Surface ages of mid-size saturnian satellites

Abstract

The observations of the surfaces of the mid-sized Saturnian satellites made by Cassini-Huygens mission have shown a variety of features that allows study of the processes that took place and are taking place on those worlds. Research of the Saturnian satellite surfaces has clear implications not only for Saturn's history and Saturn's surroundings, but also for the Solar System. Crater counting from high definition images is very important and could serve for the determination of the age of the surfaces. In a recent paper, we have calculated the production of craters on the mid-sized Saturnian satellites by Centaur objects considering the current configuration of the Solar System. Also, we have compared our results with crater counts from Cassini images by other authors and we have noted that the number of observed small craters is less than our calculated theoretical number. In this paper we estimate the age of the surface for each observed terrain on each mid-sized satellite of Saturn. All the surfaces analyzed appear to be old with the exception of Enceladus. However, we have noticed that since there are less observed small craters than calculated (except on Iapetus), this results in younger ages than expected. This could be the result of efficient endogenous or exogenous process(es) for erasing small craters and/or crater saturation at those sizes. The size limit from which the observed number of smaller craters is less than the calculated is different for each satellite, possibly indicating processes that are unique to each, but other potential common explanations for this paucity of small craters would be crater saturation and/or deposition of Ering particles. These processes are also suggested by the findings that the smaller craters are being preferentially removed, and the erasure process is gradual.On Enceladus, only mid and high latitude plains have remnants of old terrains; the other regions could be young. In particular, the regions near the South Polar Terrain could be as young as 50 Myrs old. On the contrary for Iapetus, all the surface is old and it notably registers a primordial source of craters. As the crater size is decreased, it would be perceived to approach saturation until D 2 km-craters, where saturation is complete.

Cratering and age of the small Saturnian satellites

“…Therefore, the dependence of cratering with time is the same as the dependence of encounters with time. Di Sisto & Zanardi (2016) found that this time dependence is well fitted by a logarithmic function given by:…”

“…Consequently, we test the cratering model but also infer if there may be physical processes that affect the satellite as a whole or its surface features. In this regard, Di Sisto & Zanardi (2016) analyzed the cratering process in the mid-sized saturnian satellites and calculated their surface ages. The idea is very simple and should be considered a first-order approach to the problem.…”

“…To consider this matter, we follow the method developed in Di Sisto & Zanardi (2016) to calculate the age of a satellite surface. Therefore the estimated cratering timescale or the "age" of the surface τ s is given by:…”

Surface deposition of the Enceladus plume and the zenith angle of emissions

“…Multiple particle sizes from 0.6 − 15 µm are simulated for each source location, and data are generated on the impact flux in particles/sec/m 2 and mass deposition in mm/year across the surface of Enceladus. Initial simulated maps of surface deposition from the Enceladus plume published in Kempf et al (2010) have received interest from the larger research community (for example, Di Sisto and Zanardi, 2016;Nahm and Kattenhorn, 2015;Scipioni et al, 2017) and, here, we provide a more complete set of maps and data with respect to source location and particle size. Using the newly generated surface data for a curtain-style plume (Spitale et al, 2015) and the ∼ 100 discrete jets proposed in Porco et al (2014), we provide new insight into the zenith angle of plume emissions, that is, the "tilt" of the jets.…”

Using cosmogenic Lithium, Beryllium and Boron to determine the surface ages of icy objects in the outer solar system

“…Absolute ages of geological formations on icy bodies have traditionally been estimated based on the observed crater densities for particular surface units. Different models of the impactor flux yield different age estimates, but in general these calculations indicate that the most heavily cratered icy surfaces are comparable in age to the Solar System (Zahnle et al 2003;Kirchoff and Schenk 2010;Di Sisto and Zanardi 2016;Kirchoff et al 2018). However, recent studies of the dynamical history of Saturn's satellites suggest that many of that planet's heavily-cratered mid-sized moons may be substantially less than a billion years old (Ćuk et al 2016;Asphaug and Reufer 2013).…”