Saturn's ancient regular satellites

TL;DR

This study uses advanced impact modeling and crater analysis to determine that Saturn's regular icy satellites are approximately 4.1 to 4.4 billion years old, indicating they are ancient and formed early in the Solar System's history.

Contribution

The paper introduces a new impact chronology model for Saturn's satellites based on high-resolution simulations and improved trans-Neptunian object data, providing consistent surface age estimates.

Findings

Surface ages range from 4.1 to 4.4 billion years.

Mimas and Enceladus are about 200 million years younger.

Crater production functions are similar across satellites.

Abstract

Are Saturn's regular satellites young or old? And how old are Enceladus' cratered plains? To answer these questions we computed model surface ages of the most heavily cratered terrains on Saturn's regular icy satellites using new high-resolution outer Solar System evolution simulations, and coupled with improved estimates of the trans-Neptunian objects populations. The output of the simulations allowed us to construct a model impact chronology onto Saturn which automatically applies to its regular satellites. We used crater densities and our impact chronology onto Saturn to construct model impact-crater isochrons, i.e., the scaling of the satellite crater production function with time. The surface ages derived for the cratered plains on Mimas, Enceladus, Tethys, Dione and Rhea range from 4.1 Ga to 4.4 Ga, with the surfaces of Mimas and Enceladus roughly 200 Myr younger than those of the outer three satellites. Uncertainties in these ages are less than 300 Myr. The calculated model surface ages of these satellites are consistent over as much as two orders of magnitude in the observed crater diameter. The similarity of the crater production function amongst all satellites suggests that they were bombarded by a single impactor source. This work supports the idea that Saturn's regular satellites are ancient, and has implications for their formation and their tidal evolution.