arXiv subjects

Priyankush Ghosh

Publications and source records attributed to Priyankush Ghosh.

5 recordsLinked to original sources

arXiv2025

A Comprehensive Sulfur Chemistry Network Including Excited S(1D) and SO(1{\Delta}) for the XODIAC Photochemical Model: Accounting for Missing Sulfur Processes in Venus and Exo-Venus Analogs

Sulfur chemistry plays a central role in controlling the atmospheric structure, cloud formation, and composition of Venus and Venus-like exoplanets. However, key reactions involving ground- and excited-state sulfur species remain poorly constrained, and existing photochemical models often rely on incomplete or uncertain kinetic data under high-temperature, CO2-rich conditions. In this work, we compute kinetic parameters for reactions of ground-state S(3P) and excited-state S(1D) with CO2 under Venus-like conditions, forming SO(3Sigma), SO(1Delta), and CO. We characterize the underlying potential energy surfaces, identify intermediate complexes, and derive temperature-dependent rate coefficients using a master-equation framework based on the chemically significant eigenvalue method. We also provide NASA 7-term polynomial coefficients for S and SO in both ground and excited states to enable consistent incorporation into photochemical models. Incorporating these reactions into the one-dimensional photochemical model XODIAC for Venus produces only minor effects above 60 km due to competing pathways. While the model reproduces most observed sulfur species, discrepancies remain for S3 and S4. Introducing a 1 ppm near-surface atomic sulfur source, representing unresolved deep-atmosphere or surface processes, enhances S3 and S4 abundances by 1-2 orders of magnitude and improves agreement with observations. For exo-Venus analogs, the updated chemistry produces modest changes under isothermal conditions. In contrast, in strongly irradiated atmospheres with a high-altitude isotherm and a near-surface sulfur source, it leads to pronounced changes in most sulfur-bearing species, along with significant enhancements in S(1D) and SO(1Delta). These results highlight missing sulfur pathways, including excited states and deep sources, and potential implications for shaping Venus and exo-Venus atmospheres.

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arXiv2025

Detectability of Atmospheric Biosignatures in Earth Analogs with Varying Surface Boundary Conditions: Prospects for Characterization in the UV, Visible, Near-Infrared, and Mid-Infrared Regions

The search for potentially habitable exoplanets centers on detecting biosignature molecules in Earth-like atmospheres, which makes it essential to understand their detectability under biologically and geologically influenced conditions. In this study, we model the reflection and thermal emission spectra of such atmospheres across the UV/VIS/NIR and mid-IR regions and simulate their detectability with future mission concepts such as the Habitable Worlds Observatory (HWO) and the Large Interferometer for Exoplanets (LIFE). We employ Numerical Weather Prediction (NWP) model data, based on Earth's atmosphere, to derive temperature pressure profiles and couple them with a 1D photochemical model to assess the detectability of these molecules in Earth analogs located 10 parsecs away. We investigate the dominant reaction pathways and their contributions to the atmospheric composition of an Earth analog, with a focus on how they shape the resulting molecular signatures. We also examine the role of surface boundary conditions, which indirectly trace the effects of biological and geological processes, on the detectability of these molecules using HWO- and LIFE-type mission concepts. Our findings indicate that O3 is detectable with both mission concepts, while H2O requires specific surface humidity levels for detection with LIFE and shows only potential detectability with HWO. CO2 is detectable with LIFE. Both N2O and CH4 require continuous surface outgassing for potential detection with LIFE, and CH4 further requires low surface humidity to prevent masking by water features. Our work highlights the feasibility of characterizing the atmospheres of Earth analogs in the UV/VIS/NIR and mid-IR domains using HWO- and LIFE-type mission concepts and offers guidance for the development of future missions operating in these spectral regions.

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arXiv2025

A Fast, Parallelized, GPU-Accelerated Photochemical Model, XODIAC, with Built-in Equilibrium Chemistry and Multiple Chemical Networks for Exoplanetary Atmospheres

The launch of the James Webb Space Telescope (JWST) has delivered high-quality atmospheric observations and expanded the known chemical inventory of exoplanetary atmospheres, opening new avenues for atmospheric chemistry modeling to interpret these data. Here, we present XODIAC, a fast, GPU-accelerated, one-dimensional photochemical model with a built-in equilibrium chemistry solver, an updated thermochemical database, and three chemical reaction networks. This framework enables comparative atmospheric chemistry studies, including the newly developed XODIAC-2025 network, a state-of-the-art C-H-O-N-P-S-Metals network, linking 594 species through 7,720 reactions. The other two are existing, publicly available C-H-O-N-S and C-H-O-N-S-Metals networks, from the established photochemical models VULCAN and ARGO, respectively, which are commonly used in the community. The XODIAC model has been rigorously benchmarked on the well-studied hot Jupiter HD 189733 b, with results compared against these two models. Benchmarking shows excellent agreement and demonstrates that, when the same chemical network and initial conditions are used, the numerical scheme for solving atmospheric chemistry does not significantly affect the results. We also revisited the atmospheric chemistry of HD 189733 b and performed a comparative analysis across the three networks. Sulfur chemistry shows the least variation across networks, carbon chemistry shows slightly more, and phosphorus chemistry varies the most, primarily due to the introduction of unique PHO and PN pathways comprising 390 reactions in the XODIAC-2025 network. These findings highlight XODIAC's capability to advance exoplanetary atmospheric chemistry and provide a robust framework for comparative exoplanetology.

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arXiv2025

A Next-Generation Exoplanet Atmospheric Retrieval Framework NEXOTRANS for Emission Spectroscopy: New Constraints and Atmospheric Characterization of WASP-69b Using JWST NIRCam and MIRI Observations

Thermal emission spectra provide key insights into the atmospheric composition and especially the temperature structure of an exoplanet. With broader wavelength coverage, sensitivity and higher resolution, JWST has enabled robust constraints on these properties, including detections of photochemical products. This advances the need for retrieval frameworks capable of navigating complex parameter spaces for accurate data interpretation. In this work, we introduce the emission retrieval module of NEXOTRANS, which employs both one- and two-stream radiative transfer approximations and leverages Bayesian and machine learning techniques for retrievals. It also incorporates approximate disequilibrium chemistry models to infer photochemical species like SO2. We applied NEXOTRANS to the JWST NIRCam and MIRI emission observations of WASP-69b, covering the 2-12 microns range. The retrievals place robust constraints on the volume mixing ratios (VMR) of H2O, CO2, CO, CH4, and potential SO2. The best-fit model, i.e, free chemistry combined with non-uniform aerosol coverage, yields a log(VMR) = -3.78 (+0.15/-0.17) for H2O and -5.77 (+0.09/-0.10) for CO2 which has a sharp absorption at 4.3 micron. The second best-fit model, the hybrid equilibrium chemistry (utilizing equilibrium chemistry-grids) combined with non-uniform aerosol yields a C/O of 0.42 (+0.17/-0.13) and a metallicity of log[M/H] = 1.24 (+0.17/-0.14), corresponding to approximately 17.38 times the solar value. This hybrid chemistry retrieval also constrain SO2 with a log(VMR) = -4.85 (+0.28/-0.29), indicating possible absorption features in the 7-8 microns range. These results highlight NEXOTRANS's capability to significantly advance JWST emission spectra interpretation, offering broader insights into exoplanetary atmospheres.

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arXiv2025

A Next-Generation Exoplanet Atmospheric Retrieval Framework for Transmission Spectroscopy (NEXOTRANS): Comparative Characterization for WASP-39 b Using JWST NIRISS, NIRSpec PRISM, and MIRI Observations

The advent of JWST has marked a new era in exoplanetary atmospheric studies, offering higher-resolution data and greater precision across a broader spectral range than previous space-based telescopes. Accurate analysis of these datasets requires advanced retrieval frameworks capable of navigating complex parameter spaces. We present NEXOTRANS, an atmospheric retrieval framework that integrates Bayesian inference using UltraNest/PyMultiNest with four machine learning algorithms: Random Forest, Gradient Boosting, K-Nearest Neighbor, and Stacking Regressor. This hybrid approach enables a comparison between traditional Bayesian methods and computationally efficient machine learning techniques. Additionally, NEXOTRANS incorporates NEXOCHEM, a module for solving equilibrium chemistry. We applied NEXOTRANS to JWST observations of the Saturn-mass exoplanet WASP-39 b, spanning wavelengths from 0.6 microns to 12.0 microns using NIRISS, NIRSpec PRISM, and MIRI. Four chemistry models - free, equilibrium, modified hybrid equilibrium, and modified equilibrium-offset chemistry - were explored to retrieve precise Volume Mixing Ratios (VMRs) for H2O, CO2, CO, H2S, and SO2. Absorption features in both NIRSpec PRISM and MIRI data constrained SO2 log VMRs to values between -6.25 and -5.73 for all models except equilibrium chemistry. High-altitude aerosols, including ZnS and MgSiO3, were inferred, with constraints on their VMRs, particle sizes, and terminator coverage fractions, providing insights into cloud composition. For the best-fit modified hybrid equilibrium model, we derived super-solar elemental abundances of O/H = 14.12 (+2.86/-1.82) x solar, C/H = 21.37 (+4.93/-3.18) x solar, and S/H = 5.37 (+0.79/-0.65) x solar, along with a C/O ratio of 1.35 (+0.05/-0.02) x solar, demonstrating NEXOTRANS's potential for atmospheric characterization in the JWST era and beyond.

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