1782: "Why Sound Would Break Apart on Mars"

0:00Imagine standing on Mars while someone talks to you from a hundred meters away. Their voice would have to travel through an atmosphere with less than one percent of Earth's surface pressure. And much of what they said, it would be very difficult to hear. As Perseverance Rover gave scientists a way to investigate how sound behaves in that thin air. After landing February 2021, its microphones recorded Martian winds, mechanical noises, and the sharp sounds produced when it's laser struck nearby rocks. Those recordings confirmed that sound doesn't travel at a single speed on Mars. Lower frequency sounds move at approximately 240 meters per second or 787 feet per second. Higher frequency sounds travel closer to 250 meters per second, 820 feet per second.

1:05The difference comes from carbon dioxide, which makes up most of the Martian atmosphere. Sound travels through gas as pressure waves. The dioxide molecules can absorb some of that energy through their internal vibrations, but the process takes time. At higher frequencies, those vibrations can't keep up with the changing pressure, and those sounds travel faster. Over 100 meters, 328 feet, the higher frequencies would arrive 17 milliseconds ahead of the lower tones. Mars' atmosphere also absorbs higher frequencies more strongly, causing them to fade rapidly with distance. So a distant human voice would become much quieter with its higher tones fading more quickly. The frequencies that survived would travel at slightly different speeds, changing the sound before it reached a listener. Perseverance's microphone gave scientists direct measurements of an effect that had been

2:07predicted from the properties of the Martian atmosphere and on Mars, even the frequencies with the single sound don't necessarily travel together. These are interesting things with JC.