Searching for Micrometeorites in Snow

[RJN]

Does fresh snow catch findable micrometeorites? If so, how much fresh snow, on the average, is needed to catch one micrometeorite, say 50+ microns across? If its a reasonably finite amount, do snow-captured micrometeorites create a useful time stamp, plus or minus a few days, on when these micrometeorites fell to Earth?

Quite possibly, other "impurities" besides snow, will be caught. Will these be interesting? I don't know but my astronomical interests lie more in space things like micrometeorites than Earth-created floating bits. The big goal here is to capture bits of deep space asteroids or comets with a reasonable time stamp on them. Micrometeorites flitter to Earth every day at the cited rate of one micrometeorite per square meter per day, on the average. I have two students actually catching some of these with strong magnets directly. Last year the magnets, placed in the open, caught all kinds of odd magnetic stuff. Strangely, the one spherule we think is most clearly a micrometeorite came down during the Perseids meteor shower. We are not at all sure this is a microPerseid, however.

To my knowledge, many micrometeorites are found in "ice cores" dug up in places like Greenland and Antarctica. These are great, but it seems to me that these are not "time stamped" any more accurately than a few months, at best. And it might be that the micrometeorite rate varies on a faster time scale than that. And it might be that a micrometeorite abundance could be traced back to an asteroid or comet. Since micrometeorites are not usually associated with specific asteroids or comets, that might be interesting.

The main action item, to start, is to go outside after it snows, get a bunch of fresh snow that just fell, and melt this snow onto a small but powerful magnet. Yes, use a funnel or something. Then put this magnet under a microscope and look for spherical objects of 50+ microns. At 50+ in size, objects don't blow very far across the Earth, so that a reasonable fraction of 50+ objects floated down from above.

We have already looked for micrometeorites in rain with mixed results. This time I am interested in snow. The goal is to rule out snow as uninteresting, or write a short paper documenting the result. We have a scanning electron microscope here at MTU that can and has imaged candidate micrometeorites in detail and determined their elemental abundances. That is how we know the candidate microPerseid is not a common rock fragment.

The undergraduate student I have already working on this I will ask to post to this Topic with his results. Still, others can play as well -- the more the merrier. I will also say that here in Houghton, Michigan, we get a lot of snow, which is why this project is particularly relevant here.

- RJN

[apodman]

In a book of astronomy experiments for children I have read a method for collecting and identifying cosmic dust that fell in rain water. If I remember correctly, the cosmic dust comes from space and hangs out in the atmosphere until the rain collects it and brings it to the ground. Snow also collects atmospheric dust and brings it to the ground. In general (for atmospheric dust of any origin), does snow clear the air as completely as rain does? Sounds like a question for neufer. Even if snow is less efficient at clearing the air, I'll bet you still find plenty of space particles. I think the first precipitation after a scheduled meteor shower is a good time to look for cosmic dust, whereas another rain or snowfall after a month of precipitation and no meteor showers you will get close to nothing.

[Gorkow]

Hi all, I’m the student that’s been working with RJN on collecting micrometeorites. This post goes over how we collected the particles process involved in sorting, and after that, is what I found from the rain and some ideas on snow collection.

The process starts by taking a magnet (Neodymium disc 6mm dia. by 1mm in height) and placing it outside. Then after a certain time period (usually 1 to 4 day) it’s removed and taken to the microscope. Then the magnet is place directly under the microscope and the particles size and shapes are recorded. This does sound quite simple but there are a few factors that I glazed over. Which I will now go into a little more detail.

For how to place the magnets see the follow link http://docs.google.com/fileview?id=0B7C ... ZjY2&hl=en
which is instruction I wrote this for my friends and family that helped with collecting samples. Note some of the statements in it are not intended to be taken seriously.

Collecting is the easy part deciding what is and what is not a micrometeorite would be the hard part. What I look for is as follows

-size over 30 microns (there are micrometeorites smaller then this but the number of terrestrial -particles increases significantly)
-relatively smooth, but not necessarily perfect
-spheres (note factories also produce spherical particles so be wary of your area)
-evidence of heating (this is due to atmospheric entry), but there is a stipulation since the smaller particles do not generate enough heat to melt during the entry.
- comparing the particle to known micrometeorite pictures, from journal articles.
-finally use your intuition that comes from looking at hundreds of particles.

Then we are left with a selection of candidate micrometeorites which are taken to the electron microscope to have the chemical composition analyzed. Then the composition is checked against the known micrometeorites from the ice cores, and deep sea core samples. If the composition of the particle lies within range of the known then we definitively have a micrometeorite.

So that’s how we collect the micrometeorites, now about particles falling down with the rain. I did investigate the rain a little further this summer and what I found was most of the particles in the air fall within the first 5 minutes of a rain. For more information on how I came up with the 5 minutes see this link http://docs.google.com/fileview?id=0B7C ... YWVm&hl=en
which outlines the methods, data and results.

rain and snow

Now the snow, I think this is a little different story. First does the snowflake collect particles as it falls down? The rain drop does, and my intuition says the snowflake does but, I have no hard data. If the snowflake doesn’t then the rain would be more efficient at collecting particles.

But if the snowflake does collect particles as it falls then it would be more efficient then the rain. This is because the snowflake doesn’t travel straight down and hand usually has a larger surface area, so this would “filter” more air then a raindrop. Then taking what is known from the rain study only the very begin of the snowstorm would contain the majority of the particles.

The snow just started to fall in Houghton Mi, so once I finalize how best to collect the snow we can compare the snow collection to the rain. If you have ideas on how to collect the snow they would be most welcome. The plan now is to use the snow that falls into a plastic pan (40x15x5cm a Tupperware dish) then melt it down, then dump the water in a funnel and have it drip down onto a magnet.

I probably forgot some of the steps we used to collect and analyzed the particles so if it looks a little fishy point it out and we will see if it was something I overlooked or just forgot to mention. Soon I will be posting links with pictures of candidate micrometeorites and particles collected in and around factories so those of you who want to do some collection will get a since of what is out there.

thats all for now
Gorkow

[Gorkow]

Hi,

This post is for anyone wanting to know what we collect on the magnets, and also to show you what is in the air we breath. A note on the pictures everything is under 100x and the size of the dominant particle is on the right of the photo. And don't worry to much about breathing the particles in, most of the them wouldn't make it past the nose

This link is of particles collected from inside and outside of a steal fabrication factory. This is useful to discriminate any candidate micrometeorites.
https://docs.google.com/fileview?id=0B7 ... Yjcy&hl=en

The next link is of particles collected very close to downtown Chicago.
https://docs.google.com/fileview?id=0B7 ... N2Y1&hl=en

Now here are the candidate micrometeorites so far. note this is not all of them it's like half of them.
https://docs.google.com/fileview?id=0B7 ... YTQ0&hl=en

happy meteorite hunting
Gorkow

[RJN]

It seems to me that snow has the possibility of accumulating even more micrometeors on the way down than rain. The reason is that snow typically has a slower terminal velocity than rain. Now micrometeors surely hit a terminal velocity on the way down themselves. I would guess, though, that the smaller and more dense micrometeors have a higher terminal velocity than both rain and snow. So, to exaggerate for clarity, a snow flake is essentially "frozen" (hah!) in the air as micrometeors hit them from above. A snowflake therefore both stays in the air longer than a raindrop, and has a more different terminal velocity than a raindrop. To reiterate, both effects may make snow a better micrometeorite catcher than rain. But the cool thing about science is that we will see! Any other bets?

- RJN

[neufer]

It seems to me that snow has the possibility of accumulating even more micrometeors on the way down than rain. The reason is that snow typically has a slower terminal velocity than rain. Now micrometeors surely hit a terminal velocity on the way down themselves. I would guess, though, that the smaller and more dense micrometeors have a higher terminal velocity than both rain and snow. So, to exaggerate for clarity, a snow flake is essentially "frozen" (hah!) in the air as micrometeors hit them from above. A snowflake therefore both stays in the air longer than a raindrop, and has a more different terminal velocity than a raindrop. To reiterate, both effects may make snow a better micrometeorite catcher than rain. But the cool thing about science is that we will see! Any other bets?

Code: Select all

5.0 m/s   1mm raindrop terminal velocity
1.0 m/s   Average snowflake terminal velocity
0.5 m/s   50 micrometer meteorite terminal velocity
0.1 m/s   20 micrometer meteorite terminal velocity

[Radar Blue]

1... what I found was most of the particles in the air fall within the first 5 minutes of a rain.
2. First does the snowflake collect particles as it falls down? The rain drop does, and my intuition says the snowflake does but, I have no hard data. If the snowflake doesn’t then the rain would be more efficient at collecting particles.

A space particle from outside is probably ionized, and reactive.
They are baked with wind, into molecular bonds with atmospheric particles, like water.
The materials that can come from space is usually mentioned "dust ".
But it is high value elements like lithium, helium, carbon and oxygene.
In combinations with water, and ( morphogenic ) cloud mass.
It is easy to see how clouds can go electric, and can build massive polarity.
Like lightening - because they have metal and salts.

http://en.wikipedia.org/wiki/Willamette_Meteorite

The dust is then cumulated and condensed in the clouds top, freezing layer.
1. Snow freezes water around impurities, like space dust particles.
Clouds clean the atmosphere of floating particles and connects them to the ground.
2. Same as rainfall, the droplets catch them swirling, in the earliest of the rainfall and connect paricles to earth.

From Wiki, Cloud - Condensation : As air parcels cool due to expansion of the rising air mass, water vapor begins to condense on condensation nuclei such as dust, smoke, ice or salt. This process forms clouds.

Discussion proceeds : Does the micrometorite go straight through the ice sheets, clouds and winds, stright into the earth.
If so then they have to have a certain threshold to evaporate or not.
If not, the particle can be trapped in the clouds for days after the meteor shower, and be treated as unrelated.
I think there is a good chance of finding general micrometorites in the snowfall.
Am also considering, the heaviest particles are released from the cloud at the middle of the rainshower.

[neufer]

I think there is a good chance of finding general micrometorites in the snowfall.
Am also considering, the heaviest particles are released from the cloud at the middle of the rainshower.

There are many experts collecting micrometeorites from the ice & snow of Antarctica/Greenland.
Surely one of these folks can be emailed for their ideas on such matters.

[RJN]

Neufer,
What code did you use?

[craterchains]

So, from this I take it you are only looking for micro meteorites that can only be attracted to a magnet?
What about all the others that are nonmagnetic?

[neufer]

Neufer,
What code did you use?

Code: Select all

Been away a few days...but judging by the new "Code" button
I guess that you figured this out for yourself.

"Code" is useful for tables and the like.

[Gorkow]

Houghton is now covered in snow, so here are the results from 3 snow samples.

You can find and explanation and pictures of the collection method at this link
https://docs.google.com/fileview?id=0B7 ... MWMy&hl=en

Now these samples were collected from a semi-continuous snowstorm that lasted 3 days (12/4 to 12/6). The snow samples were all the same volume (1.5gal or 6 L), so if the snowflakes where forming around these particles the samples should collect roughly the same amount of particles. The total particles collected for each sample are listed below, and are graphed on the link.
https://docs.google.com/fileview?id=0B7 ... MjFj&hl=en

12/4/09-----66 particles
12/5/09-----37 particles
12/6/09-----12 particles

So I think the decrease in the particle count means that snowflakes do not usually formed on the particles but the particles are collected on the snowflake as it falls.

Now on to what kind of particles I found. The following link is to the more interesting particles I found. The first 4 particles I classified as candidate micrometeorites.
https://docs.google.com/fileview?id=0B7 ... YzQw&hl=en

Then an answer to the following question asked

So, from this I take it you are only looking for micro meteorites that can only be attracted to a magnet?
What about all the others that are nonmagnetic?

The answer is most meteorites contain iron-nikel metal, so micrometeorites would also contain these elements thus they would attach to the magnet. Note there are rare meteorites that contain no magnetic elements, but those are harder to find.

Gorkow

[craterchains]

Gorkow,
Thanks for the answer.

In any case, have you thought of using a high power electrical magnetic field to look for copper in the micro meteorites?
Copper can only pass through a magnetic field slowly and thus you could separate them from other particles.
Just an idea for your experiment to be carried a bit farther in it's investigations of micro meteorites.
How many of the meteorites contain copper? What percentage?

[RJN]

I have found out that studying how rain and snow collect stuff in the atmosphere is actually an active topic of meteorological research. This is not uncommon for me -- many times a key to progress has been the connection to an already established field. And one way to do that is to know the right keywords that are used in that field. So after a brief conversation yesterday with an atmospheric physicist, I learned some good keywords! These include "scavenging" and "deposition." Knowing this I was able to search better on the web and find several articles. Also, here is a useful Wikipedia entry: http://en.wikipedia.org/wiki/Deposition ... physics%29

It turns out that there are at several kinds of established scavenging:

precipitation scavenging: from rain
snow scavenging: from snow
cloud scavenging: in clouds

From my preliminary readings, it seems that most current scavenging techniques primarily focus on finding and analyzing aerosol particles much smaller than about 50 microns, the smallest size which we have been searching for micrometeorites. Still, I may be mistaken, and in any event I will continue to read and try to understand.

[Gorkow]

Well, I have collected some larger snow samples with a slightly altered method than the previous posts. Method 2 involved letting the snow fall in the tub instead of going out and picking up previously fallen snow. This method allows for an accurate time stamp on the samples. The tub is about 80cm wide 30cm long and 12cm tall. Then i did some control samples using distiled water to make sure the tubs were clean.

Now the first sample collected was that of rain, which was unlikely for this location at this time of the year. The rain sample does give us something to compare the later collected snow samples to. Now with the rain i collected 0.5 gallons of water. Then after the rain the very next day it snowed considerably. The snow melted down to 3/4 gallons.

The first interest is in the size distribution, we are looking for particles around 50 microns or larger. Why those sizes? because they either they are from a local source or from space. The second interest is later when the particles are taken to be analysed, to see if there are any micrometeorites.

So i recorded the sizes of all the particles from the rain and snow (graphed on the links). There are two major items to point out, one snow collects more particles than rain, the other is snow collects more larger particles.

https://docs.google.com/fileview?id=0B7 ... M2M0&hl=en
https://docs.google.com/fileview?id=0B7 ... ZTY5&hl=en

There are 10 more snow samples to look at, so i got some work to do.

But here are some questions i would like your input on.

Why is it snow collects considerably more particles than rain? Is it due to the size, or the longer flight time, or any number of other factors.

Why does snow collect more larger particles? is it the size too or something else.

feel free to raise other questions for discussion.

Gorkow

[bystander]

This is pure speculation, but I think both might be related to surface area (SA). Rain drops, being nearly spherical, would have a minimal SA for a given volume (V) or weight (W). A larger SA:V ratio would provide a greater collecting surface and a larger SA:W ratio might allow for a longer descent (and exposure) time.

But that raises another question, is it surface area alone that is the key, or one or both of the previously mentioned ratios. For rain drops, SA:V (and SA:W) varies inversely to the size of the drop (SA/V = 1/3r, and W increases proportionately to V). For snow flakes, I'm not sure how you would calculate SA and V (probably involves fractal geometry), but i assume similar relationships would probably apply. This would imply that the smaller rain drops and snow flakes would collect more particles if the ratios were important, but less particles if just the SA was important.

I don't know how you would measure the relative size of rain drops or snow flakes, but even a subjective estimate might be interesting.

Just a thought.

[SsDd]

Rain drops, being nearly spherical

I vaguely remembered a presentation on how rain drops are not necessarily spherical. They begin spherical, but change shape as they fall down, due to air resistance. I went back and looked it up, and here is what I found

"Raindrops have sizes ranging from 0.1 millimetres (0.0039 in) to 9 millimetres (0.35 in) mean diameter, above which they tend to break up. Smaller drops are called cloud droplets, and their shape is spherical. As a raindrop increases in size, its shape becomes more oblate, with its largest cross-section facing the oncoming airflow. Large rain drops become increasingly flattened on the bottom, like hamburger buns; very large ones are shaped like parachutes."

I think, that in this particular instance, rain drops "broke up" too much as they fall, thereby "losing" any micro-meteorites that were clinging on to the droplets. Turns out the study of how water droplets coalesce and fall etc, the size, shape, etc is a subject of very high academic and research interest, and my theory is just speculation.

[RJN]

The results of Gorkow indicate that snow is about 20 times as effective as catching micrometeorites than rain, per melted volume. I did not expect that. But that is what science is all about! An atmospheric scientist I spoke with here at MTU said that he WOULD have expected snow to catch more stuff than rain, and was not surprised by the 20x number. He said he was unaware of any publication on the subject, though. But then again there might be -- he just didn't know. So this might be new knowledge, or as said on Saturday Night Live -- just new(s) to me!

A really interesting feature of this is that one can figure out how much snow one needs to catch a micrometeorite and then go out and get it. And the amount of snow would be much less than the amount of rainwater needed. Quite possibly, one could get a daily micrometeorite count by collecting snow (in northern climates) every chance once gets and then melting it, microscope-ing it, and counting the round, melted-looking, magnetic-sticking stuff that measures 50 microns and higher.

It seems to get a real micrometeorite observatory going, though, we need a faster way to tell the micrometeorites from the background gunk. Perhaps placing the size cut at well over 50 microns might work. Even so, if the fraction of micrometeorites to gunk is significant and constant, just counting candidates might itself be useful.

[Gorkow]

So I was doing some spot sampling on the 8 snow magnets i have, and it turns out that i have a surplus of particles. In other research this maybe good, but not for us. An estimate of the 2 gallons of melted snow has 200-500 particles (of 20microns and higher). You can still uses these if you really need to, but it will take a long time to process. For instants the snow results i posted on Feb 10th had 100 particles and it took me 12hrs to fully process them.

i am now trying to think ways to separate the larger particles (>50microns) so i only collect them. This would greatly decrease the particle counts since the size distribution goes as an exponential. Then we are interested in that range anyways so we don't need the smaller particles.

So if any one has an idea on how to separated the particles, so i only have to look at the larger ones, i am all ears.

Reminder on the setup i have the melted snow dripping from a funnel directly on to the magnet.

The idea i had was using the magnet field to separate the particles. To do this i would place the magnet under a microscope slide, increasing the distance the magnet was from the dripping water. This would then decrease the force from the magnet force acting on the particles as they fell with the water. The idea behind doing this was that larger particles would have a larger magnetic field (this however also depends on the composition). Because the field on the particles would be weaker hopefully only the larger particles would be collected.

[on another note having the particles on top of the slide makes them easier to isolate for the SEM]

I did exactly that Monday using 4 of the larger magnets to trap the particles. Using 4 magnets collected a lot (~300) of the particles including the small ones. Then today i tried using only 1 magnet this however collected hardly any particles. Thus i need to find some happy middle ground, and i think it might work.

please post other ideas

Gorkow

[RJN]

i am now trying to think ways to separate the larger particles (>50microns) so i only collect them.
Gorkow

There must be some commercially-available filter out there that can help. Perhaps a fine wire mesh or a vacuum cleaner paper filter. The snow melt might be drained through the filter first and only the large stuff that stuck to the filter would survive. This stuff could then be further filtered for magnetism by dumping it onto a magnet. Those that (again) survive could then be further filtered by shape to ferret out the near-spherical bits.

Since the large particle size already strongly selects for particles that fell nearly straight down (and hence did not blow over from Africa, for example), I would bet a significant fraction of this triple selection process would be actual micrometeorites.

[Gorkow]

The filter method i described before (using a magnet placing it under a slide), did remove a lot of the smaller particle. The abundance of 20 micron particles decreased by a factor of 4, and the 30 micron particles decreased by a factor of 3/4. see the link for graphs.

https://docs.google.com/fileview?id=0B7 ... ODUx&hl=en

Some tweaking is need to make the system more selective but that will be set aside for another day. Thou when you think of new filter systems please post them.

Now that we have a diverse selection of particles we'll be making a trip to the electron microscope for imaging and chemical comp. This will be done after spring break so keep you fingers crossed until then, and hopefully we'll have some micrometeorites.

Gorkow

[biddie67]

What a wonderful learning environment!!! Kudos to both Grokow and RJN!!

I have a question about the effect of a rain drop's surface tension (independent of smaller presenting surface area and higher velocity). Could it possibly repel or vector off in another direction an impacting micrometerite which would also be a factor in collecting fewer micrometerites.

Is there a difference in a snowflake's surface area that could cause a "sticky" factor for collecting micrometeorites that a rain drop doesn't have?

[Amir]

Hi,
it's the first time i'm hearing about Micrometeorites.
I'm wondering why they are so important?
don't we have enough regular size Meteorites to study?

[Gorkow]

rain drop's surface tension

I think biddie67 is on the right on track with the surface tension of the water. If the incoming particle doesn't have large enough momentum it would bounce off the water droplet instead of breaking into it. This is not the case for snowflakes the particles can get logged into the crevasses of the structure.

don't we have enough regular size Meteorites to study?

I am quite thankful that someone asked this question, far to often researchers will become encapsulated in the work (like how to collect only large particles) and lose touch with why the research was important in the first place.

So as to why micrometeorites are important. Well to most people on the street micrometeorites do not affect there life what so ever (but thats the way it goes with most space related research). In taking a step back you can see these little particles are vital to everyone. Space is full of cosmic dust and when to much is collected in one place, they start to build on each other. The collected dust or dust cloud acts as a radiator cooling the center and radiating the thermal energy out. Until the center is around 3 Kelvin, with everything moving slower the gases and the dust particles start sticking together. Coagulation continues on and on, until in the center a sun is formed and the larger dust particles start to orbit. These orbiting particles group together and forming planets, asteroid belts, comets, and such. But not all the particles are collected on these bodies they continue to float around in space. These left over particles slow rain down onto the planets, and we call them micrometeorites. (I tried to make it an simple explanation so i may have miss some steps or made some errors but if you want more info search cosmic dust/early solar system or read the first few chapters of 'the secret life of dust' by hanna holmes.)

So some micrometeorites are reanimates from the early solar system, but they also come down from comets, meteor-showers, (other large interplanetary objects)
The micrometeorites from the larger bodies have compositions similar to the parent body, which is different than the composition of the early cosmic dust. So the solar-dust micrometeorites give more information about the early solar system, when compared to regular size (>1mm) meteorites. Now how do we determine where the meteorites came from (cosmic dust or comets), I don't know of the top of my head but probably by comparing there compositions to regular size meteorites.

There are probably some other reasons for studying micrometeorites but i think i addressed one of the main ones.

Now on to the Good news, this Friday is our appointment with the electron microscope. So will be getting some better images and the elemental compositions of the particles. below are links of the particles we are taking. (note some of the particles on the first link were broken and/or were unable to mount for the microscope)
https://docs.google.com/fileview?id=0B7 ... MzA1&hl=en
https://docs.google.com/fileview?id=0B7 ... OTdm&hl=en

so everyone can look forward to Friday afternoon for a posting of the results.

cheers
Gorkow

[Gorkow]

The samples were very interesting. The images and compositions are at the following link.
https://docs.google.com/fileview?id=0B7 ... Zjgw&hl=en

The last two particles are quite interesting,

Page 5- the particle has a whole lot of different elements going on. Visually i would say it is a salt compound. the composition does contain Sodium chloride, and some other non metals, but what is Zirconium doing in the mix, it has a low earth abundance and a low solar abundance.

Page 6- this one is my favorite for being a micrometeorite, though depending on the Mg to SI ratio it maybe a volcanic particle.

The compositions will be compared using there Mg, Si, Fe. ratios to determine if they are micrometeorite. For info on that see the following paper.
https://docs.google.com/fileview?id=0B7 ... YTM4&hl=en

If you are interested in the abundances of a element just type the element name and then abundance in to Wolfram Alpha, like so Zr Abundance.

cheers
Gorkow