Science
Morning Moon Shakes: Apollo 17 Lander Base Vibrations Found To Cause Lunar Quakes
The Apollo 17 mission commander in the lunar roving vehicle at the Taurus-Littrow landing site. Lunar Module in the background. (Image: NASA/Harrison Schmitt)
When American astronauts landed on the Moon as part of the Apollo programme, they placed seismometers on its surface.
These instruments revealed that Earth's next-door neighbour experiences moonquakes, similar to how the Earth experiences earthquakes.
Scientists know of four types of moonquakes: deep, shallow, thermal, and those caused by meteorite impacts.
Recent analysis of thermal earthquake data from the Apollo 17 mission has uncovered a surprising fifth type of moonquake. This particular moonquake originates from the Apollo 17 lunar lander base itself.
During the Apollo 17 mission, three seismometers were set up on the lunar surface to record thermal earthquakes. These devices collected data from October 1976 to May 1977.
Thermal quakes occur due to significant temperature changes as the Moon transitions from day to night, with temperatures ranging from 121 degrees Celsius to -133 degrees Celsius.
Using advanced techniques, including machine learning, researchers from the California Institute of Technology analysed the data again.
They discovered that thermal quakes occur regularly during the day, but also identified new tremors in the morning that were not related to thermal quakes.
Triangulating the source of the mysterious quakes, researchers made a surprising discovery: the quakes originated from the Apollo 17 lunar lander base. This base expands and vibrates each morning as it is heated by the Sun.
The findings were published in the Journal of Geophysical Research: Planets on 5 September.
According to Allen Husker, a research professor of geophysics at Caltech who worked on the project, the lander starts "popping off" every lunar morning when the Sun hits it.
These popping sounds occur every 5-6 minutes for a period of 5-7 Earth hours. The regularity and repetition of these sounds were remarkable.
These new moonquakes, though not of natural origin, still contribute to our understanding of the Moon's seismic activity and help to plan future missions.
India's Chandrayaan-3 mission recently deployed a seismic instrument of its own on the Moon.
The Instrument for Lunar Seismic Activity (ILSA) successfully recorded a moonquake whose source is currently under investigation.
Chandrayaan-3 is now asleep during the lunar night.
Scientists are particularly interested in the Moon's south pole region, where Chandrayaan-3 landed and went about its work.
Many of the craters in this region are permanently shadowed and never receive sunlight. Placing seismometres in these areas can help detect water ice trapped beneath the surface, as seismic waves travel slower through water.
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