Triton: Part of the Ocean World Club?

OPAG February 2018 Roadmap to Identify Ocean Characterize Assess Search for Worlds Habitability Ocean The case for EnceladusOceans Life Energy Ocean Solvents Rock/Ocean Energy for Physico- Biomarkers Worlds Sources Signatures Interface Life chemical Conditions for Life

Triton World Ocean Ocean

• The Roadmap for Ocean Worlds lays out the foundation for future Ocean World research • ROW provides a framework to discover ocean worlds and then assess them for Habitability and Extant Life Identifying Triton as an Ocean World – Energy Sources • Triton is likely a captured KBO (Agnor & Hamilton, 2006) • Initial captured orbit highly eccentric – Current orbit very circular – Extreme tidal heating upon capture • Possible that ocean survives 2-3 Ga (Gaemon et al., 2012) Identifying Triton as an Ocean World – Energy Sources • Currently no tidal heating due to orbital eccentricity • High inclination leads to a large obliquity – Obliquity tidal dissipation possible, ~0.3 TW (Nimmo & Spencer, 2015) • A current energy source increases ability to maintain liquid water or slow freeze out to longer than 4.5 Ga Identifying Triton as an Ocean World – Ocean Signatures: Resurfacing • Triton exhibits extensive resurfacing • Surface age may be < 100 Myr (Schenk & Zahnle, 2007)

Ruach Planitia Identifying Triton as an Ocean World – Ocean Signatures: Resurfacing a b Resurfaced Smooth Interior

Margins of Dilated Fracture

20 km

• Some sites of extension show subsequent embayment of material Identifying Triton as an Ocean World – Ocean Signatures: Resurfacing

a b

Linear Pits

Resurfaced Smooth Region 10 km

• Set Catena may be sites of explosive cryovolcanism (Helfenstein et al. 1992; Croft et al., 1995) Identifying Triton as an Ocean World – Ocean Signatures: Tectonics Base image: PIA18668 Paul Schenk/NASA/JPL-Caltech/Lunar & Planetary Institute

• Croft 1993 suggested tectonics formed by orbital decay and spin-up stresses Identifying Triton as an Ocean World – Ocean Signatures: Tectonics

• Modest orbital decay can produce stress >100kPa for a range of tidal response values (h2) • Based on studies of Europa these levels of stress would be able to crack the surface • Stresses on a solid Triton would not be capable of fracturing the surface

Rhoden et al., 2010

Homogeneous upper limit Identifying Triton as an Ocean World – Ocean Signatures: Activity • Triton was the first active icy satellite discovered • Deposits on surface record past activity Identifying Triton as an Ocean World – Ocean Signatures: Activity

Mars Triton Enceladus

Volatile erupting CO2 N2 H2O Surface Gravity 3.71 0.779 0.113 Source vent <1 m <3 km ~9 m diameter Particle Plume height 80 m ~10 km ~70 km Particle Exit velocity ~25 m/sec ~125 m/sec ~125 m/sec Mass flux (particles) 30 – 150 gm/sec <10 kg/sec ~50 kg/sec Mass flux (vapor) 150 gm/sec Up to 400 kg/sec 200 kg/sec Temperature 140 K 38-42 K 76-170 K • Triton’s plume are more like Enceladus eruptions in many ways (Hansen personal communiqué) Roadmap to Identify Ocean Characterize Assess Search for Worlds Habitability Ocean Oceans Life Energy Ocean Solvents Rock/Ocean Energy for Physico- Biomarkers Worlds Sources Signatures Interface Life chemical Conditions for Life Extreme past Tectonics tidal heating Active Enceladus Eruptions Not here yet!!

Extensive

Ocean World Resurfacing

• Interesting clues hint that Triton may be an Ocean World • Currently all evidence is indirect • Need Direct detection of an ocean to confirm Confirming Triton as an Ocean World • Direct evidence of an ocean – Magnetometer • Detect induction of magnetic field from liquid ocean – Gravity – Thermal Imager • Search for heat anomalies on the surface – Follow-up plume observations • Continued active and its location may determine of driven by endogenic heat • Plume composition also can distinguish between models of plume activity Conclusions

• Triton is a high priority candidate for Ocean World Identification • Surface geology hints at an ocean or remnants of one at geologically recent timescales • Roadmap to Ocean Worlds is a useful framework for examining our understanding of Ocean World candidates & for determining exploration priorities