arXiv subjects

Yasuto Watanabe

Publications and source records attributed to Yasuto Watanabe.

5 recordsLinked to original sources

arXiv2026

Stellar control on atmospheric carbon chemistry, CO runaway, and organic synthesis on lifeless Earth-like planets

The abundances of atmospheric carbon species--carbon dioxide (CO2), carbon monoxide (CO), and methane (CH4)--exert fundamental controls on the climate, redox state, and prebiotic environment of terrestrial planets. As exoplanet atmospheric characterization advances, it is essential to understand how these species are regulated on habitable terrestrial planets across a wide range of stellar and planetary conditions. Here, we develop an integrated numerical model that couples atmospheric chemistry, climate, and the long-term carbon cycle to investigate the atmospheric compositions of lifeless, Earth-like planets orbiting Sun-like (F-, G-, and K-type) stars. Our simulations demonstrate that CO2, CO, and CH4 generally increase with orbital distance, and that planets near the outer edge of the habitable zone may undergo CO runaway--a photochemical instability driven by severe depletion of OH radicals. The threshold for CO runaway depends strongly on stellar spectral type and is most easily triggered around cooler, lower-mass stars. In contrast, the atmospheric production of formaldehyde (H2CO)--a key precursor for prebiotic organic chemistry--peaks around planets orbiting more massive, UV-luminous stars and is maximized at orbital distances just interior to the CO-runaway threshold. These results establish a quantitative framework linking observable system properties--stellar type and orbital distance--and the atmospheric carbon chemistry of lifeless Earth-like planets, providing new context for interpreting future spectroscopic observations and for evaluating the potential of such planets to sustain prebiotic chemistry.

astro-ph.EP↗

arXiv2025

FieldWorkArena: Agentic AI Benchmark for Real Field Work Tasks

This paper introduces FieldWorkArena, a benchmark for agentic AI targeting real-world field work. With the recent increase in demand for agentic AI, they are built to detect and document safety hazards, procedural violations, and other critical incidents across real-world manufacturing and retail environments. Whereas most agentic AI benchmarks focus on performance in simulated or digital environments, our work addresses the fundamental challenge of evaluating agents in the real-world. In this paper, we improve the evaluation function from previous methods to assess the performance of agentic AI in diverse real-world tasks. Our dataset comprises on-site captured images/videos in factories, warehouses and retails. Tasks were meticulously developed through interviews with site workers and managers. Evaluation results confirmed that performance evaluation considering the characteristics of Multimodal LLM (MLLM) such as GPT-4o is feasible. Furthermore, this study identifies both the effectiveness and limitations of the proposed new evaluation methodology. The complete dataset and evaluation program are publicly accessible on the website (https://en-documents.research.global.fujitsu.com/fieldworkarena/)

cs.AI↗

arXiv2024

Behaviors of Martian CO2-driven dry climate system and conditions for atmospheric collapses

The present Martian climate is characterized by a cold and dry environment with a thin atmosphere of carbon dioxides (CO2). In such conditions, the planetary climate and habitability are determined by the distribution of CO2 between exchangeable reservoirs, that is the atmosphere, ice caps, and regolith. This produces unique responses of the Martian CO2-driven climate system to variations of astronomical forcings. Specifically, it has been shown that the phenomenon called an atmospheric collapse occurs when the axial obliquity is low, affecting the Martian climatic evolution. However, the behavior of the Martian climate system and the accompanying changes in climate and habitability of such planets remain ambiguous. Here we employed a latitudinally-resolved Martian energy balance model and assessed the possible climate on Mars for wider ranges of orbital parameters, solar irradiance, and total exchangeable CO2 mass. We show that the atmospheric collapse occurs when the obliquity is below ~10 degrees when other parameters are kept at the present Mars condition. We also show that the climate solutions on Mars depend on orbital parameters, solar luminosity, and the total exchangeable CO2 mass. We found that the atmospheric collapse would have occurred repeatedly in the history of Mars following the variation of the axial obliquity, while the long-term evolution of atmospheric pCO2 is also affected by the changes in the total exchangeable CO2 mass in Martian history. Even considering the broad ranges of these parameters, the habitable conditions in the Martian CO2-driven dry climate system would be limited to high-latitude summers.

astro-ph.EP↗

arXiv2023

Controls of Atmospheric Methane on Early Earth and Inhabited Earth-like Terrestrial Exoplanets

Methane (CH4) is a primarily biogenic greenhouse gas. As such, it represents an essential biosignature to search for life on exoplanets. Atmospheric CH4 abundance on Earth-like inhabited exoplanets is likely controlled by marine biogenic production and atmospheric photochemical consumption. Such interactions have been previously examined for the case of the early Earth where primitive marine ecosystems supplied CH4 to the atmosphere, showing that the atmospheric CH4 response to biogenic CH4 flux variations is nonlinear, a critical property when assessing CH4 reliability as a biosignature. However, the contributions of atmospheric photochemistry, metabolic reactions, or solar irradiance to this nonlinear response are not well understood. Using an atmospheric photochemical model and a marine microbial ecosystem model, we show that production of hydroxyl radicals from water vapor photodissociation is a critical factor controlling the atmospheric CH4 abundance. Consequently, atmospheric CH4 partial pressure (pCH4) on inhabited Earth-like exoplanets orbiting Sun-like stars (F-, G-, and K-type stars) would be controlled primarily by stellar irradiance. Specifically, irradiance at wavelengths of approximately 200-210 nm is a major controlling factor for atmospheric pCH4 when the carbon dioxide partial pressure is sufficiently high to absorb most stellar irradiance at 170-200 nm. Finally, we also demonstrated that inhabited exoplanets orbiting near the outer edge of K-type stars' habitable zones are better suited for atmospheric pCH4 buildup. Such properties will valuably support future detection of life signatures.

astro-ph.EP↗

arXiv2023

Relative abundances of CO2, CO, and CH4 in atmospheres of Earth-like lifeless planets

Carbon is an essential element for life on Earth, and the relative abundances of major carbon species (CO2, CO, and CH4) in the atmosphere exert fundamental controls on planetary climate and biogeochemistry. Here, we employed a theoretical model of atmospheric chemistry to investigate diversity in the atmospheric abundances of CO2, CO, and CH4 on Earth-like lifeless planets orbiting Sun-like (F-, G-, and K-type) stars. We focused on the conditions for the formation of a CO-rich atmosphere, which would be favorable for the origin of life. Results demonstrated that elevated atmospheric CO2 levels trigger photochemical instability of the CO budget in the atmosphere (i.e., CO runaway) owing to enhanced CO2 photolysis relative to H2O photolysis. Higher volcanic outgassing fluxes of reduced C (CO and CH4) also tend to initiate CO runaway. Our systematic examinations revealed that anoxic atmospheres of Earth-like lifeless planets could be classified in the phase space of CH4/CO2 versus CO/CO2, where a distinct gap in atmospheric carbon chemistry is expected to be observed. Our findings indicate that the gap structure is a general feature of Earth-like lifeless planets with reducing atmospheres orbiting Sun-like (F-, G-, and K-type) stars.

astro-ph.EP↗