The probe would be tracked by a type of sonar, putting out seismic waves as it descended that could be detected by existing networks of seismometers. In addition to providing position data, these sound waves could be encoded to transmit measurements of temperature, electrical conductivity, and chemical composition as the probe descended. The energy required to create the initial crack and launch the probe would be equivalent to an earthquake of magnitude 7 on the Richter scale, or a megaton-sized nuclear device such as those already possessed by many nations.
To some extent, Stevenson’s idea is somewhat tongue-in-cheek, but with a serious undertone – like most good science-fiction. “I have quite low confidence that it will work. However, my motivation in writing this paper is to get people to think about ideas like this.”