Nitrogen in Solar System Minor Bodies: Delivery Pathways to Primeval Earth

Abstract

Oxygen isotope data point towards enstatite and ordinary chondrites as presumable building blocks of primordial Earth. Nitrogen was incorporated as nitrides to these first building blocks and was outgassed in the early stages of chemical segregation. However, giant impacts with planetesimals played an important role in partially eroding the atmosphere of Earth, and promoting thermal escape of diverse components. As a consequence, the Earth’s atmospheric composition could have been subjected to important changes along the eons. A last, and probably less massive, delivery of volatiles took place at the time of a gigantic cataclysm known as Late Heavy Bombardment. During a short interval roughly between 3.9 and 3.8 Gyr ago, a gravitational migration inwards of Jupiter and Saturn occurred, that perturbed hundreds of small bodies rich in water, ammonia, methane and organic compounds that were stored until then in the outer regions. Current atmospheric signatures suggest that by that mechanism a continuous shower of outer-disk primordial components enriched the volatile inventory of terrestrial planets. The relevance of such contribution is still debated, but significant progress has been made in the last decades from the study of undifferentiated bodies. Consequently, planetary scattering of undifferentiated bodies delivered to Earth a significant fraction of minerals, and light elements that could have played a key role in the volatile enrichment the terrestrial crust. I suggest some unexplored pathways to allow a safe delivery of organics to Earth’s surface, following recent evidence on meteoroid fragmentation, fireball spectra and Antarctic micrometeorite discoveries. Recent compositional studies of asteroids, comets and meteorites corroborate the need of having more precise data on the abundance and isotopic ratios of N in these minor bodies. Future space missions to primitive bodies like Rosetta, OSIRIS-Rex, Hayabusa II, or Marco Polo-R could help us to complete the big picture, and this chapter tries to compile our present knowledge of its delivery to Earth along the eons.