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Mohit Melwani Daswani

Publications and source records attributed to Mohit Melwani Daswani.

7 recordsLinked to original sources
arXiv2026

Terrestrial Analogs to Titan for Geophysical Research

Saturn's moon Titan exhibits remarkable parallels to the Earth in many geophysical and geological processes not found elsewhere in the solar system at the present day. These include a nitrogen atmosphere with a condensible gas - methane - replacing the Earth's water, leading to an active meteorology with rainfall and surface manifestations including rivers, lakes and seas, and the dissolution of karstic terrain. Other phenomena such as craters, dunes, and tectonic features are found elsewhere - e.g. on Mars and Venus - but their continuing alteration by pluvial, fluvial and lacustrine processes can be studied only on Earth and Titan. Meanwhile Titan also hosts an interior liquid water ocean with similarities to the Earth as well as to ocean worlds such as Europa and Enceladus. Our focus in this review paper is twofold: to describe the geophysical and geological parallels between Earth and Titan, and to evaluate the yet-underexploited possibilities for field analog research to gain new knowledge about these processes. To date, Titan's much colder temperature and different atmospheric and crustal materials have led to a skepticism that useful analogs can be found on Earth. Our conclusion, however, is that a much larger range of useful analog field work is possible and this work will substantially enhance our knowledge of both worlds. Such investigation will supplement the existing sparse data for Titan returned by space missions, will greatly enhance our understanding of such datasets, and will help to provide science impetus and goals for future missions.

astro-ph.EP↗
arXiv2025

Exploring the Interior Structure and Mode of Tidal Heating in Enceladus

Enceladus is among the most intriguing bodies in the solar system due to its astrobiological potential. Determining the extent and duration of habitability (i.e., sustained habitability) requires characterizing the interior properties and the level and distribution of tidal heating in Enceladus. Inferring the intensity of geophysical activity in the core has direct implications for the potential hydrothermal activity and supply of chemical species important for habitability to the ocean. We build a statistical framework to constrain the interior using estimates of libration, shape, heat flux, gravity, and total mass. We use this framework to examine the extent that geodetic measurements can improve our understanding of the interior structure, with an emphasis on partitioning of dissipation between the shell and the core. We quantify plausible ranges of gravitational (k2) and displacement (h2, l2) tidal Love numbers consistent with existing observations. We demonstrate that measuring k2 alone can only constrain the total tidally dissipated energy, but not its radial distribution. However, measuring the amplitude and phase of h2 or l2 facilitates determining the extent of tidal dissipation in the shell and the core. We provide the precisions required for measuring k2, h2, and l2 that enable distinguishing between the main tidal heating scenarios, i.e., in the shell versus the core. We also explore the effect of the structural heterogeneities of the shell on the tidal response. Lastly, we evaluate the efficacy of future geodetic measurements to constrain key interior properties essential to understand the present-day (instantaneous) and long-term (sustained) habitability at Enceladus.

astro-ph.EP↗
arXiv2025

Thermodynamic constraints on the citric acid cycle and related reactions in ocean world interiors

Icy ocean worlds attract significant interest for their astrobiological potential due to subsurface oceans, organics, and chemical energy sources. We quantify thermodynamic viability of metabolism-relevant reactions at pressure-temperature conditions of Enceladus, Europa, Titan, Ganymede, and the Lost City Hydrothermal Field for comparison. We examine the tricarboxylic acid (TCA) cycle and a plausible prebiotic reaction network leading to it, using DEWPython (based on the Deep Earth Water model) and SUPCRT to compute equilibrium constants and Gibbs free energy changes across temperatures from 0-1200°C and pressures between 1 bar-60 kbar. We found that across most oceanic P-T profiles, certain TCA cycle species accumulate (citrate, succinate) while others diminish (fumarate, oxaloacetate), suggesting ocean worlds' conditions may not thermodynamically favor a unidirectional TCA cycle, requiring additional energy to overcome bottlenecks. Similar bottlenecks exist at Lost City, which is inhabited. In the prebiotic network, pyruvate and acetate show remarkable stability, feeding the TCA cycle through citrate production, bypassing the oxaloacetate bottleneck. Formation of most TCA cycle species from inorganic compounds (CO$_2$ + H$_2$) is highly favored throughout ocean world geotherms, except for oxaloacetate. While based on uncertain chemical concentrations, our non-equilibrium thermodynamic predictions are relatively insensitive to activity changes and may aid interpretation of future mission data. [ABRIDGED]

astro-ph.EP↗
arXiv2021

DEWPython: A Python Implementation of the Deep Earth Water Model and Application to Ocean Worlds

There are two main methods of calculating the thermodynamic properties of water and solutes: mass action (including the Helgeson-Kirkham-Flowers (HKF) equations of state and model) and Gibbs free energy minimization (e.g. Leal et al., 2016). However, in certain regions of pressure and temperature the HKF model inaccurately predicts the speciation and concentration of solutes (e.g. Miron et al., 2019). The Deep Earth Water (DEW) model uses a series of HKF-type equations to calculate the properties of water and solute concentrations at high temperatures (373 - 1473 K) and pressures (0.1 - 6 GPa) (e.g. Huang and Sverjensky, 2019; Pan et al., 2013; Sverjensky et al., 2014). The DEW model is synthesized in an Excel spreadsheet and calculates Gibbs energies of formation, equilibrium constants, and standard volume changes for reactions. Here we present an object-oriented Python implementation of the DEW model, called DEWPython. Our model expands on DEW by increasing model efficiency, streamlining the input process, and incorporating SUPCRT in-line. Additionally, our model builds in minerals and aqueous species from the thermodynamic database slop16.dat (Boyer, 2019) which would normally be calculated separately. We also present a set of reactions relevant to icy ocean world interiors calculated with the DEWPython. The favorability of these reactions indicates likely formation of certain organic species under extreme pressures relevant to ocean worlds.

physics.geo-ph↗
arXiv2019

Geochemistry constrains global hydrology on Early Mars

Ancient hydrology is recorded by sedimentary rocks on Mars. The most voluminous sedimentary rocks that formed during Mars' Hesperian period are sulfate-rich rocks, explored by the $Opportunity$ rover from 2004-2012 and soon to be investigated by the $Curiosity$ rover at Gale crater. A leading hypothesis for the origin of these sulfates is that the cations were derived from evaporation of deep-sourced groundwater, as part of a global circulation of groundwater. Global groundwater circulation would imply sustained warm Earthlike conditions on Early Mars. Global circulation of groundwater including infiltration of water initially in equilibrium with Mars' CO$_2$ atmosphere implies subsurface formation of carbonate. We find that the CO$_2$ sequestration implied by the global groundwater hypothesis for the origin of sulfate-rich rocks on Mars is 30-5000 bars if the $Opportunity$ data are representative of Hesperian sulfate-rich rocks, which is so large that (even accounting for volcanic outgassing) it would bury the atmosphere. This disfavors the hypothesis that the cations for Mars' Hesperian sulfates were derived from upwelling of deep sourced groundwater. If, instead, Hesperian sulfate-rich rocks are approximated as pure Mg-sulfate (no Fe), then the CO$_2$ sequestration is 0.3-400 bars. The low end of this range is consistent with the hypothesis that the cations for Mars' Hesperian sulfates were derived from upwelling of deep sourced groundwater. In both cases, carbon sequestration by global groundwater circulation actively works to terminate surface habitability, rather than being a passive marker of warm Earthlike conditions. $Curiosity$ will soon be in a position to discriminate between these two hypotheses. Our work links Mars sulfate cation composition, carbon isotopes, and climate change.

astro-ph.EP↗
arXiv2017

Paleohydrology on Mars constrained by mass balance and mineralogy of pre-Amazonian sodium chloride lakes

Chloride-bearing deposits on Mars record high-elevation lakes during the waning stages of Mars' wet era (mid-Noachian to late Hesperian). The water source pathways, seasonality, salinity, depth, lifetime, and paleoclimatic drivers of these widespread lakes are all unknown. Here we combine reaction-transport modeling, orbital spectroscopy, and new volume estimates from high-resolution digital terrain models, in order to constrain the hydrologic boundary conditions for forming the chlorides. Considering a T = 0 degrees C system, we find: (1) individual lakes were >100 m deep and lasted decades or longer; (2) if volcanic degassing was the source of chlorine, then the water-to-rock ratio or the total water volume were probably low, consistent with brief excursions above the melting point and/or arid climate; (3) if the chlorine source was igneous chlorapatite, then Cl-leaching events would require a (cumulative) time of >10 yr at the melting point; (4) Cl masses, divided by catchment area, give column densities 0.1 - 50 kg Cl/m^2, and these column densities bracket the expected chlorapatite-Cl content for a seasonally-warm active layer. Deep groundwater was not required. Taken together, our results are consistent with Mars having a usually cold, horizontally segregated hydrosphere by the time chlorides formed.

astro-ph.EP↗