What methodology remains the gold standard for investigating a distant moon's seismic activity, as demonstrated by the Apollo missions?

The deployment of seismometers in a network across the body.

The most reliable and direct method for ascertaining internal geologic activity on a celestial body is the deployment of a seismic network. This was proven by the Apollo missions, which left behind crucial instrumentation. A successful seismic network necessitates the placement of multiple sensors distributed across the surface of the moon in question. This strategic placement allows scientists to triangulate the precise origin point of any recorded seismic event, calculate its depth of origin, and thus determine the nature of the internal forces acting upon that body. While impractical for many moons currently, this technique remains the primary objective for long-term exploration efforts on bodies like Mars’s moons.