On the Provenance of Pluto's Nitrogen (N2)

TL;DR

This paper investigates the origin and replenishment mechanisms of Pluto's atmospheric nitrogen, concluding that internal activity or early acquisition is likely responsible for its current N2 levels, as cometary impacts are insufficient.

Contribution

It provides an analysis of N2 sources on Pluto, demonstrating that comet impacts cannot account for the observed N2, implying endogenous origin or internal activity.

Findings

Comet impacts cannot supply enough N2 to Pluto's atmosphere.

Cratering could resupply N2 if the surface reservoir is deep.

Internal activity may be necessary to maintain N2 levels.

Abstract

N2 is abundant in Pluto's atmosphere and on its surface, but the supply is depleted by prodigious atmospheric escape. We demonstrate that cometary impacts could not have delivered enough N mass to resupply Pluto's N2 atmospheric escape over time; thus Pluto's N2 is likely endogenous, and therefore was either acquired early in its history or created by chemistry inside/on Pluto. We find that cratering could excavate a considerable amount of N2 to resupply the atmosphere against escape if the near-surface N2 reservoir is deep. However, we find that this process likely falls short of that necessary to resupply the atmosphere against escape by at least an order of magnitude. We conclude that either the escape of N2 from Pluto's atmosphere was on average much lower than the predictions for the current epoch, or that internal activity could be necessary to bring N2 to the surface and resupply escape losses. Observations made by the New Horizons spacecraft in mid-2015 will yield further constraints on the provenance and evolution of Pluto's surface and atmospheric N2, and could reveal evidence for past or present internal activity.