Sounds on the Moon
Earth’s atmosphere provides a good medium for sound waves to propagate. The Moon’s atmosphere is so tenuous that it is generally thought of as a near-vacuum. So no sound can ever be heard on the Moon – right? Well, not exactly. Moon Zoo forum regular Tom128 undertook a little research project recently to investigate that very question. He started looking into the Apollo archives initially for evidence of sounds during the collection of rock samples and found that hammering can be heard on some of the audio clips from the Apollo 12 mission. No hammering was heard at Halo crater though there was some discussion about how to best use the hammer (using the flat side was more successful because of the limitations of movement afforded by the spacesuits) and fragments of the hammer coating broke off and caused some concern. However, to Bean and Conrad’s surprise they did hear hammering at Sharp crater.
Over to Tom128:
It is generally understood that there is no sound on the Moon because its atmosphere is negligible. But what if an atmosphere is brought to the Moon? That was the case with the Apollo astronauts and their space suits; a self-contained atmosphere which allowed for voice communications. What is intriguing is that the sound of Alan Bean hammering on the core sample tube, which is external to his space suit, can also be heard. The reason is that the sound vibrations were conducted into his suit with each blow of the hammer, moving on up to his helmet similar, in a way, to sound vibrations on an old style Gramophone. The microphone in Alan Bean’s helmet picked up the sound and radioed it back to Mission Control on Earth.
Here is a short audio excerpt of Apollo 12 astronaut Alan Bean driving in the core sample tube at Sharp crater. It is from the Bernie Scrivener Apollo 12 audio tape recording. You can hear several short blows on the audio recording as he is hammering on the tube with the flat side of his hammer. Below is the part of the transcript of the audio recording from the Apollo 12 Surface Journal at Sharp Crater: (Here’s a video version that Tom128 put together.)
”133:03:08 Bean: Okay. In this kind of pack you could almost drive it without a hammer; but, if you’ll hand it (the hammer) to me, I’ll…
133:03:11 Conrad: Yeah, just a second.
133:03:14 Bean: I want to take a couple more shots (that is, photos) of this before we leave. (Pause) There. (Pause) Okay.
133:03:28 Conrad: Get it all the way in (and) I’ll get the pictures.
133:03:30 Bean: All right. (The sound of hammering is audible) It’s driving in real easy, Houston.
[Bean – “I didn’t know that (they could hear the hammering in Houston)!”]
[Conrad – “That’s neat!”]
[Bean – “Coming through my hand, I guess…”]
[Conrad – “Yeah, it’s coming through your hand and getting into the air in the suit and it’s transmitting all the way (to the microphones).”]
[Bean – “Isn’t that something.”]
[Jones – “Now, you had the Snoopy helmets on over your ears.”]
[Conrad – “Yeah, but the microphones are out here (in front of their lips). I never heard that before, either. You can hear you hammering just loud and clear.”]
[Bean – “I would have said it wasn’t possible.”]
As Tom128 says, Pete Conrad and Alan Bean acted as “biological sensors” or transmitters. In an e-mail exchange with Andrew Chaikin, space journalist and author of many Apollo books, about the hammer sound Tom128 received the following reply (reproduced with Andrew’s permission):
“I had heard this during my research for A Man on the Moon back in ’85, and was impressed by the fact that the sound transmitted so well through the hammer, into Alan’s suit, and up to the microphone on his Snoopy cap.”
Alerted by a discussion on the Bad Astronomy and Universe Today forum Tom128 found a further example in the Apollo 17 Lunar Surface Journal at Geology Station 2. Here is the MPEG video link of the hammering sound. You can hear 5 or 6 hammer strikes. The mission debrief concluded that Gene Cernan’s space suit was acting like a drum, similar to the Gramophone analogy.
And here’s another video Tom 128 put together of the Apollo 16 Lunar Module Orion lifting off from the Lunar surface. Listen carefully for the sound of Orion’s ascent engine ignition as the vibrations were conducted into the pressurized cabin of the Lunar Module to the onboard microphones and then relayed back to Houston. There are likely to be many more examples of sounds in the Apollo archives.
As Tom128 rightly says: “Turn up your volume and enjoy the sights and sounds once again. Wonderful!”
Jules is a volunteer moderator for the Moon Zoo forum
But Moon Zoo forum regular Tom128 deserves all the credit for this – thanks Tom!