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Huma
2012-Sep-14, 03:50 PM
Hi. I am working on a short story and I have a question about meteorites. Is there a scenario in which a large percentage of Earths surface could be impacted by meteorites from the same meteor shower? In the story, I am assuming that the meteorites are able to survive the passage thru Earth's atmosphere.

Thanks - Keith

antoniseb
2012-Sep-14, 04:30 PM
I'm not sure what you mean, but all that is required is for the direction they are crossing Earth's orbit from be roughly equatorial (The Orionids for example)... and for the shower to last several hours (most do).

ShinAce
2012-Sep-14, 05:54 PM
Yep, as long as the debris trail of meteorites is wide enough that earth has time to rotate through it(about 12 hours), it can fall on any part of Earth. As mentioned, they already do that. Meteor showers are usually noticeable on consecutive nights.

All you really need is many many large meteorites as part of a single shower and you're done. Instead of a comet coming and going through the inner solar system, you'd want a collision of two comets near the earth so that we cross through the wreckage. How much damage you want on earth will determine the size and speed of these comets.

Huma
2012-Sep-14, 07:14 PM
Thanks antoniseb and ShinAce! That's what I thought but I wanted to confirm before I got too far along in the story.

Noclevername
2012-Sep-14, 08:46 PM
It need not even be an impact (an extremely rare event except in cosmological time), perhaps the loosely-bound body passes too close to a planet or the Moon, and gravity pulls it apart. The remaining stream of debris then crosses Earth's orbit. That would also explain how it caught us by surprise-- a sudden swing in its path as it partly-orbits another world, then gets flung toward ours.

jfribrg
2012-Sep-14, 09:49 PM
In discussions about what to do with an asteroid that is on a collision course with the Earth, it is frequently mentioned that nuking a small asteroid to break it in bits would possibly make things worse because now there are many, many impacts instead of just one. If your plot allows it, maybe you can make this a man-made issue. We tried to tinker with something we didn't understand and made it worse. Who woulda thought?

Jeff Root
2012-Sep-14, 09:58 PM
Meteoroids from comets practically never survive passage
through Earth's atmosphere. Either they are made of stuff
that crumbles too easily, or they aren't large enough, or
both.

I saw scores, or more likely hundreds of meteors during the
peak night of the Leonid meteor shower about ten years ago,
when Earth was going through the densest part of the swarm.
Among them I saw many trails that must have been over a
hundred kilometers long. But chances are that all of the
meteoroids hitting all over the Earth burned up completely
in the upper atmosphere.

The Leonids happen to be unusually fast, hitting Earth at
71 kilometers per second. So the trails I saw were all made
in under two seconds. They were made by meteoroids which
grazed the atmosphere, roughly parallel to the surface that
I was watching from. I watched until the sky became light,
when the radiant was well up in the sky, so at that time I
would have been seeing meteoroids which were falling more
nearly straight down at me, so their trails would have looked
much shorter to me. But they were very, very short, because
none of those meteoroids lasted nearly one second. They
were falling too steeply to burn up "gradually" over a period
of more than a second. Instead they hit dense atmosphere
right away and disintegrated in well under a second.

The high speed of the Leonids may be a major factor in
their not reaching the ground. Slower meteoroids with the
same composition might have a chance. But maybe not.
I suspect that they are just too fragile and fall apart too
readily.

My non-expert guess at the time was that the longest
meteor trails I saw were made by lumps of dust about the
size of baseballs. They made dark smoke trails visible in
ordinary binoculars for several minutes.

The image of "dust" on Earth is probably dominated by
fibers from plants, animals, and synthetic materials.
Of course none of those are in meteoroids. Instead,
think of microscopic bits of rock clinging together.

I have seen and handled a number of large meteorites,
meteoroids which did reach the ground. They tend to
be very, very dense. I've never seen or handled a
carbonaceous chondrite, which I think would be the
least dense. What I have seen are ordinary chondrites
and irons. I was also handed a very impressive little
chunk of the Allende meteorite, a Pallasite, which is
a mix of transparent green rock spheres in an iron
matrix.

An ordinary chondrite which fell in Minnesota in the late
19th Century was sawn through and then ground and
polished to reveal its interior. The chondrules are obvious
circular shapes about half a centimeter to a centimeter in
diameter, packed tight together. My (again, non-expert)
understanding is that they are lumps of dust that were
heated when the Sun became very, very bright shortly
after its formation, melting the dust together into solid
rock. The Leonid meteoroids may be composed of lumps
of dust that were too far from the Sun to melt together
into rock.

The chondrite that fell in Minnesota was just one of four
pieces found. It is about the size of a baby's head. I
don't know how big the other pieces were. The entire
outer surface of the piece I had was covered with a black
crust less than a millimeter thick, where the rock was
melted by collision with Earth's atmosphere.

The biggest hunk of meteoritic iron I've handled is from
the Barringer Meteor Crater in Arizona. It is a flat plate
sawn from a chunk that was probably very irregular in
shape, but may have had a volume similar to that of a
basketball. It is about a centimeter thick. It is every
bit as heavy as you'd expect a chunk of iron that size
to be. It is essentially a solid chunck of stainless steel.
It has several different inclusions which are just minor
impurities to the iron and nickel. Mostly sulfur and
graphite, I think.

These meteorites reached the ground because they were
large enough and solid enough not to burn up or crumble
when they hit the atmosphere. They are apparently both
remnants of larger asteroids which must have collided
with other asteroids millions of years ago, and broke into
pieces which probably would have been too small to see
from Earth before they hit the atmosphere.

-- Jeff, in Minneapolis

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