2019AJ....157...80C

Atmospheric nitrogen may be a necessary ingredient for the habitability of a planet as its presence helps to prevent water loss from a planet. The present-day nitrogen isotopic ratio, ¹⁵N/¹⁴N, in the Earth's atmosphere is a combination of the primitive Earth's ratio and the ratio that might have been delivered in comets and asteroids. Asteroids have a nitrogen isotopic ratio that is close to the Earth's. This indicates either a similar formation environment to the Earth or that the main source of nitrogen was delivery by asteroids. However, according to geological records, the Earth's atmosphere could have been enriched in ¹⁵N during the Archean era. Comets have a higher ¹⁵N/¹⁴N ratio than the current atmosphere of the Earth, and we find that about 5% ∼ 10% of nitrogen in the atmosphere of the Earth may have been delivered by comets to explain the current atmosphere of the Earth or the enriched ¹⁵N atmosphere of the Earth. We model the evolution of the radii of the snow lines of molecular nitrogen and ammonia in a protoplanetary disk and find that both have radii that put them farther from the Sun than the main asteroid belt. With an analytic secular resonance model and N-body simulations we find that the ν₈ apsidal precession secular resonance with Neptune, which is located in the Kuiper Belt, is a likely origin for the nitrogen-delivering comets that impact the Earth.