Results from the Apollo Passive Seismic Experiment (Latham et al., 1977)
- Source document: 1977-latham-apollo-passive-seismic-results-ntrs-19780005006.txt
— text edition (user-extracted, page-tagged), with the extraction’s
structural metadata kept as the sibling
....json. The scanned original (13 pp) is not stored; it lives at NTRS 19780005006 (direct PDF). - Original: G. Latham, Y. Nakamura, J. Dorman, F. Duennebier, M. Ewing, and D. Lammlein (Marine Science Institute, Univ. of Texas, Galveston), “Results from the Apollo Passive Seismic Experiment,” in Cosmochemistry of the Moon and Planets (NASA SP-370), 1977, pp. 390 ff. (Contribution No. 44 of the Marine Science Institute.)
Summary
Section titled “Summary”The PSE team’s network-era results paper — the citable statement of what the seismometers the Apollo crews left behind actually found. It reviews the Apollo Seismic Network (the RTG-powered stations of missions 12/14/15/16, completed April 1974) and reports the headline findings: an extraordinarily quiet Moon, a small population of moonquakes in three classes, and a differentiated interior with a crust, a thick cumulate mantle layer, and a probably molten small core. For this library it is the experiment’s “what happened next,” closing the arc the Apollo 11 station opened.
Key takeaways
Section titled “Key takeaways”- The Apollo 11 station’s fate, stated plainly: “powered by solar cells and intended for operation only during the lunar day, [it] failed after exposure to the first nighttime period.” The four later, RTG-powered stations form the network (16 seismometers, all but two still operating; ~10-yr expected station lifetimes).
- The Moon is seismically quiet — with numbers. Surface noise is so low the instruments run at ~20-million magnification, “two to three orders of magnitude higher than can normally be used on Earth,” detecting motions of ~½ ångström. Total annual moonquake energy release is < 10¹⁵ ergs/yr — about nine orders of magnitude below Earth’s; with terrestrial-sensitivity instruments “we would have recorded no moonquakes at all.”
- Three classes of moonquakes plus impacts: rare but energetic high-frequency shallow events (11 identified in 3 years — the largest natural signals recorded); numerous tiny deep moonquakes (max Richter ~2) concentrated at 600–800 km depth, whose occurrence shows tidal periodicities — “tides play a dominant role” in generating them; and near-surface thermal moonquakes tracking the day-night temperature cycle. Several hundred meteoroid impacts register per station per year, with the Saturn S-IVB stage impacts used as calibration shots.
- A differentiated interior: primitive differentiation of the outer shell to ~300 km; best crust model 40–80 km thick (anorthositic gabbro grading to gabbro) over an ~250-km olivine-pyroxene cumulate; and a central region presently molten to a radius of 200–300 km (missing/attenuated shear waves from far-side events), with iron or iron sulphide the best core candidate. Short accretion times are implied if accretional energy did the early melting.