Titan's past and future: 3D modeling of a pure nitrogen atmosphere and geological implications

TL;DR

This study uses a 3D climate model to explore Titan's past and future nitrogen atmospheres, revealing potential nitrogen lakes, seas, and surface erosion processes that influence its geological features.

Contribution

It introduces a comprehensive 3D climate model including nitrogen cycle and clouds to simulate Titan's exotic nitrogen-dominated climates over geological timescales.

Findings

Past nitrogen seas could have flooded equatorial regions.

Surface erosion may be driven by nitrogen flows and rain.

A paleo-nitrogen cycle could explain surface features and methane outgassing.

Abstract

Several clues indicate that Titan's atmosphere has been depleted in methane during some period of its history, possibly as recently as 0.5-1 billion years ago. It could also happen in the future. Under these conditions, the atmosphere becomes only composed of nitrogen with a range of temperature and pressure allowing liquid or solid nitrogen to condense. Here, we explore these exotic climates throughout Titan's history with a 3D Global Climate Model (GCM) including the nitrogen cycle and the radiative effect of nitrogen clouds. We show that for the last billion years, only small polar nitrogen lakes should have formed. Yet, before 1 Ga, a significant part of the atmosphere could have condensed, forming deep nitrogen polar seas, which could have flowed and flooded the equatorial regions. Alternatively, nitrogen could be frozen on the surface like on Triton, but this would require an initial surface albedo higher than 0.65 at 4 Ga. Such a state could be stable even today if nitrogen ice albedo is higher than this value. According to our model, nitrogen flows and rain may have been efficient to erode the surface. Thus, we can speculate that a paleo-nitrogen cycle may explain the erosion and the age of Titan's surface, and may have produced some of the present valley networks and shorelines. Moreover, by diffusion of liquid nitrogen in the crust, a paleo-nitrogen cycle could be responsible of the flattening of the polar regions and be at the origin of the methane outgassing on Titan.