General Factors Associated With Sonic Booms Sonic booms created by vehicles the size and mass of the space shuttle are very distinguishable and two distinct booms are easily heard. Most people on the ground cannot distinguish between the two and they are usually heard as a single sonic boom. They are usually of similar strength and the time interval between the two as they reach the ground is primarily dependent on the size of the aircraft and its altitude. It is the rate of change, the sudden onset of the pressure change, that makes the sonic boom audible.Īll aircraft generate two cones, at the nose and at the tail. The change in air pressure associated with a sonic boom is only a few pounds per square foot - about the same pressure change experienced riding an elevator down two or three floors. The sharp release of pressure, after the buildup by the shock wave, is heard as the sonic boom.
As the cone spreads across the landscape along the flight path, they create a continuous sonic boom along the full width of the cone's base. The shock wave forms a cone of pressurized air molecules which move outward and rearward in all directions and extend to the ground. The bigger and heavier the aircraft, the more air it displaces. As objects travel through the air, the air molecules are pushed aside with great force and this forms a shock wave much like a boat creates a bow wave. You can read the conference paper on the conference website.A sonic boom is the thunder-like noise a person on the ground hears when an aircraft or other type of aerospace vehicle flies overhead faster than the speed of sound or supersonic.Īir reacts like a fluid to supersonic objects. They also plan to compare acoustic temperature readings to readings from other instruments to try to figure out the large fluctuations. The team plans to continue using SuperCam microphone data to observe how things like daily and seasonal variations might affect the speed of sound on Mars. This data can help fill in some of the blanks on Mars' rapidly changing planetary boundary layer. Given that any human astronauts traveling to Mars anytime soon will need to be wearing pressurized spacesuits with comms equipment, or living in pressurized habitat modules, this is unlikely to pose an immediate problem – but it could be a fun concept for science-fiction writers to tinker with.īecause the speed of sound changes due to temperature fluctuations, the team was also able to use the microphone to measure large and rapid temperature changes on the Martian surface that other sensors had not been able to detect. This could lead to what the researchers call a "unique listening experience" on Mars, with higher-pitched sounds arriving sooner to the listener than lower ones. The result of this is that sound travels more than 10 meters per second faster at higher frequencies than it does at low ones.
Chide and his team measured the time between the laser firing and the sound reaching the SuperCam microphone at 2.1 meters altitude, to measure the speed of sound at the surface.Īt frequencies above 240 Hertz, the collision-activated vibrational modes of carbon dioxide molecules do not have enough time to relax, or return to their original state. This came with an excellent benefit, as it turns out. The SuperCam microphone was included to record acoustic pressure fluctuations from the rover's laser-induced breakdown spectroscopy instrument as it ablates rock and soil samples at the Martian surface. Fortunately, Perseverance has something unique: microphones that can allow us to hear the sounds of Mars, and a laser that can trigger a perfectly timed noise. That alone means that sound would propagate differently on the red planet.īut the layer of the atmosphere just above the surface, known as the Planetary Boundary Layer, has added complications: During the day, the warming of the surface generates convective updrafts that create strong turbulence.Ĭonventional instruments for testing surface thermal gradients are highly accurate, but can suffer from various interference effects. Mars' atmosphere is a lot more tenuous than Earth's, around 0.020 kg/m 3, compared to about 1.2 kg/m 3 for Earth.