Building a geologic map of Neptune’s moon Triton

National Aeronautics and Space Administration Planetary Data Archiving, Restoration, and Tools Program

Subaward to PSI from Smithsonian Institution

PI: Emily Martin (Smithsonian Institution)

Start Date: 09/01/2017
Project #: 1544
End Date: 07/31/2021
Award #: 17SUBC-440-0000-384938
Project Description

In 1989, Voyager 2 encountered the Neptune system and returned images of its largest moon (~1350 km radius), Triton – and these images remain the primary data for our understanding of the satellite (Fig. 1). Triton was revealed to be a geologically active moon [Smith et al., 1989], and its activity has been linked to its dynamical history as a captured Kuiper Belt Object (KBO) [e.g. McKinnon et al., 1995]. Until the New Horizons mission flew by Pluto in 2015, Triton was the only KBO visited by spacecraft; however, Triton’s role as our only close-up example of a probable KBO was always dogged by the question of whether its geology was representative of other KBOs, or resulted from its unique history. That question has not yet been rigorously reassessed in the post Pluto-encounter era. Additionally, Triton bridges a gap between KBOs and icy satellites. As a likely KBO captured into Neptune’s orbit [e.g. McKinnon et al., 1995] it contributes to the diverse population of icy satellites, but its origin is unique relative to those of the icy satellites and likely contributes to its young surface and exotic terrains (Fig. 2) [Schenk & Jackson, 1993]. The capture of Triton by Neptune likely resulted in a massive heating event that resulted in resurfacing [McKinnon, 1984; 1992], possibly by cryovolcanism [Croft, 1990; Schenk, 1992]. Crater counts for both Triton [Schenk & Zahnle, 2007] and portions of Pluto [Stern et al., 2015] suggest that both surfaces are exceptionally young, which may indicate that neither Triton nor Pluto retain their original surfaces. The successful New Horizons flyby through the Pluto system opened the door to another part of the solar system revealing an extraordinary diversity of terrains, renewing interest in the origin, evolution, and diversity of KBOs [Stern et al., 2016], and by extension, Trition.

Voyager 2’s encounter with Triton and Neptune occurred on August 25, 1989 with closest approach to Triton of 39,800 km [Chapman & Cruikshank, 1995; Stone & Miner, 1989], but the inherent challenge with flyby missions, especially in the outer solar system, mean extremely limited data sets with long time lapses between missions. These obstacles are overcome by creative solutions for maximizing the data return, including detailed geologic mapping.

We propose to produce a complete framework of accessible data products and establish, through mapping, a geological foundation to facilitate and foster the resurging interest in Triton and KBOs. We propose to create a USGS global-scale geologic map of Triton to inform ongoing and future exploration of Triton and other KBOs. Additionally, we aim to restore and archive Voyager 2 data products that exist only on compact disks (CDs) at the USGS Astrogeology Science Center.

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