1 00:00:00,120 --> 00:00:05,000 What is a moonquake? Earth's Moon might appear to be dead, calm and 2 00:00:05,120 --> 00:00:09,599 still on the outside, but below the surface, the Moon is an active, 3 00:00:09,880 --> 00:00:14,839 vibrating body. We know this because humans have caused moonquakes ourselves with the 4 00:00:14,880 --> 00:00:20,879 Apollo missions, and the remains of that technology are still causing tremors on the 5 00:00:20,920 --> 00:00:26,559 Moon as we speak. So today we are going to investigate the truth behind 6 00:00:26,559 --> 00:00:32,679 the mysterious moonquake. This is the space race. On November nineteenth, nineteen 7 00:00:32,759 --> 00:00:37,000 sixty nine, the Apollo twelve mission, commanded by Pede Conrad and albeen, 8 00:00:37,240 --> 00:00:41,640 landed on the surface of the Moon in a region known as the Ocean of 9 00:00:41,840 --> 00:00:46,280 Storms. Part of their mission was to deploy a payload known as the Apollo 10 00:00:46,359 --> 00:00:52,719 Lunar Surface Experiment Package, a collection of scientific instruments that included a remote seismic 11 00:00:52,799 --> 00:00:57,679 monitoring station, the kind of device that we would typically use to detect an 12 00:00:57,719 --> 00:01:03,479 earthquake. After complete eating their moonwalk and returning to the command module, Apollo 13 00:01:03,560 --> 00:01:07,200 twelve released their lunar ascent stage on a trajectory back to the Moon's surface. 14 00:01:07,640 --> 00:01:14,359 They purposefully crashed the vehicle into the Moon. It impacted the surface forty miles 15 00:01:14,400 --> 00:01:18,359 away from the landing site with the force of about one ton of TNT. 16 00:01:19,120 --> 00:01:23,480 The seismic monitoring station was then able to measure the resulting shockwave from that impact. 17 00:01:23,840 --> 00:01:27,280 It took eight minutes for the moonquake to build up and reach its peak, 18 00:01:27,519 --> 00:01:33,480 and then another hour for the tremor to fully dissipate. A similar event 19 00:01:33,560 --> 00:01:37,719 happened on Apollo thirteen. They never landed on the Moon due to a technical 20 00:01:37,719 --> 00:01:42,560 failure en route, but one thing that Apollo thirteen did accomplish was generating a 21 00:01:42,840 --> 00:01:46,959 massive moonquake. As part of their mission profile, the third stage of the 22 00:01:46,959 --> 00:01:51,079 Saturn five rocket, known as the S four B, would be deployed on 23 00:01:51,159 --> 00:01:55,480 a crash course for the Moon. The S four B was a hydrogen propulsion 24 00:01:55,519 --> 00:01:59,959 stage that consisted of two large fuel tanks and a J two rocket, an 25 00:02:00,079 --> 00:02:04,879 engine much larger and heavier than the lunar ascent vehicle, so when this thing 26 00:02:04,959 --> 00:02:07,639 hit the Moon, it generated the force of eleven and a half tons of 27 00:02:07,680 --> 00:02:15,479 TNT, creating shockwaves thirty times greater and lasting four times longer than the Apollo 28 00:02:15,479 --> 00:02:20,479 twelve impact. In both of these experiments, the vibrations recorded by the remote 29 00:02:20,520 --> 00:02:27,759 seismic monitoring station lasted much longer than scientists had expected, far longer than any 30 00:02:27,840 --> 00:02:32,719 equivalent vibrations on the Earth, and this observation led NASA officials to comment that 31 00:02:32,759 --> 00:02:38,639 the moon quote rang like a bell. Those particular words would go on to 32 00:02:38,719 --> 00:02:42,840 birth one of the more fringe conspiracy theories out there, known as the hollow 33 00:02:42,879 --> 00:02:46,599 Moon. The idea is that since the moon rang like a bell, and 34 00:02:46,680 --> 00:02:51,520 bells are hollow, then the moon must therefore also be hollow. The generally 35 00:02:51,560 --> 00:02:54,919 agreed upon explanation for the hollow moon is that we are actually being orbited by 36 00:02:54,960 --> 00:03:00,360 an ancient alien spaceship. So, first of all, an object does not 37 00:03:00,439 --> 00:03:04,000 need to be hollow in order to vibrate or even to ring. Case in 38 00:03:04,039 --> 00:03:07,800 point, the glockenspiel, which uses solid metal bars to create sustaining bell like 39 00:03:07,879 --> 00:03:13,199 tones, or even its more primitive sister instrument, the xylophone, which creates 40 00:03:13,280 --> 00:03:19,080 ringing musical notes from blocks of wood. And second off, the moon isn't 41 00:03:19,159 --> 00:03:22,360 hollow anyway. We'll get to the real reason that the moon rings like a 42 00:03:22,400 --> 00:03:25,159 bell in a little bit, but first let's talk about some natural tremors on 43 00:03:25,199 --> 00:03:30,879 the Moon that are not created by humans crashing stuff into it. The Apollo 44 00:03:30,960 --> 00:03:35,240 Lunar Surface Experiment packages that were deployed on the Moon between nineteen sixty nine and 45 00:03:35,319 --> 00:03:40,120 nineteen seventy two continued to operate and monitor activity for several years until they were 46 00:03:40,159 --> 00:03:46,120 remotely shut down in nineteen seventy seven, and in that time NASA was able 47 00:03:46,120 --> 00:03:50,800 to record a large amount of data about the natural seismic activity of the Moon. 48 00:03:51,360 --> 00:03:55,280 This is fascinating information to have because we know that earthquakes are caused by 49 00:03:55,280 --> 00:03:59,759 the movement of tectonic plates that make up the surface of the Earth, but 50 00:03:59,800 --> 00:04:04,879 the the Moon does not have tectonic plates. The surface is all one continuous 51 00:04:04,960 --> 00:04:11,719 shell. So what causes moonquakes well. One known variety of lunar activity is 52 00:04:11,759 --> 00:04:15,759 the emergent thermal quake. This is the easiest one to understand because we know 53 00:04:15,839 --> 00:04:19,680 that each half of the Moon will experience fourteen days of continuous sunlight followed by 54 00:04:19,720 --> 00:04:25,040 fourteen days of continuous darkness, and since the Moon has no atmosphere to insulate 55 00:04:25,079 --> 00:04:29,800 the surface and maintain a consistent temperature, the surface can range from positive two 56 00:04:29,920 --> 00:04:33,360 hundred and fifty degrees fahrenheit during the daylight periods to negative two hundred and eight 57 00:04:33,399 --> 00:04:39,040 fahrenheit during the night time periods, and just like any other solid material that 58 00:04:39,160 --> 00:04:43,839 is exposed to these drastic temperature swings, the surface of the Moon will actually 59 00:04:43,839 --> 00:04:48,720 expand and contract as it moves from day to night. This movement causes significant 60 00:04:48,759 --> 00:04:54,920 vibrations to travel through the surface of the Moon. Another common seismic activity on 61 00:04:54,959 --> 00:04:59,480 the Moon is the tidal moonquake. On Earth, we experience the physical effect 62 00:04:59,480 --> 00:05:02,920 of the Moon's gravity in the rising and falling of the ocean tides. By 63 00:05:02,920 --> 00:05:06,480 the same measure, the gravity of the Earth will also have an effect on 64 00:05:06,519 --> 00:05:11,879 the surface of the Moon, pulling and stretching the surface material. This will 65 00:05:11,920 --> 00:05:16,279 also cause some residual seismic activity. And then, of course, the Moon 66 00:05:16,399 --> 00:05:21,920 also experiences a pretty high frequency of natural impacts. In addition to humans throwing 67 00:05:23,000 --> 00:05:27,720 chunks of spaceships at it, the Moon gets hit by asteroids of varying sizes 68 00:05:28,199 --> 00:05:32,480 all the way from micrometeorites to metal boulders, each one leaving behind a seismic 69 00:05:32,519 --> 00:05:39,600 footprint. We know all of this information because of the scientific instruments left behind 70 00:05:39,639 --> 00:05:44,319 by Apollo Missions twelve and beyond. With Apollo seventeen, the final crude lunar 71 00:05:44,360 --> 00:05:49,759 mission carrying the most advanced instruments on a payload named the Lunar Seismic Profiling Experiment. 72 00:05:50,199 --> 00:05:54,439 At the time, this was cutting edge research, but it was also 73 00:05:54,560 --> 00:05:58,720 the nineteen seventies, so the communication between the instruments on the Moon and the 74 00:05:58,759 --> 00:06:03,519 receivers on Earth was relatively low bandwidth by modern standards. However, in twenty 75 00:06:03,560 --> 00:06:09,680 twenty three, researchers at the California Institute of Technology found a way to extract 76 00:06:09,759 --> 00:06:15,680 more detail from the Lunar Seismic Profiling Experiment data. They used artificial intelligence and 77 00:06:15,879 --> 00:06:20,879 machine learning algorithms to fill in the missing pieces of the seismic recordings. This 78 00:06:21,120 --> 00:06:28,800 AI upscaling gave the researchers enough detail to begin separating naturally occurring moonquakes from external 79 00:06:28,800 --> 00:06:34,319 influences. One of the more amazing discoveries was that the Apollo seventeen lunar lander, 80 00:06:34,519 --> 00:06:40,360 which was left behind only around one hundred meters from the seismic measuring equipment, 81 00:06:40,839 --> 00:06:46,959 is actually causing moonquakes itself. So what's been happening is that the lander 82 00:06:46,040 --> 00:06:50,160 has been traveling through the lunar day and night cycle for years, and as 83 00:06:50,199 --> 00:06:55,240 the temperatures swing from one extreme to the other, the metal structure has been 84 00:06:55,360 --> 00:07:00,120 expanding and contracting. That movement of the metal over the ground was enough to 85 00:07:00,160 --> 00:07:04,879 cause vibrations that traveled through the surface and reached the monitoring equipment. Now, 86 00:07:04,959 --> 00:07:09,680 this is an incredibly subtle tremor. If you were standing on the Moon next 87 00:07:09,720 --> 00:07:13,720 to the lander, you wouldn't actively notice the vibration. But the fact that 88 00:07:13,759 --> 00:07:18,519 these micro moonquakes were present enough to be extracted from fifty year old recording data 89 00:07:18,879 --> 00:07:25,879 just reinforces the fact that the Moon's surface is a very strong conductor of vibrations, 90 00:07:26,000 --> 00:07:30,480 even very tiny ones. So does this new discovery lend any more credibility 91 00:07:30,560 --> 00:07:34,639 to the hollow moon theory? How could the moon be so incredibly resonant without 92 00:07:34,680 --> 00:07:39,680 being a hollow bell after all? Well, let's go back to the xylophone 93 00:07:39,680 --> 00:07:44,160 for a minute. The keys of the instrument are made from simple wooden blocks 94 00:07:44,160 --> 00:07:47,279 that are sized to create a specific pitch. But not every type of wood 95 00:07:47,360 --> 00:07:53,600 is suitable to make a xylophone block. Only hardwood varieties that have been thoroughly 96 00:07:53,680 --> 00:07:58,439 dried out can resonate freely enough to be musical. A soggy, softwood is 97 00:07:58,480 --> 00:08:03,399 going to deaden the vibration before it can ring out. If we think about 98 00:08:03,439 --> 00:08:05,959 the surface of the Earth, it's covered in a lot of water. The 99 00:08:07,000 --> 00:08:11,199 more moisture there is present in the surface materials, the less dense their structure 100 00:08:11,199 --> 00:08:15,759 will be. This damp material works like a sponge to absorb and deaden the 101 00:08:15,839 --> 00:08:20,639 vibrations created by an earthquake. It helps to keep the most severe effect localized 102 00:08:20,759 --> 00:08:24,560 to one area. If we think about the surface of the Moon, it 103 00:08:24,720 --> 00:08:30,639 is totally dry. No moisture exists on the Moon. The entire crust of 104 00:08:30,680 --> 00:08:35,480 the Moon is one continuous, cold, and rigid structure. So even if 105 00:08:35,519 --> 00:08:39,879 a moonquake is less intense than an earthquake, there is nothing to deaden the 106 00:08:39,960 --> 00:08:43,080 vibrations on the Moon. They just continue to move back and forth through the 107 00:08:43,120 --> 00:08:48,519 body of the Moon like a ringing bell until the solid stone eventually stops them. 108 00:08:50,039 --> 00:08:52,840 Okay, so the Moon might not be hollow, but it definitely is 109 00:08:54,120 --> 00:08:58,519 unusual, at least by Earth's standards, and this, unfortunately, is something 110 00:08:58,519 --> 00:09:01,759 that we are going to have to be considered of as we move forward with 111 00:09:01,799 --> 00:09:07,200 the eventual settlement and colonization of the Moon. We know that mining and long 112 00:09:07,279 --> 00:09:11,200 term construction on the Moon is an eventual goal of Mass's Artemis program. We 113 00:09:11,240 --> 00:09:16,120 know that China and their allies also want to establish a permanent base on the 114 00:09:16,159 --> 00:09:20,120 Moon. What we don't know is how this massive increase in surface activity is 115 00:09:20,159 --> 00:09:26,519 going to affect the environment of the Moon. If one relatively small lunar lander 116 00:09:26,600 --> 00:09:31,600 scraping back and forth over a few millimeters of surface as it expands and contracts 117 00:09:31,799 --> 00:09:35,279 with the temperature, can create enough vibration through the Moon's surface to be detectable 118 00:09:35,320 --> 00:09:41,200 with a primitive seismograph, then what do we think that a mining operation is 119 00:09:41,240 --> 00:09:45,759 going to do. Or the frequent landing and takeoff of a giant vehicle like 120 00:09:45,759 --> 00:09:50,080 the SpaceX starship. We are going to have to accept the fact that a 121 00:09:50,159 --> 00:09:54,080 colonized Moon will end up going into a constant state of seismic activity, a 122 00:09:54,480 --> 00:10:01,240 permanent moonquake, in addition to all of the naturally occurring moonquakes. So just 123 00:10:01,320 --> 00:10:05,559 one of the many obstacles that humanity will need to overcome on a very long 124 00:10:05,639 --> 00:10:09,600 and difficult journey to becoming a multiplanetary civilization.