New constraints on the delivery of cometary water and nitrogen to Earth from the 15N/14N isotopic ratio

TL;DR

This study uses nitrogen isotopic ratios to constrain the amount of water and nitrogen delivered to Earth by comets, suggesting comets contributed only a small fraction of Earth's water but potentially a significant part of atmospheric nitrogen.

Contribution

It provides new constraints on cometary contributions to Earth's water and nitrogen using isotopic measurements, applicable to both Oort-cloud and Kuiper-belt comets.

Findings

Comets contributed no more than a few percent of Earth's water.

A significant part of Earth's atmospheric nitrogen may originate from comets.

The isotopic ratio is similar in Oort-cloud and Kuiper-belt comets.

Abstract

New independent constraints on the amount of water delivered to Earth by comets are derived using the 15N/14N isotopic ratio, measured to be roughly twice as high in cometary CN and HCN as in the present Earth. Under reasonable assumptions, we find that no more than a few percent of Earth's water can be attributed to comets, in agreement with the constraints derived from D/H. Our results also suggest that a significant part of Earth's atmospheric nitrogen might come from comets. Since the 15N/14N isotopic ratio is not different in Oort-cloud and Kuiper-belt comets, our estimates apply to the contribution of both types of objects.