[meteorite-list] Dumb Questions About Meteors & Meteorites

[Robert Woolard]

Hello Eric,

  I'm very sure others on the List will supply you with much better info in short order, but here are 3 quick "quotes" I found that states that very tiny micrometeorites make it through the atmosphere without burning up. I've read better explanations (it involves the ratio of surface area to weight) but I can't find it right now. Like I said, I know others will explain it better, but perhaps this will be of some interest to you:

1. A meteor, or shooting star is produced by the heating and vaporization of meteoroids which enter earth's atmosphere at high speeds. Most are about the size of a grain of sand. An average of about six per hour can be seen by a patient observer on a clear night. Several times as many may be seen during a meteor shower, when the earth encounters a swarm of meteoroids. 


2. Meteorites are the remains of meteoroids which were large enough to survive the trip through the atmosphere, and thus reach the ground after a fiery descent. Micrometeorites are so small that they slow down before burning up, and land gently as dust particles. 

3. Small meteors (about 1--10 grams in mass down to almost a nanogram (0.000000001 gram)) burn up in the Earth’s atmosphere before reaching the ground. Extremely small-sized particles (very fine dust) can make it through the atmosphere unmelted. Meteors larger than about 10 grams are partly melted, but the interior reaches Earth’s surface intact.


  Best wishes,
  Robert Woolard
 
--- On Mon, 1/25/10, Meteorites USA <eric at meteoritesusa.com> wrote:

> From: Meteorites USA <eric at meteoritesusa.com>
> Subject: [meteorite-list] Dumb Questions About Meteors & Meteorites
> To: "Meteorite-list" <meteorite-list at meteoritecentral.com>
> Date: Monday, January 25, 2010, 9:26 PM
> Hi Everyone,
> 
> I'm not too sure how to broach the subject without stepping
> on toes, so I say this will all due respect to everyone who
> would be offended by the questions.
> 
> I've been reading "Meteorites" by Caroline Smith, Sara
> Russell, and Gretchen Benedix, Firefly Books, 2009. Lovely
> book, with lots of information on meteorites, their origins,
> and composition, with loads of illustrations and great
> photography.
> 
> As I was flipping through I found a mention about the total
> weight of meteoritic material which falls on our planet
> every year. On page 89 it states "...approximately
> 40,000-60,000 t of extraterrestrial material lands on Earth
> every year, the majority of which is in the form of tiny
> dust grains usually less than 1 mm (1/25 in) in size;
> importantly, most of this dust is believed to originate from
> comets..."
> 
> Doesn't this go against what science tells us about meteor
> showers? Don't the particles and sand-grain sized particles
> burn up in the atmosphere like science tells us they do? And
> if they don't burn up completely why does just about every
> text on meteors say they do? And if that the case, then how
> is it possible to weigh something that doesn't exist,
> anymore?
> 
> I've read this in other places as well, some sources say
> that there is thousands of tons to millions of tons of
> meteoritic material landing on Earth every year. Yet...
> 
> We all "know" that small dust to sand grain sized particles
> burn up high in the atmosphere, and there is debate on what
> it takes, or rather how large meteoroids must be to reach
> the ground and become meteorites. We know Asteroid 
> 2008 TC3 was small but much larger than dust. So if a 3-6
> meter asteroid can hit Earth, how small of a piece of debris
> can make it to Earth through the atmosphere? How big was
> Whetstone Mountain before entering our atmosphere? There was
> not much of that piece recovered, and the video showed 3
> distinct fragments flying briefly through the field of view
> of the camera. West Texas was a daylight fireball seen from
> hundreds of miles away, and it produced a good bit of
> material. Buzzard Coulee too. These recent meteorite falls
> have been hunted by a large number of very professional
> meteorite hunters and scientists and yet the TKW of the
> falls are small except maybe the BC fall. Buzzard Coulee had
> a HUGE 13 kilo piece http://www.skyriver.ca/astro/bruce/marsden_meteorite%205.JPG
> that impacted the ground and hundreds of other smaller
> stones recovered.
> 
> So how big "does" a meteoroid have to be to reach the
> ground? Do we really know?
> 
> Regards,
> Eric Wichman
> Meteorites USA
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