Chapter 15 - A likely ocean world fostering a rare mixing of CO and N2 ice molecules on Neptune’s Moon Triton

Abstract

Neptune’s largest moon Triton is considered to be the highest priority “Candidate Ocean World.” NASA’s Voyager 2 mission showed that Triton has active resurfacing, with the potential for erupting plumes. Coupled with an ionosphere that can create organic snow and the potential for an interior ocean, Triton is an exciting exploration target to understand how habitable worlds may develop in our solar system and others. Triton is deemed the highest priority target to address as part of an Ocean Worlds Program mooted by NASA. This priority is given based on the extraordinary hints of activity shown by the Voyager spacecraft (e.g., plume activity; cantaloupe terrain suggestive of convection) and the potential for ocean-driven activity. Triton’s activity remains unclear, all active bodies in the solar system are driven by endogenic heat sources, and Triton’s activity coupled with the young surface age makes investigation of an endogenic source important. It is believed that great science is possible with a Neptune–Triton flyby. Triton is unique among all large moons in the solar system in the sense that it was born in Kuiper belt and later on pulled into the gravitational influence of its host planet Neptune. Apart from the existence of dust-devils-like ∼8-km-tall plumes of gas and dark material rising through Triton’s atmosphere, there are indications that an inner ocean possibly exists within the ice shell of this distant moon. A fascinating discovery made in the year 2019 is Triton fostering a rare mixing of CO and N2 ice molecules, operating in tandem rather than in isolation. This discovery is expected to shed more light on Triton’s geysers. Apart from these thought-provoking topics, other interesting aspects of Triton addressed in this chapter include general features of Triton, its origin, youthfulness of its surface, ridges, its low surface temperature and weak atmospheric pressure, chemical composition of its atmosphere & surface, interesting consequences arising from its nitrogen deposits, and spectral features of some molecules on the surface of this moon. This chapter concludes with a discussion on the forthcoming mission to map Triton—TRIDENT mission—characterizing its active processes, and determining the existence of the predicted subsurface ocean.