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Evidence of icy moonquakes on the surface of Europa[1]

Icy moonquakes are sudden vibrations or shaking events that occur on the surfaces of icy moons, resulting from the abrupt release of energy within their interiors. Although direct seismic measurements from these moons remain elusive,[2] tectonic landforms such as ridges, troughs, bands, and undulations observed on Europa, Ganymede, and Enceladus[3] suggest active tectonism beneath their icy moons. These moons are known to harbor subsurface oceans beneath their icy crusts, which may play a role in driving such processes.[4]

Current understanding of icy moonquakes is primarily based on data from spacecraft missions such as Galileo and Cassini, which have provided high-resolution imagery and stereo-derived topography.[5] These datasets were studied to analyze geological features such as fault scarps, smooth terrains, and landslides—interpreted as the surface expressions of tectonic processes like extensional faulting and mass wasting,[5] potentially triggered by seismic activity.

Unlike Earth, where earthquakes are typically caused by the movement of tectonic plates, icy moonquakes result from geological and tidal forces.[2] Studying these processes is essential for understanding the internal structures/dynamics and potential habitability of icy moons in the outer solar system.[2]

Seismic sources on icy moons

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Tidal interactions are the primary driver of seismic activity on icy moons.[6] The gravitational pull of their host planets induces tidal stresses and heating on these satellites through diurnal cycles and non-synchronous rotation.[5][7][6][8] These stresses manifest as tectonic features such as strike slip faults, normal faults, and scarp faces observed on the surface of Europa, Ganymede, and Enceladus.[6] Seismicity driven by diurnal tides is likely to produce more frequent but low magnitude events, whereas activity linked to non-synchronous rotation may generate less frequent but potentially higher magnitude events, with estimates ranging up to Mw ≈5.3[9] or ≈6.0[10] depending on the shear modulus of icy crust.

In addition to tidal forces, several other geological processes are thought to generate moonquakes on icy satellites, including impact events, cryovolcanism, and internal silicate tectonic activity.[2] Although impacts are relatively rare on moons like Europa,[11] they can still produce detectable seismic disturbances. Ganymede, for example, is estimated to experience roughly twice as many impacts as Europa, though these typically occur at lower velocities—about 30% less[12]—potentially reducing their seismic effectiveness.[2] Cryovolcanism is another possible contributor to seismic activity on icy moons. This phenomenon involves fracturing older terrain and extruding water, slushy ice, or warm ductile ice from the subsurface.[13] Cryovolcanic activity is generally classified into effusive and eruptive forms,[14] the latter of which can produce distinct seismic signals during eruptions. Evidence of widespread cryovolcanic resurfacing has been observed on bodies such as Ganymede and Europa.[13] Some icy moons may also harbor geologically active silicate interiors, which can support tectonic processes that generate seismic energy.[2] High-resolution imagery from the Galileo mission suggests that Ganymede’s surface has undergone significant modification through tectonic resurfacing, where older features are disrupted or replaced by fault-induced activity[15]—an interpretation that has also been proposed for Enceladus.[16]

Observed features and evidence

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Europa

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Europa has a young (<60 Ma), ice-covered surface shaped by a long and complex history of tectonic activity.[12][17] Its crust is marked by numerous fractures and relatively few large craters, pointing to recent resurfacing.[12][17] Prominent geological features include ridges, troughs, bands, and surface undulations.[3] Troughs, often V-shaped and curved, are thought to form through tension similar to crevasses on Earth. Ridges—Europa’s most common landform—typically appear in double formations flanking a central trough and are believed to result from various extensional forces such as tidal stress or subsurface activity.[3] Bands are another distinct feature, defined by sharp edges and evidence of lateral movement, suggesting significant strike-slip motion.[3] Their structure can often be reconstructed through geometric modeling, highlighting Europa’s active and dynamic ice shell.

Enceladus

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The dichotomy of Enceladus' terrain, ancient terrain, approximately 4.2 billion years old, and geologically young regions less than a million years old indicates a wide variety of tectonism.[16] This diversity of terrains makes Enceladus one of the most geologically interesting icy bodies in the solar system. The south-polar region of Enceladus has a series of subparallel troughs flanked by ridges. Informally described as "tiger stripes," these features are likely associated with thermal anomalies and active plumes of water vapor.[18] The region also contains arcuate scarps, while the older north polar cratered terrain remains largely undeformed. The Cassini spacecraft observed active plumes at the South pole of Enceladus, which gave evidence of Enceladus's active tectonism.[3]

Ganymede

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Ganymede's surface features two distinct terrains: dark, ancient regions (33%) with low albedo and heavy cratering and lighter, younger regions (67%) with higher albedo, tectonic activity, and fewer craters.[19] The light terrain forms ridged bands through extensional processes, where a brittle upper layer over a viscous interior undulates, creating parallel ridges and grooves.[19][20] High-resolution images reveal smooth, textureless areas with faint lineations and striated slopes with fine downslope grooves.[21] These features reflect ongoing tectonic reshaping and surface renewal on Ganymede.

Future missions and research

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Europa Clipper Mission Spacecraft - Artist's Rendering.[22]

NASA and the European Space Agency (ESA) have launched two missions—Europa Clipper (NASA) and JUICE (ESA)—to study Jupiter’s icy moons Europa and Ganymede, investigating their potential for habitability and signs of life beyond Earth. These two missions are en route to Jupiter.

Europa Clipper Mission

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NASA's Europa Clipper, launched on October 14, 2024, will reach the Jupiter's orbit and orbit Jupiter by April 2030 to study Europa's ice shell, subsurface ocean, composition, and geology.[23] During nearly 50 flybys as low as 16 miles (25 km) above the surface, it will scan the entire moon to assess its astrobiological potential and habitability beyond Earth.[23]

JUICE (Jupiter Icy Moons Explorer)

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Juice Space craft concept.[24]

ESA's JUICE mission, launched April 14, 2023, from French Guiana via Ariane 5, will study Jupiter's icy moons (Ganymede, Europa, Callisto) as potential habitats and analyze Jupiter's environment as a model for gas giants.[25] After an 8-year journey with flybys of Venus, Earth, and the Moon, it will enter Jupiter orbit in July 2031.[25] The spacecraft will conduct science operations six months before orbital insertion, perform multiple moon flybys, and culminate in a dedicated orbital study of Ganymede.[25]

See also

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References

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  1. ^ "NASA Image and Video Library". NASA Image and Video Library. Retrieved 2025-05-08.
  2. ^ a b c d e f Vance, Steven D.; Kedar, Sharon; Panning, Mark P.; Stähler, Simon C.; Bills, Bruce G.; Lorenz, Ralph D.; Huang, Hsin-Hua; Pike, W.T.; Castillo, Julie C.; Lognonné, Philippe; Tsai, Victor C.; Rhoden, Alyssa R. (January 2018). "Vital Signs: Seismology of Icy Ocean Worlds". Astrobiology. 18 (1): 37–53. doi:10.1089/ast.2016.1612. ISSN 1531-1074.
  3. ^ a b c d e Watters, Thomas R.; Schultz, Richard A. (2009-12-17), "Planetary tectonics: introduction", Planetary Tectonics, Cambridge University Press, pp. 1–14, ISBN 978-0-521-76573-2, retrieved 2025-05-08
  4. ^ Schubert, G.; Sohl, F.; Hussmann, H., "Interior of Europa", Europa, University of Arizona Press, pp. 353–368, retrieved 2025-05-07
  5. ^ a b c Pappalardo, Robert; Mills, Mackenzie; Panning, Mark; Leonard, Erin; Howell, Samuel (2023-05-15). "Moonquake-Triggered Mass Wasting Processes on Icy Worlds". doi.org. Retrieved 2025-05-07.
  6. ^ a b c Marusiak, A. G.; Schmerr, N. C.; Pettit, E. C.; Avenson, B.; Bailey, S. H.; Bray, V. J.; Dahl, P.; DellaGiustina, D. N.; Wagner, N.; Weber, R. C. (March 2022). "The Detection of Seismicity on Icy Ocean Worlds by Single‐Station and Small‐Aperture Seismometer Arrays". Earth and Space Science. 9 (3). doi:10.1029/2021ea002065. ISSN 2333-5084.
  7. ^ Marusiak, Angela Giuliano; Panning, Mark Paul; Vance, Steven Douglas; Nunn, Ceri; Stähler, Simon C.; Tharimena, Saikiran (2021-12-15). "Seismic detection of euroquakes originating from Europa's silicate interior". doi.org. Retrieved 2025-05-07.
  8. ^ Ashkenazy, Yosef; Tziperman, Eli; Nimmo, Francis (2023-05-16). "Non‐Synchronous Rotation on Europa Driven by Ocean Currents". AGU Advances. 4 (3). arXiv:2210.04961. doi:10.1029/2022av000849. ISSN 2576-604X.
  9. ^ Nimmo, F.; Schenk, P. (December 2006). "Normal faulting on Europa: implications for ice shell properties". Journal of Structural Geology. 28 (12): 2194–2203. doi:10.1016/j.jsg.2005.08.009. ISSN 0191-8141.
  10. ^ Panning, M.; Lekic, V.; Manga, M.; Cammarano, F.; Romanowicz, B. (December 2006). "Long‐period seismology on Europa: 2. Predicted seismic response". Journal of Geophysical Research: Planets. 111 (E12). doi:10.1029/2006je002712. ISSN 0148-0227.
  11. ^ Tsuji, Daisuke; Teanby, Nicholas A. (October 2016). "Europa's small impactor flux and seismic detection predictions". Icarus. 277: 39–55. doi:10.1016/j.icarus.2016.04.036. hdl:1983/5f0b7af7-e838-4397-a80f-a5fe1b513bb2. ISSN 0019-1035.
  12. ^ a b c Zahnle, Kevin; Schenk, Paul; Levison, Harold; Dones, Luke (June 2003). "Cratering rates in the outer Solar System". Icarus. 163 (2): 263–289. doi:10.1016/s0019-1035(03)00048-4. ISSN 0019-1035.
  13. ^ a b Geissler, Paul (2015), "Cryovolcanism in the Outer Solar System", The Encyclopedia of Volcanoes, Elsevier, pp. 763–776, ISBN 978-0-12-385938-9, retrieved 2025-05-07
  14. ^ Nimmo, Francis (2018-06-25), "Icy Satellites: Interior Structure, Dynamics, and Evolution", Oxford Research Encyclopedia of Planetary Science, Oxford University Press, ISBN 978-0-19-064792-6, retrieved 2025-05-08
  15. ^ "Jupiter: the planet, satellites and magnetosphere". Choice Reviews Online. 42 (09): 42–5246-42-5246. 2005-05-01. doi:10.5860/choice.42-5246. ISSN 0009-4978.
  16. ^ a b Schenk, Paul M.; Clark, Roger N.; Howett, Carly J. A.; Verbiscer, Anne J.; Waite, J. Hunter (2018-11-27). Enceladus and the Icy Moons of Saturn. University of Arizona Press. ISBN 978-0-8165-3748-8.
  17. ^ a b Bierhaus, Edward B.; Zahnle, Kevin; Chapman, Clark R., "Europa's Crater Distributions and Surface Ages", Europa, University of Arizona Press, pp. 161–180, retrieved 2025-05-08
  18. ^ Collins, Geoffrey C.; McKinnon, William B.; Moore, Jeffrey M.; Nimmo, Francis; Pappalardo, Robert T.; Prockter, Louise M.; Schenk, Paul M. (2009-12-17), "Tectonics of the outer planet satellites", Planetary Tectonics, Cambridge University Press, pp. 264–350, ISBN 978-0-521-76573-2, retrieved 2025-05-08
  19. ^ a b Collins, Geoffrey C.; Patterson, G. Wesley; Head, James W.; Pappalardo, Robert T.; Prockter, Louise M.; Lucchitta, Baerbel K.; Kay, Johnathan P. (2014). "Global geologic map of Ganymede". Scientific Investigations Map. doi:10.3133/sim3237. ISSN 2329-132X.
  20. ^ Patterson, G. Wesley; Collins, Geoffrey C.; Head, James W.; Pappalardo, Robert T.; Prockter, Louise M.; Lucchitta, Baerbel K.; Kay, Jonathan P. (June 2010). "Global geological mapping of Ganymede". Icarus. 207 (2): 845–867. doi:10.1016/j.icarus.2009.11.035. ISSN 0019-1035.
  21. ^ Pappalardo, Robert T.; Head, James W.; Collins, Geoffrey C.; Kirk, Randolph L.; Neukum, Gerhard; Oberst, Juergen; Giese, Bernd; Greeley, Ronald; Chapman, Clark R.; Helfenstein, Paul; Moore, Jeffrey M.; McEwen, Alfred; Tufts, B.Randy; Senske, David A.; Breneman, H.Herbert (September 1998). "Grooved Terrain on Ganymede: First Results from Galileo High-Resolution Imaging". Icarus. 135 (1): 276–302. doi:10.1006/icar.1998.5966. ISSN 0019-1035.
  22. ^ "Europa Clipper Spacecraft (Artist's Concept)". NASA Jet Propulsion Laboratory (JPL). Retrieved 2025-05-08.
  23. ^ a b "Overview | Mission". NASA's Europa Clipper. Retrieved 2025-05-08.
  24. ^ "Juice launch kit". www.esa.int. Retrieved 2025-05-08.
  25. ^ a b c "Juice factsheet". www.esa.int. Retrieved 2025-05-08.
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