Past Events

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.