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Old 12-16-2017, 01:10 PM
HeyHomie HeyHomie is offline
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The K-T Asteroid: Would Modern Instrumentation Have Seen It Coming?

Would the equipment we use now to watch for ELE asteroids have picked up the K-T asteroid? If humans had been on the ground at the time, when would they have been able to see it with their own eyes? Hours before impact? Minutes? Seconds?
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Old 12-16-2017, 01:44 PM
Stranger On A Train Stranger On A Train is offline
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The answer is a qualified maybe. The asteroid that preceded and presumably caused the Cretaceous–Paleogene (K-Pg) extinction event was very large, on the order of 10 km in width. Since the mod-‘Nineties, starting with Spacewatch astronomers have been surveying the skies for Near Earth Objects that could pose a future hazard. Assuming a power law distribution of object sizes holds (and it appears to from observations of the asteroid belt and impact craters on the Moon) they’ve found the vast majority of objects >1 km that are likely to cross Earth orbit at some point, and discovery of new objects has trailed off as most objects are cataloged. There remains, however, the potential for very long period comets or large extrasolar bodies which we have limited or no information about and might only have a few months warning. Even if we did spot such objects there is no practical sceme for deflecting such large objects and no way to protect human civilization from the effects of such an event.

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Old 12-16-2017, 02:06 PM
SamuelA SamuelA is offline
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Approximately 90% of the 1km+ asteroids have been found. This is based on a statistical argument. (that if you sample a random section of the sky and more than 90% of the asteroids you see in the part of the sky you've already found, then you probably have found about 90% of them)

So we'd probably see the asteroid months beforehand.

As for if humans were watching for it- during the night an object like that would be visible if you were looking in the right place. It would grow increasingly brighter over time. During the minutes before impact, that wouldn't take very long - you're talking an impact at 7+ kilometers per second. The actual rock is so fast all you'd see is a trail blurring to the surface.

I would hope that if we knew it was coming we'd try a parallel, herculean effort similar to the Manhattan project. Not just 1 main effort but several. We are a very rich civilization. There's at least a chance we'd be able to nudge it off course by setting off dozens of nukes on one side.

Each one would be a nuclear shaped charge, they'd fire gas at high velocity into the side of the object, imparting a velocity change to it. The weapon itself wouldn't actually try to "blow up" the asteroid or anything silly like that. No drilling either.

Last edited by SamuelA; 12-16-2017 at 02:08 PM.
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Old 12-16-2017, 02:24 PM
Darren Garrison Darren Garrison is offline
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Originally Posted by HeyHomie View Post
Would the equipment we use now to watch for ELE asteroids have picked up the K-T asteroid? If humans had been on the ground at the time, when would they have been able to see it with their own eyes? Hours before impact? Minutes? Seconds?
The katey asteroid was estimated to be traveling at 20 kilometers per second. As SoaT mentioned, it was somewhere around 10 kilometers in diameter. So let's pick round number times--10 hours, 10 minutes, 10 seconds (and ignore complicating issues such as the angle it arrived from.) At 10 hours, it would be 720,000 km away and cover around 0.047 minutes of arc, or roughly 1/10th the diameter of Mars viewed from Earth. At 10 minutes, it would be 12,000 km away and cover 2.86 minutes of arc, or roughly 1/10th the diameter of the moon viewed from Earth. At 10 seconds, it would be 200 km away and cover 172 minutes of arc, or close to 6 times the diameter of the moon viewed from. The brightness depends on the reflectivity of the asteroid and the angle to the sun (are we seeing a "full asteroid", "first quarter asteroid", "new asteroid" etc.)
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Old 12-16-2017, 03:07 PM
Banksiaman Banksiaman is offline
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...The weapon itself wouldn't actually try to "blow up" the asteroid or anything silly like that. No drilling either.
But we still could round up a bunch of old actors and send them hurtling into an almost certain death, couldn't we? If I and my world is going to perish in a horrific interstellar holocaust, it would still give me some small comfort to know I'd ticked that off my bucket list.
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Old 12-16-2017, 03:08 PM
ssgenius ssgenius is online now
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Approximately 90% of the 1km+ asteroids have been found. This is based on a statistical argument. (that if you sample a random section of the sky and more than 90% of the asteroids you see in the part of the sky you've already found, then you probably have found about 90% of them)

So we'd probably see the asteroid months beforehand.

As for if humans were watching for it- during the night an object like that would be visible if you were looking in the right place. It would grow increasingly brighter over time. During the minutes before impact, that wouldn't take very long - you're talking an impact at 7+ kilometers per second. The actual rock is so fast all you'd see is a trail blurring to the surface.

I would hope that if we knew it was coming we'd try a parallel, herculean effort similar to the Manhattan project. Not just 1 main effort but several. We are a very rich civilization. There's at least a chance we'd be able to nudge it off course by setting off dozens of nukes on one side.

Each one would be a nuclear shaped charge, they'd fire gas at high velocity into the side of the object, imparting a velocity change to it. The weapon itself wouldn't actually try to "blow up" the asteroid or anything silly like that. No drilling either.
That would be a very difficult weapon to design (Shaped nuclear charge) and you may be overstating the effectiveness of a nuclear explosion on a very large asteroid ( > 10 km diameter)

Even an all out effort would take longer than expected.
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Old 12-16-2017, 03:38 PM
Stranger On A Train Stranger On A Train is offline
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That would be a very difficult weapon to design (Shaped nuclear charge) and you may be overstating the effectiveness of a nuclear explosion on a very large asteroid ( > 10 km diameter)

Even an all out effort would take longer than expected.
As it happens, I’ve worked on a study of this very issue, and proposed a concept for redirecting objects of moderate size (~1 km diameter iron-nickel bolide). In this post I addressed the feasibility of shifting the trajectory of an incoming hazardous object. Redirecting an object of such size is at least remotely feasible, provided you can deliver several dozen devices to intercept with the object, which is more of a logistical challenge than a technical one. Redirecting a much larger object, however, becomes a substantial challenge not only because of the additional mass but because the impulse will impinge upon only by a fraction of aspect of the body and would likely be absorbed as deformation within the body (inelastic transfer or liquification) rather than uniformly delivered to the entire aspect. Moving really large masses requires some fundamentally different method of propulsion than just pushing because at those scales a “solid” body doesn’t act very solid.

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Old 12-16-2017, 03:49 PM
Darren Garrison Darren Garrison is offline
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Not to mention how many asteroids are rubble piles. Turn a bullet into a shotgun blast, you aren't really helping.
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Old 12-16-2017, 04:34 PM
Alessan Alessan is offline
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Not to mention how many asteroids are rubble piles. Turn a bullet into a shotgun blast, you aren't really helping.
Really? Because shotgun blasts have much lower penetration. It's the difference between being slapped and being punched - the smaller the surface area, the more energy is focused at the point of impact.
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Old 12-16-2017, 04:59 PM
Darren Garrison Darren Garrison is offline
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Really? Because shotgun blasts have much lower penetration. It's the difference between being slapped and being punched - the smaller the surface area, the more energy is focused at the point of impact.
More like the difference between someone dropping a 10,000 pound rock on your head from a mile up and someone dropping 1,000 10 pound rocks on 1,000 people's heads from a mile up. The huge rock is enough overkill that if you break it up and spread it about, there is plenty of kill left in each of the fragments to take out even more people. With the asteroid, instead of just super-duper killing one major city, you could just plain kill dozens.
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Old 12-16-2017, 05:01 PM
Gorsnak Gorsnak is online now
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Really? Because shotgun blasts have much lower penetration. It's the difference between being slapped and being punched - the smaller the surface area, the more energy is focused at the point of impact.
If the asteroid is on an impact path, all of its kinetic energy is getting absorbed one way or another. With an object on the scale of the K-T asteroid the magnitude of the energy is such that it doesn't make much difference whether a bit more of it is absorbed in the form of atmospheric heating vs melting the crust on impact. Either way, the entire globe is in for a really bad day.
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Old 12-16-2017, 05:40 PM
joema joema is offline
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That would be a very difficult weapon to design (Shaped nuclear charge) and you may be overstating the effectiveness of a nuclear explosion on a very large asteroid ( > 10 km diameter)...Even an all out effort would take longer than expected.
A nuclear warhead detonated in the vacuum of space produces no fireball and no blast. It is simply an intense pulse of X and neutron radiation. A precision stand-off detonation would just vaporize a thin layer of the asteroid's surface material -- whether that was a monolithic object or a gravel pile -- creating an ablative impulse and associated delta-V in the opposite direction.

Re time to implement, there are plenty of ready launch vehicles for this -- they're called ICBMs. A Titan II ICBM launched the Clementine probe to the moon, so it's a matter of reducing the payload for increased delta-V. However the guidance system would have to be replaced, as it's not designed for extended deep space use, and a terminal homing and fusing system would have to be devised.

I don't know how long that would take, but the basic technology already exists in ABMs: https://en.wikipedia.org/wiki/Exoatm...c_Kill_Vehicle. By coincidence the last of 528 nuclear detonations within earth's atmosphere was a Nike Hercules anti-ballistic missile interceptor in 1962, Operation Dominic Tightrope: http://www.thisdayinaviation.com/tag...inic-tightrope

See "Deflecting Asteroids by Means of Standoff Nuclear Explosions": http://research.dynamicpatterns.com/...Explosions.pdf

"Nuclear Explosion Near Surface of Asteroids and Comets - General Description of the Phenomenon": http://csc.ac.ru/news/1997_1/ae27.pdf
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Old 12-16-2017, 05:56 PM
t-bonham@scc.net t-bonham@scc.net is offline
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Since the mod-‘Nineties, ...
C'mon, Stranger -- the Mods were in the 1960's, not the 90's.

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Old 12-16-2017, 06:06 PM
ssgenius ssgenius is online now
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A nuclear warhead detonated in the vacuum of space produces no fireball and no blast. It is simply an intense pulse of X and neutron radiation. A precision stand-off detonation would just vaporize a thin layer of the asteroid's surface material -- whether that was a monolithic object or a gravel pile -- creating an ablative impulse and associated delta-V in the opposite direction.

Re time to implement, there are plenty of ready launch vehicles for this -- they're called ICBMs. A Titan II ICBM launched the Clementine probe to the moon, so it's a matter of reducing the payload for increased delta-V. However the guidance system would have to be replaced, as it's not designed for extended deep space use, and a terminal homing and fusing system would have to be devised.

I don't know how long that would take, but the basic technology already exists in ABMs: https://en.wikipedia.org/wiki/Exoatm...c_Kill_Vehicle. By coincidence the last of 528 nuclear detonations within earth's atmosphere was a Nike Hercules anti-ballistic missile interceptor in 1962, Operation Dominic Tightrope: http://www.thisdayinaviation.com/tag...inic-tightrope

See "Deflecting Asteroids by Means of Standoff Nuclear Explosions": http://research.dynamicpatterns.com/...Explosions.pdf

"Nuclear Explosion Near Surface of Asteroids and Comets - General Description of the Phenomenon": http://csc.ac.ru/news/1997_1/ae27.pdf
Fascinating topics and perfect for this topic.

However, the nuclear weapons described are NOT a shaped directional charge and the maximum size to be effective is closer to 1100m in diameter, not the 10 km of the K-T asteroid . Although still sufficient for this task for anything not discovered yet!! as the really big asteroids are all charted fairly well
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Old 12-16-2017, 06:09 PM
ssgenius ssgenius is online now
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I still love this link for showing just how many there are

http://www.asterank.com/3d/
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Old 12-16-2017, 08:21 PM
Chronos Chronos is online now
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Depending on the size and timing, and on the composition of the object, it might be better not to use your nuclear power in a big dramatic blast, but to instead do something more gradual. If you've got an icy object, you might want to burrow a reactor into it, to heat portions of the object's material into steam, released in a jet.
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Old 12-16-2017, 08:33 PM
SamuelA SamuelA is offline
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Depending on the size and timing, and on the composition of the object, it might be better not to use your nuclear power in a big dramatic blast, but to instead do something more gradual. If you've got an icy object, you might want to burrow a reactor into it, to heat portions of the object's material into steam, released in a jet.
Maybe so. It seems like a series of small nukes would accomplish the same thing. Either by ablating layers off the asteroid with each flash or by impinging hot gas onto the side of it to push it in the direction you want. You could use spacecraft that are Apollo lander size, loaded with dozens of nukes each, that deliver this continuous series of detonations.

I don't understand why stranger claims that the asteroid being "springy" makes any difference. If the asteroid gives off a jet of gas or absorbs a jet of high velocity gas from the nuke, either way, the total momentum of the asteroid has been changed. Internal forces don't matter. Doesn't matter if the asteroid is spinning, either. It just matters where you set the nuke off.

But yeah, even pushed to the absolute limit, with all the countries of the world building rockets in parallel, with emergency commandeering and building new plants, with round the clock shifts to build optimized devices to do this, it does sound like it would take on the order of 2-3 years. (numbers based on ww2 performance)

Last edited by SamuelA; 12-16-2017 at 08:36 PM.
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Old 12-17-2017, 09:03 AM
Alessan Alessan is offline
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If the asteroid is on an impact path, all of its kinetic energy is getting absorbed one way or another. With an object on the scale of the K-T asteroid the magnitude of the energy is such that it doesn't make much difference whether a bit more of it is absorbed in the form of atmospheric heating vs melting the crust on impact. Either way, the entire globe is in for a really bad day.
I get that anyone within a few thousand miles of the point of impact would be toast either way. That goes without saying. It's just that I was under the impression that another aspect of a dinosaur-killer's impact would be the nuclear winter caused by the billions of tons of water and/or dirt blown into the atmosphere by its impact. If most of it is burned up in the atmosphere, would that still happen? Or is that basically irrelevant?
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Old 12-17-2017, 09:52 AM
AK84 AK84 is offline
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Not to mention how many asteroids are rubble piles. Turn a bullet into a shotgun blast, you aren't really helping.
The erstwhile bullet, now shotgun blast

1) Is composed of several smaller objects.
2) Many of which will now be on a “miss earth trajectory”
3) Others will be burnt up by our planetary protection system, i.e the atmosphere
4) As for the rest, well it’s not like we are going to fire just the one, or a single salvo. It’ll be more like “ok now they are 25, pieces, 6 of which look dangerous, launch on them”.
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Old 12-17-2017, 10:46 AM
Stranger On A Train Stranger On A Train is offline
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The atmosphere is not a “planetary protection system”; it is a critical part of our biosphere that performs a variety of functions needed for life to exist, including selective filtering of sunlight, moderating the day/night temperature cycle, the transport medium for the hydrological cycle, providing wind for dispersing pollen, and of course, we and other animals use it as a readily available oxidizer for respiration. Meteors much larger than ~20 meters in width will not “burn up” in the atmosphere and will result in ground impact which can throw millions of tons of debris into the stratosphere; even those that do deconsolidate can release enormous destructive impulse through rapid atmospheric heating that could destroy structures and kill people if it occurs over a dense urban or suburban area.

It would be far better to push a hazardous object aside into an orbit that will not intersect the Earth rather than to break it into smaller and more difficult to track components which may pose an indefinite hazard. Unfortunately, as Darren Garrison, many asteroids are loose aggregations of material that will not remain intact with any lateral impulse, and so in order to deflect the entire mass some way has to be found to either secure the mass together or give a distributed push that shoves all parts equally. Just blasting away at an object in the hope that it will deconsolidate into small components not large enough to be a hazard (especially if they will still collectively impact the Earth) is not a good plan.

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Old 12-17-2017, 11:48 AM
dtilque dtilque is offline
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If the asteroid gives off a jet of gas or absorbs a jet of high velocity gas from the nuke, either way, the total momentum of the asteroid has been changed. Internal forces don't matter. Doesn't matter if the asteroid is spinning, either. It just matters where you set the nuke off.
This is a way too simplistic view of what would happen. First, as someone else pointed out, nukes in a vacuum do not produce a blast. They just emit several metric buttloads of high energy radiation. Some of that radiation will be absorbed by the asteroid (also by any space vessels nearby) but it won't produce a single jet in response. Not only that, but what does jet out from the asteroid will go in various directions (some opposed to each other), partly because of the spin and internal forces (also internal composition) that you dismiss so cavalierly.
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Old 12-17-2017, 12:08 PM
Peter Morris Peter Morris is offline
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BTW, is calling it an "asteroid" the correct terminology? I thought an asteroid orbits the sun, and a rock that falls from space is a meteorite.
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Old 12-17-2017, 12:21 PM
dtilque dtilque is offline
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BTW, is calling it an "asteroid" the correct terminology? I thought an asteroid orbits the sun, and a rock that falls from space is a meteorite.
It's still going to be in orbit around the sun at the time we try to change its trajectory. Waiting for it to get to the edge of the atmosphere is way too late.
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Old 12-17-2017, 12:41 PM
SamuelA SamuelA is offline
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This is a way too simplistic view of what would happen. First, as someone else pointed out, nukes in a vacuum do not produce a blast. They just emit several metric buttloads of high energy radiation. Some of that radiation will be absorbed by the asteroid (also by any space vessels nearby) but it won't produce a single jet in response. Not only that, but what does jet out from the asteroid will go in various directions (some opposed to each other), partly because of the spin and internal forces (also internal composition) that you dismiss so cavalierly.
The sudden flash is what generates most of the impulse. I dismiss it cavalierly because I know what I'm talking about.

And a nuclear shaped charges, where fragments of the weapon are impinging on the asteroid itself, are completely unaffected by the asteroid's spin. Note that "shaped" is a misnomer, it's just a warhead where a big chunk of material is facing the asteroid at detonation, forming a high velocity jet that impacts and embeds itself into the asteroid.

Last edited by SamuelA; 12-17-2017 at 12:42 PM.
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Old 12-17-2017, 12:46 PM
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The atmosphere is not a “planetary protection system”; it is a critical part of our biosphere that performs a variety of functions needed for life to exist, including selective filtering of sunlight, moderating the day/night temperature cycle, the transport medium for the hydrological cycle, providing wind for dispersing pollen, and of course, we and other animals use it as a readily available oxidizer for respiration. Meteors much larger than ~20 meters in width will not “burn up” in the atmosphere and will result in ground impact which can throw millions of tons of debris into the stratosphere; even those that do deconsolidate can release enormous destructive impulse through rapid atmospheric heating that could destroy structures and kill people if it occurs over a dense urban or suburban area.
Like the Chelyabinsk meteor did a few years ago. About 2000 injuries IIRC. I thought post-Chelyabinsk the rereading of data revealed that such strikes happened multiple times a year but were often missed since they usually occurred in the Ocean or in uninhabited areas?
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It would be far better to push a hazardous object aside into an orbit that will not intersect the Earth rather than to break it into smaller and more difficult to track components which may pose an indefinite hazard. Unfortunately, as Darren Garrison, many asteroids are loose aggregations of material that will not remain intact with any lateral impulse, and so in order to deflect the entire mass some way has to be found to either secure the mass together or give a distributed push that shoves all parts equally. Just blasting away at an object in the hope that it will deconsolidate into small components not large enough to be a hazard (especially if they will still collectively impact the Earth) is not a good plan.

Stranger
Ok, won't a large blast or at least multiple large one, especially if the warhead strikes when the object is well away from the planet, cause sufficient change in trajectory that the object will miss the Earth?
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Old 12-17-2017, 01:02 PM
dtilque dtilque is offline
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The sudden flash is what generates most of the impulse. I dismiss it cavalierly because I know what I'm talking about.
That situation is not the same as the random heterogenous material found in an asteroid. There's going to be all kinds of irregularities in an asteroid: surfaces pointing in multitudinal directions, internal voids, variation in composition, etc. The radiation from the nuke will not just ablate away the surface, but will be absorbed at various distances within the asteroid. There may be a voids that accumulate gases generated by the radiation and it may be several minutes to hours later that it gets released. At which time, the rotation of the asteroid has changed the direction it goes.
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Old 12-17-2017, 01:59 PM
Darren Garrison Darren Garrison is offline
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Asteroid=big rock that orbits the sun

Meteoroid=small rock that orbits the sun. The line between asteroid and meteoroid is fuzzily defined, call it 1 meter, call it 10 meters, call it "too small to detect with a telescope."

Meteor=the visible effect of a meteoroid moving deepish in the atmosphere

Bolide=really bright meteor

Meteorite=a fragment of a meteoroid (or asteroid) that has landed on the ground.

When a meteoroid is traveling through the atmosphere and ablating (not really "burning") that heat has to go somewhere. If the meteor is big enough and close enough to you, the heat from it will roast you as surely as would the heat from an atmospheric nuclear explosion. A single bigger asteroid would keep most of its mass and most of its kinetic energy would go into excavating a crater. Break it into multiple chunks with multiple trajectories, and thanks to massively increased surface area the collected fragments would release far more energy into the atmosphere than the intact original.

There is only so bad you can be killed-being exposed to 5,000 degree air isn't going to make you more dead than being exposed to 1,000 degree air. (For similar reasons if you wanted to maximize bang for the buck you'd make 50 1mt nukes instead of 1 50mt nuke.)
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Old 12-17-2017, 02:49 PM
Leo Bloom Leo Bloom is offline
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I still love this link for showing just how many there are

http://www.asterank.com/3d/
Cool data viz. Didn't see the compiler/presenter, but he does have a field filter for "most valuable."

But what we need (demand!?) is their ranking on most blowable-upable.
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Old 12-26-2017, 04:53 PM
Stranger On A Train Stranger On A Train is offline
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Redirecting a much larger object, however, becomes a substantial challenge not only because of the additional mass but because the impulse will impinge upon only by a fraction of aspect of the body and would likely be absorbed as deformation within the body (inelastic transfer or liquification) rather than uniformly delivered to the entire aspect. Moving really large masses requires some fundamentally different method of propulsion than just pushing because at those scales a “solid” body doesn’t act very solid.
I have been informed that there is some drama about this statement, and specifically the interpretation that I implied here or elsewhere that momentum (impulse) is not conserved, which was not the intent. The problem with striking only a small portion of the aspect of an asteroid or comet is that it will not act as a single object but will fragment or liquify, ejecting material or disaggregating into multiple objects with potentially diverging trajectories which could still pose a significant or unintended hazard, each of which have to be tracked and redirected if they are still a potential hazard. Even if such an object does not directly strike the Earth with enough energy to pose a threat, if it is sufficiently dispersed into a wide debris field it could pose a hazard to satellites as it passes by, and particularly if it is in a periodic orbit. Striking the entire aspect of the object with an impulse of roughly equal proportion will at least impart a roughly equal velocity change, so that even if it is disaggregated it is still in a localized field for subsequent impulses.

Relying on the the heating of the surface of the object by impingment of X-rays to provide suffiicent impulse will give very poor efficiency and likely cause massive thermal stresses, hence the need to form a directional jet of some sacrificial material to uniformly push the object and mediate the impulse to minimize inelastic behavior. Even at that, the impulse is likely to fragment the object but with the expectation that the aggregate will remain on a similar trajectory. On the study I worked on some consideration was given to trying to wrap the object in some kind of a net to hold it together, but modeling found this to be unworkable and potentially even counterproductive, notwithstanding the logistics of delivering a separate spacecraft to attempt to deploy the net.

In any case, a ~10 km diameter object will have enough mass that hitting it with impulses from even very large nuclear weapons is about as effective as stopping an oncoming train by shooting at it with a pistol, and trying to push on it from some surface-mounted propulsion system is more likely crack it into pieces than redirect the entire object, and hence, would require an entirely different approach. The “gravity tug” idea that is often floated around is one of those notions that is a nice concept provided you have essentially magical propulsion technology that can maintain constant thrust for an intermittant duration, or an ability to propel other large objects to rendezvous on a swing-by pass to incrementally modify the trajectory. In reality, this is no more practical with any extant or practicable technology than invoking a Celestial Babe Ruth to knock the object out of the solar system.

Stranger
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Old 12-26-2017, 09:30 PM
Xema Xema is offline
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But we still could round up a bunch of old actors and send them hurtling into an almost certain death, couldn't we? If I and my world is going to perish in a horrific interstellar holocaust, it would still give me some small comfort to know I'd ticked that off my bucket list.
Destroying quantities of old actors seems a quirky bucket-list item. (But not necessarily a bad one, mind.)
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Old 03-19-2018, 07:33 AM
Darren Garrison Darren Garrison is offline
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Bump. Hammertime.
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Old 03-19-2018, 09:57 AM
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Here is the horrifically fascinating Last Day of the Dinosaurs. I start it about 11 minutes in, twenty minutes before impact.
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Old 03-19-2018, 10:08 AM
Stranger On A Train Stranger On A Train is offline
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Originally Posted by Darren Garrison View Post
Bump. Hammertime.
I don’t remember when I saw it, but this article is at least a year or two old, and simply updated recently. 101955 Bennu has been known about for several years and Hypervelocity Asteroid Mitgation Mission for Emergency Response (HAMMER) has been around for a while in different guises, presented here to the NASA Small Bodies Assessment Group. Kinetic interception is well and good if you can manage it, but most asteroids larger than 50 m in largest dimension are not solid bodies but agglomerations of material that will readily fracture and disperse on impact, making multiple threats that have to be independently tracked and diverted, notwithstanding the expense of launching dozens of intercept missions to divert, hence the consideration of radiation-augmented momentum transfer or the use of a mediated nuclear pulse to apply a large impulse spread across the entire aspect to impart momentum to the entire body.

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  #34  
Old 03-19-2018, 10:28 AM
Jasmine Jasmine is offline
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Considering the fact that an asteroid might very well have the mass of Mount Everest, it would take a tremendous force detonating at precisely the right place to give it the "nudge" needed. Considering the fact that it might be chugging in at 150,000 MPH (give or take), that kind of precision is very difficult, especially over a large distance. If something of that mass and speed is even inside the moon's orbit, we won't be able to give it a big enough "nudge" to do any good.

Another fact to take into consideration is that most asteroids are spinning or, even worse, tumbling their way through space. If they are irregularly shaped, the correct spot for a detonation is going to change from second to second because it's shape and mass relative to the detonation point will be constantly changing.
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  #35  
Old 03-19-2018, 11:22 AM
kunilou kunilou is online now
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Not to mention how many asteroids are rubble piles. Turn a bullet into a shotgun blast, you aren't really helping.
But that's not the real issue. The real issue is if we blow one 10km hunk of rock into a bunch of smaller, 1km rocks, will they have the same effect as one big rock? That is, would a bunch of smaller impacts still churn enough stuff into the atmosphere to cause the global temperature drop that triggers mass extinction?

Or, do the smaller rocks, having lesser mass, not smash into the Earth with enough force? Sure, there'd be a lot of smaller impacts, but I can tap a piece of drywall in a bunch of different places with a 2-pound hammer and leave only dimples. If I put the same force behind a 100-pound hammer, I'll probably break through.
  #36  
Old 03-19-2018, 11:45 AM
Darren Garrison Darren Garrison is offline
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But that's not the real issue. The real issue is if we blow one 10km hunk of rock into a bunch of smaller, 1km rocks, will they have the same effect as one big rock? That is, would a bunch of smaller impacts still churn enough stuff into the atmosphere to cause the global temperature drop that triggers mass extinction?
Being roasted/pulped by the heat and concussion of a million airbursts will kill you just as dead as a nuclear winter. (As the strange train guy tried to get sunk in in this thread from 2010 that I found while googling for this one.)
  #37  
Old 03-19-2018, 12:04 PM
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That was a fun one.
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Last edited by Grey; 03-19-2018 at 12:04 PM.
  #38  
Old 03-19-2018, 12:15 PM
Stranger On A Train Stranger On A Train is offline
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Originally Posted by kunilou View Post
But that's not the real issue. The real issue is if we blow one 10km hunk of rock into a bunch of smaller, 1km rocks, will they have the same effect as one big rock? That is, would a bunch of smaller impacts still churn enough stuff into the atmosphere to cause the global temperature drop that triggers mass extinction?

Or, do the smaller rocks, having lesser mass, not smash into the Earth with enough force? Sure, there'd be a lot of smaller impacts, but I can tap a piece of drywall in a bunch of different places with a 2-pound hammer and leave only dimples. If I put the same force behind a 100-pound hammer, I'll probably break through.
A 10 km diameter spheroid broken into ~1 km diameter smaller spheriods would produce approximately seventy such objects plus the smaller interstitial debris, assuming it is essentially uniform in density. Impact of an object of ~1000 m in diameter, impacting the Earth at a velocity on the order of Earth orbital speed would cause global devastation. Fortunately, it is expected that there are no objects on the order of 10 km in orbital periods of less than a century that are unaccounted for, and should one appear within the plane of the ecliptic we would expect to identify it long before it approaches the Earth. (Very long period and rogue planetoids approaching from a direction oblique to the ecliptic plane are another matter, and unless they have a very high albedo we would probably not see them, but the likelihood of one intercepting the Earth’s orbit, much less actually striking the planet, are thought to be exceedingly remote.)

There is a common misconception that that just breaking up a very large hazardous celestial object into smaller components so that it “burns up in the atmosphere” will address the problem, which ignores the fact that the atmosphere is part of the Earth and is actually a very critical part of regulating the terrestrial biosphere. Breaking, say, a 1 km object into seventy-odd 100 m objects would produce a level of devastation which would not be much if at all reduced from that presented by the intact object. Although the results may differ somewhat in type, the end result would still be a massive amount of kinetic energy delivered to the atmosphere, converted to thermal and blast effects as well as ground impacts kicking fine dust and ash from firestorms into the upper atmosphere and the resulting climate impacts. It is possible that the initial disruption that breaks up the object may put the smaller objects on differing trajectories so that they do not all impact at once and could even be spread across centuries or millenia, but that may be actually worse as whatever civilization survives the initial impact will be subject to periodic disruption before being able to rebuild an industrial culture sufficient to develop the technology to protect against subsequent impacts. The Earth-intercepting debris from such an impact could also destroy satellites and produce an unintended Kessler syndrome, denying access to orbital space for some indeterminate period and potentially eliminating our ability to track further hazards.

Attempting to intercept a hazardous object within days or hours of an impact, e.g. within the orbit of the Moon, is a case of far too little and way too late. This is why there is a need for long term tracking of all potentially hazardous objects, both Near Earth Asteroids in periodic crossing orbits and longer period transNeptunian objects which could be perturbed into an Earth-orbit-crossing trajectory by some cosmic confluence of events. The interception and redirection should occur decades or centuries before the potential for impact rises to the probability > 1% at a confidence of 50% (P99/50), and preferably using some mechanism that maintains the integrity of the object while gently pushing it into an orbit which will assuredly miss the Earth and any other valuable assets.

A constellation of solar orbiting observatories and communications relay satellites between the orbit of Venus and Earth would serve well to both space hazard observation as well as provide a communications infrastructure for expansion of future space exploration of the outer planets rather than depending on the antiquidated ground-based NASA Deep Space Network, and would be a smart investment for the United States going forward, not only for our own capabilities but to lease paid access to other nations with ambitions on interplanetary exploration. Unfortunately, that is not part of any Decadal plan (was eliminated from the 2010 Decadal survey and not even included in the 2020 survey as a proposal). Except for the very occasional use of the Hubble Space Telescope to look at known objects in the solar system we don’t have any space-based capability dedicated to look for such hazards, and ground observation has some significant limitation, particularly in looking at objects inside of Earth orbit. So we’re not doing much to address the issue beyond PowerPoint presentations and flashy pop-science articles.

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  #39  
Old 03-19-2018, 02:27 PM
rsat3acr rsat3acr is offline
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Originally Posted by Darren Garrison View Post
Not to mention how many asteroids are rubble piles. Turn a bullet into a shotgun blast, you aren't really helping.
I'd guess a bit more would burn up entering the atmosphere if it was a lot of pieces v. one large one. probably wouldn't really make much difference though.
  #40  
Old 03-19-2018, 04:11 PM
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The katey asteroid was estimated to be traveling at 20 kilometers per second. As SoaT mentioned, it was somewhere around 10 kilometers in diameter. So let's pick round number times--10 hours, 10 minutes, 10 seconds (and ignore complicating issues such as the angle it arrived from.) At 10 hours, it would be 720,000 km away and cover around 0.047 minutes of arc, or roughly 1/10th the diameter of Mars viewed from Earth. At 10 minutes, it would be 12,000 km away and cover 2.86 minutes of arc, or roughly 1/10th the diameter of the moon viewed from Earth. At 10 seconds, it would be 200 km away and cover 172 minutes of arc, or close to 6 times the diameter of the moon viewed from. The brightness depends on the reflectivity of the asteroid and the angle to the sun (are we seeing a "full asteroid", "first quarter asteroid", "new asteroid" etc.)
Getting back to the OP (too late), this raises a good question, the difference in time warning between naked eye (at the time) and telescopic (modern day) of impact. I imagine one big difference is at a distance it would still have a lateral movement against the background stars vs close up (naked eye distance) it would be moving pretty much head on.
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  #41  
Old 03-19-2018, 06:21 PM
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...So let's pick round number times--10 hours, 10 minutes, 10 seconds (and ignore complicating issues such as the angle it arrived from.) At 10 hours, it would be 720,000 km away and cover around 0.047 minutes of arc, or roughly 1/10th the diameter of Mars viewed from Earth. At 10 minutes, it would be 12,000 km away and cover 2.86 minutes of arc, or roughly 1/10th the diameter of the moon viewed from Earth. At 10 seconds, it would be 200 km away and cover 172 minutes of arc, or close to 6 times the diameter of the moon viewed from...
Has anyone done a video of this?
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  #42  
Old 03-19-2018, 06:26 PM
Darren Garrison Darren Garrison is offline
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Has anyone done a video of this?
A real-time video of what it would look like as it slowly grew in size from the POV of Earth's surface over a number of hours? Probably not--it'd be pretty dull up until the end.
  #43  
Old 03-19-2018, 06:31 PM
Chronos Chronos is online now
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On the other hand, if you blast the object into a large enough cloud of shotgun pellets, then some fraction of the cloud will miss the Earth, and that would be a real benefit.
  #44  
Old 03-19-2018, 06:56 PM
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Originally Posted by Darren Garrison View Post
A real-time video of what it would look like as it slowly grew in size from the POV of Earth's surface over a number of hours? Probably not--it'd be pretty dull up until the end.
Videos of asteroids hitting the Earth are almost always unrealistically speeded up. In reality, if you were at a viewpoint where the Earth looked to be the size of a basketball (1 inch = 1000 miles), an asteroid traveling at a typical speed of 40,000 miles per hour would look like it was moving a little over a half inch per minute. You'd be hard pressed to even tell that it was moving.
  #45  
Old 03-21-2018, 12:31 AM
jharvey963 jharvey963 is offline
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I get that anyone within a few thousand miles of the point of impact would be toast either way. That goes without saying. It's just that I was under the impression that another aspect of a dinosaur-killer's impact would be the nuclear winter caused by the billions of tons of water and/or dirt blown into the atmosphere by its impact. If most of it is burned up in the atmosphere, would that still happen? Or is that basically irrelevant?
Stranger on a Train is definitely the expert on this issue, but I'll take a chance and hope that I don't embarrass myself too badly. The "old" idea is that the asteroid would cause a nuclear winter scenario: sun light is blocked out, plants die, herbivores die, predators die. However, and this may still be controversial and not universally accepted, a new theory is that the mass extinction happened world wide within HOURS of impact, not months or years. How? The amount of matter vaporized and ejected into space was unimaginably huge. Scientists estimate that the impact crater was 20 miles deep and 100 miles wide. Take a minute to picture that. TWENTY MILES DEEP! Much or most of this material was ejected into space above the atmosphere, condensed once it reached the cold of space, circled the earth, and reentered the atmosphere (world wide), burning up as it did so.

This next is paraphrased from the PBS Documentary, The Day the Dinosaurs Died:
<Cue dramatic music>
As this material returned to earth...

The sky turned red...
Lava fell from the sky...

And the Entire

World

Burned...


The world-wide firestorm incinerated any land animal without underground or underwater shelter.

So under this hypothesis, the title of the Documentary -- the DAY the Dinosaurs Died -- is literally true.

Can't type any more now. Past my bedtime.

J.
  #46  
Old 03-21-2018, 12:43 AM
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I understand that large aquatic creatures perished during the K-T event as well. So presumably a precipitous drop in sunlight and consequent collapse of the ocean's ecosystem played a role as well.
  #47  
Old 03-21-2018, 06:15 AM
Chronos Chronos is online now
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Or there's sufficient interaction between the land and water ecosystems that the loss of so many land species affected the ocean, too.
  #48  
Old 03-21-2018, 09:30 AM
Earl Snake-Hips Tucker Earl Snake-Hips Tucker is offline
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I saw a doc on the KT event and (if I'm remembering correctly), and one of the interviewees said that the submarine impact site might have taken. . . . 300,000 years to finally cool off!
  #49  
Old 03-21-2018, 09:56 AM
Darren Garrison Darren Garrison is offline
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I saw a doc on the KT event and (if I'm remembering correctly), and one of the interviewees said that the submarine impact site might have taken. . . . 300,000 years to finally cool off!
That sounds like too many zeros.
  #50  
Old 03-21-2018, 10:00 AM
HeyHomie HeyHomie is offline
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Here is the horrifically fascinating Last Day of the Dinosaurs. I start it about 11 minutes in, twenty minutes before impact.
Fascinating indeed!

Do we know that it came from the south like that, or is that artistic license on the part of the video-makers?
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