Oxygen Isotopes and Sampling of the Solar System

• Published in: Space science reviews 2020-03, Vol.216 (2), Article 25
• Main Authors: Ireland, Trevor R., Avila, Janaina, Greenwood, Richard C., Hicks, Leon J., Bridges, John C.
• Format: Article
• Language: English
• Subjects: Abundance; Aerospace Technology and Astronautics; Asteroid missions; Asteroids; Astrochemistry; Astrophysics and Astroparticles; Carbon monoxide; Cavity ringdown; Chondrites; Computational fluid dynamics; Fractionation; Hydrosphere; Inclusions; Inner solar system; Instrumentation; Isotope composition; Isotopes; Mars; Mars missions; Mars satellites; Mercury; Mercury (planet); Meteorites; Meteors & meteorites; Molecular clouds; Moon; Oxygen; Oxygen isotopes; Physics; Physics and Astronomy; Planet formation; Planetary composition; Planetary evolution; Planetary systems; Planetology; Role of Sample Return in Addressing Major Questions in Planetary Sciences; Shielding; Silicates; Solar system; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Spectroscopy; Temperature dependence; Venus; Vesta asteroid; Water ice
• ISSN: 0038-6308; 1572-9672
• DOI: 10.1007/s11214-020-0645-3

Oxygen is the dominant element in our planetary system. It is therefore remarkable that it shows substantial isotopic diversity both in mass-dependent fractionation, because it is a light element, and in mass-independent fractionation, primarily associated with variation in abundance of 16 O. On Earth, the primary variation in isotopic composition is related to temperature-dependent kinetic mass fractionation between hydrosphere and atmosphere. Meteorites provide samples of primitive bodies, that have not experienced melting, and planetesimals that have melted early in their history. Samples of Mars, Vesta, and the Moon are present in the meteorite collections. In meteorites, the cosmochemical fractionation related to the abundance of 16 O provides a useful classification scheme. Inclusions in chondrites show a large range in 16 O abundances from highly enriched (solar) through to compositions closer to terrestrial (planetary). The variability in 16 O appears originally to be related to predissociation and self-shielding of carbon monoxide likely in the primordial molecular cloud. Within the chondrite parent bodies, exchange between 16 O-poor fluids and relatively 16 O-rich solids created isotopic mixing lines. This model makes specific predictions for isotopic compositions of silicates and water ice throughout the solar system. One prediction, that the Earth should be isotopically heavier than the Sun, appears to be verified. But other tests based on oxygen isotopes within the solar system require either remote analysis or sample return missions. Remote analysis will require new instrumentation and analytical techniques to achieve the precision and accuracy required for three oxygen isotope analysis. Methodologies associated with cavity ring-down spectroscopy appear promising. Sample return appears viable only for the inner solar system including Mars and asteroids. While sample return missions to either Venus or Mercury appear highly challenging, the scientific benefits are immense both in oxygen isotope characterisation, and in a variety of other geochemical analyses. Measurement of three oxygen isotopes throughout the solar system would further our concepts for formation of other solar systems, and give us insight into the general mechanisms of planetary system formation and the role of water in the formation and evolution of the chondrite parent bodies and planets.