Differential elemental ablation of micrometeoroids

By Phil Plait | April 25, 2009 9:37 am

Sometimes, I love the jargony science speak!

The title refers to something I find totally cool.

Space is not empty. This close to a star like the Sun, even after billions of years, space is filled with junk. Tiny bits of rock, ice, and metal are everywhere, the leftover shrapnel from asteroid collisions, or detritus sloughed off of comets. Every day, the Earth plows through many tons of such material, which mostly burns up in our atmosphere.

Stardust reentering Earth’s air

Scientists have now detected for the first time (PDF journal paper here) that as a particle enters our atmosphere, the different materials in it burn off at different times. They found that sodium and potassium burn off first, when temperatures are still low in the meteoroid. As the little chunk of cosmic fluff penetrates deeper into our atmosphere, the air thickens and the meteoroid heats up. When it hits about 1800 K (1500 C or 2800 F) materials like silicon, iron, and magnesium that have a higher vaporization energy — that, is, need to get hotter to vaporize — start to burn off. At 2500 K (2200 C or 4000 F) the calcium, titanium, and aluminum finally boil away.

What’s amazing to me is that were able to determine this at all. The micrometeoroids we’re talking about here are very tiny, maybe 10-11 to 10-4 grams — in some cases, too small to see. Even at the bigger end that’s a tiny little piece of debris. Normally, the chemicals in an object like this would be measured using spectra — breaking the light up into colors and examining them; different elements emit different colors of light.

But these meteors are too small to create enough light to measure. So scientists got clever: they used radar! Radar reflects off of ionized air, and the amount of ionization — the amount of free electrons in the air — changes the strength of that reflection. By carefully measuring just how strongly a meteor reflects radar as it burns up, scientists were able to figure out just when various elements burned off the hot little visitor.

This is the first time measurements like this have been done, and show that this appears to be the main method that micron-sized particles of metal get into the mesosphere and lower thermosphere, the region of the atmosphere around 100 km (60 miles) high. That may not seem terribly important, but this is one more component that makes up the vastly complex tapestry of the Earth’s atmosphere. Every time a new puzzle piece falls into place is a time when we understand a little bit more about the ocean of air above our heads. And since we need it to, say, breathe, I’m glad there are folks out there working so hard to piece it all together.

Plus, I’m fascinated by meteors. These little guys come screaming in from outer space, booking along at dozens of kilometers per second relative to us. They slam into our air, heat it up, vaporize, and leave that lovely and ephemeral glowing tail stretched out behind them. There’s always a thrill, a shock, when you see one, and it’s hard not to gasp and say "Oooooohhhhhhhh!" when one flashes into your field of view.

And, like everything else in the Universe, there are multiple facets to meteors; we can appreciate them for their sudden flare of beauty and surprise… and we can also study them to see what they can teach us. Science and beauty are two sides of the same coin, and don’t let anyone ever tell you differently.

CATEGORIZED UNDER: Astronomy, Cool stuff, Science

Comments (31)

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  1. Interesting Stuff: Early May 2009 « The Outer Hoard | May 8, 2009
  1. StevoR

    Interesting post thanks BA but what I’m really hanging out for is your take on the new exoplanets found around Gliese 581 the other day incl,. one very low mass superEarth.

    Could you please post on that sometime? Did you miss hearing about it? Or …what?

    I luv me exoplanets! ;-)

  2. Phil:
    Remember the objective prism that belongs with the 10″ Cooke astrograph on Fan Mtn? It got broken at some point but the department still has it. Could something like that be used to study this phenomenon? I wonder… The meteor would leave differing spectra as it moved through its trail on a time exposure, and the spectral wash would change as it went…

  3. Plutonium Being from Pluto

    Space is not empty. This close to a star like the Sun, even after billions of years, space is filled with junk.

    What about space further from our daytime star?

    What about extrasolar meteors coming from the space around Alpha Centauri or Branard’s Star or Wolf 359?

    Is it possible some meteoric material formed betyond our solar system – and would we be able to tell and learn from it?

    I do recall hearing or reading something somewhere about a comet being detected with diffrent chmeistry or different (hyperbolic ?) orbit indicating that this particular comet was extrasolar in origin – so any particles from that comet that entered our atmosphere would be extrasolar too ..

  4. Plutonium Being from Pluto

    That’s Barnard’s Star obvioulsy not Branard’s! ;-)

    Argh! Typos. Please BA, please give us the capability to edit here.

  5. ChemBob

    I think it’s cool that they measured this, but isn’t it pretty predictable based on the simple chemistry of temperature versus heats of vaporization? Am I missing something (probable).

  6. “Science and beauty are two sides of the same coin”

    I’ve always said that science and technology are two side of the same coins. since one need the other in order to progress. better tech, better telescopes. better telescopes better science, and so on. science (and engineering which is just applied math, the language of science) develops better computers which make better models on phenomena we see in the Cosmos, which Both are beautiful.

    it makes me pause and thrill to think of all the science that goes into, well, EVERYTHING in our world

  7. Bart

    I’m probably simply forgetting some of my basic chemistry here, but …

    What happens to those tons of e.g. titanium after it vaporizes? It can’t remain at 2500+K for long, and it hasn’t changed into something other than titanium (has it?). Falls to the ground as individual atoms, perhaps in rain? Floats around in the atmosphere indefinitely? First the latter, then the former?

    Are there experiments that try to collect micrometeoroids before they burn up, maybe using something like aerogel suspended from a balloon?

  8. ChemBob

    Bart

    As an example, the ionized Ti is most likely to combine with oxygen and form TiO or TiO2. Relatively benign, found in white paint.

  9. Blind Squirrel FCD

    Richard drumm the astronomy bum: Didn’t you read the article? What part of

    But these meteors are too small to create enough light to measure.

    don’t you understand?
    BS

  10. MadScientist

    You can also ‘hear’ meteors on radio. :) I never did stop to think of why that’s so – is it just the streaming ions creating pulses which effectively emit over a very broad range of frequencies?

    @Bart: as a vapor that stuff can stay in the atmosphere a very very long time. I imagine they occasionally agglomerate or are deposited on other particles (ice?) and slowly settle out. The earth has a shell of sodium vapor at about 80km and that’s been known for over a century; if you view the sun with a spectroscope you can see two dark lines in the yellow region where the sodium vapor is absorbing the light. I can’t remember if it was the early 1960s or early 1970s when a large laser was built to probe the “sodium layer” and confirm the height and amount of sodium. Since the layer has somewhat definite boundaries (not much sodium vapor below or above) it gives us an idea of when meteors lose their sodium and it also indicates that the sodium must then react with something else to form a compound and perhaps settle down to earth.

  11. BS:
    Not -ALL- meteors are too dim.
    Brighter ones might be worth studying in this fashion.

  12. Rowan Bulpit

    “Science and beauty are two sides of the same coin” A truer statement has not been said, yet it takes a lot of convincing to get some people to realise that understanding the science behind something does not destroy it’s beauty, but adds to it *rolls eyes*

  13. Ethanol

    Astronomy Bum-

    quite true – but does this prism come with an array detector? It would be the only suitable way to monitor the change in spectra over a short period of time. And would you just point the telescope at the sky and hope that a suitable meteor flashed across the view?

  14. MadScientist

    @Ethanol:

    Point at the sky and hope a suitable meteor flashed across? Absolutely. Known comet tracks are quite reliable for providing a fairly large number; if that weren’t the case we wouldn’t be hearing about the Perseids and Leonids every year. In dark areas my astronomer buddies tell me you can spot one every few minutes at any time of year; if they’re not lying through their teeth that implies that a wide-field camera with a suitable spectrograph attached could get some info.

    Unfortunately I have to wait until I return to civilization before I get access to the journal article … oh, how I wish all that information was free.

  15. EtOH:
    The objective prism is basically a 10″ (11″ maybe) circle of glass, thicker on one side than the other. It is probably 2 “D” shaped pieces now that it’s broken, but I’ll bet the metal frame is keeping them together nicely.

    The detector could be as simple as a DSLR camera on a tripod. No guiding necessary. Set the camera up with the prism in front of the wide-angle lens, open the electronic shutter and sit back to wait. Do this during a meteor shower and you won’t have to wait too long.

    I just thought it might be a good activity for the undergrads to try.
    RDTAB

  16. CelticMinstrel

    A question just popped into my head upon reading this: If the Earth plows through many tons of space debris… does that mean it’s slowly gaining mass?

  17. Torbjörn Larsson, OM

    Is it possible some meteoric material formed betyond our solar system

    I believe I read of such a sample yesterday or so, air captured high up, or at least IIRC it was primordial to our planetary disc. (I assume that means it is likelier to have originated elsewhere than surviving the disc processes unscathed. Any astronomers who knows?)

    Interestingly, and again IIRC, a carbonated shell had encapsulated and protected silicon minerals of the sample. Carbon is beneficial for anything, it seems. :-)

    Can’t find the link, sorry.

    If the Earth plows through many tons of space debris… does that mean it’s slowly gaining mass?

    Interesting question. Does the aging Earth gain or loose mass?

    Now I’m going to be plain lazy and refer to vague and fallible memories: yes, I believe the net between atmospheric losses and meteoritic capture is a mass gain. Also, water may be one of those materials where we gain more than loose. (Certainly hydrogen has been a net loss, or our sea water and atmosphere would still be primitively acidic respectively reducing?!)

    Despite that I’m lazy I hope anyone who knows for sure will clarify.

    Follow-up question:

    A terrestrial planet in the habitable zone seems to loose it’s atmosphere over the course of 10 Gy or so, according to some papers IIRC, and slower for such planets around red dwarfs. [Which means that we would be halfway to biosphere death – but because the Sun will increase heat output it will happen much sooner anyway.] Also, presumably the amount of meteoritic mass supply will dwindle over some huge period of time, despite the Oort cloud potentially replenishing it and perhaps maintaining a steady state for the time being.

    If there is a net mass gain, but the atmosphere goes (and perhaps the meteoritic mass flow as well), will there eventually be a reversal to net loss? And if so, when?

  18. Ethanol

    Astronomy Bum:

    So the image of the meteor would be dispersed by color, and you would analyze the intensity across different parts of that streak as it moved across the field of view? How do you assign absolute wavelength values? Sorry from a chemistry background I am more use to taking spectra of things that are sitting in the lab, not moving across the sky

  19. Torbjörn Larsson, OM

    Um, poorly thought out follow up question. Perhaps I should ask, if there are potential periods of mass gain – loss – gain (end state; atmosphere gone), or it it is just one single period of mass loss.

  20. EtOH:
    The spectra of the stars would be a number of narrow, colorful stripes on the black background of space while the meteor’s spectra would be a rectangle of colors. So since the sodium burns off first you’d have the upper part of the spectral wash heavy with the double line of sodium and the numerous potassium lines.

    Then as the meteor got hotter you’d see the Mg doublet plus all the lines of Si & Fe mixed in. Then you should see the numerous lines of Ca, Ti & the orangish Al lines mixed together toward the end of the trail.

    It’d make a pretty picture that would be fun to analyze. It might be tricky, though, with stellar spectra mixed in with the meteor’s spectra. If you had a really bright meteor in a part of the sky that didn’t have a bunch of bright stars, then you might get a clean spectrogram.

    We saw one such meteor last Friday night at Fan Mountain Observatory, stunningly bright! “The Noisy Astronomer” was sitting there and saw the tail end of it. Moments later I said to it “Welcome to Earth, pebble! If you have any metals we might melt them down someday and build a spacecraft with them and send part of you back out into space!”
    It didn’t reply… ;^)

  21. American Voyager

    Beauty was what first attracted me to astronomy. The interest in learning about it came later – when I was old enough to appreciate. 40 years later beauty has not taken a backseat yet.

  22. Kit

    I’m confused about the use of both the words vaporization and burning here. To me burning is an exothermic process when sometime oxidizes quickly. Vaporization is when something gets hot enough to turn into a gas. I suppose when something is burning, like a candle, the wax tends to vaporize and then the gas oxidizes giving off heat which vaporizes more wax. When a meteoroid enters the atmosphere, is the light it gives off from the meteoroid and its vapors getting hot enough to glow or is the light from the gases oxidizing quickly?

  23. If often wondered, if the fact that when we look back in time to something a hundred years old or 1000 years old on earth we have to dig down, how much of that covering is caused by meteoric infall.

    If as the article says we pick up tons – I’ve heard numbers from 20 to 200 tons – per day it certainly must be a factor.

  24. Nigel Depledge

    ChemBob said:

    I think it’s cool that they measured this, but isn’t it pretty predictable based on the simple chemistry of temperature versus heats of vaporization? Am I missing something (probable).

    I think it also has to do with how accessible the various elements are, since it is only the front surface of the meteor that ablates as it passes through the atmosphere. The spectrum would be an emission spec, I think, but the meteor would radiate like a black body. So, temp from the black-body radiation of the meteor, and elemental composition from the trail.

  25. Nigel Depledge

    ChemBob said:

    As an example, the ionized Ti is most likely to combine with oxygen and form TiO or TiO2. Relatively benign, found in white paint.

    And toothpaste. Don’t forget the toothpaste.

  26. Nigel Depledge

    Blind Squirrel FCD said:

    Richard drumm the astronomy bum: Didn’t you read the article? What part of

    But these meteors are too small to create enough light to measure.

    don’t you understand?

    which I read shortly after I had posted this:

    I think it also has to do with how accessible the various elements are, since it is only the front surface of the meteor that ablates as it passes through the atmosphere. The spectrum would be an emission spec, I think, but the meteor would radiate like a black body. So, temp from the black-body radiation of the meteor, and elemental composition from the trail.

    Oops.

  27. Nigel Depledge

    Richard Dinning said:

    If often wondered, if the fact that when we look back in time to something a hundred years old or 1000 years old on earth we have to dig down, how much of that covering is caused by meteoric infall.

    If as the article says we pick up tons – I’ve heard numbers from 20 to 200 tons – per day it certainly must be a factor.

    Well, we can work this out…

    Assuming a spherical Earth, its surface area is given by A = 4[pi]r2.

    From www{dot}nineplanets{dot}org, the diamater of Earth is 12,756.3 km, so its radius is 6,378.15 km.

    Thus, surface area is 511,209,977.3 km2 Assuming your figure of 20 tons / day, and then assuming metric tonnes because that makes the sums easier, we get 0.039122867 g per km<sup2 per day.

    Taking per year (assuming a year as 365.25 days) and making it a more accessible area, we end up with 14.28962721 µg / m2 / year.

    I’m not sure we would even notice the acumulation from 10,000 years’ worth of micrometeroids.

  28. Nigel Depledge

    I said:

    we get 0.039122867 g per km per day.

    Oops. Of course, I mean g / km2 / day.

  29. Laith Preston

    @MadScientist
    Good point about “hearing” them on the radio.

    At certain times of the year amateur radio operators can get extra distance on communications due to the affect the scientists are using here to “see” the meteors. Just as radio signals can bounce off different layers of the atmosphere, you can get occasional bounced signals off the ionization trails from meteors.

  30. StevoRaine

    Aussies, Kiwis & other Southern Hemispherics here may be interested in knowing that this morning & next (5th & 6th May) is the peak of the Eta Aquarid meteor shower.

    The Eta Aquarid shower is derived from Halley’s comet & may result in 60 meteors per hour being visible – that’s a meteor a minute! ;-)

    Go outside and look above the square of Pegasus (Aquarius makes up “the horses ears” asterism! ;-) ) around 3 a.m. Adelaide time – the radiant should be about a thrid of the way up in the eastern sky. (Adelaide = 35 degrees South latitude, same as Sydney if that helps anyone.)

    – With thanks to Joe Grida for his usual monthly astronomy column in the ’tiser, P.40, 2009- April-25th.

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