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It is claimed that about 25 million meteors enter Earth's atmosphere each day and most of them burn up and turn into dust.

About 25 million meteors enter the Earth's atmosphere every day (duck!). Most burn up and about 1 million kilograms of dust per day settles to the Earth's surface.

Source: University of Oregon, Astronomy 121 lectures

You can see five or six meteors each hour from any given vantage point on Earth when atmospheric conditions allow. Up to 25 million meteors arrive each day, dropping about 100 tons of material. Most meteors are composed of debris left behind by comets as they orbit the Sun.

Source: Pib Burns personal site

Earth is bombarded with millions of tons of space material each day. Most of the objects vaporize in our atmosphere

Source: Chris Jones' Space Facts

Is it true? Is the number really that high? Is there any research about the measurement of this number? A source with details?

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    An important question to ask when considering these kinds of claims is 'How big (or small) does an object have to be to count as "a meteor"?' Set that value low enough and you can hit that number easily.
    – dmckee --- ex-moderator kitten
    Nov 4, 2014 at 19:16
  • Unless you have a specific reason to be skeptical about the claim, I'd suggest a better fit for this would be the Physics SE, which absorbed the Astronomy SE beta.
    – Larry OBrien
    Nov 5, 2014 at 21:51
  • @LarryOBrien: Specific reason is that the number claimed is too high in my opinion.
    – ermanen
    Nov 5, 2014 at 21:53
  • Those claims are all over the map, aren't they! The first says "about 1 million kilograms" which is 1000 tons; the second says, "about 100 tons"; and the third says, "millions of tons".
    – ChrisW
    Nov 5, 2014 at 23:50
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    BTW @LarryOBrien Physics absorbed the first astronomy.se, but it's back (with some new support I think).
    – dmckee --- ex-moderator kitten
    Nov 6, 2014 at 3:10

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The number of meteors is almost impossible to estimate, as it depends on the sizes you are considering. Dinosaur killers only hit once every hundred million years or so, city-killers every hundred years or so. The wiki page about major impact events gives some estimated frequencies for large meteorites. The latest known ones were at Tunguska (1908) and Chelyabinsk (2013). More may have landed in the oceans. Fortunately, the Chelyabinsk meteor burned up high in the atmosphere; otherwise its effect might have been similar to Tunguska. At the other end of the scale, the number of micron-sized meteors is uncountable.

Scientists use automated camera networks to count the number of meteors and, by triangulation, to determine the direction each one came from. We know that some of them come in so-called meteor showers, which are associated with extinct comets.

It is easier to estimate the total amount of meteoric material that hits the earth and your quote of 100 tons/day is towards the lower end of the estimate range. 100 tons/day is 36,500 tons/year. Estimates vary widely and range from 15,000 to 70,000 tons/year. Another way of looking at these numbers is the estimate that roughly 100 meteorites heavier than 10 grams fall per million square kilometers per year, or one per year in an area the size of a small country. This is not something you'll notice readily, and is presumably one of the reasons why until about 1800 scientists believed that meteorites were earth rocks, not space rocks.

A steady 35,000 tons per year since the birth of earth would amount to about 1.5*10^14 kg which is insignificant compared to the total mass of the earth of 5.97*10^24 kg. I know that the bombardment was much heavier at the beginning - but then, as part of the bombardment the earth also lost an entire moon! Another way of looking at these numbers is the estimate that roughly 100 meteorites heavier than 10 grams fall per million square kilometers per year, or 1 per year in an area the size of a small country.

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  • I don't see where your estimates of "15,000" and "70,000 tons/year" come from. Can you please quote the relevant sentence from each of those two references, to show where those numbers come from?
    – ChrisW
    Nov 6, 2014 at 0:36
  • @ChrisW the reference for 15000 gives 44 tones per day (2nd paragraph), or 16060 per year. The 70000 reference says 37,000-78,000 (3rd paragraph). As they're only estimates, and obviously with wide error margins, I used round numbers.
    – hdhondt
    Nov 6, 2014 at 0:48
  • Both of sentences say, "falls on the Earth". Are we assuming, I suppose, that the total quantity which "falls on the earth" (which is estimated in your references) is pretty well the same as the quantity which "enters the atmosphere" (which is the subject of the question)?
    – ChrisW
    Nov 6, 2014 at 0:53
  • When a meteor enters the atmosphere, it will almost certainly fall onto the earth as well - although it may just gradually drift down as dust rather than with a bang. Some meteors may escape after streaking through the atmosphere, but most will not.
    – hdhondt
    Nov 6, 2014 at 0:59
  • 70,000 tons/year => 200 tons/day. If 200 tons is divided into 25 million pieces, that's an average of about 10 grams per piece. A better answer would add the size-versus-frequency distribution of meteors (instead of assuming the mass is all 10-gram pieces) but IMO your numbers with this calculation shows that "25 million/day" is plausible if we're considering as "meteors" pieces as small as a gram or less.
    – ChrisW
    Nov 6, 2014 at 1:07

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