How to build an ice-diving probe that won’t freeze up
Rather than boring through rock-hard ice, future robotic explorers to ice worlds will melt their way in
Some of the most intriguing objects in the Solar System are ice worlds. The moons Europa and Enceladus are hiding large bodies of liquid water deep under their surfaces, sealed beneath a shell of hard-frozen ice. Liquid water is thought to be one of the fundamental requirements for supporting life, and so many planetary scientists are very keen to explore these alien oceans.
The challenge, though, will be penetrating down through a substantial thickness of rock-hard ice to access these exciting environments. On Earth, this sort of operation (like drilling down into Lake Vostok buried deep beneath the Antarctic ice) is accomplished with huge, industrial machinery and a team of human engineers to maintain it: a mission using a setup of this type is simply not feasible in the near-term of space exploration.
So how will we be able to reach the interior of these icy worlds with current robotic technology? The most promising solution is a melter probe. A roughly cylindrical canister holds a suite of scientific instruments, and sports a heated plate at the front to slowly melt its way down.
But there remain a number of engineering problems that need to be solved, say Kai Schüller and Julia Kowalski from RWTH Aachen University in Germany. For one, the probe needs to melt the ice immediately beneath it, whilst ensuring that it doesn’t refreeze too quickly in the channel that’s been created and trap the probe. While designs can be tested on Earth, the much colder ice and lower gravity of the icy moons would slow the downwards progression of the probe and so increase the risk of such a lock-in.
Schüller and Kowalski have been studying how to make the most efficient use of the heating power a small probe could deliver and ensure it doesn’t become stuck. They’ve modelled a simple design to see how parameters like the length of the probe, the power of its heated head and the physical properties of the icy world affect its ability to burrow down. “To prevent itself getting stuck an extraterrestrial melter probe will almost certainly need heaters along its sides as well”
They’ve found that the gravitational pull of a world, and hence the downwards force exerted by the probe, does indeed have a significant impact. To prevent getting itself stuck, an extraterrestrial melter probe about a metre long and delivering a reasonable power to its front heater will almost certainly also need heaters along its sides as well. And for somewhere like Enceladus, with its low gravity, an additional mechanism to keep pushing the heating head forward into close contact with the ice needs to be considered.
Recent discoveries have made just this kind of melter-probe technology even more relevant. In July of this year, scientists announced the discovery of a large lake of water beneath the ice cap on the south pole of Mars. This too could be a potential habitat for life, and so is another extremely inviting target for extraterrestrial subglacial exploration. Just this sort of melter probe design, originally conceived for Europa, would therefore make an ideal mission for the Martian pole.
An artist’s impression of a probe melting itsway into Europa