roadmap for ocean worlds ceres and small bodies€¦ · roadmap for ocean worlds ceres and small...
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Roadmap for Ocean Worlds Ceres and Small Bodies
J. Castillo-Rogez J. Scully, M. Neveu, S. Hosseini, B. Schmidt, M. Eubanks, M. Poston
A. Hendrix and T. Hurford – Chairs
OPAG Charge to ROW • OPAG chartered ROW; we are coordinating with SBAG since some
“SBAG-owned” bodies could be ocean worlds • Identify and prioritize science objectives for Ocean Worlds
– tied to the Decadal Survey • Design roadmap to explore these worlds to address science
objectives – Mission sequences, sustained exploration effort
• Assess where each Ocean World fits into the overall roadmap • Summarize broad mission concepts
– Considering mission dependences & international cooperation • Recommend technology development and detailed mission studies
in support of the next decadal survey • Place exploration of Ocean Worlds into the larger context of Solar
System exploration
Ocean World Themes
• Four themes – Identify ocean worlds – Characterize Oceans – Assess Habitability – Search for Life
• Theme groups came up with an initial set of science questions for each theme – Ranging from high level to very detailed
Ceres/Small Bodies WG
• Focused on Ceres, Large Asteroids, Trojan Asteroids • Looked at observational constraints and theoretical
predictions • The geophysical prospect for the long-term
preservation of liquid is unfavorable for most asteroids – Ceres is the exception – but it’s a dwarf planet!
Search for
Life
Identify Ocean Worlds
Characterize
Oceans
Assess Habitability
Energy Sources
Ocean Signatures
Solvents Rock/Ocean Interface
Energy for Life
Physico-chemical Conditions for Life
Biomarkers
Oce
an W
orld
s
Enceladus
Europa
Titan
Ganymede
Callisto
Poss
ible
Oce
an W
orld
s
Ceres
Pluto/Charon/ KBOs
Triton
Other Saturnian Icy Satellites *
Other Uranian Icy Satellites **
* Mimas, Tethys, Dione, Rhea, Iapetus ** Miranda, Ariel, Umbriel, Titania, Oberon
Primary Mission Contributor
New Horizons: 2006-Present
Voyager: 1977-Present
Galileo: 1996-2003
Cassini: 2004-2017
Dawn: 2007-Present
Solid Foundation
Key Information
• 482 x 482 x 446 km • mean radius 470 km • Rotation period 9.074 hr • Ceres’ surface reflects <10% of
incident sunlight • Surface temperature 110-155K • Density 2.162 kg m-3
• Rock mass fraction ~73 wt.% • Ceres as a whole is ~50 vol.% water
NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Ceres is Large – Geophysically Speaking
Most previous models predicted the long-term preservation of a deep ocean
EUROPA Surface temp: 102K Energy source: tidal
CERES Surface temp: 160K Energy source: solar, 40K
ENCELADUS Surface temp: 94K Energy source: tidal
Vol.%
Rock
Water/ice
C, H, N, O, S?
C, H, N, O
H, O, S
Ceres and Other Ocean Worlds
Global, Homogenous Composition: Ammoniated clays, serpentine, carbonates De Sanctis et al. (2015), Ammannito et al. (2016)
Points to global episode of hydrothermal alteration
Sodium carbonates Ammonium Salts De Sanctis et al. (2016)
Lake Searles Enceladus
Ceres’ surface shows mineralogy found only on Earth and Enceladus, so far
Ceres’ Surface Displays Material Formed at Depth
Organics!
Geology is Driven by Brines • Sodium bicarbonate and
ammonium salts found in bright deposits at Occator and other places (De Sanctis et al. 2016)
• The emplacement of Ahuna Mons implies the presence of brines at depth (Ruesch et al. 2016)
• Activity is recent – 10s My • Occurrence of salts in many
settings suggest near-surface abundance (Stein et al. 2017)
• Brine mixture eutectic is about 245K, possibly lower if ammonia remains
Ceres is Physically and Chemically Differentiated
Crater morphologies indicate ice content <40% (Bland et al. 2016)
Rocky Mantle ~2.4 g/cm3
Gravity suggests partially differentiated interior (Park et al. 2016)
Topography is explained by strong shell (<45 km) over soft, muddy interior Ermakov et al. (submitted), Fu et al. (submitted)
Ice/clathrates/ Salts/Silicates
~1.3 g/cm3
Ceres has a Muddy Interior Below a Frozen Ocean
• Ceres’ ocean has been slowly freezing due to the insulating role of salts and other hydrates – Brines accumulate between frozen ocean and rocky
core, in a mud • The icy shell was partially removed by impact-
accelerated sublimation and mixed with salts, clathrates, clays
• Clays offer a medium amenable to biochemical reactions
• Brines may be subject to radiolysis due to U and K decay creation of local redox gradients (Bouquet et al. 2017; Castillo-Rogez et al. 2017)
Muddy/Salty Ocean
Core with large rock particles
Ice
Rocky Core
Mud
Frozen Ocean
Oceanic material readily accessible below the regolith
Ceres is an Ocean World, Habitability TBD • Ceres shares same chemistry as Europa and Enceladus • Geology indicates recent (10s My) endogenic activity • Abundance of hydrated material led to slow freezing and
preservation of liquid until present • Ceres’s ocean is muddy – good for biochemistry • Surface exhibits oceanic material at shallow depth
KEY OPEN QUESTIONS: o Thickness and extent of mud layer? o Conditions of past and current liquid
environments? o Past and present extent of geochemical
gradients? o Origin of organics observed on the surface?
An in situ mission is the natural next step in the exploration of Ceres, the ocean world closest to Earth