Post contributed by Dr. Emily S. Martin, Research Fellow, Center for Earth and Planetary Studies, National Air & Space Museum, Smithsonian Institution.
Pit chains are linear assemblages of circular to elliptical pits and have been observed across the solar system. Pit chains have been found on Venus, Earth, Mars, Phobos, Eros, Gaspra, Ida, and Vesta. Across the solar system, pit chains may form through a variety of mechanisms including the collapse of lava tubes, karst, venting, extensional fracturing, or dilational faulting. Saturn’s tiny icy moon Enceladus is the first body of the outer solar system on which pit chains have been identified. Enceladus is only 500 km in diameter and is best known for its warm south pole and its watery plume emanating from prominent ridges known as tiger stripes. The source of the plume is likely a global liquid water ocean beneath an icy shell.
Enceladus’ pit chains are found primarily within the ancient cratered terrains of the Saturnian and anti-Saturnian hemispheres and based on cross-cutting relationships, pit chains are among the youngest features on Enceladus’ surface. The presence of pit chains in the cratered terrains suggests that these terrains are undergoing tectonic dissection, which further suggests Enceladus’ South Pole may not be the only active region on Enceladus’ surface.
The morphology and distribution of pit chains in parallel fracture sets makes extensional fracturing or dilational faulting the favored mechanisms for the formation of pit chains on Enceladus. These mechanisms require a layer of regolith distributed across Enceladus’ surface where pit chains are observed. Estimates of the depth of the regolith where pit chains are present range from 90-290 m deep. The regolith on Enceladus is likely sourced from both impact-generated regolith (not including the mega-regolith of the upper crust) and fall-back material from Enceladus’ south polar plume. Observations of pit chains across Enceladus signal the presence of a deep layer of regolith across the ancient cratered terrains. Regolith likely insulates Enceladus’ surface, which influences the effective surface temperature and thermal state of Enceladus’ ice shell, perhaps even helping to maintain Enceladus’ interior ocean.
Further Reading:
Martin, E. S. et al., (2017), Pit Chains on Enceladus Signal the Recent Tectonic Dissection of the Ancient Cratered Terrains. Icarus, 294, 209-217.
Ferrill, D. A., et al., (2004), Dilational fault slip and pit chain formation on Mars. GSA Today 14, (10), 4-12.
Ferrill, D. A., et al., (2011), Coseismic, dilational-fault and extension-fracture related pit chain formation in Iceland: analog for pit chains on Mars, Lithosphere 3 (2), 133-142.
Wyrick, D., et al., (2004), Distribution, morphology, and origins of Martian pit crater chains. J. Geophys. Res. 109, E06005.
intergalacticplanetary
/ August 30, 2017Typo: 500 km diameter 🙂
Why these mechanisms (extensional fracturing or dilational faulting) require a layer of regolith?
Haruki Chou
/ December 1, 2017images much too small.
why page so narrow?