What comet dust and asteroids do you think it finds towards our fair planet and falls to earth every year?
Go ahead, I guess. At the? Ten tons?
New research on micrometeorites (literally microscopic pieces of meteorites, rock particles, and space metals falling to Earth) shows that approximately 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. A less. This equates to the mass of a garbage truck every day.
Oof.
Note that this includes some warnings, but the big picture is that we are affected by many interplanetary detritus all the time.
In addition, these are very small things, less than a millimeter in size and some smaller than the width of a human hair. There is no reason to panic*. It slows from interplanetary speeds to 0 basically in the atmosphere and then goes down to earth. It’s no danger and, in fact, it’s welcome, as it tells us a lot about what’s going on in space.
You might think that most of this material that makes it reach the ground would be in the form of meteorites of decent size, about an inch or more in diameter. However, it turns out that things on the ground are dominated by particles smaller than a millimeter. In this case, the numbers count: there are so many more small particles than large ones that make up the majority of the mass that reaches the ground.
The obvious way to do this study is to collect a sample of micrometeorites on the ground and count them. Of course, nothing is that simple. The number you find is small, so you need to make sure you look for a lot of area. You don’t want it to interfere with the weather (such as washing rain from one place to another, artificially increasing or decreasing the number you find). You don’t want to be close to human activity for the same reason. And it would be useful if you could easily test the terrain over a long but known period of time, so collect as many samples as possible and calculate a fee.
There is one place that fits all these criteria: Antarctica. In addition, the Dome-C area where the Concordia research station is located. It is located about 1,700 kilometers away from the South Pole, at an altitude of 3,200 meters above sea level. It’s almost ideal: it’s not very windy, so the snow settles evenly and the speed is measured well: about 2.7 grams of snow fall per square centimeter there a year (a depth of about cm / year).
For a period of years, the scientists used carefully cleaned equipment to dig several trenches, each more than 2 meters deep, to make sure they reached the snow that fell before the humans built the station. in 1995 and excavated them several hundred meters from the facility’s wind. . They extracted snow from depths ranging from 3 to 8 meters, representing a range of snow time that fell from 1920 to 1980.
The snow melted and the water was 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 major classes: unmelted micrometeorites and cosmic spheres. The first are irregularly shaped pieces that survived the atmospheric entrance unaltered, while the spheres come from pieces that were heated by their hypersonic passage through our air and formed small balls.
In total, they found 1,280 unmelted micrometeorites and 808 cosmic spheres with a size of 30 to 350 microns. Measuring the masses and sizes and using the dates and amounts of snow they found, they find that the speed at which these things fall to the ground is about 3 and 5.6 micrograms per square meter per year. So not much.
But when multiplied by the very large area of the Earth (and extrapolated to a slightly larger size range of 12 to 700 microns), the number of 5,200 tons per year, or 14 tons per day, is obtained. .
I have to admit, when I read that I was surprised. The number I usually see on this material is that it almost hits us 100 tons per day! Is any of these wrong?
In fact, they are compatible. I had a suspicion about it, but to make sure I contacted one of the authors, Jean Duprat, and 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 this material is removed from the meteoroid (heated and exploded by rapid passage through the air), creating “smoke” particles even less than 30 microns. This material tends to stay in the upper atmosphere, creating a layer of meteoroid dust between 90 and 100 km above the ground. Even if it falls to the ground, it would not have been counted in this study because the particles are too small.
Therefore, the total amount of material to hit us per year is much bigger. Interestingly, on average, the largest amount of meteorite material (what you normally think are meteorites) that affects us is much smaller, only about 10 tons a year. Bigger things are much rarer.
Scientists were able to get an idea of where this material came from by looking at its composition and found that about 80% comes from comets and other asteroids. This decants decently with what we know of the dust of the inner solar system, although some questions remain.
The next time you go out on a dark, clear, moonless night, you may be lucky enough to see a bright streak of meteors across the sky. If you do, think for a moment about your destiny. Most will end up being part of our atmosphere, and some small portion will end up reaching you … and now we have a better idea of how much it makes.
*Well, considering the last year or two, I can think of many reasons to panic, but it doesn’t come from astronomical sources.