What is a moonquake? Earth's Moon might appear to be dead, calm and
still on the outside, but below the surface, the Moon is an active,
vibrating body. We know this because humans have caused moonquakes ourselves with the
Apollo missions, and the remains of that technology are still causing tremors on the
Moon as we speak. So today we are going to investigate the truth behind
the mysterious moonquake. This is the space race. On November nineteenth, nineteen
sixty nine, the Apollo twelve mission, commanded by Pede Conrad and albeen,
landed on the surface of the Moon in a region known as the Ocean of
Storms. Part of their mission was to deploy a payload known as the Apollo
Lunar Surface Experiment Package, a collection of scientific instruments that included a remote seismic
monitoring station, the kind of device that we would typically use to detect an
earthquake. After complete eating their moonwalk and returning to the command module, Apollo
twelve released their lunar ascent stage on a trajectory back to the Moon's surface.
They purposefully crashed the vehicle into the Moon. It impacted the surface forty miles
away from the landing site with the force of about one ton of TNT.
The seismic monitoring station was then able to measure the resulting shockwave from that impact.
It took eight minutes for the moonquake to build up and reach its peak,
and then another hour for the tremor to fully dissipate. A similar event
happened on Apollo thirteen. They never landed on the Moon due to a technical
failure en route, but one thing that Apollo thirteen did accomplish was generating a
massive moonquake. As part of their mission profile, the third stage of the
Saturn five rocket, known as the S four B, would be deployed on
a crash course for the Moon. The S four B was a hydrogen propulsion
stage that consisted of two large fuel tanks and a J two rocket, an
engine much larger and heavier than the lunar ascent vehicle, so when this thing
hit the Moon, it generated the force of eleven and a half tons of
TNT, creating shockwaves thirty times greater and lasting four times longer than the Apollo
twelve impact. In both of these experiments, the vibrations recorded by the remote
seismic monitoring station lasted much longer than scientists had expected, far longer than any
equivalent vibrations on the Earth, and this observation led NASA officials to comment that
the moon quote rang like a bell. Those particular words would go on to
birth one of the more fringe conspiracy theories out there, known as the hollow
Moon. The idea is that since the moon rang like a bell, and
bells are hollow, then the moon must therefore also be hollow. The generally
agreed upon explanation for the hollow moon is that we are actually being orbited by
an ancient alien spaceship. So, first of all, an object does not
need to be hollow in order to vibrate or even to ring. Case in
point, the glockenspiel, which uses solid metal bars to create sustaining bell like
tones, or even its more primitive sister instrument, the xylophone, which creates
ringing musical notes from blocks of wood. And second off, the moon isn't
hollow anyway. We'll get to the real reason that the moon rings like a
bell in a little bit, but first let's talk about some natural tremors on
the Moon that are not created by humans crashing stuff into it. The Apollo
Lunar Surface Experiment packages that were deployed on the Moon between nineteen sixty nine and
nineteen seventy two continued to operate and monitor activity for several years until they were
remotely shut down in nineteen seventy seven, and in that time NASA was able
to record a large amount of data about the natural seismic activity of the Moon.
This is fascinating information to have because we know that earthquakes are caused by
the movement of tectonic plates that make up the surface of the Earth, but
the the Moon does not have tectonic plates. The surface is all one continuous
shell. So what causes moonquakes well. One known variety of lunar activity is
the emergent thermal quake. This is the easiest one to understand because we know
that each half of the Moon will experience fourteen days of continuous sunlight followed by
fourteen days of continuous darkness, and since the Moon has no atmosphere to insulate
the surface and maintain a consistent temperature, the surface can range from positive two
hundred and fifty degrees fahrenheit during the daylight periods to negative two hundred and eight
fahrenheit during the night time periods, and just like any other solid material that
is exposed to these drastic temperature swings, the surface of the Moon will actually
expand and contract as it moves from day to night. This movement causes significant
vibrations to travel through the surface of the Moon. Another common seismic activity on
the Moon is the tidal moonquake. On Earth, we experience the physical effect
of the Moon's gravity in the rising and falling of the ocean tides. By
the same measure, the gravity of the Earth will also have an effect on
the surface of the Moon, pulling and stretching the surface material. This will
also cause some residual seismic activity. And then, of course, the Moon
also experiences a pretty high frequency of natural impacts. In addition to humans throwing
chunks of spaceships at it, the Moon gets hit by asteroids of varying sizes
all the way from micrometeorites to metal boulders, each one leaving behind a seismic
footprint. We know all of this information because of the scientific instruments left behind
by Apollo Missions twelve and beyond. With Apollo seventeen, the final crude lunar
mission carrying the most advanced instruments on a payload named the Lunar Seismic Profiling Experiment.
At the time, this was cutting edge research, but it was also
the nineteen seventies, so the communication between the instruments on the Moon and the
receivers on Earth was relatively low bandwidth by modern standards. However, in twenty
twenty three, researchers at the California Institute of Technology found a way to extract
more detail from the Lunar Seismic Profiling Experiment data. They used artificial intelligence and
machine learning algorithms to fill in the missing pieces of the seismic recordings. This
AI upscaling gave the researchers enough detail to begin separating naturally occurring moonquakes from external
influences. One of the more amazing discoveries was that the Apollo seventeen lunar lander,
which was left behind only around one hundred meters from the seismic measuring equipment,
is actually causing moonquakes itself. So what's been happening is that the lander
has been traveling through the lunar day and night cycle for years, and as
the temperatures swing from one extreme to the other, the metal structure has been
expanding and contracting. That movement of the metal over the ground was enough to
cause vibrations that traveled through the surface and reached the monitoring equipment. Now,
this is an incredibly subtle tremor. If you were standing on the Moon next
to the lander, you wouldn't actively notice the vibration. But the fact that
these micro moonquakes were present enough to be extracted from fifty year old recording data
just reinforces the fact that the Moon's surface is a very strong conductor of vibrations,
even very tiny ones. So does this new discovery lend any more credibility
to the hollow moon theory? How could the moon be so incredibly resonant without
being a hollow bell after all? Well, let's go back to the xylophone
for a minute. The keys of the instrument are made from simple wooden blocks
that are sized to create a specific pitch. But not every type of wood
is suitable to make a xylophone block. Only hardwood varieties that have been thoroughly
dried out can resonate freely enough to be musical. A soggy, softwood is
going to deaden the vibration before it can ring out. If we think about
the surface of the Earth, it's covered in a lot of water. The
more moisture there is present in the surface materials, the less dense their structure
will be. This damp material works like a sponge to absorb and deaden the
vibrations created by an earthquake. It helps to keep the most severe effect localized
to one area. If we think about the surface of the Moon, it
is totally dry. No moisture exists on the Moon. The entire crust of
the Moon is one continuous, cold, and rigid structure. So even if
a moonquake is less intense than an earthquake, there is nothing to deaden the
vibrations on the Moon. They just continue to move back and forth through the
body of the Moon like a ringing bell until the solid stone eventually stops them.
Okay, so the Moon might not be hollow, but it definitely is
unusual, at least by Earth's standards, and this, unfortunately, is something
that we are going to have to be considered of as we move forward with
the eventual settlement and colonization of the Moon. We know that mining and long
term construction on the Moon is an eventual goal of Mass's Artemis program. We
know that China and their allies also want to establish a permanent base on the
Moon. What we don't know is how this massive increase in surface activity is
going to affect the environment of the Moon. If one relatively small lunar lander
scraping back and forth over a few millimeters of surface as it expands and contracts
with the temperature, can create enough vibration through the Moon's surface to be detectable
with a primitive seismograph, then what do we think that a mining operation is
going to do. Or the frequent landing and takeoff of a giant vehicle like
the SpaceX starship. We are going to have to accept the fact that a
colonized Moon will end up going into a constant state of seismic activity, a
permanent moonquake, in addition to all of the naturally occurring moonquakes. So just
one of the many obstacles that humanity will need to overcome on a very long
and difficult journey to becoming a multiplanetary civilization.