Active eruptions from the south polar region of Saturn’s ~500-km-diameter moon Enceladus are concentrated along a series of lineaments known as the ‘tiger stripes’1,2, thought to be partially open fissures that connect to the liquid water ocean beneath the ice shell3,4. To date, no study simultaneously explains why the tiger stripes should be located only at the south pole, why there are multiple approximately parallel and regularly spaced fractures, what accounts for their spacing of about 35 km, and why similarly active fissures have not been observed on other icy bodies. Here we propose that secular cooling, which leads to a thickening of the ice shell and building of global tensile stresses5,6, causes the first fracture to form at one of the poles, where the ice shell is thinnest owing to tidal heating7. The tensile stresses are thereby relieved, preventing a similar failure at the opposite pole. The steadily erupting water ice loads the flanks of the open fissure, causing bending in the surrounding elastic plate and further tensile failure in bands parallel to the first fracture—a process that may be unique to Enceladus, where the gravity is too weak for compressive stresses to prevent fracture propagation through the thin ice shell. The sequence of fissures then cascades outwards until the loading becomes too weak or the background shell thickness becomes too great to permit through-going fractures.
Your institute does not have access to this article
Subscribe to Nature+
Get immediate online access to the entire Nature family of 50+ journals
Subscribe to Journal
Get full journal access for 1 year
only $8.25 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
All required data are available in the published literature as indicated.
The computer code required to carry out the calculations discussed herein is available on request from the corresponding author.
Porco, C. C. et al. Cassini observes the active south pole of Enceladus. Science 311, 1393–1401 (2006).
Porco, C., DiNino, D. & Nimmo, F. How the geysers, tidal stresses, and thermal emission across the south polar terrain of Enceladus are related. Astron. J. 148, 45 (2014).
Ingersoll, A. P. & Nakajima, M. Controlled boiling on Enceladus. 2. Model of the liquid-filled cracks. Icarus 272, 319–326 (2016).
Kite, E. S. & Rubin, A. M. Sustained eruptions on Enceladus explained by turbulent dissipation in tiger stripes. Proc. Natl Acad. Sci. USA 113, 3972–3975 (2016).
Manga, M. & Wang, C. Y. Pressurized oceans and the eruption of liquid water on Europa and Enceladus. Geophys. Res. Lett. 34, 1–5 (2007).
Rudolph, M. L. & Manga, M. Fracture penetration in planetary ice shells. Icarus 199, 536–541 (2009).
Hemingway, D. J. & Mittal, T. Enceladus’s ice shell structure as a window on internal heat production. Icarus 332, 111–131 (2019).
Postberg, F., Schmidt, J., Hillier, J., Kempf, S. & Srama, R. A salt-water reservoir as the source of a compositionally stratified plume on Enceladus. Nature 474, 620–622 (2011).
Iess, L. et al. The gravity field and interior structure of Enceladus. Science 344, 78–80 (2014).
Thomas, P. et al. Enceladus’s measured physical libration requires a global subsurface ocean. Icarus 264, 37–47 (2016).
Spencer, R. et al. in Enceladus and the Icy Moons of Saturn (eds Schenk, P. M., Clark, R. N., Howett, C. J. A. & Verbiscer, A. J.) 163–174 (Univ. Arizona Press, 2018).
Patthoff, D. A. & Kattenhorn, S. A. A fracture history on Enceladus provides evidence for a global ocean. Geophys. Res. Lett. 38, 1–6 (2011).
Bland, M. T., McKinnon, W. B. & Schenk, P. M. Constraining the heat flux between Enceladus’ tiger stripes: numerical modeling of funiscular plains formation. Icarus 260, 232–245 (2015).
Yin, A. & Pappalardo, R. T. Gravitational spreading, bookshelf faulting, and tectonic evolution of the south polar terrain of Saturn’s moon Enceladus. Icarus 260, 409–439 (2015).
Yin, A., Zuza, A. V. & Pappalardo, R. T. Mechanics of evenly spaced strike-slip faults and its implications for the formation of tiger-stripe fractures on Saturn’s moon Enceladus. Icarus 266, 204–216 (2016).
Nakajima, M. & Ingersoll, A. P. Controlled boiling on Enceladus. 1. Model of the vapor-driven jets. Icarus 272, 309–318 (2016).
Nimmo, F., Barr, A. C., Běhounková, M. & Mckinnon, W. B. in Enceladus and the Icy Moons of Saturn (eds Schenk, P. M., Clark, R. N., Howett, C. J. A. & Verbiscer, A. J.) 79–94 (Univ. Arizona Press, 2018).
Kamata, S. & Nimmo, F. Interior thermal state of Enceladus inferred from the viscoelastic state of the ice shell. Icarus 284, 387–393 (2017).
Čadek, O., Běhounková, M., Tobie, G. & Choblet, G. Viscoelastic relaxation of Enceladus’s ice shell. Icarus 291, 31–35 (2017).
Choblet, G. et al. Powering prolonged hydrothermal activity inside Enceladus. Nat. Astron. 1, 841–487 (2017).
Tajeddine, R. et al. True polar wander of Enceladus from topographic data. Icarus 295, 46–60 (2017).
Nimmo, F. & Pappalardo, R. T. Diapir-induced reorientation of Saturn’s moon Enceladus. Nature 441, 614–6 (2006).
Roberts, J. H. & Stickle, A. M. Break the world’s shell: an impact on Enceladus: bringing the ocean to the surface. In Lunar and Planetary Science XLVIII 1955 (LPI, 2017).
Nimmo, F., Spencer, J. R., Pappalardo, R. T. & Mullen, M. E. Shear heating as the origin of the plumes and heat flux on Enceladus. Nature 447, 289–91 (2007).
Ingersoll, A. P. & Ewald, S. P. Total particulate mass in Enceladus plumes and mass of Saturn’s E ring inferred from Cassini ISS images. Icarus 216, 492–506 (2011).
Degruyter, W. & Manga, M. Cryoclastic origin of particles on the surface of Enceladus. Geophys. Res. Lett. 38, L16201 (2011).
Crow-Willard, E. N. & Pappalardo, R. T. Structural mapping of Enceladus and implications for formation of tectonized regions. J. Geophys. Res. Planets 120, 928–950 (2015).
Turcotte, D. L. & Schubert, G. Geodynamics (Cambridge Univ. Press, 1982).
Billings, S. E. & Kattenhorn, S. A. The great thickness debate: ice shell thickness models for Europa and comparisons with estimates based on flexure at ridges. Icarus 177, 397–412 (2005).
tenBrink, U. Volcano spacing and plate rigidity. Geology 19, 397–400 (1991).
Hieronymus, C. F. & Bercovici, D. Discrete alternating hotspot islands formed by interaction of magma transport and lithospheric flexure. Nature 397, 604–607 (1999).
Nimmo, F. Non-Newtonian topographic relaxation on Europa. Icarus 168, 205–208 (2004).
Nimmo, F., Pappalardo, R. T. & Giese, B. Effective elastic thickness and heat flux estimates on Ganymede. Geophys. Res. Lett. 29, 1158 (2002).
Kalousová, K., Soucek, O. & Cadek, O. Deformation of an elastic shell with variable thickness: a comparison of different methods. Geophys. J. Int. 190, 726–744 (2012).
Crouch, S. L. & Starfield, A. M. Boundary Element Methods in Solid Mechanics (George Allen and Unwin, 1983).
Qin, R., Buck, W. R. & Germanovich, L. Comment on “Mechanics of tidally driven fractures in Europa’s ice shell” by S. Lee, R. T. Pappalardo, and N. C. Makris [2005. Icarus 177, 367–379]. Icarus 189, 595–597 (2007).
Dombard, A. J., Patterson, G. W., Lederer, A. P. & Prockter, L. M. Flanking fractures and the formation of double ridges on Europa. Icarus 223, 74–81 (2013).
Bland, M. T., Beyer, R. A. & Showman, A. P. Unstable extension of Enceladus’ lithosphere. Icarus 192, 92–105 (2007).
Giese, B. et al. Enceladus: an estimate of heat flux and lithospheric thickness from flexurally supported topography. Geophys. Res. Lett. 35, 1–5 (2008).
Hammond, N. P., Barr, A. C., Cooper, R. F., Caswell, T. E. & Hirth, G. Experimental constraints on the fatigue of icy satellite lithospheres by tidal forces. J. Geophys. Res. Planets 123, 1–15 (2018).
Petrenko, V. F. & Whitworth, R. W. Physics of Ice (Oxford Univ. Press, 1999).
Hurford, T. A., Helfenstein, P., Hoppa, G. V., Greenberg, R. & Bills, B. G. Eruptions arising from tidally controlled periodic openings of rifts on Enceladus. Nature 447, 292–294 (2007).
Nimmo, F., Porco, C. & Mitchell, C. Tidally modulated eruptions on Enceladus: Cassini ISS observations and models. Astron. J. 148, 46 (2014).
Ingersoll, A. P. & Ewald, S. P. Decadal timescale variability of the Enceladus plumes inferred from Cassini images. Icarus 282, 260–275 (2017).
Spohn, T. & Schubert, G. Oceans in the icy Galilean satellites of Jupiter? Icarus 161, 456–467 (2003).
Béghin, C., Sotin, C. & Hamelin, M. Titan’s native ocean revealed beneath some 45 km of ice by a Schumann-like resonance. C. R. Geosci. 342, 425–433 (2010).
Hemingway, D. J., Nimmo, F., Zebker, H. & Iess, L. A rigid and weathered ice shell on Titan. Nature 500, 550–552 (2013).
Vance, S., Bouffard, M., Choukroun, M. & Sotin, C. Ganymede’s internal structure including thermodynamics of magnesium sulfate oceans in contact with ice. Planet. Space Sci. 96, 62–70 (2014).
This work was made possible by the NASA/ESA Cassini mission to Saturn and, in particular, the work of the Imaging Science Subsystem team. D.J.H. was funded in part by the Miller Institute for Basic Research in Science at the University of California Berkeley and in part by the Carnegie Institution for Science in Washington DC. D.J.H. and M.M. acknowledge support from the Center for Integrative Planetary Science (CIPS) at the University of California Berkeley. M.M. was supported in part by NASA Solar System Workings grant 80NSSC19K0557. M.L.R. was supported in part by NSF DMS-1624776. We thank the CIDER working group, supported by NSF EAR-1135452, for early discussions that contributed to parts of this work. We thank M. Bland, R. Citron, J. Jordan, S. Kattenhorn, E. Kite and T. Mittal for helpful discussions.
The authors declare no competing interests.
Peer review information Nature Astronomy thanks Gaël Choblet and An Yin for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Hemingway, D.J., Rudolph, M.L. & Manga, M. Cascading parallel fractures on Enceladus. Nat Astron 4, 234–239 (2020). https://doi.org/10.1038/s41550-019-0958-x