THE man in the moon is humming a tune, but thankfully the noise won’t drown out sensors on future missions peeking at the lunar interior.
A steady barrage of small meteorite impacts should cause the moon to “ring”, but no seismometers sent to the moon to date have been sensitive enough to hear it. So Philippe Lognonnâ© at the Institute of Earth Physics of Paris and colleagues decided to work out how loud the ring is.
The team estimated the meteoroid population in the solar neighbourhood, and calculated the likely seismic signals the space rocks would create if they struck the moon at a range of sizes and velocities.
To determine how the vibrations from these impacts would be seen by seismometers, the team used data taken by Apollo seismometers four decades ago. These measured the vibrations created by the landings of lunar modules and spent rocket stages.
Since the precise locations and timing of these landings were known, they could be used to gauge how long it would take vibrations caused by meteorite impacts to travel through the moon, and how much the signals might dim.
Their calculations revealed space rocks with masses ranging from a gram to a kilogram do indeed create a hum, but it is subtle. Earth’s hum — created by pounding waves — is more than 1000 times louder.
“This shows that all planets may hum, those with and those without atmosphere,” says Lognonnâ©.