# Melting probe technology for subsurface exploration of extraterrestrial ice - Critical refreezing length and the role of gravity

## TL;DR

This paper models melting probe performance in extraterrestrial ice environments, considering gravity effects and heat losses, to inform the design of future icy moon exploration technologies.

## Contribution

It introduces a detailed physical model of melting probes that accounts for gravity variations and heat transfer, improving upon simplistic energy balance approaches.

## Key findings

- Melting regimes vary significantly with gravitational acceleration.
- Heat losses can be exploited to reduce side wall heating requirements.
- The concept of 'Critical Refreezing Length' helps prevent probe stall.

## Abstract

The 'Ocean Worlds' of our Solar System are covered with ice, hence the water is not directly accessible. Using melting probe technology is one of the promising technological approaches to reach those scientifically interesting water reservoirs. Melting probes basically consist of a heated melting head on top of an elongated body that contains the scientific payload. The traditional engineering approach to design such melting probes starts from a global energy balance around the melting head and quantifies the power necessary to sustain a specific melting velocity while preventing the probe from refreezing and stall in the channel. Though this approach is sufficient to design simple melting probes for terrestrial applications, it is too simplistic to study the probe's performance for environmental conditions found on some of the Ocean's Worlds, e.g. a lower value of the gravitational acceleration. This will be important, however, when designing exploration technologies for extraterrestrial purposes. We tackle the problem by explicitly modeling the physical processes in the thin melt film between the probe and the underlying ice. Our model allows to study melting regimes on bodies of different gravitational acceleration, and we explicitly compare melting regimes on Europa, Enceladus and Mars. In addition to that, our model allows to quantify the heat losses due to convective transport around the melting probe. We discuss to which extent these heat losses can be utilized to avoid the necessity of a side wall heating system to prevent stall, and introduce the notion of the 'Critical Refreezing Length'. Our results allow to draw important conclusions towards the design of melting probe technology for future missions to icy bodies in our Solar System.