Lunar Seismic Profiling Experiment

Lunar Seismic Profiling Experiment. The Lunar Seismic Profiling Experiment was a sophisticated geophysical investigation deployed during the final Apollo lunar landing mission. Designed to probe the shallow subsurface structure of the Moon, it combined active seismic sources with a linear array of detectors. The experiment provided unprecedented data on lunar regolith properties, bedrock depth, and local geological structure, significantly advancing the field of planetary science.

Overview and Objectives

The primary objective was to determine the detailed structure of the upper kilometer of the lunar crust at the Taurus–Littrow landing site. Scientists from NASA and principal investigators like Dr. Robert L. Kovach of Stanford University aimed to measure the thickness and layering of the regolith, detect the presence of buried lava flows or rift valley structures, and characterize the physical properties of the subsurface materials. This experiment was distinct from the earlier Passive Seismic Experiment deployed by Apollo 11 and Apollo 12, as it utilized controlled, artificial seismic sources. The data was intended to complement findings from the Lunar Surface Magnetometer and other instruments in the Apollo Lunar Surface Experiments Package.

Instrumentation and Deployment

The experiment hardware was manufactured by the Bendix Corporation and consisted of three main components: a central geophone station, a linear array of four additional geophones, and a package of eight explosive seismic charges. The geophone array was deployed in a roughly 3.5-kilometer line extending south from the Apollo 17 Lunar Module by astronauts Eugene Cernan and Harrison Schmitt during their extravehicular activity. The explosive charges, ranging in size, were placed at varying distances from the array by the crew using the Lunar Roving Vehicle. These charges were later detonated by remote command from Mission Control in Houston after the crew's departure, creating known seismic sources.

Data Collection and Results

Data collection occurred in two phases: passive monitoring of natural moonquakes and active profiling from the detonated charges. The detonations, including one from a pre-existing Saturn V S-IVB impact, generated clear seismic signals recorded by the geophone array. The experiment successfully recorded data for several months, transmitting it to receiving stations like the Goldstone Deep Space Communications Complex. Key results included the direct measurement of seismic wave velocities in the shallow crust, which were significantly slower than in deeper layers, indicating highly fractured and porous material. The data also revealed distinct seismic reflections, suggesting interfaces between layers of differing density.

Scientific Findings and Analysis

Analysis of the seismic profiles by teams at the United States Geological Survey and NASA Ames Research Center led to several major findings. Researchers determined the regolith thickness at the site to be approximately 8 to 12 meters, overlying a zone of fragmented bedrock. Evidence for a distinct layer, interpreted as a buried mare basalt flow, was found at a depth of about 1.4 kilometers. The very low seismic wave attenuation confirmed the Moon's extremely dry and rigid nature, as previously suggested by the Lunar Laser Ranging experiment. These results provided ground truth for orbital data from missions like Lunar Orbiter and informed models of impact crater formation and volcanism on the Moon.

Legacy and Impact

The experiment set a benchmark for active seismic exploration on other worlds and influenced the design of instruments for later missions to Mars, such as the InSight lander's Seismic Experiment for Interior Structure. Its detailed subsurface model remains a crucial reference for interpreting global data from spacecraft like NASA's Gravity Recovery and Interior Laboratory and the Lunar Reconnaissance Orbiter. The success demonstrated the high scientific return of complex, crew-deployed surface experiments, a hallmark of the later Apollo missions. Data from the experiment continues to be re-analyzed with modern techniques, contributing to ongoing studies of lunar evolution and resource potential.

Category:Apollo program Category:Lunar science Category:NASA programs