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Breaking up a rubble pile asteroid impacter



 
 
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  #1  
Old December 31st 09, 09:14 PM posted to sci.space.policy
Frogwatch[_2_]
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Posts: 65
Default Breaking up a rubble pile asteroid impacter

OK, so we have a pile of rubble asteroid that is gonna hit the earth.
As it approaches, the looser rubble gets removed by the atmosphere but
most of the stuff stays together until impact making one big hole.
So, which is worse, one big hole or several smaller ones? Clearly a 1
Km sized rock is gonna ruin everyones day but if we break it up into a
bunch of 100 meter sized rocks, their surface area to volume ratio is
big and so the atmosphere burns up a lot more. Even then, the sum of
the damage done by the smaller craters is going to be less than the
damage done by a single big rock.
This is even more true considering the oceans where a big rock is
going to cause major problems whereas a bunch of smaller rocks are
not.
So, if there's gonna be an impact, I say use nukes to break it up.
  #2  
Old December 31st 09, 09:59 PM posted to sci.space.policy
Alain Fournier[_2_]
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Posts: 373
Default Breaking up a rubble pile asteroid impacter

Frogwatch wrote:

OK, so we have a pile of rubble asteroid that is gonna hit the earth.
As it approaches, the looser rubble gets removed by the atmosphere but
most of the stuff stays together until impact making one big hole.
So, which is worse, one big hole or several smaller ones? Clearly a 1
Km sized rock is gonna ruin everyones day but if we break it up into a
bunch of 100 meter sized rocks, their surface area to volume ratio is
big and so the atmosphere burns up a lot more. Even then, the sum of
the damage done by the smaller craters is going to be less than the
damage done by a single big rock.
This is even more true considering the oceans where a big rock is
going to cause major problems whereas a bunch of smaller rocks are
not.
So, if there's gonna be an impact, I say use nukes to break it up.


If you break up an asteroid into smaller ones, with the smaller ones
having sides 10 times smaller than the original, you get 1000 smaller
asteroids. If you ever saw a 10-meter asteroid coming in, you know
that you get something of comparable brightness to the sun. You are
talking about having 1000 objects coming in, each of which has
1000 times the energy of that 10-meter asteroid. Imagine having
1000 suns in the sky, lots of frying will go on. Not good. Not good
at all. I prefer the single km sized object. It is better to have
much of the energy of the asteroid being used to melt rock than
to have it ionize the atmosphere.


Alain Fournier
  #3  
Old January 1st 10, 03:39 AM posted to sci.space.policy
Greg D. Moore \(Strider\)[_616_]
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Posts: 1
Default Breaking up a rubble pile asteroid impacter

"Frogwatch" wrote in message
...
OK, so we have a pile of rubble asteroid that is gonna hit the earth.
As it approaches, the looser rubble gets removed by the atmosphere but
most of the stuff stays together until impact making one big hole.
So, which is worse, one big hole or several smaller ones? Clearly a 1
Km sized rock is gonna ruin everyones day but if we break it up into a
bunch of 100 meter sized rocks, their surface area to volume ratio is
big and so the atmosphere burns up a lot more. Even then, the sum of
the damage done by the smaller craters is going to be less than the
damage done by a single big rock.
This is even more true considering the oceans where a big rock is
going to cause major problems whereas a bunch of smaller rocks are
not.
So, if there's gonna be an impact, I say use nukes to break it up.


Keep in mind a large part of the energy of 100s of smaller objects will be
dissipated in the atmosphere. That's not necessarily a net improvement.

Remember it's the total energy we have to deal with, one way or the other.

--
Greg Moore
Ask me about lily, an RPI based CMC.


  #4  
Old January 1st 10, 07:47 AM posted to sci.space.policy
Frogwatch
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Posts: 147
Default Breaking up a rubble pile asteroid impacter

On Dec 31 2009, 9:39*pm, "Greg D. Moore \(Strider\)"
wrote:
"Frogwatch" wrote in message

...

OK, so we have a pile of rubble asteroid that is gonna hit the earth.
As it approaches, the looser rubble gets removed by the atmosphere but
most of the stuff stays together until impact making one big hole.
So, which is worse, one big hole or several smaller ones? *Clearly a 1
Km sized rock is gonna ruin everyones day but if we break it up into a
bunch of 100 meter sized rocks, their surface area to volume ratio is
big and so the atmosphere burns up a lot more. *Even then, the sum of
the damage done by the smaller craters is going to be less than the
damage done by a single big rock.
This is even more true considering the oceans where a big rock is
going to cause major problems whereas a bunch of smaller rocks are
not.
So, if there's gonna be an impact, I say use nukes to break it up.


Keep in mind a large part of the energy of 100s of smaller objects will be
dissipated in the atmosphere. *That's not necessarily a net improvement..

Remember it's the total energy we have to deal with, one way or the other..

--
Greg Moore
Ask me about lily, an RPI based CMC.


A large part of the problem is putting that much kinetic energy into a
tiny spot whereas if you spread that energy over a much larger area,
probably not a big problem. When a big rock hits, the bad effects are
basically the result of the high power density whereas with many
smaller impacts the power density is much lower. Total energy is the
same but I propose to spread it over a much larger area and over a
greater time interval. The time interval may be increased by only a
few seconds but that is a major improvement over milliseconds.
  #5  
Old January 1st 10, 07:49 PM posted to sci.space.policy
[email protected] |
external usenet poster
 
Posts: 307
Default Breaking up a rubble pile asteroid impacter

On Dec 31 2009, 10:47*pm, Frogwatch wrote:
On Dec 31 2009, 9:39*pm, "Greg D. Moore \(Strider\)"



wrote:
"Frogwatch" wrote in message


...


OK, so we have a pile of rubble asteroid that is gonna hit the earth.
As it approaches, the looser rubble gets removed by the atmosphere but
most of the stuff stays together until impact making one big hole.
So, which is worse, one big hole or several smaller ones? *Clearly a 1
Km sized rock is gonna ruin everyones day but if we break it up into a
bunch of 100 meter sized rocks, their surface area to volume ratio is
big and so the atmosphere burns up a lot more. *Even then, the sum of
the damage done by the smaller craters is going to be less than the
damage done by a single big rock.
This is even more true considering the oceans where a big rock is
going to cause major problems whereas a bunch of smaller rocks are
not.
So, if there's gonna be an impact, I say use nukes to break it up.


Keep in mind a large part of the energy of 100s of smaller objects will be
dissipated in the atmosphere. *That's not necessarily a net improvement.

  #6  
Old January 2nd 10, 02:09 AM posted to sci.space.policy
Alain Fournier[_2_]
external usenet poster
 
Posts: 373
Default Breaking up a rubble pile asteroid impacter

| wrote:
On Dec 31 2009, 10:47 pm, Frogwatch wrote:

On Dec 31 2009, 9:39 pm, "Greg D. Moore \(Strider\)"



wrote:

"Frogwatch" wrote in message


...


OK, so we have a pile of rubble asteroid that is gonna hit the earth.
As it approaches, the looser rubble gets removed by the atmosphere but
most of the stuff stays together until impact making one big hole.
So, which is worse, one big hole or several smaller ones? Clearly a 1
Km sized rock is gonna ruin everyones day but if we break it up into a
bunch of 100 meter sized rocks, their surface area to volume ratio is
big and so the atmosphere burns up a lot more. Even then, the sum of
the damage done by the smaller craters is going to be less than the
damage done by a single big rock.
This is even more true considering the oceans where a big rock is
going to cause major problems whereas a bunch of smaller rocks are
not.
So, if there's gonna be an impact, I say use nukes to break it up.


Keep in mind a large part of the energy of 100s of smaller objects will be
dissipated in the atmosphere. That's not necessarily a net improvement.


Remember it's the total energy we have to deal with, one way or the other.


--
Greg Moore
Ask me about lily, an RPI based CMC.


A large part of the problem is putting that much kinetic energy into a
tiny spot whereas if you spread that energy over a much larger area,
probably not a big problem. When a big rock hits, the bad effects are
basically the result of the high power density whereas with many
smaller impacts the power density is much lower. Total energy is the
same but I propose to spread it over a much larger area and over a
greater time interval. The time interval may be increased by only a
few seconds but that is a major improvement over milliseconds.



Surely with an early enough intervention you'd be right at some point.
And that detail is well beyond me.


There are some cases where it is favourable to break up an incoming
asteroid. But for a 1 km sized asteroid, unless breaking it up
means a good part of it is going to miss the planet entirely or
that the fragments are going to hit within a very large time interval
(much more than hours), I don't see how breaking it up could be
good. The thing has enough energy to heat the entire atmosphere
to thousands of degrees if all of its energy is dumped in the
atmosphere. You want most of the energy to be used to melt rock,
not to heat the atmosphere. Small pieces will tend to heat the
atmosphere more.


Alain Fournier


  #7  
Old January 2nd 10, 04:46 AM posted to sci.space.policy
BradGuth
external usenet poster
 
Posts: 21,544
Default Breaking up a rubble pile asteroid impacter

On Dec 31 2009, 12:14*pm, Frogwatch wrote:
OK, so we have a pile of rubble asteroid that is gonna hit the earth.
As it approaches, the looser rubble gets removed by the atmosphere but
most of the stuff stays together until impact making one big hole.
So, which is worse, one big hole or several smaller ones? *Clearly a 1
Km sized rock is gonna ruin everyones day but if we break it up into a
bunch of 100 meter sized rocks, their surface area to volume ratio is
big and so the atmosphere burns up a lot more. *Even then, the sum of
the damage done by the smaller craters is going to be less than the
damage done by a single big rock.
This is even more true considering the oceans where a big rock is
going to cause major problems whereas a bunch of smaller rocks are
not.
So, if there's gonna be an impact, I say use nukes to break it up.


Why not stuff the entire pile into the moon?

~ BG
  #8  
Old January 2nd 10, 05:15 AM posted to sci.space.policy
Frogwatch
external usenet poster
 
Posts: 147
Default Breaking up a rubble pile asteroid impacter

On Jan 1, 10:46*pm, BradGuth wrote:
On Dec 31 2009, 12:14*pm, Frogwatch wrote:

OK, so we have a pile of rubble asteroid that is gonna hit the earth.
As it approaches, the looser rubble gets removed by the atmosphere but
most of the stuff stays together until impact making one big hole.
So, which is worse, one big hole or several smaller ones? *Clearly a 1
Km sized rock is gonna ruin everyones day but if we break it up into a
bunch of 100 meter sized rocks, their surface area to volume ratio is
big and so the atmosphere burns up a lot more. *Even then, the sum of
the damage done by the smaller craters is going to be less than the
damage done by a single big rock.
This is even more true considering the oceans where a big rock is
going to cause major problems whereas a bunch of smaller rocks are
not.
So, if there's gonna be an impact, I say use nukes to break it up.


Why not stuff the entire pile into the moon?

*~ BG


This brings up another topic that interests me: Why do we see so few
impact features on the earth? The usual reason is weathering and
plate tectonics but even on Venus we see them and it has extreme
weathering. We see impact features on Europa with an extreme version
of plate tectonics with big plates of ice moving over an ocean
underneath. I think there is another reason and that reason is the
moon.
The moon is just large enough to move the center of mass of the earth-
moon system 1000 miles away from the earths center (actually, I forget
the exact number but I remember it is substantial). So, while the
moon subtends a tiny solid angle in the sky, it actually has a
substantial effect on the "impact paramater" of the earth reducing the
effective cross section by almost half.
OTOH, earth does not protect the moon but actually causes the moon to
take more hits than if it was alone. The same is true of most small
bodies in orbit about large bodies and the small bodies take a lot of
hits.
Thus, is a "Pandora" type moon likely to evolve intelligent life
considering the increased probability of impacts?
Is the near necessity of a moon of just the right size to protect the
primary one reason why we do not detect nearby intelligent life?
  #9  
Old January 2nd 10, 05:57 AM posted to sci.space.policy
BradGuth
external usenet poster
 
Posts: 21,544
Default Breaking up a rubble pile asteroid impacter

On Jan 1, 8:15*pm, Frogwatch wrote:
On Jan 1, 10:46*pm, BradGuth wrote:



On Dec 31 2009, 12:14*pm, Frogwatch wrote:


OK, so we have a pile of rubble asteroid that is gonna hit the earth.
As it approaches, the looser rubble gets removed by the atmosphere but
most of the stuff stays together until impact making one big hole.
So, which is worse, one big hole or several smaller ones? *Clearly a 1
Km sized rock is gonna ruin everyones day but if we break it up into a
bunch of 100 meter sized rocks, their surface area to volume ratio is
big and so the atmosphere burns up a lot more. *Even then, the sum of
the damage done by the smaller craters is going to be less than the
damage done by a single big rock.
This is even more true considering the oceans where a big rock is
going to cause major problems whereas a bunch of smaller rocks are
not.
So, if there's gonna be an impact, I say use nukes to break it up.


Why not stuff the entire pile into the moon?


*~ BG


This brings up another topic that interests me: *Why do we see so few
impact features on the earth? *The usual reason is weathering and
plate tectonics but even on Venus we see them and it has extreme
weathering. *We see impact features on Europa with an extreme version
of plate tectonics with big plates of ice moving over an ocean
underneath. *I think there is another reason and that reason is the
moon.
The moon is just large enough to move the center of mass of the earth-
moon system 1000 miles away from the earths center (actually, I forget
the exact number but I remember it is substantial). *So, while the
moon subtends a tiny solid angle in the sky, it actually has a
substantial effect on the "impact paramater" of the earth reducing the
effective cross section by almost half.
OTOH, earth does not protect the moon but actually causes the moon to
take more hits than if it was alone. *The same is true of most small
bodies in orbit about large bodies and the small bodies take a lot of
hits.
Thus, is a "Pandora" type moon likely to evolve intelligent life
considering the increased probability of impacts?
Is the near necessity of a moon of just the right size to protect the
primary one reason why we do not detect nearby intelligent life?


Having a moon is a good thing, except for the secondary global
warming.

We get to deal with 2e20 N/sec because of our moon(Selene).

It's thought Venus once had a moon the size and similar mass of
Selene.

~ BG
  #10  
Old January 2nd 10, 09:22 AM posted to sci.space.policy
Pat Flannery
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Posts: 18,465
Default Breaking up a rubble pile asteroid impacter

Frogwatch wrote:

This brings up another topic that interests me: Why do we see so few
impact features on the earth? The usual reason is weathering and
plate tectonics but even on Venus we see them and it has extreme
weathering. We see impact features on Europa with an extreme version
of plate tectonics with big plates of ice moving over an ocean
underneath.


Most of the objects that enter the Earth's atmosphere are fairly small
in size and break up before they hit the surface due to the rapid
deceleration they experience on the way down. In the case of a lot of
them they are so fragile to begin with that they break up into very
small pieces during entry so that almost nothing gets to the ground,
like in the Tunguska blast. Since crater size is a function of both the
mass of the impactor and its impact velocity, the small pieces slow down
in the atmosphere enough that they just fall out of the sky at their
terminal velocity, like you had tossed them out of an aircraft at high
altitude, rather than keeping any of the high velocity they had as they
traveled through space.
Venus has such a dense atmosphere that most objects break up before
impact and only the biggest chunks get through to make any crater on the
surface; the smallest single-impact crater spotted on Venus was 3 km in
diameter (smaller ones are sub-craters created by parts of a object that
had broken up on the way down).
Also, without water weathering from rain or rivers, frequent day-night
temperature extremes, and high surface winds, weathering moves very
slowly on Venus.
Article on Venus cratering he http://www.solarviews.com/eng/vencrate.htm

Pat
 




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