Abstract
We study the size frequency distribution of the blocks located in the deeply fractured, geologically active Enceladus South Polar Terrain with the aim to suggest their formative mechanisms. Through the Cassini ISS images, we identify ~17,000 blocks with sizes ranging from ~25 m to 366 m, and located at different distances from the Damascus, Baghdad and Cairo Sulci. On all counts and for both Damascus and Baghdad cases, the power-law fitting curve has an index that is similar to the one obtained on the deeply fractured, actively sublimating Hathor cliff on comet 67P/Churyumov-Gerasimenko, where several non-dislodged blocks are observed. This suggests that as for 67P, sublimation and surface stresses favor similar fractures development in the Enceladus icy matrix, hence resulting in comparable block disaggregation. A steeper power-law index for Cairo counts may suggest a higher degree of fragmentation, which could be the result of localized, stronger tectonic disruption of lithospheric ice. Eventually, we show that the smallest blocks identified are located from tens of m to 20–25 km from the Sulci fissures, while the largest blocks are found closer to the tiger stripes. This result supports the ejection hypothesis mechanism as the possible source of blocks.
Highlights
Academic Editor: Maria-Paz ZorzanoReceived: 5 February 2021Accepted: 25 March 2021Published: 30 March 2021Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Enceladus is a ~500 km-size icy moon of Saturn [1], orbiting at a distance of 3.94 Saturn radii from the planet
The paper is structured as follows: after identifying and counting the blocks located in the Damascus-Baghdad-Cairo Sulci area, we study their size-frequency distribution (SFD), applying a statistical method to evaluate if the data can be fitted by power-law curves
In order to identify the icy blocks located in the Enceladus South Polar Terrain (SPT), we downloaded the full Cassini ISS-NAC [5] imagery dataset presented in Table 1 of Martens et al [1], and publicly available through the Planetary Data System (PDS) Archive
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Acquired high-resolution images of the moon’s surface [6], revealing an almost craterless, fracture-dominated and geologically active province surrounding the South Pole of Enceladus, called the South Polar Terrain (SPT). Inside this unit (called csp, i.e., central south polar, surrounded by the southern curvilinear unit, called cl3, [7]), both cryovolcanic and tectonic activities are evident [7,8,9], with icy geysers emanating water vapor plumes from four, 100 km-long -spaced tension fractures [6], called “tiger stripes” (hereafter named TS), Figure 1
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