Year: 2025
Type: dissertation
Abstract: The potential habitability of Mars has long been a driving force behind both the previous and ongoing Martian explorations.Present-day Mars is extremely cold and dry, but geomorphological and geochemical evidence indicates a warm environment compatible with surface liquid water on early Mars.In addition to water, the existence of genomic and catalytic bio-molecules that support the fundamentals of life is critical for habitability.The Sample Analysis at Mars instrument onboard the Curiosity rover discovered organic matter in the early Martian sediment.Moreover, a recent analysis discovered highly variable and 13 C-depleted carbon isotopic values in its organic.However, its origin and the availability of biologically important molecules on early Mars remain uncertain.Formaldehyde (H2CO), a highly soluble and reactive molecule, can be formed through photochemical reactions in planetary atmospheres.Dissolved H2CO in water would subsequently form diverse organic matter, including bio-important molecules, such as sugars and amino acids, by the formose-type reaction.Moreover, H2CO can be generated from 13 Cdepleted CO derived from CO2 photolysis in the atmosphere.The deposition of this photochemically produced H2CO may explain the origin of the strong isotopic depletion observed in Martian organic matter.Therefore, investigating the atmospheric synthesis of H2CO on early Mars is crucial for understanding prebiotic chemistry toward the potential of ancient Martian life.The goal of this thesis is to elucidate the prebiotic chemistry involved in the formation of organic matter from H2CO, and to advance the understanding of the early Martian habitability.This paper first investigated the global average production and deposition of H2CO in Chapter 2, followed by its global distribution in Chapter 3, and finally its stable carbon isotope evolution in Chapter 4. First, we investigated the global average atmospheric production and deposition of H2CO in a 2-bar CO2-dominated atmosphere with H2 and CO on early Mars at ~4-3 billion years ago.We adapted a 1D photochemistry model, PROTEUS (Photochemical and RaiatiOn Transport model for Extensive USe), for early Martian conditions.We utilized the temperature and H2O vapor density profiles from the global mean results computed by a 3D Paleo-Mars Global Climate Model (PMGCM) for a 2-bar CO2-dominated atmosphere with 0, 3, and 6 % H2 and an obliquity of 40°.Our results show that a larger amount of H2 leads to a more significant focus on my PhD work, not only in research, but also in my daily life.Whenever I tried something new, he always encouraged me, and when I was away from academia, he made it possible for me to return at any time.I am profoundly grateful to my co
Author: Koyama, Shungo
Language: English
Subfield: Space and Planetary Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: green
OpenAlex ID: W7145474765