A Fly-Through Mission Strategy Targeting Peptide as a Signature of Chemical Evolution and Possible Life in Enceladus Plumes

In situ detection of organic molecules in the extraterrestrial environment provides a key step towards better understanding the variety and the distribution of building blocks of life and it may ultimately lead to finding extraterrestrial life within the Solar System. Here we present combined results of two separate experiments that enable us to realize such in situ life signature detection from the deep habitats of the "Ocean World": a hydrothermal reactor experiment simulating complex organic synthesis and a simulated fly-through capture experiment of organic-bearing microparticles using silica aerogels, followed by subsequent analysis. Both experiments employ peptide as a plausible organics existing in Encleadus plume particles produced in its subsurface ocean. Recent laboratory hydrothermal experiments and a theoretical model on silica saturation indicated an on going hydrothermal reactions in subsurface Enceladus ocean. Given the porous chondritic origin of the core, it is likely that organic compounds originated by radiation chemistry such as amino acid precursors could have been provided, leached, and altered through widespread water-rock interactions. By using the same laboratory experimental setup from the latest water-rock interaction study, we performed amino acid polymerization experiments for 144 days and monitored the organic complexity changing over time. So far over 3,000 peaks up to the size of greater than 600 MW were observed through the analysis of capillary electrophoresis time-of-flight mass spectrometry (CE-TOF-MS) with an indication of amino acid derivatives and short peptides. Generally abiotic polymerization of enantiomeric amino acids results in forming stereoisomeric peptides with identical molecular weight and formula as opposed to homochiral biopolymers. Assuming Enceladus plume particles may contain a mixture of stereoisomeric peptides, we were able to distinguish 16 of the 17 stereoisomeric tripeptides as a test sample using capillary electrophoresis (CE) under optimized conditions. We further conducted Enceladus plume fly-through capture experiment by accelerating peptides soaked in rock particles up to a speed of 5.7 km/s and capturing with originally developed hydrophobic silica aerogels. Direct peptide extraction with acetonitrile-water followed by CE analysis led to detection of only but two stereoisomeric acidic peptide peaks, presenting the first run-through hypervelocuty impact sample analysis targeting peptides as key molecule to to understand the ongoing astrobiology on Enceladus

In situ measurement of liquid and gas CO₂ with high purity at deep-sea hydrothermal vents in the Mariana Arc using Raman spectroscopy

Supercritical and liquid CO2 (sc-/liq-CO2) emitted from deep-sea hydrothermal vents create a unique dry environment distinct from seawater and hydrothermal fluids, whose physicochemical characteristics could play an important role in the ocean biogeochemical cycles of the present Earth and even in the prebiotic chemical evolution of the early Earth. While previous studies attempted to sample and analyze sc-/liq-CO2 in several hydrothermal fields, the sampling and analysis without seawater contamination have been unsuccessful. In this study, we developed the method and apparatus for sampling and analyzing CO2 in different phases in which in situ Raman measurements can be directly performed and applied them to the CO2 emissions in two hydrothermal vent fields in the Mariana Arc. The in situ Raman spectra taken at both fields indicate that the high purity of CO2 emissions without seawater contamination was successfully sampled and measured. In the North-West Eifuku seamount, the collected hydrothermal fluid was monitored from the seafloor (approximately 1600  m) to the surface. The phase transitions of CO2─hydrate, liquid, and gas─were successfully observed in the Raman spectra. At the Daikoku seamount, the in situ Raman spectra taken at the seafloor (approximately 400 m) identified that the CO2 emission consisted of the gas phase. The in situ Raman measurement also revealed that gas H2S was abundant in the emissions at both the fields. This study demonstrates the ability of the Raman spectroscopic technique to monitor the phase transition of hydrothermal CO2 emissions and the chemical composition in different phases of CO2 in the oceans in real time

Thioester Synthesis through Geoelectrochemical CO2 Fixation on Ni Sulfides

Thioester synthesis by CO dehydrogenase/acetyl-CoA synthase is among the most ancient autotrophic metabolisms. Although the preceding prebiotic CO2 fixation routes to thioesters are often suggested, none has any experimentally supported evidence. Here we demonstrate that, under an electrochemical condition realizable in early ocean hydrothermal systems, nickel sulfide (NiS) gradually reduces to Ni0, while accumulating surface-bound CO due to CO2 electroreduction. The resultant partially reduced NiS facilitates thioester (S-methyl thioacetate) formation from CO and methanethiol even at room temperature and neutral pH. This thioester formation can further be enhanced up to a selectivity of 56% by NiS coprecipitating with FeS or CoS. Considering the central role of Ni in the enzymatic process mentioned above, our demonstrated thioester synthesis with the partially reduced NiS could have a direct implication to the autotrophic origin of life.<br /