Nitrogen Atmospheres of the Icy Bodies in the Solar System

TL;DR

This review discusses the origins and evolution of nitrogen atmospheres on icy solar system bodies like Titan, Triton, and Pluto, emphasizing isotopic signatures as key insights into their history and processes.

Contribution

It highlights the importance of isotopic ratios in understanding the origin and evolution of nitrogen atmospheres on icy bodies, proposing future missions for deeper insights.

Findings

Titan's nitrogen likely originated from ammonia ices.

Titan's $^{14}$N/$^{15}$N ratio is 167.7, indicating atmospheric evolution.

The origins of Pluto's and Triton's atmospheres remain uncertain.

Abstract

This brief review will discuss the current knowledge on the origin and evolution of the nitrogen atmospheres of the icy bodies in the solar system, particularly of Titan, Triton and Pluto. An important tool to analyse and understand the origin and evolution of these atmospheres can be found in the different isotopic signatures of their atmospheric constituents. The $^{14}$N/$^{15}$N ratio of the N$_2$-dominated atmospheres of these bodies serve as a footprint of the building blocks from which Titan, Triton and Pluto originated and of the diverse fractionation processes that shaped these atmospheres over their entire evolution. Together with other measured isotopic and elemental ratios such as $^{12}$C/$^{13}$C or Ar/N these atmospheres can give important insights into the history of the icy bodies in the solar system, the diverse processes that affect their N$_2$-dominated atmospheres, and the therewith connected solar activity evolution. Titan's gaseous envelope most likely originated from ammonia ices with possible contributions from refractory organics. Its isotopic signatures can yet be seen in the - compared to Earth - comparatively heavy $^{14}$N/$^{15}$N ratio of 167.7, even though this value slightly evolved over its history due to atmospheric escape and photodissociation of N$_2$. The origin and evolution of Pluto's and Triton's tenuous nitrogen atmospheres remain unclear, even though it might be likely that their atmospheres originated from the protosolar nebula or from comets. An in-situ space mission to Triton such as the recently proposed Trident mission, and/or to the ice giants would be a crucial cornerstone for a better understanding of the origin and evolution of the icy bodies in the outer solar system and their atmospheres in general.