How much dust from comets and asteroids do you think makes its way to our fair planet and falls to the ground every year?
Go ahead, guess what. When on? Ten tons?
New research on micrometeorites – literally microscopic pieces of meteorites, particles of rocks and metals from space falling to Earth – shows that about 5,200 tons of this cosmic debris settles on the ground every year. 5.2 million kilos per year, or about 14 tons per day. Bee leastThat is equal to the mass of a garbage truck per day.
Oof.
Mind you, this comes with some caveats, but the big picture here is that we are hit by a lot of interplanetary debris all the time.
This is also very small stuff, less than a millimeter in size and some less than the width of a human hair. There is no need to panicIt slows down from interplanetary speeds to essentially 0 up in the atmosphere and then drifts to the ground. It is not a danger, and in fact is very welcome, because it tells us a lot about what is happening in space.
You might think that the majority of this material reaching the ground would be in the form of decent sized meteorites, an inch or more in diameter. However, it turns out that the stuff on the ground is actually dominated by particles smaller than a millimeter. In this case, numbers count: there are just so many more small particles than large ones that they make up most of the mass that ends up on the ground.
The obvious way to conduct this study is to collect a sample of micrometeorites on the ground and count them. Nothing is so simple, of course. The number you will find is small so you need to make sure to look at many areas. You don’t want the weather to interfere (like washing material from one place to another, artificially increasing or decreasing the number you find). For the same reason, you don’t want to be around human activity. And it would help if you could easily sample the soil over a long but known span of time, collecting as many samples as possible and calculating a rate.
There is one place that meets all those criteria: Antarctica. Additionally, the Dome-C area is where the Concordia Research Station is located. This is about 1,700 kilometers from the South Pole, at an altitude of 3,200 meters above sea level. It’s almost ideal: it doesn’t have much wind, so the snow is deposited evenly and the speed is well measured – about 2.7 grams of snow fall on every square centimeter there per year (a depth of a few inches / year).
For years, scientists used carefully cleaned equipment to dig several trenches, each more than 2 meters deep, to make sure they ended up in the snow that fell before the people built the station in 1995, and put them several hundred meters above the wind. of the facility. . They took the snow from depths ranging from 3 to more than 8 meters, representing a period of snow that fell from 1920 to 1980.
The snow was melted and the water filtered to extract solids to a size of about 30 microns (0.03 mm, slightly smaller than the width of a human hair).
The micrometeorites they found are in two broad classes: unmelted micrometeorites and cosmic spheres. The first are irregularly shaped pieces that survived the atmospheric input unchanged, while the spheres come from pieces that were heated by their hypersonic passage through our air and formed tiny spheres.
In total, they found 1,280 unmelted micrometeorites and 808 cosmic spheres ranging in size from 30 to 350 microns. By measuring the masses and dimensions and using the dates and amounts of snow in which they were found, they found that the rate at which these things fall to the ground is about 3 and 5.6 micrograms per square meter per year. So not much.
But if you multiply by the very large surface area of the Earth (and extrapolate to a slightly wider range of 12-700 microns), they get their number of 5,200 tons per year, or 14 tons per day.
I have to admit, when I read that, I was surprised. The number that I usually see back and forth across this material is that we’re about to get hit by it 100 tons per day! Are any of these wrong?
They are actually compatible. I suspected it, but to make sure I contacted one of the authors, Jean Duprat, he kindly told me how this works (and confirmed my suspicion). Most of the material that enters our atmosphere (called meteoroids) is small, smaller than a grain of sand. Much of that material dissipates from the meteoroid (heats up and is blown away by the rapid passage through air), creating “smoke” particles that are even smaller than 30 microns. This material usually remains in the upper atmosphere, creating a layer of meteoroid dust 90 – 100 km above the ground. Even if it fell to the ground, it would not have been counted in this study because the particles are too small.
So the total amount of material to beat us per year is much higher. Interestingly, on average, the amount of larger meteorite material – what you normally think of as meteorites – that strikes us is much lower, only about 10 tons per year. Bigger stuff is much rarer.
The scientists were able to get a sense of where this material came from by looking at its composition and found that about 80% of it comes from comets and the rest from asteroids. That is quite consistent with what we know about inner solar system dust, although there are still some questions.
The next time you’re on a dark, clear, moonless night, you might be lucky enough to see a bright meteor shoot through the sky. If you do, think about his fate for a moment. Most of them will eventually be part of our atmosphere, and a small portion will eventually come to you … and now we have a better idea of how much of it.
Given the past year or two, I can think of many reasons to panic, but that’s not from astronomical sources.