On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective.

Presented here are the observations and interpretations from a comprehensive analysis of 16 representative particles returned from the C-type asteroid Ryugu by the Hayabusa2 mission. On average Ryugu particles consist of 50% phyllosilicate matrix, 41% porosity and 9% minor phases, including organic matter. The abundances of 70 elements from the particles are in close agreement with those of CI chondrites. Bulk Ryugu particles show higher δ18O, Δ17O, and ε54Cr values than CI chondrites. As such, Ryugu sampled the most primitive and least-thermally processed protosolar nebula reservoirs. Such a finding is consistent with multi-scale H-C-N isotopic compositions that are compatible with an origin for Ryugu organic matter within both the protosolar nebula and the interstellar medium. The analytical data obtained here, suggests that complex soluble organic matter formed during aqueous alteration on the Ryugu progenitor planetesimal (several 10's of km), <2.6 Myr after CAI formation. Subsequently, the Ryugu progenitor planetesimal was fragmented and evolved into the current asteroid Ryugu through sublimation.

Photochemical formation of hydroxyl radicals in tissue extracts of the coral Galaxea fascicularis.

Various stresses induce the formation of reactive oxygen species (ROS) in biological cells. In addition to stress-induced ROS, we studied the photochemical formation of hydroxyl radicals (˙OH), the most potent ROS, in coral tissues using phosphate buffer-extracted solutions and a simulated sunlight irradiation system. ˙OH formation was seen in extracts of both coral host and endosymbiont zooxanthellae. This study is the first to report quantitative measurements of ˙OH photoformation in coral tissue extracts. Our results indicated that whether or not coral bleaching occurred, coral tissues and symbiotic zooxanthellae have the potential to photochemically produce ˙OH under sunlight. However, no significant difference was found in the protein content-normalized formation rates of ˙OH between corals incubated under different temperatures and irradiance conditions. ˙OH formation rates were reduced by 40% by reducing the UV radiation in the illumination. It was indicated that UV radiation strongly affected ˙OH formation in coral tissue and zooxanthellae, in addition to its formation through photoinhibition processes.

Contribution of fulvic acid to the photochemical formation of Fe(II) in acidic Suwannee River fulvic acid solutions.

We investigated the contribution of fulvic acid to the photoformation of Fe(II) using aqueous Suwannee River fulvic acid (SRFA) as a surrogate for the humic-like substances (HULIS) found in atmospheric condensed phases. The effects of pH (3.2, 4.1, and 5.0) and wavelength (313, 334, 366, and 405nm) on Fe(II) photoformation were studied using monochromatic radiation at 20 degrees C. We calculated the wavelength-dependent Fe(II) photoformation efficiency values ("E-value"), defined here as a weighted sum of the product of the quantum yield and molar absorptivity of each Fe(II)-forming chemical species, and found that the E-values of acidic SRFA solutions were similar to those of Fe(OH)(2+). In addition, a comparison showed that the acidic SRFA solutions did not form Fe(II) fast enough to account for the observed Fe(II) formation efficiencies of the aqueous extracts of authentic aerosol samples. It was observed that 17-73% of Fe(III) had been reduced to Fe(II) in the dark in acidic SRFA solutions with added Fe(III) ranging from 0.5 to 10muM. The results of this study suggest that HULIS is unlikely to be the major reducing ligand in the process of photochemical formation of Fe(II) in acidic atmospheric drops. However, HULIS could reduce Fe(III) to Fe(II) in the dark, which in turn, could be important for night-time ()OH formation via the reaction between Fe(II) and H(2)O(2) (the Fenton reaction).