Meteorites falling on your head

[Johnny L.A.]

I've heard that a good place to find meteorites is in the gutters of your roof. Put a magnet into a plastic bag. Flush your gutters into a bucket. Swish the magnet around the contents of the bucket. Rinse the magnetic meteorites off of the plastic into a separate container.

The idea is that we are dusted with very, very small meteorites all the time. Much of it lands on roofs, and is flushed into the gutters. Obviously this 'space dust' is not something you're going to see on Meteorite Hunters, and there are also ferrous materials of terrestrial origin that gets blown about. ISTM that collecting meteorites from roof gutters is an exercise for people who want to test the theory and want to go to all of the trouble of doing it and then identifying which bits come from space and which ones don't.

I've heard that there's only one person who has been known to have been hit by 'A Meteorite'. (IIRC it came through her roof, bounced off the floor, and hit her in the thigh.) But since a 'meteorite' (as opposed to 'A Meteorite', if you follow) is matter that has come from space and has reached the surface, I think even microscopic 'space dust' counts.

Thus: Do we have meteorites falling on our heads all the time, and we don't know it?

[FoieGrasIsEvil]

Meteorites falling on your head

That doesn't mean my eyes will soon be turning red...

[TriPolar]

A meteorite hit my car once. Broke the side view mirror.

[Chronos]

Thus: Do we have meteorites falling on our heads all the time, and we don't know it?

I'd never thought about it before, but now that you mention it, I don't see how it couldn't be the case, as long as you go outside sometimes without a hat on.

And there was one other case recently claimed to be "person dramatically hit by meteorite", but I don't know if it was ever confirmed.

[ZenBeam]

Originally Posted by Johnny L.A.

I've heard that a good place to find meteorites is in the gutters of your roof. Put a magnet into a plastic bag. Flush your gutters into a bucket. Swish the magnet around the contents of the bucket. Rinse the magnetic meteorites off of the plastic into a separate container.

I've heard this also, but I'm skeptical. If you look at your typical asphalt shingle up close, it's covered with large grains of rock. Also, it isn't just meteorites that are magnetic. Somewhere between all and almost-all of the rock material you get out of your gutter, magnetic or not, is going to have come from the shingles, not from space.

[TriPolar]

Originally Posted by ZenBeam

I've heard this also, but I'm skeptical. If you look at your typical asphalt shingle up close, it's covered with large grains of rock. Also, it isn't just meteorites that are magnetic. Somewhere between all and almost-all of the rock material you get out of your gutter, magnetic or not, is going to have come from the shingles, not from space.

That's probably the case if you use the magnet in the gutter method of finding them. Drag a magnet almost anywhere and you'll pick up bits of magnetite. But there still must be a lot of tiny metorites that hit the planet.

[beowulff]

You need to examine the magnetic material under a microscope. The micro-meteors will be rounded, the terrestrial magnetic material will be angular.

[Michael63129]

According to this site, you can collect micrometeorites just by putting a piece of paper on the ground for a few hours, although I don't know how practical it is, although it would seem to work since most meteorites are very small, dust-particle sized or smaller (small enough so they don't fall fast enough to burn up; you'd never notice if one landed on you; as beowulff said, you'll also need a microscope to see if they are rounded).

[Mangetout]

I did the magnet prospecting thing here.

I harvested a surprisingly large amount of particles (although this was collected from a very large area of roof) - there are a lot of different potential sources of contamination - metal particles from the roofing materials, from local welding spatter, from nearby chimneys - especially if there's a foundry, incinerator or power station close by, etc.

But some of the particles I found were quite conspicuously rounded in shape. Could do with a better microscope though.

[ZenBeam]

From Cecil's column, 10,000 to 100,000 tons of meteorites hit the Earth each year. Let's use near the upper end of the range, for about 10^11 g/year. Assuming that the meteorites have the same density as nickel, 9 gm/cm^3, we get a volume of about 10^10 cm^3 per year. Let's further assume that they don't oxidize at all, and instead completely divide into little 1 mm cubes, about the size I typically see in my gutter. Then we get about 10^13 pieces per year.

The Earth's surface is about 5 * 10^8 km^2, or about 5 * 10^14 m^2. That means we'd expect one 1 mm^3 piece per year for each 50 square meters of area. A typical roof on a house is maybe about 150 square meters (1600 square feet). So you might expect three tiny pieces of meteorite landing on you roof each year. I suspect most of the mass of meteorites doesn't end up as little 1 mm cubes, but rather gets vaporized or oxidized, so the number would be even less.

Almost all of the grains you see in your gutter did not come from space, and you'd have to look at all of them to maybe find a single example. There might be more individual pieces landing on your root if the bits are smaller, but those are even more likely to just get washed down the gutter in every rain storm. And you're still talking about on the order of 1 cubic mm, or more likely much less, total volume of meteorite landing in your gutter per year. Almost all the particles landing on a piece of paper set out are terrestrial in origin as well, following the same reasoning.

I'm not disputing that meteorites hit the Earth, and that that material must come down. But I don't think that's the thought process here. I think it's more along the lines of "Look at these little rocks in my gutter, some of them are magnetic! And how could they even get there? They must be meteors!"

Originally Posted by beowulff

You need to examine the magnetic material under a microscope. The micro-meteors will be rounded, the terrestrial magnetic material will be angular.

Do you have a decent cite that rounded grains implies meteors? It's not like wind-blown grains can't become rounded. Even if all meteoric grains are rounded and most terrestrial grains are jagged, there will be so many terrestrial grains than meteoric ones, that I'm highly skeptical that most rounded grains will be meteoric.

ETA: From Mangetout's link:

Approximately one tenth of the material recovered by the magnet was composed of these little balls of metal

Check my math above, but if a tenth of them are rounded, that's way too many for them to all be meteors.

[beowulff]

I think 1mm is WAY too big.
Most are 10s-100s of microns range:
http://www.lpi.usra.edu/meetings/dust2005/pdf/4014.pdf

[Mangetout]

Originally Posted by ZenBeam

From Cecil's column, 10,000 to 100,000 tons of meteorites hit the Earth each year.

This source (NASA) says it could be more than 10,000 tons a day.

[Mangetout]

Also...

Originally Posted by ZenBeam

ETA: From Mangetout's link: Check my math above, but if a tenth of them are rounded, that's way too many for them to all be meteors.

Not one tenth of the solids recovered from the roof - about one tenth of the tiny proportion of metallic particles harvested out of a couple of kilograms of solids that accumulated over the course of a couple of years. Probably less than 1000th of 1 percent of the total solids from the roof were little metal balls.

[robert_columbia]

Originally Posted by TriPolar

A meteorite hit my car once. Broke the side view mirror.

A moose once bit my sister.

[Leo Bloom]

That's why she snapped my aerial.

[Mangetout]

Originally Posted by beowulff

I think 1mm is WAY too big.
Most are 10s-100s of microns range:
http://www.lpi.usra.edu/meetings/dust2005/pdf/4014.pdf

Concur. 1mm is grit. The material that collects on my roof is more like fine silt.

[ZenBeam]

Do you have any evidence that all those little balls are meteors? "Attracted to a magnet" isn't proof.

[Mangetout]

Originally Posted by ZenBeam

Do you have any evidence that all those little balls are meteors? "Attracted to a magnet" isn't proof.

What kind of evidence would convince you, at this point?

[Crafter_Man]

This is a well known occurrence. If I recall correctly, the song Meteorites Keep Fallin' on my Head was written for the film Butch Cassidy and the Sundance Kid.

[ZenBeam]

Originally Posted by Mangetout

What kind of evidence would convince you, at this point?

Do you have any evidence at all?

[Exapno Mapcase]

Originally Posted by Mangetout

What kind of evidence would convince you, at this point?

I would require a spectroscopic analysis to ensure that the composition matches that of known meteors. You can't do that though, and I can't think of anything home-brewed that would pass the sniff test.

[Bill Door]

If the NASA guys are right about 10,000 tons per day, the Earth has a surface area slightly over 2 billion square kilometers, so we're talking about less than 5 micrograms per square meter per day, assuming equal distribution. You won't catch much on a piece of paper, that's for sure.

[Mangetout]

Originally Posted by ZenBeam

Do you have any evidence at all?

Only what you gave already seen.

I'm not the first person to have done this. Are you doubtful of all the others too?

[Exapno Mapcase]

Originally Posted by Mangetout

Are you doubtful of all the others too?

Yes, unless they've actually done the proper tests.

[ZenBeam]

Originally Posted by Mangetout

I'm not the first person to have done this. Are you doubtful of all the others too?

I'm not doubtful that you and others found little particles.

[Mangetout]

Originally Posted by Exapno Mapcase

I would require a spectroscopic analysis to ensure that the composition matches that of known meteors. You can't do that though, and I can't think of anything home-brewed that would pass the sniff test.

Reading around a bit, it seems that a test for Nickel is considered conclusive by many - and that's fairly simple to do.

[Mangetout]

Originally Posted by ZenBeam

I'm not doubtful that you and others found little particles.

Thank you. That actually tells me everything I needed to know.