used to study the underlying processes. Our distinguished lecturers Prof. Goldsby and Prof. Misra bring together decades of experimental & theoretical experience in areas as diverse as mantle rheology, fault friction and ice mechanics to provide a unique opportunity for early career researchers to learn the state of the art in rock deformation.

Abstract:
Knowledge of the rheological behavior of ice over a wide range of stresses is critical for understanding the mechanics and dynamics of glaciers, ice sheets, and icy planetary bodies. In glaciology, the flow behavior of ice has been classically described by the Glen law, a power law relationship between strain rate and stress with a canonical value of the stress exponent of ~3. We have demonstrated that the Glen law does not describe a single creep mechanism, but rather averages the contributions from two creep mechanisms, dislocation creep at comparatively high stresses and grain boundary sliding creep at lower stresses. Each of these creep mechanisms dominates the flow behavior of terrestrial and planetary ice bodies at appropriate conditions of temperature, stress and grain size. At higher and lower stresses than are accessible in most ice deformation apparatus, transitions to plasticity and diffusion creep, respectively, are expected. Here I will describe our recent experimental efforts to study these deformation mechanisms by 1) mapping out the transition from dislocation creep to power law breakdown and plasticity in a high-pressure gas apparatus, and 2) discovering the diffusion creep regime for ice via cryo-nanoindentation.

Abstract:
Numerous geochemical studies on Mid-Ocean Ridge Basalts (MORB) have established the presence of both compositional and lithological heterogeneities in the upper mantle. These studies have successfully constrained the composition and age of long-lived Earth’s upper mantle heterogeneities. However, the origin of those heterogeneities remains highly debated. The Chile Mid-Ocean Ridge in the southeast Pacific Ocean, located far away from any hotspot, is colliding and subducting under the South America plate promoting the formation of a slab window. Comprehensive geochemical data (major, trace, volatile element contents and Sr, Nd, Hf, and Pb isotope ratios) on Chile ridge submarine glasses collected over the 1000 km ridge length demonstrate significant mantle compositional variability. Four main mantle components have been recognized: the Pacific depleted MORB mantle, an enriched mantle (e.i., EM-1), a subduction-modified mantle, and a depleted mantle with unusually high Hf isotope ratios. Surprisingly, despite the large compositional variability, all glasses - including those with a subduction signature - have volatile-refractory element ratios within the range of the Pacific normal MORB. We find a remarkable similarity in the isotopic compositions (Sr, Nd, Hf, and Pb) of the Chile ridge lavas, the adjacent Patagonia lithospheric mantle, and the south Atlantic MORB mantle. Although the trace element compositions of the Chile ridge basalts with subduction signatures are similar to those of the Cenozoic Andean lavas, the former has higher radiogenic Pb isotopes pointing to an older subduction-modified mantle. We propose that old (~late Proterozoic) Patagonia sub-continental lithospheric mantle variably metasomatized by subduction processes since the Early Paleozoic is foundering into an asthenospheric mantle with a south Atlantic MORB mantle composition. Furthermore, the geochemical data from the Chile ridge basalts point to an East to West mantle flow across the slab window, in contrast to the well-accepted geodynamic model that predicts the opposite direction of mantle flow.

Abstract: Propagating atmospheric vortices roughly 1,000 km in diameter, known as monsoon low‐pressure systems (LPS), produce intense precipitation over South Asia. They are traditionally categorized as monsoon lows, monsoon depressions, and more intense cyclonic storms. India Meteorological Department (IMD) has tracked monsoon depressions for over a century, finding a significant decline in their number in recent decades. Still, their methods have changed over time and do not include monsoon lows. A review of LPS statistics using a fast, objective tracking algorithm in five reanalysis shows none of the datasets had a detectable trend in monsoon depression counts since 1979 and a step‐like reduction in depression counts when they began using geostationary satellite data. So, the trends in existing data products may be artifacts of change in the observing network; further analysis is warranted. Despite much research on trends in their formation frequency, long-term trends in the rain rates of these storms have remained unknown. The satellite and gauge-based precipitation estimates with atmospheric reanalysis show that precipitation in monsoon depressions has intensified in recent decades. This intensification occurred as near-surface humidity over India increased more rapidly than anywhere else on Earth. Yet precipitation in monsoon depressions rose several times that of specific humidity, suggesting that upward motion in these storms became more intense. Future projection of LPS shows a shift in genesis from ocean to land and an increase in LPS precipitation near 7%/K in the multi-model mean. These changes in genesis and rain rates contribute to a projected future increase in seasonal mean and extreme precipitation over South Asian land.

Abstract:
Groundbreaking discoveries of extrasolar planets in the past decades changed our perception of the Universe. We are now able to search for Earth-like planets orbiting other stars in our solar system. We found thousands of exotic planets that are much closer to their stars, orbiting much faster, and with much hotter atmospheres. To understand the evolution of these exotic planetary atmospheres, we need new laboratory data. We have built an instrument to achieve this - study the atmospheric composition of hot-Jupiters.

Abstract:
Gas hydrates are ice–like compounds found in marine sediments and permafrosts. A significant fraction of all known hydrocarbons in nature is in the form of hydrate. Gas hydrates are a potential energy resource, with possible roles in seafloor slope stability and climate change. As such, improved geophysical methods are needed to identify and quantify in situ natural hydrates to better study their potential impacts. Current estimates of the distribution and volume of gas hydrates vary widely, by orders of magnitude, largely because of uncertainties in our understanding of how gas hydrate affects geophysical properties of host sediments and hence inversion results.

We conducted multi frequency (ultrasonic, sonic, and seismic) geophysical (P and S wave velocity and attenuation) experiments; also used electrical resistivity tomography and high resolution synchrotron imaging to understand properties of gas hydrate. We found that not all the gas formed hydrate, even when the system was under hydrate stability conditions with excess water. The synchrotron CT results suggest that the dominant mechanism for co-existing gas is the formation of hydrate films on gas bubbles; these bubbles either rupture, releasing trapped gas, or remain trapped within an aggregate of hydrate grains. From a geophysical remote sensing perspective, such co-existing gas could cause errors in hydrate saturation estimates from electrical resistivity as both gas and hydrate are resistive compared to saline pore fluid. Hydrate starts forming in the pore-floating morphology (where hydrate grains are surrounded by brine) and evolves into the pore-bridging morphology (where hydrate connects mineral grains). Eventually, hydrate from adjacent pores joins and forms a pore hydrate framework, interlocking with the sand grain framework and separated by thin water films. We related these changes in morphology to our elastic wave measurements using the HBES (Hydrate Bearing Effective Sediment) rock physics model. We show that direct estimates of the permeability of hydrate-bearing geological formations are possible from remote measurements of shear wave velocity (Vs) and attenuation (Qs-1). We implemented changes in permeability with hydrate saturation into well-known Biot-type poro-elastic models. We inverted for permeability using our poro-elastic models from Vs and Qs-1. This inverted permeability agrees with permeability obtained independently from electrical resistivity. We demonstrate a good match of our models to shear wave data at 200 Hz and 2 kHz frequencies from the literature, indicating the general applicability of the models.

Such multi scale and multi property observations can help us in understanding several complicated fluid flow systems in the subsurface, like carbon seqruestration, gas chimney, etc.

Abstract:
As a rapidly growing economy, India faces the critical challenge of meeting its growing energy requirements
while minimizing its carbon footprint. Expanding nuclear power as a clean energy source requires discovering
new uranium deposits locally. This talk describes an exploration exercise conducted in northern Karnataka,
employing a manual and an artificial intelligence-based approach to identify new locations that could potentially
host undiscovered uranium deposits.

Abstract:
In this talk I will start off by discussing my contribution in the development of the two new radial velocity spectrographs - the Habitable zone Planet Finder (HPF) and NEID. HPF is a near infrared spectrograph that specializes in the search for planets around mid-to-late M dwarfs, while NEID is an optical spectrograph achieving sub m/s precision around G,K, and early M dwarfs. I will discuss how we use these two instruments to follow up on TESS planet candidates around M dwarf hosts. In addition, I've helped develop novel nonparametric tools to model the mass-radius plane for exoplanets.
Finally, I will briefly discuss plans for future characterization of the M dwarf planetary population using a combination of precise RVs, high dimensional nonparametric techniques, and estimates of TESS occurrence rates for planets orbiting M dwarfs. By simultaneously fitting 4-5 dimensions (planetary mass, radius, period, stellar mass, stellar metallicity, etc.) using these flexible nonparametric methods, we hope to search for trends in the sample that can give clues about the validity of different formation mechanisms. For example: Giant planets orbiting M dwarfs - bridging the gap between the long period RV planets and the short period transiting planets. The former shows a weaker correlation with metallicity that hints at disk instability as a potential formation mechanism. On the contrary, the sample of transiting giant planets around M dwarfs strongly favours the core accretion theory of planet formation.

Abstract:
The deformation of rocks in the upper mantle governs mantle dynamics and consequently plays a crucial role in the modeling of plate motion and dynamics of solid Earth. As the mineral olivine is the largest and usually the weakest phase of the upper mantle, it is important to estimate the viscosity of olivine in order to model mantle dynamics. The mathematical equations (flow laws) that govern olivine rheology are usually constrained by numerically fitting to experimental data on the deformation of olivine aggregates. The results are then extrapolated to upper mantle conditions to predict mantle viscosity. Past efforts to estimate the flow-law parameters made a number of simplifying assumptions that reduced the accuracy of their mathematical model and also introduced some disparities between the inversion results from different studies. Moreover, if errors in data have not been correctly considered in previous studies, can we be sure of the robustness of their results?

I will present a new analysis of existing experimental data on the deformation of olivine aggregates, based on the Markov Chain Monte Carlo inversion scheme, that not only uses a more physically sound flow law to model experimental data but also provides a more statistically robust means to conduct such data inversion. Our analysis suggests that the upper mantle rheology is more poorly constrained than we realize and can introduce significant variance in the predictions of dynamic models. Our approach to data inversion is versatile enough to be applied to other fields in physical sciences and highlights some common problems that occur when results are extrapolated from laboratory scale to Earth-like scales

Abstract:
In the scientific world, applied research has a crucial role to play compared to fundamental research, especially in planetary science. In the last few decades, technological leapfrogging has furnished the research community with several high-resolution remote imageries to explore science. Side-by-side, data analytics has also made advancements to reduce laborious and time-consuming exploration by human experts. Towards this, automation in the methodology is the prerequisite for data-intensive analysis. However, excluding expert knowledge and its frequent intervention might create a vacuum in a practical remote analysis from various aspects. This talk involves several methodological solutions to mineralogical exploration considering the current advancements in data analytics (e.g., shallow/ deep learning) for the wide acceptance of scientific findings. This talk will also address the following queries- Is the analytical algorithm of automation robust enough to interpret any remote sensing imagery of a planetary body? How far is automated analysis reliable for "per-pixel" mineral exploration of remote imagery covering the Earth or Moon's surface? Hope, it will be a pleasant experience to discuss the relevance of engineering practices to the geological research field in front of an intellectual audience of NISER (National Institute of Science Education and Research). In this talk, I would also like to add an overview of my past and ongoing research activities, and future research endeavours.

Abstract:
The rate-dependence of friction during sliding within faults is believed to control the stability of fault sliding; velocity weakening is considered to be a requirement for earthquake initiation on faults. Velocity-strengthening sliding is generally thought to produce stable slip or creep.

In this work we present simulations of a gouge-filled fault zone, using a 2D, gravity-free, layer of grains, sheared by a constant stress boundary. Shear stress on the wall, τ, is incrementally increased up to τ =μstatic σN, (μstatic=friction coefficient at failure, σN= normal stress), at which point the layer fails and starts accelerating until reaching a steady-state. We next incrementally reduce the driving shear stress. Consequently, the layer sliding rate slows down linearly with decreasing stress, finally stopping at τ=μ0 σN, where μstatic>μ0 . Thus, a hysteresis effect emerges between friction and velocity, with similar behavior also observed for other state variables like porosity and grain coordination numbers. For granular layers with no imposed intergranular friction we see significant reduction in this hysteretic behavior, suggesting intergranular strength plays a major role in frictional strengthening during motion. Both behaviors of the granular friction, the hysteresis and the velocity strengthening, agree with previously published experimental results.

We next simulate a spring-block model, sliding on this grain layer. Numerical results show variable stick-slip events, i.e. earthquakes. We explain and predict this with a simple mathematical model that describes friction with both the hysteresis and the velocity-strengthening granular features. Our results predict a novel path to unstable sliding: hysteresis can offset velocity -strengthening, so that measurements of velocity strengthening by themselves do not preclude earthquakes and can be co-seismic.

Abstract:
The James Webb Space Telescope promises to characterize the atmosphere of several terrestrial exoplanets. The atmosphere chemistry of terrestrial exoplanets depends on the composition of the interior. However, the knowledge of interior-surface-atmosphere interactions is limited to the composition of Earth and neighboring terrestrial bodies. In this talk, I will focus on the role of the interior as well as the surface in regulating the atmosphere composition of terrestrial exoplanets. For example, how do magma oceans influence the chemistry of early atmospheres? What is the role of carbon cycle and ocean chemistry in regulating atmospheric CO2? I will attempt to show how geoscience knowledge and tools can help answering these questions.

Abstract:
The emplacement mechanism of the Deccan Volcanic Province (DVP) in India has been argued by researchers to a great extent. One of the most favoured hypotheses is “eruption through fissures” like pre-existing faults and fractures formed by major pre or syn-Deccan crustal extension. Like all the large igneous provinces of world, Deccan is also ornamented with three dyke swarm i.e., west coast dyke swarm (N-S trending), the Narmada-Satpura-Tapi (N-S- T)/Dhule-Nandurbar Deccan (DND) dyke swarm (E-W trending), and the Pune-Nasik (P-N) swarm. DND swarm, being the largest and least studied one amongst the three swarms, has been selected as the area of investigation for this project. Key objective was to understand the flow dynamics in the dykes of this swarm and geodynamical scenario during its emplacement using Anisotropy of magnetic Susceptibility (AMS), rock magnetic and paleomagnetic technique. The cumulative flow geometry and lack of any particular pattern suggest the dominance of polycentric flow coming from several shallow magma chambers. A rapid northward drift during the emplacement of DND dyke swarm was interpreted considering the deviation in paleolatitude of DND dykes with respect to the surrounding country rocks of older Deccan flows. The plausible hypothesis is that the higher plate velocities are the resultant of enhanced tensional stresses on the Indian lithosphere creating numerous long fractures along the already existing, weaker Narmada Son lineament (NSL) through which DND dykes got emplaced.

Abstract: Internal gravity waves (also internal waves) exist in the ocean interior due to differences in fluid densities. Interactions between internal tides (internal waves at the tidal frequencies) and near-inertial waves generated by winds near the ocean surface yield a spectrum of internal waves at many frequencies that can propagate thousands of kilometers from their generation sites. Using regional ocean numerical simulations, we show improved internal wave spectrum in high-resolution models and its sensitivity to a widely-used vertical mixing parameterisation scheme. Internal waves exchange energy and go unstable via different mechanisms and eventually break with consequences to ocean temperature and nutrient redistribution. Hence, improved internal wave representation in ocean models can play an important role in the accurate representation of internal-wave-driven mixing in ocean simulations and interpretation of internal wave signatures from the upcoming NASA--CNES Surface Water and Ocean Topography mission. Following this, we also show some properties of geophysical turbulence obtained from the Bay of Bengal with consequences to the Indian monsoon and theoretical attempts in understanding instabilities and routes to turbulence in stratified flows.

Abstract:
The laboratory study of stardust is an important sub-field of astrophysics. It combines sophisticated chemical, structural, and isotopic laboratory measurements, on micron-sub-micron stardust particles, with the theoretical ideas of nucleosynthesis and stellar evolution that exist to understand astrophysical observations. Isotopic data for these grains reveal more precise information about their parent stars than do spectroscopic observations of circumstellar dust. The goal of laboratory measurements is to provide clues on the stellar environments in which the grains formed and on their subsequent histories. Additionally, investigations into the preservation of these grains in different meteorites provide information about early solar system conditions and chronology. These goals can be achieved by coordinated, multi-technique investigations of stardust grains in the laboratory. This talk will focus on some key results from coordinated, multi-technique measurements of stardust grains and what they tell us about the stars that contributed presolar materials to our nascent Solar System. I will also talk about other new laboratory investigations on extraterrestrial samples

Abstract: Thousands of exoplanets -- planets beyond our own solar system, orbiting stars other than our sun -- have been discovered over the last twenty years; indeed, we now know that our galaxy contains more planets than stars. The study of exoplanets has now moved on from the discovery phase to the characterisation of all these planets, with the ultimate goal of understanding whether some of them are habitable, and whether any actually harbour life. In this talk, I will discuss how we find and study exoplanets, what we have learned so far about their properties and habitability, and prospects for identifying the signatures of alien life in the not-too-distant future.

Abstract: In this talk I will show how the dynamics on vertically stable terrestrial oceans are influenced by mesoscale eddies, while those on an icy moon's ocean are likely to be governed by convection.

In the first part of the talk, I will focus on terrestrial eastern boundary currents. One would expect that a narrow boundary current on the eastern boundary would broaden and eventually dissipate towards the west due to the influence of Rossby waves. The role of topography in trapping such currents at the boundary is well-known. I show that eddies could perform such trapping even in the absence of topography. Additionally, the boundary layers, predominantly the eastern downwelling one, are broadened by the westward drift of aforementioned eddies. This has implications for the location of deep water formation sites.

In the second part of the talk, I will focus on global oceanic circulation on icy moons. The overarching goal of this study is to decipher the likely ocean circulation in terms of quantities that could be relatively easily observed from space (rotation rate, bottom heating, and depth of the ocean). I perform numerical simulations to characterize the nature of convection in terms of non-dimensional numbers. The learnings from the non-dimensional numbers could then be applied to other icy moons not covered by simulations. Moreover, I find that oceans in which small convective plumes are not resolved tend to transfer most of the bottom heat to the ice shell near the equator thereby indicating thinner equatorial ice sheet. On the other hand, oceans with plumes tend to transfer heat to the ice sheet near the poles indicating thinner polar ice sheet.

Abstract: Unprecedented sea ice loss and an amplified warming have been observed over the Arctic in the recent decade and is expected to continue in future climate projections. At the same time, an increasing frequency of extreme winter events across North America and Europe has gained socio-economic attention. Possible linkage between the Arctic warming and Northern Hemisphere midlatitude circulation has been suggested but remains inconclusive. In this talk, I will focus on the remote influence of the Arctic warming and the underlying dynamical mechanism. Specifically, I’ll discuss how the troposphere-stratosphere dynamical coupling mechanism can play an important role in this teleconnection using a hierarchy of models and observations.

Observations of about 5000 extra-solar planets (exoplanets) have revealed a much larger chemical and physical diversity than found in the Solar System. The recently-launched James Webb Space Telescope is expected to characterize the atmosphere of large terrestrial exoplanets. The atmosphere of terrestrial exoplanets is formed as a result of outgassing and influenced by the chemistry (mineralogy) of the interior. How different can an exoplanetary interior (e.g., carbon-rich) be from that of Earth? Which extreme mineralogies can exist? What is the role of surface mineralogy in regulating the atmospheric composition of (e.g., carbonate-silicate cycle)? What can observations tell us about chemical conditions on terrestrial exoplanets? I will attempt to answer some of these questions with the help of experimental and theoretical tools from geosciences.

Space Physics, or Heliophysics, is the study of the medium between the Sun and the planets in our solar system, and the medium between stars and their planets. The space between stars and their planets is filled with a continuous flow of plasma, also called ''Solar/Stellar wind, and this outflow can impact the top of the atmosphere of planets on a short- and long range. Moreover, the interaction can be affected if the planet has an internal magnetic field. In my talk, I will review the modeling approach of solar and stellar wind. I will also discuss how the solar/stellar wind interacts with the planetary/exoplanetary atmosphere.

Continents, plate tectonics and life make our Earth unique in the solar system and perhaps, in the entire universe (at least, so far). However, none of them was present when  the planet formed some 4.56 billion years ago (Ga). Therefore, understanding how, when, and why they appeared is critical to understand planetary evolution and habitability. My work directly deals with these questions. For the past few years, I am working on elucidating in what form plate tectonics appeared on the early Earth (> 2 Ga) and what imprints it left on the different system components of the planet (e.g., crust-mantle, hydrosphere, atmosphere etc.). I find answers to these questions by integrating the classical approaches ofsolid Earth geology (field geology and petrology) with the novel methods like diffusion modelling of micron-scale compositional zonings in minerals to unravel geological timescales  (diffusion chronometry) and numerical modelling of large-scale tectonics (100s-1000s of km). So far, my studies have revealed that plate tectonics processes were substantially different > 2 Ga  from their modern nature and, for the first time, showed how timescales of large-scale processes can help us identify it from the natural rock record. In particular, I proposed a new style of continent-continent collision (called peel-back orogenesis) for that time period, which is found to have massive implications for building continents and driving the rise of O₂ in the atmosphere.

Interstellar Polycyclic Aromatic Hydrocarbon (PAH) molecules exist in diverse forms depending on the local physical environment of the Interstellar Medium (ISM). Formation of ionized PAHs is favorable in the extreme condition of the ISM. Besides its pure form, PAHs are likely to exist in substituted forms, for example, PAHs with functional groups, nitrogenated PAHs, protonated and deuterated PAHs, etc. These PAHs may convert into alternate forms as a result of ongoing chemical processes in the ISM. The spectral evidence of PAH molecules and its variants in the ISM are observed via the mid-infrared emission bands, particularly at 3.3, 6.2, 7.7, 8.6, 11.2 and 12.7 μm. These bands, also known as ‘Aromatic Infrared Bands (AIBs)’ are widely observed towards a varied range of astronomical sources and arise from the vibrational relaxation of PAH molecules on absorption of background UV photons. However, the exact form of PAH molecules that are responsible for the AIBs is still ambiguous. Here, we discuss a few of the possible forms of interstellar PAH molecules (for example: deuteronated, nitrogenated and aliphatic PAHs etc.) as carriers for AIBs. Density Functional Theory (DFT) calculation on several classes of PAHs is employed to study its spectral characteristics in infrared which is compared with the observed bands in quest of any similarity that establishes its presence in the ISM.

Abstract: The interaction of UV radiation with molecules (photochemistry) plays a key role in the surface-atmosphere system of rocky planets. In this talk, I will explore how photochemistry controls the chemical context in which life arose on Earth, and affects the molecular signposts with which we hope to detect life elsewhere. I will specifically discuss (1) photochemical insights into sulfur and nitrogen speciation in natural waters on early Earth, (2) the UV environment on planets orbiting Sunlike stars compared to M-dwarf exoplanets, and (3) the accumulation of potential biosignature gases in rocky planet atmospheres. I will connect each of these theoretical studies to empirical advances, such as the discovery of new pathways for prebiotic ribonucleotide synthesis, a possible opportunity to use exoplanets to test theories of the origin of life, and the recent discovery of phosphine on Venus. I will conclude by emphasizing the synergistic roles of experiment and theory.