arXiv subjects

Nicholas J. Tosca

Publications and source records attributed to Nicholas J. Tosca.

4 recordsLinked to original sources

arXiv2026

Tidal Rock Grinding as a Source of H2 on Enceladus

The Solar System hosts multiple potentially habitable environments, including the subsurface ocean beneath the icy crust of Saturn's moon Enceladus. This ocean's composition is unusually well constrained thanks to Cassini's observations of Enceladus's south polar plume during multiple flybys. Among the plume's more surprising components is molecular hydrogen (H2), detected in trace amounts. The presence of observable amounts of H2 is intriguing not only because it is difficult to explain through conventional geochemical processes, but also because it could serve as both an energy source for life and a driver of prebiotic organic chemistry. In this study, we explore whether tidally induced rock grinding within Enceladus's core could account for the observed H2. Laboratory experiments show that H2 can be efficiently produced when freshly fractured rock reacts with water. Using these experimentally determined production efficiencies, we estimate H2 generation rates as a function of the fraction of tidal energy dissipated through rock grinding. Our results suggest that tidal grinding could plausibly produce the observed levels of H2, with instantaneous production rates potentially exceeding those from radiolysis or serpentinization. However, sustaining such production over geological timescales would require efficient healing of silicate surfaces in the core to allow repeated grinding. Without such healing, tidally induced rock grinding may instead lead to episodic bursts of chemical activity lasting up to millions of years--potentially sufficient to initiate new prebiotic pathways. This transient mechanism would complement the longer-term, lower-energy contributions from serpentinization (over hundreds of millions of years) and radiolysis (over billions of years).

astro-ph.EP↗

arXiv2026

Prebiotic magnetite enables chirality-magnetic surface feedback

The emergence of biomolecular homochirality requires both an initial symmetry-breaking event and a mechanism to amplify and preserve a chiral imbalance. Magnetic minerals have been shown to function as chiral agents through the chiral-induced spin selectivity (CISS) effect and may have enabled homochirality on early Earth, yet the magnetic properties of magnetite formed under realistic prebiotic conditions remain unexplored. Here we show that magnetite synthesized through two geochemically plausible pathways - UV-driven photo-oxidation and nitrite-mediated oxidation of Fe(II) - produces particles dominated by single-vortex and multi-vortex magnetic domain states. Magnetic measurements and electron microscopy confirm that these populations differ markedly from the nano-fabricated thin-film substrates conventionally used in previous CISS experiments. Using 3D micromagnetic simulations, we demonstrate that single-domain and vortex-state grains undergo irreversible, exchange-driven re-magnetization when interacting with spin-polarized homochiral compounds. This magnetic irreversibility provides a robust mechanism for storing and reinforcing weak chiral bias, suggesting that prebiotic magnetite could have contributed to the emergence and stabilization of persistent chiral bias on the early Earth.

physics.chem-ph↗

arXiv2024

In-situ crystallographic mapping constrains sulfate deposition and timing in Jezero crater, Mars

Late-stage Ca-sulfate-filled fractures are common on Mars. Notably, the Shenandoah formation in the western edge of Jezero crater preserves a variety of Ca-sulfate minerals in the fine-grained siliciclastic rocks explored by the Perseverance rover. However, the depositional environment and timing of the formation of these sulfates is unknown. To address this outstanding problem, we developed a new technique to map the crystal textures of these sulfates in situ at two stratigraphically similar locations in the Shenandoah formation, allowing us to constrain the burial depth and paleoenvironment at the time of their deposition. Our results suggest that some Ca-sulfate analyzed was formed at a burial depth greater than 80m, whereas Ca-sulfates present at another outcrop likely precipitated in a shallow-subsurface environment. These results indicate that samples collected for potential return to Earth at the two studied locations capture two different times and distinct chemical conditions in the depositional history of the Shenandoah formation providing multiple opportunities to evaluate surface and subsurface habitability.

astro-ph.EP↗

arXiv2022

Properties of the Nili Fossae Olivine-clay-carbonate lithology: orbital and in situ at Séítah

We examine the observed properties of the Nili Fossae olivine-clay-carbonate lithology from orbital data and in situ by the Mars 2020 rover at the Séítah unit in Jezero crater, including: 1) composition (Liu, 2022) 2) grain size (Tice, 2022) 3) inferred viscosity (calculated based on geochemistry collected by SuperCam (Wiens, 2022)). Based on the low viscosity and distribution of the unit we postulate a flood lava origin for the olivine-clay-carbonate at Séítah. We include a new CRISM map of the clay 2.38 μm band and use in situ data to show that the clay in the olivine cumulate in the Séítah formation is consistent with talc or serpentine from Mars 2020 SuperCam LIBS and VISIR and MastCam-Z observations. We discuss two intertwining aspects of the history of the lithology: 1) the emplacement and properties of the cumulate layer within a lava lake, based on terrestrial analogs in the Pilbara, Western Australia, and using previously published models of flood lavas and lava lakes, and 2) the limited extent of post emplacement alteration, including clay and carbonate alteration (Clave, 2022; Mandon, 2022).

astro-ph.EP↗