Does space dust fall on the roof of my house? | Hacker News Reader

Does space dust fall on the roof of my house?

astronomy.stackexchange.com

88 pointsfirebaze49 comments

I don't have a SO account, so I'll post here. I'm having trouble finding the reference, but there's an IKEA in Sweden or Norway that is really far away from industrial pollution, and so gets basically no soot deposited on its perfectly white painted roof. Some intrepid amateur astronomer put 2 + 2 together and realized it's a perfect collection mechanism for space dust. They thoroughly cleaned the roof, then came back a week later and carefully collected the accumulated dust. Looking at it under a microscope confirmed minerals that only form in microgravity environments.

Reminds me of this hunt utilizing an English cathedral: https://www.bbc.com/news/uk-england-kent-66707859

Sahara dust or vulcanic ash has a global reach, and easily reaches Norway.

Yeah. If Sahara dust can travel 8,000km across the Atlantic, it can certainly reach Northern Europe.

It often does, turns snow orange in the Alps.

You can also find it all over your car

>> confirmed minerals that only form in microgravity environments.

So? That doesn't mean they landed on the roof from space. The really tiny stuff can be blown around. It may land on the ground at point A and then be blown onto a roof miles away at point B. This is why we should not use the simple math of a roof's size to determine the rate of material falling from space.

Are you saying these did not originate in space? Isn't that what microgravity means?

They originate in space but do not necessarily come directly from space. Stuff is landing on earth all the time. Much of it then becomes dust/sand and gets moved around. What appears on a roof can be new falls from space, but also space stuff blown from elsewhere. Take a an amount of topsoil or sand. Run a magnet over it and you will find tiny flecks of space rock.

I think finding such stuff is regarded by the author as cool. I don't remember the author saying so, but personally I would think finding it is cool whether it first landed on my neighbor's tree, or went straight to my roof.

But then by this logic isn’t everything made of space dust?

Some of the earth is made from space rocks; early planet forming and moon forming collisions, and later impact crater scale chunks.

Some of the earth is decayed earlier material - radon gas formed here on earth as a daughter product from uranium in granite.

Some of the earth has been created by man on earth in the atomic age ... all those extra elements tacked to the end of the periodic table.

> Some of the earth has been created by man on earth in the atomic age ... all those extra elements tacked to the end of the periodic table.

Don't those decay immediately? They would account for 0% of the earth.

Not all of them .. and some of the material made in nuclear labs is new to earth and not sourced from space but identical to material that is.

There are a lot of isotopes.

A significant amount of carbon-14 was added to the atmosphere from nuclear weapons testing. Since it has a half-life of about 5,000 years, most of it is still around. (The rest of it comes from cosmic rays smashing into atmospheric nitrogen.)

Granted, that's an isotope of a well-known element, not one of the "extra elements tacked to the end of the periodic table". I can point out that [tiny traces of plutonium-244 have been found in the ocean seafloor](https://www.npr.org/2021/05/13/996499035/freshly-made-pluton...). That has a half-life of about 80 million years; it's probably the result of ejecta from a supernova washing over the Earth several million years ago.

Hmmm, so you say if a particle reaches a spot not in straight and shortest line from space then it does not count as a particle originated in space fallen on that spot? Could we have a wiggle room still? Like allowing trade winds carry it some limited km laterally, or such?

Is most dust from soot though?

Dust is composed of things like pollen, dirt, tiny particles of sand, dried plant material, and so forth. There is plenty of outdoor dust that is natural.

I have an incredibly hard time seeing how an outdoor IKEA roof, with tons of shoppers in their cars and delivery trucks and whatnot, is going to be some kind of pristine collection area.

I'm guessing the bottleneck lies in surface area to effectively collect samples rather than the effort to inspect samples and processing them to determine origin. The roof is going to have contaminants, sure, but so is any other collection area. Using a magnet to get iron based particulate then picking out rocks with unique elements is likely a lot cheaper than a purpose built facility to collect micrometeoroid samples with reduced contamination

Yeah it was the fact that they could power wash the roof clean and then use it as a collection mechanism, and it was high enough to be isolated from other sources of dust.

I think this is the same amateur astronomer I was reading about: https://www.cbc.ca/radio/quirks/september-30-2018-1.4312266/...

I have to imagine there were still other particles, but there numbers were lower enough to make the space particles findable.

It’s the difference between finding a needle in a haystack and a needle on a kitchen table with 10 pieces of hay strewn on it.

> Jon Larsen, a Norwegian jazz musician and creator of Project Stardust, was able to show that it is possible to find micrometeorites in more populated areas. In a study published in January 2017 in the journal Geology, he and his colleagues catalogued more than 500 lustrous micrometeorites (and counting), all recovered from rooftops in urban areas.

https://www.sciencefriday.com/articles/up-on-the-roof-a-hand...

He was featured in Werner Herzogs 2020 film, Fireball: Visitors from Darker Worlds.

Thanks!

It was demonstrated to me a a young kid that running a strong magnet through beach sand would collect tons of black magnetite, at least some of which is likely meteorite derived.

If you ever get a chance to play with a magnet fishing magnet, it's fun to see how many straight-up magnetic rocks there are lying around, too. Probably not meteorites of course...

> An article by Phil Plait (The Bad Astronomer) says that each square meter of surface is hit by 1 - 2 micrometeorites per year.

A much cooler way to put this is that if you spend 1 hour per day on average not under a roof, and if we ignore some complications, your expected micrometeorite-strikes-per-lifetime is about 0.5:

    (1/24 of the time outside) * (1.5 per meter squared per year) * (80 years) * (pi * 8 inches * 6 inches) = 0.486 [1]

where the last term here is an approximate cross-sectional area of the human head as viewed from above. (Micrometeorites reach terminal velocity at a very high altitude, so they should be falling almost vertically as they strike the ground, minimizing your cross-sectional area unless you happen to be lying down.)

Someone doing manual labor or other primarily-outdoor work has an expected-micrometeorites-per-lifetime much greater than 1, and therefore is overwhelmingly likely to have space dust in their hair at least once in their life. If you spend 8 hours outside per day (so your workday + some miscellaneous non-work time that covers days you're not working), your expected lifetime impacts is ~4, so your chance of >= 1 impact is 1 - Pois(0; 4) = 1 - e^-4 = about 98%.

A better calculation would account for the fact that Earth's orbital motion makes the relative motion of impacts non-uniform in the same way the front of a moving car is hit by more raindrops than the rear. This means most strikes occur around dawn, because that's the time when you're on the "front" of the Earth as it moves in its orbit.

Early-morning workers, like agricultural, sanitation, or custodial workers, might be out for the peak of impacts nearly every day, while the average reader here who drifts into the office hours after dawn (if at all) and spends most of their outdoor time in the evening might almost entirely miss their opportunity to have a bit of space fall on their head. (I think this is rather poetic: if you want to touch the stars, go pick up trash!)

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[1] https://www.wolframalpha.com/input?i=%281+hour%2F24+hour%29+...

The micro-meteorites.com website appears to be down, but you can see pictures from the book on the Internet Archive here[0]

[0]https://archive.org/details/insearchofstardu0000lars/mode/1u...

The site is back up again...

For anyone interested in an archive link of the meat of this: https://web.archive.org/web/20240414181406/https://micro-met...

I thought everything was space dust, in the final reckoning of things, wasn't it?

Yes, but I think most folks are interested in the recently arrived stuff.

I think you mean star dust

potato, potato :-)

I read about the magnet method when I was young. I always thought that was so cool. It never occurred to me until now that I never tried it!

More likely the roof than your basement, though in the latter case, you'd likely not need me to tell you ...

A prime meteorite and meteoric-dust hunting ground is Antarctica. With an ice cap that's kilometres thick, odds are high that all rocks, and much dust, found on the surface of the snow are meteoric in origin.

2018 story on that: "Hot on the trail of Antarctic meteorites" <https://www.snexplores.org/article/hot-trail-antarctic-meteo...>

And yes, there's a global warming angle on this as well: "Thousands of hidden meteorites could be lost forever as they sink in Antarctic ice, taking their cosmic secrets with them" <https://www.livescience.com/space/meteoroids/thousands-of-hi...> (2024)

Clearly explains the crumbs around be office chair

Probably, but neutrinos definitely pass through your house (and you).

That's horrible! What can we do to defend ourselves against this constant neutrino bombardment?

A lead suit helps.

Of course you'd want it to be something like a light year thick. That may be impractical. Plus there are minor structural problems, such as how to stop it from spontaneously collapsing into a black hole.

Your comment makes me want to re-read the hitchhiker's guide.

As I recall from school, your lead suit would need to be more than 3 lightyears thick to make the chance of a neutrino (that was already heading towards you) going through you fall to 50%.

When I said helps, I didn't say by how much...

I find I can almost always dodge them instead.

Cover a baking tin with transparent film and put it outdoors. Micrometeorites have enough velocity to punch through, but windblown dirt rarely does. Classic grade school experiment.

Really?

Wouldn't that be far more dependent on particle size? Micrometeorites are going to reach terminal velocity fairly quickly, and that's largely going to be based on particle size and density, rather than original velocity.

Sand-grain-sized micrometeorites (or the sand-grain-sized surviving fragments of larger meteors) will have a terminal velocity of on the order of a metre per second or so.

That's enough to punch through thin plastic wrap. But if the pan is sheltered from wind, random dirt in the air won't punch through.

Here's a good video running through one way to do this at home - https://www.youtube.com/watch?v=9q3uNcJh4pc (I really like the ending, it's real science which is rare these days)

There are a heap of better links to micrometeorites stories than this stackexchange. Discussed many times on HN.

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