List of ocean worlds in the Solar System

Earth's surface is dominated by the ocean, which forms 71% of Earth's surface.
Two possible models of Europa

This is a list of ocean worlds in the Solar System, planets or satellites known or suspected to harbor substantial volumes of liquid water, either as subsurface oceans beneath ice shells or, in the case of Io, a global magma ocean. The existence of such oceans is inferred through a range of methods, including spacecraft measurements of induced magnetic fields, tidal Love numbers, libration amplitudes, surface geology, and isotopic geochemistry.

As of 2026, three worlds have strong or confirmed evidence of present-day global oceans: Enceladus, where the Cassini spacecraft directly sampled water-ice plumes erupting from a tidally heated interior;[1][2] Europa, whose Galileo-detected induced magnetic field implies a conductive saltwater layer;[3] and Ganymede, where Hubble Space Telescope observations of auroral oscillations point to an ocean that may exceed the volume of Earth's oceans.[4] Callisto and Pluto are considered probable ocean worlds, while the status of Titan—long thought to host a global water–ammonia ocean—was called into question by a 2025 reanalysis of Cassini tidal data that favors a slushy interior with localized liquid pockets rather than a continuous ocean.[5]

Beyond these, a growing number of icy moons, dwarf planets, and trans-Neptunian objects are considered candidates on the basis of interior modeling, spacecraft gravity data, or recent James Webb Space Telescope observations of surface chemistry indicative of geothermal activity.[6][7][8] Several bodies, including Charon, Rhea, and Tethys, may have possessed oceans in the past that have since frozen. NASA's Ocean Worlds Exploration Program, established in 2016, coordinates exploration of these targets, with Europa Clipper (launched 2024), JUICE (launched 2023), and Dragonfly (planned launch in 2028) representing the next generation of dedicated missions.[9]

List

Ocean worlds of the Solar System
WorldConfirmed?Ocean volume (vs. Earth)ActivityKey observations/evidenceDedicated missions (past → planned)
EarthYes (surface + subsurface)1× (reference: ~1.335 billion km3)[10]Plate tectonics; hydrothermal vents; active water cycleDirect observation; only known world with stable surface liquid water and confirmed biosphere—
MarsDeep crustal liquid water (aquifer, not discrete ocean)Potentially large (≥ Earth's oceans by volume, if global)Ancient surface water; no present surface activity (see also Mars ocean hypothesis)InSight seismic data: low-velocity mid-crust layer at ~5–20 km depth consistent with liquid-water-saturated rock;[11][12] contested MARSIS radar detection of possible subglacial lake[13] (see also Chronology of discoveries of water on Mars)Viking, Mars Express, InSight, Tianwen-1/Zhurong, Perseverance (all past/active)
EuropaStrong evidence≈ 2–3×Possible plumes; young/chaotic iceInduced magnetic field (Galileo); reanalysis/plume hints (HST/Galileo)[3][14]Galileo → Europa Clipper (launched Oct 2024; Jupiter arrival April 2030); JUICE flybys
EnceladusYes (global)≪ Earth (tiny; sub-percent)Active south-polar plumes; hydrothermal indicatorsCassini plume sampling (H₂, salts); gravity+libration ⇒ global ocean[1][2]Cassini → (concept) Enceladus Orbilander
GanymedeStrong evidenceLikely > Earth (ocean alone may exceed Earth's)No known plumes; intrinsic magnetosphereHST auroral oval "rocking" consistent with conductive layer (ocean); interior models[4][15]Galileo, Juno flyby → JUICE (Jupiter arrival July 2031; Ganymede orbit Dec 2034)
CallistoProbableUnknownGeologically quietInduced magnetic field (Galileo); later analyses strengthen case[3][14]Galileo → JUICE flybys
TitanDisputed (challenged 2025)Unknown (water–ammonia)Active methane cycle; cryovolcanism unconfirmedGravity/tides (Love number k₂) & rotation anomalies initially implied ocean;[16] 2025 reanalysis argues tidal dissipation precludes a global ocean, favoring slushy ice with liquid pockets[5]Cassini–Huygens → Dragonfly rotorcraft (launch July 2028; arrival ~2034)
TritonPossibleUnknownGeysers/cryovolcanism seen by Voyager 2Geology/topography and thermal models; possible deep ocean[17][18]Voyager 2 → (no selected mission; Trident not chosen)
DioneCandidateUnknownLow current activityCassini gravity/topography; possible global ocean[19][20]Cassini flybys
RheaDisfavored (possibly past)UnknownNo endogenic activity observedHussmann et al. modeled possible ocean;[6] more recent data suggest homogeneous interior, ocean unlikely to persist today[21]Cassini flybys
TethysDisfavored (possibly past)UnknownExtensional tectonics (Ithaca Chasma)Surface fractures attributed to past ocean freezing; no present ocean expected[6][9]Cassini flybys
MimasNew evidence (young global ocean)≪ Earth (very small)No obvious surface activityCassini astrometry/periapsis drift ⇒ ocean at depth 20–30 km; ocean <25 Myr old[22]Cassini flybys
MirandaCandidateUnknownAncient extreme tectonicsVoyager 2 imagery; Uranus-system radiation data suggests activity[23]Voyager 2 → (proposed) Uranus Orbiter & Probe
ArielCandidate (may be active)UnknownYoung resurfacingUranus radiation-belt/ring data modeling; geology[23][8]Voyager 2 → (proposed) Uranus Orbiter & Probe
TitaniaCandidateUnknownTectonic featuresInterior modeling (possible ocean)[6][8]Voyager 2 → (proposed) Uranus Orbiter & Probe
UmbrielCandidateUnknownDark, old surfaceModeling; possible ammonia-rich ocean[6][8]Voyager 2 → (proposed) Uranus Orbiter & Probe
OberonCandidateUnknownFractures/tectonicsModeling (possible ocean)[6][8]Voyager 2 → (proposed) Uranus Orbiter & Probe
CeresRegional brines (not global)Negligible vs EarthRecent brine upwelling (Occator), cryovolcanismDawn gravity/geomorphology ⇒ subsurface brines[24]Dawn orbiter (2015–2018)
PlutoLikelyUnknownTectonics; ongoing surface reshapingNew Horizons: Sputnik Planitia reorientation ⇒ subsurface ocean[25]New Horizons flyby (2015)
CharonPast ocean (now frozen)UnknownExtensional tectonics; cryovolcanic plainsCanyons and smooth plains (Vulcan Planitia) consistent with refreezing ocean; thermal-orbital models[26][27]New Horizons flyby (2015)
ErisHypothesizedUnknownUnknownJWST methane isotopologue D/H ratios suggest geothermal interior;[7] tidal locking with Dysnomia implies dissipative interior[28]—
MakemakeHypothesizedUnknownUnknownJWST methane D/H ratios suggest internal geochemical activity[7]—
SednaHypothesizedUnknownUnknownInterior modeling predicts possible ocean with ammonia antifreeze;[6] JWST observations of similar TNOs suggest internal differentiation may be common[7]—
QuaoarHypothesizedUnknownPossible cryovolcanism (methane/ethane detected)Theoretical modeling; JWST spectroscopy suggests internal differentiation and possible geothermal activity[6][9]—
GonggongHypothesizedUnknownUnknownTheoretical modeling; JWST spectroscopy consistent with endogenic processes on large TNOs[6][9]—
OrcusHypothesizedUnknownUnknownInterior modeling predicts possible ocean with ammonia antifreeze (modeled as "2004 DW")[6]—
IoMagma ocean (silicate), not watern/aExtreme volcanismElectromagnetic/induction signatures ⇒ global magma ocean[29]Galileo, Juno flybys

See also

References

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  2. 1 2 Thomas, P. C.; Tajeddine, R.; Tiscareno, M. S.; Burns, J. A.; Joseph, J.; Loredo, T. J.; Helfenstein, P.; Porco, C. (2016). "Enceladus's measured physical libration requires a global subsurface ocean". Icarus. 264: 37–47. arXiv:1509.07555. Bibcode:2016Icar..264...37T. doi:10.1016/j.icarus.2015.08.037.
  3. 1 2 3 Khurana, K. K.; Kivelson, M. G.; Stevenson, D. J.; Schubert, G.; Russell, C. T.; Walker, R. J.; Polanskey, C. (1998). "Induced magnetic fields as evidence for subsurface oceans in Europa and Callisto" (PDF). Nature. 395 (6704): 777–780. Bibcode:1998Natur.395..777K. doi:10.1038/27394. PMID 9796812. S2CID 4424606. Archived (PDF) from the original on 2022-10-09.
  4. 1 2 Saur, Joachim; Duling, Stefan; Roth, Lorenz; Jia, Xianzhe; et al. (March 2015). "The search for a subsurface ocean in Ganymede with Hubble Space Telescope observations of its auroral ovals". Journal of Geophysical Research: Space Physics. 120 (3): 1715–1737. Bibcode:2015JGRA..120.1715S. doi:10.1002/2014JA020778. hdl:2027.42/111157.
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  6. 1 2 3 4 5 6 7 8 9 10 Hussmann, Hauke; Sohl, Frank; Spohn, Tilman (November 2006). "Subsurface oceans and deep interiors of medium-sized outer planet satellites and large trans-neptunian objects". Icarus. 185 (1): 258–273. Bibcode:2006Icar..185..258H. doi:10.1016/j.icarus.2006.06.005.
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  9. 1 2 3 4 Hendrix, Amanda R.; Hurford, Terry A.; Barge, Laura M.; Bland, Michael T.; Bowman, Jeff S.; Brinckerhoff, William; Buratti, Bonnie J.; Cable, Morgan L.; Castillo-Rogez, Julie; Collins, Geoffrey C.; et al. (2019). "The NASA Roadmap to Ocean Worlds". Astrobiology. 19 (1): 1–27. Bibcode:2019AsBio..19....1H. doi:10.1089/ast.2018.1955. PMC 6338575. PMID 30346215.
  10. ↑ "How Much Water is There on Earth?". United States Geological Survey. 25 September 2018. Retrieved 2024-02-09.
  11. ↑ Wright, Vashan; Manga, Michael; Morzfeld, Matthias (2024). "Liquid water in the Martian mid-crust". Proceedings of the National Academy of Sciences. 121 (35) e2409983121. doi:10.1073/pnas.2409983121.
  12. ↑ Huang, Qingbo; Schmerr, Nicholas C. (2025). "Seismic evidence of liquid water at the base of Mars' upper crust". National Science Review. 12 (6) nwaf166. doi:10.1093/nsr/nwaf166. PMC 12125978.
  13. ↑ Orosei, R.; Lauro, S. E.; Pettinelli, E.; Cicchetti, A.; Coradini, M.; Cosciotti, B.; Di Paolo, F.; Flamini, E.; Mattei, E.; et al. (2018). "Radar evidence of subglacial liquid water on Mars". Science. 361 (6401): 490–493. arXiv:2004.04587. doi:10.1126/science.aar7268. PMID 30045881.
  14. 1 2 Zimmer, C.; Khurana, K. K.; Kivelson, Margaret G. (2000). "Subsurface Oceans on Europa and Callisto: Constraints from Galileo Magnetometer Observations" (PDF). Icarus. 147 (2): 329–347. Bibcode:2000Icar..147..329Z. CiteSeerX 10.1.1.366.7700. doi:10.1006/icar.2000.6456. Archived (PDF) from the original on 2022-10-09. {{cite journal}}: Cite uses deprecated parameter |citeseerx= (help)
  15. ↑ Vance, Steve; Bouffard, Mathieu; Choukroun, Mathieu; Sotin, Christophe (12 April 2014). "Ganymede's internal structure including thermodynamics of magnesium sulfate oceans in contact with ice". Planetary and Space Science. 96: 62–70. Bibcode:2014P&SS...96...62V. doi:10.1016/j.pss.2014.03.011.
  16. ↑ Iess, L.; Jacobson, R. A.; Ducci, M.; Stevenson, D. J.; Lunine, J. I.; Armstrong, J. W.; Asmar, S. W.; Racioppa, P.; Rappaport, N. J.; Tortora, P. (2012). "The tides of Titan". Science. 337 (6093): 457–459. Bibcode:2012Sci...337..457I. doi:10.1126/science.1219631. PMID 22745254.
  17. ↑ Schenk, Paul; Beddingfield, Chloe; Bertrand, Tanguy; et al. (September 2021). "Triton: Topography and Geology of a Probable Ocean World with Comparison to Pluto and Charon". Remote Sensing. 13 (17): 3476. Bibcode:2021RemS...13.3476S. doi:10.3390/rs13173476. hdl:10150/661940.
  18. ↑ Ruiz, Javier (December 2003). "Heat flow and depth to a possible internal ocean on Triton" (PDF). Icarus. 166 (2): 436–439. Bibcode:2003Icar..166..436R. doi:10.1016/j.icarus.2003.09.009.
  19. ↑ Beuthe, Mikael; Rivoldini, Attilio; Trinh, Antony (2016). "Enceladus' and Dione's floating ice shells supported by minimum stress isostasy". Geophysical Research Letters. 43 (19): 10088–10096. arXiv:1610.00548. Bibcode:2016GeoRL..4310088B. doi:10.1002/2016GL070650.
  20. ↑ Zannoni, Marco; Hemingway, Douglas; Gomez Casajus, Luis; Tortora, Paolo (2020). "The gravity field and interior structure of Dione". Icarus. 345 113713. arXiv:1908.07284. Bibcode:2020Icar..34513713Z. doi:10.1016/j.icarus.2020.113713.
  21. ↑ Anderson, John D.; Schubert, Gerald (2007). "Saturn's satellite Rhea is a homogeneous mix of rock and ice". Geophysical Research Letters. 34 (2): L02202. Bibcode:2007GeoRL..34.2202A. doi:10.1029/2006GL028100.
  22. ↑ Lainey, V.; Rambaux, N.; Tobie, G.; Cooper, N.; Zhang, Q.; Noyelles, B.; Baillié, K. (February 2024). "A recently formed ocean inside Saturn's moon Mimas". Nature. 626 (7998): 280–282. Bibcode:2024Natur.626..280L. doi:10.1038/s41586-023-06975-9. ISSN 1476-4687. PMID 38326592.
  23. 1 2 Rehm, Jeremy (16 March 2023). "Two of Uranus' Moons May Harbor Active Oceans, Radiation Data Suggests". Johns Hopkins University Applied Physics Laboratory. Johns Hopkins University. Archived from the original on 28 January 2024. Retrieved 9 February 2024.
  24. ↑ Raymond, Carol A.; Ermakov, Anton I.; Castillo-Rogez, Julie C.; Marchi, Simone; Johnson, Brandon C.; Hesse, Marc A.; Scully, Jennifer E. C.; Russell, Christopher T.; et al. (2020). "Impact-driven mobilization of deep crustal brines on dwarf planet Ceres". Nature Astronomy. 4 (8): 741–747. Bibcode:2020NatAs...4..741R. doi:10.1038/s41550-020-1168-2.
  25. ↑ Nimmo, F.; Hamilton, D. P.; McKinnon, W. B.; Schenk, P. M.; Binzel, R. P.; Bierson, C. J.; Beyer, R. A.; Moore, J. M.; Stern, S. A.; Weaver, H. A.; et al. (2016). "Reorientation of Sputnik Planitia implies a subsurface ocean on Pluto". Nature. 540 (7631): 94–96. arXiv:1903.05574. Bibcode:2016Natur.540...94N. doi:10.1038/nature20148. PMID 27851735.
  26. ↑ Rhoden, Alyssa R.; Rudolph, Maxwell L.; Manga, Michael (2023). "The challenges of driving Charon's cryovolcanism from a freezing ocean". Icarus. 392 115391. Bibcode:2023Icar..39215391R. doi:10.1016/j.icarus.2022.115391.
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  28. ↑ Nimmo, Francis; Brown, Michael E. (2023). "The internal structure of Eris inferred from its spin and orbit evolution". Science Advances. 9 (46). doi:10.1126/sciadv.adi9201.
  29. ↑ Khurana, K. K.; Jia, X.; Kivelson, M. G.; Nimmo, F.; Schubert, G.; Russell, C. T. (2011). "Evidence of a Global Magma Ocean in Io's Interior". Science. 332 (6034): 1186–1189. Bibcode:2011Sci...332.1186K. doi:10.1126/science.1201425. PMID 21566160.
  30. Vance, Steve; Harnmeijer, Jelte; Kimura, Jun; Hussmann, Hauke; deMartin, Brian; Brown, J. Michael (2007). "Hydrothermal Systems in Small Ocean Planets". Astrobiology. 7 (6): 987–1005. Bibcode:2007AsBio...7..987V. doi:10.1089/ast.2007.0075. PMID 18163874.
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