Mercedes Mullins
The Apollo 11 mission to the moon in 1969 was a historic event, but it also came with some nervy moments. As the lunar module descended to the moon's surface, a fuel light blinked on, indicating that the tank was nearly dry. The astronauts had to act quickly to ensure a safe landing. While the Apollo missions are known for their successful moon landings, the spent spacecraft also served another purpose. NASA directed these modules for controlled crashes on the Moon, causing moonquakes and vibrations that scientists studied to better understand the Moon's internal structure. These impacts created a strange phenomenon, with the Moon ringing like a bell for nearly an hour, providing valuable insights into its composition.
| Characteristics | Values |
|---|---|
| Did the moon ring when Apollo dropped its fuel tank? | No, but the moon rang like a bell for nearly an hour when one of the stages from Apollo 12 was deliberately crashed into the moon. |
| Reason | The vibrations from the impact of the crash caused the moon to ring like a bell. |
| Apollo 11 | The Apollo 11 lunar module was on its historic descent to the moon on 20 July 1969 when a fuel light blinked on. |
| Apollo 13 | Something similar happened on Apollo 13. The S-IVB impacted the Moon 85 miles from Apollo 12's ALSEP. |
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What You'll Learn
Apollo 11's fuel tank nearly empty before landing
The Apollo 11 mission was a historic feat, but it was also a close call. As the lunar module descended towards the Moon's surface on July 20, 1969, a fuel light blinked on, indicating that the Eagle's tank was almost empty. The astronauts, Buzz Aldrin and Neil Armstrong, had less than 60 seconds to make it to the lunar surface, and they were still 100 feet (30 metres) above the ground.
In a nail-biting interview, Aldrin recalled his thoughts at that momentous juncture: "OK. One hundred feet. Sixty seconds. We'd better ease down." Aldrin kept his composure, choosing not to urge Armstrong to hurry. The Eagle dropped 90 feet in the next 30 seconds, leaving the crew with a further 30 seconds of fuel to navigate the final 10 feet to the Moon's surface.
It was a precarious situation, and the landing succeeded by the finest of margins. Aldrin estimated that they had about 15 seconds of fuel left when they touched down. The astronauts' skill and composure under pressure were instrumental in ensuring the mission's success.
The Apollo 11 mission's fuel situation was a well-managed near miss. Had they completely run out of fuel, the astronauts would have aborted the landing and returned to the command module using the fuel allocated for that purpose. The modular design of the Apollo missions allowed for such contingencies.
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Apollo 12 caused the moon to ring like a bell
The Apollo 12 mission caused the moon to ring like a bell. One of the stages from the Apollo 12 mission was deliberately crashed into the moon, causing it to vibrate for nearly an hour. This phenomenon, known as "moonquakes," provided scientists with valuable insights into the Moon's internal structure and composition.
The Apollo lunar modules played a crucial role in these seismic experiments. After fulfilling their primary purpose of landing astronauts on the lunar surface, NASA directed these modules towards controlled crashes on the Moon. The impact of these crashes generated vibrations that reverberated through the Moon's core.
The vibrations from the Apollo 12 impact were particularly intriguing. They lasted far longer than expected, exceeding the duration of similar vibrations on Earth. This unusual behavior suggested that the Moon's dry, cool, and rigid composition allowed vibrations to propagate without dampening, much like how sound waves travel through a solid rock.
The "ringing bell" effect is a result of shockwaves reverberating through the Moon's solid interior. While the Moon's near vacuum prevents the transmission of sound, the seismic waves detected by instruments provided valuable data for scientists to decipher the Moon's composition and underlying structure.
The Apollo 13 mission also contributed to our understanding of moonquakes. The impact of its S-IVB stage on the Moon resulted in shockwaves 30 times greater and four times longer than those from Apollo 12's LM impact. These impacts and their subsequent vibrations offered further insights into the unique characteristics of the Moon's geology.
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Apollo 13 impacted the moon, resulting in shockwaves
The Apollo 13 mission resulted in an unexpected discovery about the Moon's composition. The S-IVB third stage rocket impacted the Moon about 85 miles from Apollo 12's ALSEP, with a force of 11.5 tons of TNT. This impact caused a seismic shockwave that peaked after seven minutes, with reverberations lasting far longer than scientists expected—longer than any equivalent vibrations on Earth. The vibrations from the impact of the Apollo 13 rocket stage on the Moon's surface caused it to ring like a bell, with shockwaves 30 times greater and four times longer than those from Apollo 12's LM impact.
This phenomenon is due to the Moon's dry, cool, and rigid composition, lacking the moisture present on Earth that would otherwise absorb the energy of such waves. The vibrations caused by the impact of Apollo 13's rocket stage travelled through the Moon's solid rock, with no atmosphere to dampen or impede their propagation. This resulted in a unique and prolonged ringing effect, akin to the sustained vibrations of a bell after it has been struck.
The Apollo 13 impact provided valuable data for scientists studying the Moon's internal structure. By analysing the moonquakes generated by the impact, researchers could gain insights into the Moon's composition and underlying geology. These seismic experiments were a crucial part of the Apollo missions, with remote seismic stations deployed as part of the Apollo Lunar Surface Experiment Packages on Apollos 11, 12, 14, 15, 16, and 17.
The unique vibrational properties of the Moon, highlighted by the Apollo 13 impact, offer a fascinating insight into the differences between Earth and its natural satellite. While the Moon's lack of atmosphere and distinct composition contribute to its ability to ring like a bell, the frequency of these vibrations is likely far below the range of human hearing. This highlights the complex and multi-faceted nature of lunar science and the ongoing quest to unravel the mysteries of our celestial neighbour.
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Lunar module designed for two men to land on the moon
The Apollo Lunar Module (LM) was a two-stage vehicle designed to land two astronauts on the Moon and return them safely to the Command Module orbiting above. It was the first crewed spacecraft to operate exclusively in the airless vacuum of space and remains the only crewed vehicle to land anywhere beyond Earth.
The LM was designed to support two astronauts for 45 hours, but it could actually support three astronauts for 90 hours. It had four landing legs with round footpads, which held the bottom of the stage 1.5 m above the surface. The distance between the ends of the footpads on opposite landing legs was 9.4 m. One of the legs had a small astronaut egress platform and ladder.
The LM's descent stage was an octagonal prism 4.2 meters across and 1.7 m thick. It contained the landing rocket, two tanks of aerozine 50 fuel, two tanks of nitrogen tetroxide oxidizer, water, oxygen, helium, and storage space for lunar equipment and experiments. The ascent stage was launched from the Moon at the end of lunar surface operations and returned the astronauts to the Command Module. It was an irregularly shaped unit approximately 2.8 m high and 4.0 by 4.3 meters in width, mounted on top of the descent stage. The ascent stage housed the astronauts in a pressurized crew compartment with a volume of 6.65 cubic meters, which functioned as the base of operations for lunar operations.
The Lunar Module was developed by the Grumman Aerospace Corporation (now the Northrop Grumman Corporation) and overseen by Grumman. During the life of the Apollo program, 13 Lunar Modules were built, six of which made lunar landings. The LM was never flight tested because the lunar environment couldn’t be replicated.
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The moon's internal structure revealed by vibrations
The Moon is a differentiated body, composed of distinct layers: a crust, mantle, and core. The core is dense and metallic, composed mainly of iron, with some nickel and a small amount of sulfur. It has a radius of about 350 km or less, which is relatively small compared to other terrestrial bodies. Above the core is the mantle, composed predominantly of the minerals olivine, orthopyroxene, and clinopyroxene, and is more iron-rich than the Earth's mantle. The lunar mantle is about 1350 km thick, much deeper than the crust, which has an average thickness of 50 km. The crust is composed primarily of oxygen, silicon, magnesium, iron, calcium, and aluminium, with minor elements such as titanium and uranium.
Seismometers left on the Moon's surface by Apollo astronauts have revealed the occurrence of moonquakes, which are deep within the Moon's mantle, about 1,000 km below the surface. These moonquakes are caused by tidal stresses due to the Moon's eccentric orbit around the Earth. Shallow moonquakes have also been detected, but they are less frequent and unrelated to lunar tides. By studying these moonquakes and the Moon's internal structure, scientists aim to understand the ringing sound that the Moon produces, a phenomenon that has long fascinated researchers.
One theory attributes the Moon's ringing sound to vibrations travelling through its internal structure due to meteoroid impacts. These vibrations resonate throughout the Moon's structure and can be detected and measured by sensors placed on the lunar surface. By analyzing the patterns and frequencies of these vibrations, scientists can gain insights into the Moon's composition and structure. Additionally, the Moon's weaker gravity compared to Earth's enables it to vibrate more easily, generating sound waves that contribute to the ringing sound.
The Moon's lack of atmosphere may also play a role in the reverberation of sound waves, as they are not absorbed and dispersed as they are on Earth. The study of lunar resonance, which involves examining the Moon's internal structure, low gravity, and lack of atmosphere, is helping scientists unlock the mystery behind the Moon's ringing sound.
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Frequently asked questions
No, the moon did not ring when Apollo 11 dropped its fuel tank. However, the Eagle landed with only 15 seconds of fuel left, a feat that succeeded by the finest of margins.
Yes, NASA deliberately crashed the Apollo 12 module into the moon, causing it to ring like a bell for nearly an hour.
NASA used the spent spacecraft for science experiments. The crashes caused moonquakes, and scientists measured the vibrations moving through the moon to better understand its internal structure.
The vibrations did not produce a sound since there is practically no atmosphere on the moon for sound to travel. The "ringing like a bell" refers to the shock waves reverberating through the moon's solid rock body.
Scientists studied the overtones and higher-frequency vibrations to learn about the moon's internal structure. They discovered that the moon is dry, cool, and rigid, and that its composition is unlike that of Earth, where damp materials absorb the energy of waves and deaden their effects.
