Perseverance Rover is well on its way to Mars. In fact, it is more than halfway in miles traveled. In 91 days – February 18, 2021 – it begins its descent to the red planet and hits the thin air there at hypersonic speeds and brakes to where a parachute can be used to brake it further and then lowered by a rocket-propelled sky crane to the surface.
Yes, seriously. Remember seven minutes of terror? Literally the same here: Endurance uses the same entry, descent and landing sequence (or EDL) as Curiosity used.
One difference, though, is a specially installed microphone that records it all. It will hear the wind rushing, the cloud crane shooting, and maybe even dust and sand rattling as it stirs down.
But on October 1
And what it heard was the heat-repellent fluid pump humming along:
Now I know: the sound itself is a little overwhelming. But you have to understand what you hear. And why.
March winters are extremely cold. It’s not exactly Florida there even in summer, but in winter it’s cold enough to freeze carbon dioxide straight out of the air. A lot of equipment on the rover does not work well in that kind of cold and needs to be heated.
Fortunately, endurance carries a piece of plutonium with it.
Oh, did not you know that this sucker is nuclear? Yup. Solar panels work on Mars, but the rover has many moving parts that need more power than the sun can supply, so it has what is called a radioisotope thermoelectric generator (or RTG), which uses the decay of plutonium to produce electricity. It is very efficient – it generates 110 watts – and lasts a long time. They have been used successfully on many missions to the outer solar system and were even used by the Apollo missions to the Moon.
It also generates a significant amount of heat (worth 2000 watts, about the same amount of heat 20 people emit just by being alive). So the rover has pipes running through it, filled with coolant (CFC-11 and Galden HT-170, if you will – the chassis and some endurance architecture are the same as for curiosity). They take heat from the RTG and distribute it through the rover where necessary. Moving the liquid requires pumps to move it together, and these pumps have parts that spin quickly, creating the whirrrrrrr that the microphone picked up.
So the somewhat overwhelmingly low, muffled hum you heard? It is actually fast-spinning parts inside a pump designed to move antifreeze through a 1-ton migratory nuclear-powered mobile chemistry lab that will look for signs of really old life in a dried lake bottom on another planet. While it was still in space on the way.
Now does that sound have more influence?
You might be wondering why we can hear anything at all, considering the rover is in space. Sound needs a medium to travel through, a kind of substance, and for us on the surface of the earth it is usually air. But sound can move through water and even solidify, compress and rare the material it passes through. The pumps push liquid and the constant vibration is transmitted through the body of the rover to the microphone. here. Sound.
Oh, by the way, there’s another microphone on the Perseverance designed to listen in on the SuperCam, an instrument placed in the rover’s head that also has a powerful laser that will zap rocks, evaporate them and make them glow briefly. . A spectroscope in the camera then refracts the light into colors that allow scientists to determine what is in the rocks and in what surfaces.
So endurance is actually a 1-tone traveling nuclear-powered laser-eyed mobile chemistry lab.
Finally, after saying all that, did you know that it is possible to make sound move through space? You just need to make sure the space is not completely empty. In nebulae – gas clouds – the gas is incredibly thin, basically a laboratory-grade vacuum with perhaps only a few thousand atoms per second. Cubic centimeters. But when you are a few light years across, do one lot cubic centimeters, which adds a significant amount of gas. It is close enough to sound waves with very low frequency (or long wavelength if you prefer) able to travel through them. These sometimes have visible effects, such as when a black hole has cut huge ripples in ambient gas, or even ripples made in the urplasma that fill the universe shortly after the Big Bang (try dropping the sentence baryon acoustic oscillations into your next conversation).
These are, of course, pretty violent events. I guess if you make it high enough in space, everybody can hear you screaming.
Or, in case of perseverance, silence the hum.