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Most of the meteorites that land on this planet are pretty tiny. And enough of them fall to Earth each day that, theoretically, you could find micrometeorite yourself.

Host: Reid Reimers

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When we think of space rocks falling to Earth, we usually think of meteors blazing dramatically across the sky or dinosaur-killing asteroids, but most of the meteorites that land on this planet are pretty teeny, like smaller than a grain of sand.  They're called micrometeorites and astronomers estimate 60 tons of them or more fall to the Earth every day.  That means they're theoretically everywhere, so you could have a little meteorite for yourself if you wanted.

Fair warning, though, it'll take a bit of work to find it.  Micrometeorites begin as bits of comets and asteroids.  When asteroids collide, loose pebbles and dust are knocked off and comets are composed of rocky debris and dust encased in ice, so as they approach the Sun, the water often sublimates, releasing the dust it once held.  If this space dust survives its trip through Earth's atmosphere, it lands on our planet and the tiny particles are called micrometeorites.

They range in size, but the average is around 200 micrometers, which is tiny, wider than a strand of hair but only barely.  Basically, you need a microscope to see them properly, but they're worth seeing and many of them are beautiful.  They're often metallic or glass-like, though they can be all sorts of shapes, colors, and textures.  Among the most distinctive are cosmic spherules, which are almost perfectly round because they melt and then re-form upon entry into the atmosphere.

Setting aside the gee whiz factor, micrometeorites are also cool because they give us a better sampling of the galaxy and can help us learn different things about it than their larger cousins.  For one thing, there's just more of them to look at, but they also have a different travel experience out there in space than larger rocks do, which means they can sometimes be a more representative sample of where they originally came from and if that's not cool enough for you, one astronomer hypothesized that they could help account for the missing mass in the universe that's usually attributed to dark matter.

Okay, so now you know how truly awesome these little space rocks are and you want one for yourself.  Well, in theory, they're not all that difficult to find.  Really, all you need is a strong magnet, some Ziploc bags, a microscope, and the goop in your rain gutters.  The idea is is that your rain gutters collect all the stuff that lands on your roof and gather it into one convenient location, so you'll want to collect that goop and pick the leaves and stuff out. 

Then, you can use a strong magnet to find any tiny magnetic bits.  Not all space dust is magnetic, but metallic micrometeorites containing nickel and iron are the only ones you'll have a chance of distinguishing from bits of Earth dust and you'll want to place a Ziploc bag over the magnet first so that you can get the stuff that sticks to it off again.  Once you've collected your magnetic dust, you'll want to use a microscope to look for dark, metallic, or glassy semi-spherical objects with weird patterning to them.  Those should be your teeny space rocks, though there's a bit of a catch.

See, there are other things that fit that description, too.  In particular, welding debris, fly ash from furnaces, and industrial dust from coal power plants can masquerade as micrometeorites and it can sometimes be tough to separate those from actual space dust without expensive scientific equipment.  That's why most researchers look for them in remote places, to avoid confusing space dust with Earth dust. 

In fact, until recently, they didn't really think it was possible to find urban micrometeorites, but then, in 2017, a scientist leading an effort called Project Stardust published a paper identifying over 500 of them from rooftops in Oslo, the capital of Norway.  It was the culmination of years of work and he and a team of volunteers had to comb through 300 kilograms of roof goop to find them.  From the 500 micrometeorites they identified, the researchers selected 48 particularly likely suspects to study under an electron microscope.  That closer look allowed them to classify all of them as cosmic sperules.  They also performed chemical analyses to confirm that they actually included the kinds of irons, silicate, and minerals you'd expect in something that's from space and all of them did, demonstrating that you really can find micrometeorites pretty much anywhere if you look hard enough.

One thing that's rather cool is that these micrometeorites tended to be much younger than the ones researchers usually find in Antarctica and other remote places, probably because, well, gutters get cleaned fairly regularly.  They were likely only about 6-50 years old when they were recovered.  This means that they can tell us things about space that we might not learn from micrometeorites we find elsewhere, including stuff about what's happened out there more recently.

For instance, the researchers found that the different types of micrometeorites tended to occur in different amounts in the urban sample than in older samples, which implies that they arrived at Earth at different velocities.  The researchers suggest this could imply changes in the orbits of the clouds of dust that Earth encounters over time.  Based on their findings, the team estimated that roughly two micrometeorites fall on every square meter of roof each year, though they only recovered one thousandth of that in their search.

So yeah, there are probably micrometeorites on your roof or will be somewhat soon, and with some simple tools, you can go space rock hunting right at home.  It's definitely possible you'll find something.  It just might take a while.  Have you ever tried to find a micrometeorite?  If so, let us know how it went in the comments, and if you liked learning about these teeny little meteorites, you might like our episode on three weird kinds of meteorites, so maybe you want to watch that one next and thanks for watching SciShow Space.