Impact crater morphology and the structure of Europa's ice shell

TL;DR

This study uses numerical simulations to explore how impact crater features on Europa can reveal the thickness and structure of its ice shell, considering both conductive and convective models.

Contribution

It introduces detailed impact simulations to constrain Europa's ice shell thickness and structure, comparing conductive and convective scenarios with observed crater morphologies.

Findings

Both thin conductive and thick conductive-convective shells can match observed crater features.

Estimated ice shell thickness ranges from about 5 to 8 km depending on thermal conditions.

Crater central features' timing influences the preferred shell model.

Abstract

We performed numerical simulations of impact crater formation on Europa to infer the thickness and structure of its ice shell. The simulations were performed using iSALE to test both the conductive ice shell over ocean and the conductive lid over warm convective ice scenarios for a variety of conditions. The modeled crater depth-diameter is strongly dependent on thermal gradient and temperature of the warm convective ice. Our results indicate that both a fully conductive (thin) shell and a conductive-convective (thick) shell can reproduce the observed crater depth-diameter and morphologies. For the conductive ice shell over ocean, the best fit is an approximately 8 km thick conductive ice shell. Depending on the temperature (255 - 265 K) and therefore strength of warm convective ice, the thickness of the conductive ice lid is estimated at 5 - 7 km. If central features within the crater, such as pits and domes, form during crater collapse, our simulations are in better agreement with the fully conductive shell (thin shell). If central features form well after the impact, however, our simulations suggest a conductive-convective shell (thick shell) is more likely. Although our study does not provide firm conclusion regarding the thickness of Europa's ice shell, our work indicates that Valhalla-class multiring basins on Europa may provide robust constraints on the thickness of Europa's ice shell.