Last week, NASA reported that a micrometeoroid struck its Lunar Reconnaissance Orbiter in October 2014. NASA noted that the impact didn’t damage the orbiter, but made for a “fascinating example” of how the data from the spacecraft can be used in unexpected ways, including what that impact sounds like.
Scientists discovered the incident when they received a distorted image from the spacecraft on October 13th, 2014, which scientists determined was caused by a sudden movement from one of the orbiter’s three cameras. After ruling out normal equipment activity such as movement from the solar panels or antenna, they concluded that it must have been from a meteoroid.
The LRO creates its images one line at a time using the Lunar Reconnaissance Orbiter Camera (LROC), a system of three cameras — Two Narrow Angle Cameras (NACs), which take high resolution black-and-white images, and a Wide Angle Camera (WAC), which takes a slightly lower-resolution images that returns images of the composition and color of the surface. NASA determined that the meteoroid struck the left NAC. The impact doesn’t appear to have damaged the orbiter, which has continued to capture some stunning images.
When the LRO launched, scientists developed a computer model to test that the cameras wouldn’t be damaged by the vibrations during the vehicle’s launch in 2009. Using the same model, project scientists were able to determine that the meteoroid was really small: “about half the size of a pinhead (0.8 millimeter), assuming a velocity of about 4.3 miles (7 kilometers) per second and a density of an ordinary chondrite meteorite (2.7 grams/cm3),” traveling much faster than a bullet.
“In this case, LROC did not dodge a speeding bullet,” says Mark Robinson, professor and principal investigator of LROC at Arizona State University’s School of Earth and Space Exploration, “but rather survived a speeding bullet!”
A planetary scientist named Alex Parker took the data a step further: he took the information from the raw images and correlated “the image offsets line-by-line, and [did] a dead-reckoning reconstruction of camera motion.” From there, he was able to reconstruct the sound that the impact would have made, posting it in a short video:
Here's a first-pass audio reconstruction of Lunar Reconnaissance Orbiter micrometeoroid strike, estimated from image oscillation.— Alex Parker (@Alex_Parker) May 26, 2017
What does a micrometeoroid sound like when it strikes a spacecraft? *Plonk*!