A Microseismometer for Penetrometer Deployment

Seismology is unique in its ability to resolve the deep internal structure of the bodies in the solar system, producing powerful insights into both their current state and past evolution. The success of seismology in looking deep into the interior of the Earth, and later the Moon, has motivated the inclusion of seismometers in the payload on several previous missions. However, since Apollo the resources required to land, deploy and operate seismometers based on conventional seismic technology have so far prevented the successful operation of a seismic network. We propose to develop a subsystem of the cancelled ExoMars seismic system, a micromachined silicon sensor, as a potential instrument which should enable penetrometer-delivered seismic stations and networks. A penetrometer would land at very high velocity, burying itself below the surface of the planet or moon we wish to study. This has the advantage of producing an excellent mechanical connection between to the instrument and good protection from temperature swings and any wind on the surface. Compared to a lander, a penetrometer is a much simpler way of getting such an instrument deployed allowing many more instruments to be deployed for the same budget. The overiding challenge for such an instrument is to have the sensitivity to detect the weak quakes expected while being extremely robust to withstand the very high shock levels expected during the impact of the penetrometer. The microseismometer is based on a set of silicon beams thinner than a human hair that provide a set of near perfect springs for detection of any quakes. Preliminary impact testing has suggested one potential technology route for such an instrument based on packing the springs with a sublimant, protecting them during the initial impact but later disappearing to free up the springs. We will pursue this in parallel with alternative shock-mitigation approaches for both the sensor and electronics. Fabrication of the silicon suspension of the microseismometer will be combined with testing at Imperial and Oxford, with Oxford also developing the electronics needed to pick up the seismic signal.