3 million mph neutron star

[Tumbleweed]

I read recently about a supernova in our galaxy that shot a neutron star out of the Milky Way at 3 million MPH. There must have been a LOT of other ejecta flung out at the same speed or even higher. So that has me wondering. How many of these lateral blasts do we get to pass through on every 26000 year journey around the galaxy? How would you ever see one coming? And since we are currently passing through the Milky Way disc from one side to the other, does that increase the density of super high speed matter that might hit us. And finally, could the object that just hit Jupiter be one of these 3 million mph objects. It wouldn't take a very big one to cause much damage at THAT speed, something far below detectable limits

[shadron]

I don't quite understand what you mean by "lots of other ejecta". Picture this: you have a neutron star and another star rotating around each other. The other star explodes for any of several reasons (like a Type 2 supernova, or a Type 1a nova), so the neutron star is slung off in the direction it was headed at the point when the gravitation of the other star disappeared (actually, "suddenly got much weaker" because the mass suddenly surrounded the NS and canceled itself out). There is no other debris going off with the NS except what may be in orbit with it. The flotsam cast off with the nova is the same whether there is an NS in the neighborhood or not.

So, what are the chances of being skewered by a Manhattan-sized NS while traveling in a galaxy? Very, very, very small. The average density of stars out here is such that if you reduced the sun to a 5" ball, the scaled distance from the sun to Alpha Centauri would be the distance from LA to New York City. If you're flying along that path, say, somewhere outside of Kansas City, what are the chances that an object the size of a bacterium, or a hundred such objects in a space the size of Venus's orbit, would hit your ship, which is the size of a virus? The number of such objects cannot exceed the number of star explosions for a period of time; in the MW, that is about 5 a year, I would imagine, and they can travel vertical to the galactic plane as well as along it.

Any gasses that might accompany the NS on it's journey would soon be waylayed by the interstellar gasses that exist between the stars. Over the distances the friction is intense. Even the NS feels the friction, and it will eventually slow it down, unless the NS has the momentum to get away from interstellar space into intergalactic space.

If the object that hit Jupiter was a neutron star, we'd have known it. It would have easily perturbed orbits all over the solar system; it is many times more massive than Jupiter. That object was likely a comet or asteroid, at a maximum speed of perhaps 50,000 mph, which is 14 miles/sec, or 7.5e-5 lights. Since the energy of the collision goes up with the square of the increase in velocity and proportional to mass, such a thing (a NS running at 3e6 mph) striking Jupiter would have creamed it, and probably us in the bargain, from gamma radiation.

[ben m]

I don't quite understand what you mean by "lots of other ejecta". Picture this: you have a neutron star and another star rotating around each other. The other star explodes for any of several reasons (like a Type 2 supernova, or a Type 1a nova), so the neutron star is slung off in the direction it was headed at the point when the gravitation of the other star disappeared (actually, "suddenly got much weaker" because the mass suddenly surrounded the NS and canceled itself out).

That's not quite right; neutron star "kicks" are thought to come from asymmetries in the collapse of the parent star; there are several models for what generates this asymmetry. It could be just hydrodynamics, in which case the neutron star's kick-momentum will be balanced by the rest of the supernova debris moving (on average) in the opposite direction. (This sort of "spray" would be diffuse, and probably only slightly more hazardous in the downstream direction than the upstream.) In other models, the kick momentum is balanced by neutrinos, which are basically harmless over astronomical distance scales.

The number of such objects cannot exceed the number of star explosions for a period of time; in the MW, that is about 5 a year, I would imagine, and they can travel vertical to the galactic plane as well as along it.


That number is not too well known, but the number that floats around the neutrino community is one or two per century. It would have been much higher in the Milky Way's younger days when the star formation rate was higher.

Any gasses that might accompany the NS on it's journey would soon be waylayed by the interstellar gasses that exist between the stars. Over the distances the friction is intense. Even the NS feels the friction, and it will eventually slow it down, unless the NS has the momentum to get away from interstellar space into intergalactic space.


Those forces are really tiny and probably irrelevant. There's a collective star-star gravitational scattering effect called "dynamical friction" which is more important, but whose force drops off as 1/v^2---all told, I suspect that hypervelocity stars will remain hypervelocity stars for much longer than the lifetime of the Universe.

[edd]

I don't quite understand what you mean by "lots of other ejecta". Picture this: you have a neutron star and another star rotating around each other. The other star explodes for any of several reasons (like a Type 2 supernova, or a Type 1a nova), so the neutron star is slung off in the direction it was headed at the point when the gravitation of the other star disappeared (actually, "suddenly got much weaker" because the mass suddenly surrounded the NS and canceled itself out). There is no other debris going off with the NS except what may be in orbit with it. The flotsam cast off with the nova is the same whether there is an NS in the neighborhood or not.
To be clear, as I understand it that's a mechanism for producing 'ordinary' runaway stars, but fast moving neutron stars would come about through the mechanism ben m says.

[Monketey Ghost]

I read recently about a supernova in our galaxy that shot a neutron star out of the Milky Way at 3 million MPH.

I recall the article. High speed parabola.

There must have been a LOT of other ejecta flung out at the same speed or even higher. So that has me wondering.

Me too...wut? :)

How many of these lateral blasts do we get to pass through on every 26000 year journey around the galaxy?

Few if any whatever you may mean by 'lateral blasts'. Our galaxy is a hugely empty thing. Imagine there are only two flies in all of the US, and imagine what the chances would be of them ever meeting.

How would you ever see one coming?

The only way we could see anything in the way or on the way: telescopes, telescopes, telescopes. If we're to avoid what might be coming, we need telescopes that can see a wide variety of wavelengths. Professional, backyard, we need eyes on the skies.

And since we are currently passing through the Milky Way disc from one side to the other,

We are? I didn't know that.

does that increase the density of super high speed matter that might hit us.

Traveling through the plane of the galaxy does increase the matter density. Above the plane, stars and dust clouds and interstellar hydrogen thin out comparatively well.

And finally, could the object that just hit Jupiter be one of these 3 million mph objects. It wouldn't take a very big one to cause much damage at THAT speed, something far below detectable limits

Whatever hit Jupiter was traveling at much lower speeds, and was not a SN remnant. It was most likely cometary in nature.

[godless dave]

And since we are currently passing through the Milky Way disc from one side to the other,

We aren't passing through it, we're revolving around the center like we always do.

[edd]

The sun moves up and down through the plane of the galaxy several times per orbit.

[TriskettheKid]

26000 year journey around the galaxy?

That number's off by at least an order of magnitude. It takes around 200 million years for the solar system to revolve around the galaxy.

[Tumbleweed]

26000 year journey around the galaxy?

That number's off by at least an order of magnitude. It takes around 200 million years for the solar system to revolve around the galaxy.
ooops, sorry. I did some googling and found the sun aligns with the center of the galaxy every 26000 years and that is where the number came from- So the gist of what I read suggests that there are no asteroids speeding within the galaxy at 3 million mph, just neutron stars. Darn! I was going to suggest a tiny 3 million MPH asteroid caused Tunguska and that is why no remnants were found

[Tumbleweed]

If a force exists that can fling a super heavy neutron star 3 million mph, it would seem that force could also propel something much lighter at the same or greater speed. Or does it have to be as dense as a neutron star to be flung that fast to begin with

[portlandatheist]

Is it possible for such a body at that velocity to escape the local group completely and find itself all alone forever?

[Zeuzzz]

This reminds me of the enigmatic pulsar that David started a thread about: Astrophysics overturned by baffling pulsar: http://forums.randi.org/showpost.php?p=3711109&postcount=15

[Reality Check]

Start with the actual thread Astrophysics over by baffling pulsar (http://forums.randi.org/showthread.php?t=113811) rather than a single post by Zeuzzz.

[ben m]

If a force exists that can fling a super heavy neutron star 3 million mph, it would seem that force could also propel something much lighter at the same or greater speed. Or does it have to be as dense as a neutron star to be flung that fast to begin with

Well, it's no huge surprise that very large forces can occur in these explosions. Forget about the neutron star for a moment---think about the rest of the a supernova's debris or ejecta, which is most of the mass of the parent star, which gets blown away at thousands of kilometers per second. Those are huge forces just as much as "accelerating a neutron star to 0.01c" is. The surprising thing about the hypervelocity stars is this: we're accustomed (or used to be) to thinking of supernovae as spherically symmetric. Sure, runaway burning makes a huge interior pressure rise, and it's easy to see that that exerts a huge force pointing radially outward. But surely the neutron star is born at the *center* and gets equal forces from all sides, so no net force and no acceleration? That's what you'd have expected, but the data says otherwise, and theory is perhaps beginning to catch up.

Whatever is going on, it's probably not a generic "force" which could be harnessed to whatever is in the neighborhood---neutron star, baseball, Honda Civic, etc.. It could be something specifically generated by proton-to-neutron conversions (acting only on just-forming NS matter) or nuclear-burning conditions generated by the neutron star's own gravity, or whatever.

[shadron]

ooops, sorry. I did some googling and found the sun aligns with the center of the galaxy every 26000 years and that is where the number came from- So the gist of what I read suggests that there are no asteroids speeding within the galaxy at 3 million mph, just neutron stars. Darn! I was going to suggest a tiny 3 million MPH asteroid caused Tunguska and that is why no remnants were found

The Tunguska event released an estimated 1.8e15 Joules of energy. A single gram (say, a US penny), travelling at 3 million mph, has 23e15 Joules, so the penny would be equivalent to about 12 Tunguskas. There are no remnants in either case because the energy released is more than is required to convert up to about 2.5e11 grams to iron vapor, which certainly encompasses either.

Tunguska was a rather small event in the scheme of things. It would have flattened most all of modern Washington, DC. The Barringer crater in New Mexico was a hugely larger event, and the Chicxulub meteorite that wiped out the dinosaurs much, much bigger than that.

[edd]

A single gram (say, a US penny), travelling at 3 million mph, has 23e15 Joules
Please recalculate (http://www.google.com/search?client=safari&rls=en&q=0.5+gram+(3+million+miles/hour)%5E2&ie=UTF-8&oe=UTF-8)?

[Checkmite]

By passing through lateral blasts, do you mean passing through the supernova remnants, like the Crab Nebula for instance? Good question. The reason we can see M1 at all is because we're so far away; I reckon if we were passing through it we wouldn't be able to see it, so I guess we would have no way of knowing unless a piece of debris just happened to smack into us (unlikely, as mentioned above).

[Tumbleweed]

By passing through lateral blasts, do you mean passing through the supernova remnants, like the Crab Nebula for instance? Good question. The reason we can see M1 at all is because we're so far away; I reckon if we were passing through it we wouldn't be able to see it, so I guess we would have no way of knowing unless a piece of debris just happened to smack into us (unlikely, as mentioned above).
Yes that is exactly what I am referring to. And IF there are 5 a year in our galaxy that means the debris of hundreds of millions on super nova are flinging around at super speed- well the stuff that hasn't recoalesced anyway. That makes the odds of hitting some of it a lot bigger. And I just find it curious that no pictures have yet shown the object that hit Jupiter. It must have been very small to escape all detection. And since we are currently going through the densest part of the Milky Way disc - or so I read - it increases my paranoia!

[Tumbleweed]

The Tunguska event released an estimated 1.8e15 Joules of energy. A single gram (say, a US penny), travelling at 3 million mph, has 23e15 Joules, so the penny would be equivalent to about 12 Tunguskas. There are no remnants in either case because the energy released is more than is required to convert up to about 2.5e11 grams to iron vapor, which certainly encompasses either.

Tunguska was a rather small event in the scheme of things. It would have flattened most all of modern Washington, DC. The Barringer crater in New Mexico was a hugely larger event, and the Chicxulub meteorite that wiped out the dinosaurs much, much bigger than that.

Thank you for the math, its what I thought. SO- what if there were an entire meteor shower of Tunguska events every so often, say every 26,000 years? If no craters are formed and there VERY little debris, how would you prove they happened? Won't all traces of Tunguska be gone in say, 500 years? Such explosions would cause no or very few extinctions, just a mess like a hurricane or tidal wave. But there is a way. Those Tunguska meteors WOULD hit the surface of the moon and there would be evidence there if they occurred in clusters. But how would you discern the difference between a super high velocity crater made by a small object from a crater created by a large 'slow" moving object

[Tumbleweed]

Please recalculate (http://www.google.com/search?client=safari&rls=en&q=0.5+gram+(3+million+miles/hour)%5E2&ie=UTF-8&oe=UTF-8)?
I did and it took one million grams to come up with the energy released by Tonkuska - at 3 million mph. So something doesn't click -it would take trillions of grams to get that energy at say, 20,000 mph and something that large would have dented us I would think

[shadron]

Please recalculate (http://www.google.com/search?client=safari&rls=en&q=0.5+gram+%283+million+miles/hour%29%5E2&ie=UTF-8&oe=UTF-8)?

Well, le'see:

v = 3e6 mile/hr m = .5 g = .0005 kg
KE = (m v^2) / 2

v = 3e6 mile/hr = 8.3e2 mile/sec = 1.3e3 km/sec = 1.3e6 m/sec
KE = .0005 / 2 * (1.3e6)^2 = .25e-3 * 3.9e12 = 1e9 J.

You win. That's teach me to try to use my tired brain and a calculator against a computer. I probably multiplied by 3600 in the first step rather than dividing.

[KingMerv00]

We aren't passing through it, we're revolving around the center like we always do.

As the sun orbits the center of the Milky Way, it also "bobs" up and down across the galactic equator. If I remember Phil's latest book correctly, it takes 62 million years to complete one full up-down trip.

[shadron]

OK, Tunguska is estimated at 1.8e15 J. v^2 = 3.9e12 M^2 / sec^2. Mass required at 3 million mph is then

m = 2 * KE / v^2 = 3.6e15 / 3.9e12 = .9e3 = 900 kg.

At iron's density (7.9g/cc = 7.9e6 g/M^3 = 7.9e3 kg/M^3), that's 900 / 7.9e3 = .11 cu M., a sphere with the diameter of .32 M, about a foot across. A chrondite of the same mass would be about an inch wider.

Gees, I hope that's right.


For the more sedate 50,000mph (average for a comet entry); that's 22e3 M/sec (learning to use the tools, yessir). Squared, 4.84e8 M^2/sec^2.

m = 3.6e15 / 4.8e8 = 7.5e6 kg.

In iron, that's 7.5e6 / 7.9e3 = 1e3 M^3, a cube 10 meters on a side.

If it had a density of Tempel1, the old Jupiter orbiting comet we hit with Deep Impact a couple of years ago, (670 Kg/M^3, it would readily float in water,) it would be more like 7.5e6 / 6.7e2 - 11,000 M^3, 22 meters on a side. Certainly not unreasonable for a comet; the old one we hit with the probe a couple of years ago, Tempel1, was 5 miles long by 3 miles wide? Tunguska was a small comet, if it was a comet, or an even smaller meteor.

[Tumbleweed]

OK, Tunguska is estimated at 1.8e15 J. v^2 = 3.9e12 M^2 / sec^2. Mass required at 3 million mph is then

m = 2 * KE / v^2 = 3.6e15 / 3.9e12 = .9e3 = 900 kg.

At iron's density (7.9g/cc = 7.9e6 g/M^3 = 7.9e3 kg/M^3), that's 900 / 7.9e3 = .11 cu M., a sphere with the diameter of .32 M, about a foot across. A chrondite of the same mass would be about an inch wider.

Gees, I hope that's right.


For the more sedate 50,000mph (average for a comet entry); that's 22e3 M/sec (learning to use the tools, yessir). Squared, 4.84e8 M^2/sec^2.

m = 3.6e15 / 4.8e8 = 7.5e6 kg.

In iron, that's 7.5e6 / 7.9e3 = 1e3 M^3, a cube 10 meters on a side.

If it had a density of Tempel1, the old Jupiter orbiting comet we hit with Deep Impact a couple of years ago, (670 Kg/M^3, it would readily float in water,) it would be more like 7.5e6 / 6.7e2 - 11,000 M^3, 22 meters on a side. Certainly not unreasonable for a comet; the old one we hit with the probe a couple of years ago, Tempel1, was 5 miles long by 3 miles wide? Tunguska was a small comet, if it was a comet, or an even smaller meteor.
Okay I have faith in your math. So the Tunguska asteroid was 1000 cubic meters big? Isn't that the size of a three story house full of lead? So the obvious question is would something that big have made a dent or left sizable fragments or trace amounts? Beats me! But I'm gonna guess and say no. How big WOULD an asteroid need to be (at 50 grand on the odometer)) to make a dent

[Reality Check]

Okay I have faith in your math. So the Tunguska asteroid was 1000 cubic meters big? Isn't that the size of a three story house full of lead? So the obvious question is would something that big have made a dent or left sizable fragments or trace amounts? Beats me! But I'm gonna guess and say no. How big WOULD an asteroid need to be (at 50 grand on the odometer)) to make a dent
The Tunguska asteroid or comet (http://en.wikipedia.org/wiki/Tunguska_event) is thought not have made a dent since it was an air burst about 10 kilometers above the surface of the Earth. This means that it came in at a low enough angle that it heated up and exploded in the atmosphere. The blast from the explosion caused the effects on the ground.

As for dents: List of impact craters on Earth (http://en.wikipedia.org/wiki/List_of_impact_craters_on_Earth).

Your question cannot be answered until you say how big a dent.

[Tumbleweed]

The Tunguska asteroid or comet (http://en.wikipedia.org/wiki/Tunguska_event) is thought not have made a dent since it was an air burst about 10 kilometers above the surface of the Earth. This means that it came in at a low enough angle that it heated up and exploded in the atmosphere. The blast from the explosion caused the effects on the ground.

As for dents: List of impact craters on Earth (http://en.wikipedia.org/wiki/List_of_impact_craters_on_Earth).

Your question cannot be answered until you say how big a dent.
Well let's just say survive in pieces big enough to find. Assuming both a perpendicular and oblique hit. So if the dinosaur asteroid had been oblique enough they would still be around? Or was it so big as to be oblique proof

[Reality Check]

Well let's just say survive in pieces big enough to find. Assuming both a perpendicular and oblique hit. So if the dinosaur asteroid had been oblique enough they would still be around? Or was it so big as to be oblique proof
Then very very small is the answer: Micrometeoroid (http://en.wikipedia.org/wiki/Micrometeoroid)

[Tumbleweed]

Then very very small is the answer: Micrometeoroid (http://en.wikipedia.org/wiki/Micrometeoroid)
So we must have a continuous dusting of this stuff raining down on Earth. Have they found density levels of them in the ice, so many per cubic meter for example? I'll amend my criteria to a dent that someone could notice and not just a bounce - on land or ice.
And have asteroids been found on the Columbia ice field in Canada now that it is melting out fast? Seems a few fly overs with a magnometer would be in order

[Reality Check]

So we must have a continuous dusting of this stuff raining down on Earth. Have they found density levels of them in the ice, so many per cubic meter for example? I'll amend my criteria to a dent that someone could notice and not just a bounce - on land or ice.
And have asteroids been found on the Columbia ice field in Canada now that it is melting out fast? Seems a few fly overs with a magnometer would be in order
This is all stuff that you can find out for yourself.
I can give you a general reference: Meteorite (http://en.wikipedia.org/wiki/Meteorite)

ETA
"How big WOULD an asteroid need to be (at 50 grand on the odometer) to make a dent".
A golf ball (45.93 grams) dropped from a height of a meter will create a dent. Its velocity would be 4.4 m/s. The energy of impact would be 0.44 joules.
You can do the math for an asteroid (hint - it will be a lot less than 45.93 grams!).

[Zeuzzz]

tum tee tum Was the 1908 Tunguska Explosion an Electrical Event? (http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4346310) Plasma Science, 2007. ICOPS 2007. IEEE 34th International Conference on

:scarper:

[Reality Check]

tum tee tum Was the 1908 Tunguska Explosion an Electrical Event? (http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4346310) Plasma Science, 2007. ICOPS 2007. IEEE 34th International Conference on

:scarper:
No it was not.
:scarper:

[KingMerv00]

tum tee tum Was the 1908 Tunguska Explosion an Electrical Event? (http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4346310) Plasma Science, 2007. ICOPS 2007. IEEE 34th International Conference on
:scarper:

Just because someone suggests a hypothesis does not mean you have to you have to post it. From what I've seen of your posts you seem to reject every mainstream scientific explanation for everything. Why is that? Can't mainstream be right every once in awhile?

BTW, the fact that the author asks "Why no crater?" implies that he doesn't know anything about the theory he is trying to fight.

[Zeuzzz]

From what I've seen of your posts you seem to reject every mainstream scientific explanation for everything. Why is that?


Its called being a skeptic. Get used to it. Its a skeptics forum mate :)

Can't mainstream be right every once in awhile?


Yes, it usually is.

[KingMerv00]

Its called being a skeptic. Get used to it. Its a skeptics forum mate :)

You are completely wrong. You don't reject popular ideas just because they are popular. You don't accept ideas just because they are anti-establishment. Considering the pattern of your beliefs, it seems like you are doing just that.

[shadron]

Okay I have faith in your math. So the Tunguska asteroid was 1000 cubic meters big? Isn't that the size of a three story house full of lead? So the obvious question is would something that big have made a dent or left sizable fragments or trace amounts? Beats me! But I'm gonna guess and say no. How big WOULD an asteroid need to be (at 50 grand on the odometer)) to make a dent

Uhhhhh, no. It would be a 22 meter cube (about 72' if you're American - about 6 stories) filled with snow such that it's density is about 2/3's that of water. Or a 10 meter cube of iron, perhaps 12 meters for rock. Could it have made a dent? Sure. Did it? Don't know. Ground zero under Tunguska was before and after a valley of bog lakes. It wasn't looked at by humans until 13 years after it occurred; it's not clear whether any of the lakes were craters or not; several were dredged and excavated but provided no samples. What would a trace amount of water look like? More water, I suppose. Anything can make a dent, if it comes in slow enough to not create enough friction, or is immediately slowed down by atmosphere to enter fluttering. I think I remember someone computing that a sheet of paper dropped from the ISS would re-enter without harm, but a paper airplane probably would not. When SkyLab bored in, several large tank fragments made it down, and dented Western Australia.

Beringer, who tried to mine the crater in Arizona, thought the mile wide create had been made by a mile wide iron meteor; that's a hefty chunk of pure iron, and what he was looking for. Only later did enough experience with craters show that the meteor need only have been 150' across, still a nice find but vastly smaller. Alas, even morer analysis showed that the iron meteorite pretty much totally vaporized on impact, raining down on, probably, the entire Earth's surface.

[TriskettheKid]

Beringer, who tried to mine the crater in Arizona, thought the mile wide create had been made by a mile wide iron meteor; that's a hefty chunk of pure iron, and what he was looking for. Only later did enough experience with craters show that the meteor need only have been 150' across, still a nice find but vastly smaller. Alas, even morer analysis showed that the iron meteorite pretty much totally vaporized on impact, raining down on, probably, the entire Earth's surface.

Correct me if I'm wrong, but I'm fairly certain that there was no impact event at the crater in Arizona.

I believe that meteorite vaporized prior to impact, with the gases/force of the vaporization causing the crater to form.

[shadron]

I think it is a question of degree rather than kind. It is fair to say that almost no meteorites coming in at 30+ kph ever actually physically touch the surface, solid to solid, until somewhat after the impact, due to the gases that separate the two at meeting, those from the evaporating asteroid and those being vaporized on the surface by the former. Consider the Tunguska event that definitely exploded before impact at the likely height of 5-10 kilometers - it left no discernible crater at all, just as most air burst atomic weapons don't (wiki: "Because Little Boy was an air burst 1,900 feet (580 m) above the ground, there was no bomb crater and no local radioactive fallout."). Therefore, if it didn't "touch" the surface, it must have come extremely close, within a couple of hundred yards, no more. The difference between impacting and exploding at that scale is effectively nothing.

There are some neat essays on the crater's home page, which don't resolve the issue but are nontheless interesting; see http://www.barringercrater.com/news/main3.htm, and click on some of the other side links.

I have seen videos of physics experiments using ultra-high speed shots in which the pellet is actually vaporized in its entirety (i.e., doesn't explode, merely vaporizes). The result doesn't make much difference; the incoming plasma arrow is essentially a military shaped charge, and wreaks the havoc expected of its mass * velocity ^ 2 regardless of its physical phase.

[Tumbleweed]

tum tee tum Was the 1908 Tunguska Explosion an Electrical Event? (http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4346310) Plasma Science, 2007. ICOPS 2007. IEEE 34th International Conference on

:scarper:
Well, if you are blaming it on Tesla, the BIG question becomes: Did or did not he conduct an experiment anywhere near the time of the Tunguksa event. If no, then end of story -- (or is it top secret so the conspiracy theory lives on like Roswell). If so, further investigation is required

[Tumbleweed]

I think it is a question of degree rather than kind. It is fair to say that almost no meteorites coming in at 30+ kph ever actually physically touch the surface, solid to solid, until somewhat after the impact, due to the gases that separate the two at meeting, those from the evaporating asteroid and those being vaporized on the surface by the former. Consider the Tunguska event that definitely exploded before impact at the likely height of 5-10 kilometers - it left no discernible crater at all, just as most air burst atomic weapons don't (wiki: "Because Little Boy was an air burst 1,900 feet (580 m) above the ground, there was no bomb crater and no local radioactive fallout."). Therefore, if it didn't "touch" the surface, it must have come extremely close, within a couple of hundred yards, no more. The difference between impacting and exploding at that scale is effectively nothing.

There are some neat essays on the crater's home page, which don't resolve the issue but are nontheless interesting; see http://www.barringercrater.com/news/main3.htm, and click on some of the other side links.

I have seen videos of physics experiments using ultra-high speed shots in which the pellet is actually vaporized in its entirety (i.e., doesn't explode, merely vaporizes). The result doesn't make much difference; the incoming plasma arrow is essentially a military shaped charge, and wreaks the havoc expected of its mass * velocity ^ 2 regardless of its physical phase.
Well, I was interested in iron objects coming in at 3 million mph, not paper trash tossed out of the space shuttle. So my contention that 3 million mph "debris" from a super nova could be crossing our path as we orbit the galaxy is valid, a small virtually undetectable object going that speed can cause havoc upon "impact" is valid, and that such an object would likely as not leave no impact crater or other evidence is valid. Untold numbers of these events could have occured in the Earth's past and not leave a trace, evolutionary or geologically. And there is no reason to believe they could not occur in clusters or "showers". And if they had, there could be evidence on the moon

[shadron]

Well, I was interested in iron objects coming in at 3 million mph, not paper trash tossed out of the space shuttle.

Got a problem with discussion? How are you ever going to expand your mind that way?

So my contention that 3 million mph "debris" from a super nova could be crossing our path as we orbit the galaxy is valid, a small virtually undetectable object going that speed can cause havoc upon "impact" is valid, and that such an object would likely as not leave no impact crater or other evidence is valid.So far so good. The only "debris" of a sort we can encounter, providing we're more than a few parsecs from the blast is the neutron star cannonball; the rest of such debris gets slowed pretty quickly through interaction with relatively static interstellar dust and gases, not the least of which is the stuff such stars usually emit in the million years before the final Nova explosion. The planetary nebula that we witness around such objects is usually evidence of the friction and slowing down.

Untold numbers of these events could have occured in the Earth's past and not leave a trace, evolutionary or geologically. And there is no reason to believe they could not occur in clusters or "showers". And if they had, there could be evidence on the moonHere's where we part company. While we may have encountered untold numbers of comets and asteroids whose origin is basically our own solar system, our chances of ever encountering even a single one of these careening neutron stars in the life of the planet is literally astronomical. To wit:

- they are produced no more often than one per year in the galaxy (and that is a conservative figure);
- the earth is a miniscule target. As I stated above, if you reduced the distance from the sun to A Centauri to the distance form LA to NYC, the earth would be a ball about 1/20" in diameter. The galaxy would be the entire region of Venus' orbit. And it would have to be perfectly aimed, since at that speed the earth's gravity is going to have far too small an influence to "suck it in", though such a close encounter would likely make the Earth a galactic roamer as well. Rather, the earth would be jerked violently towards the NS.
- the bullet is truely tiny; in the scale above, it would be the size of a bacteria.
- the bullet moves in three dimensions, not just two. Many leave teh galaxy by the shortest route, toward the galactice poles, making short chances very much shorter.
- the star are so far apart that the chances of any star collision when two galaxies collide is tiny.

If you think these conclusions are wrong, you're welcome to look up the distances yourself. Now, compute the chance that in 4 billion years a moving bacteria created at random once a year with a velocity of a few thousandths of a centimeter per second in a random direction somewhere within the volume of a galactic disk with the size of Venus will hit a given arbitrary flyspeck somewhere else in the disk, approximately as far out as Mercury's orbit.

No, it hasn't happened. The probability is way, way too small, and we have empirical evidence, too. If such a neutron star had collided with (or even just passed through) the solar system the system would simply no longer exist.

There is every theoretical reason they could not exist as showers. They are created, as far as we know at this time, by a very unusual set of circumstances.

If they (or rather it) had occurred by hitting the moon as you hope to find, we simply wouldn't have a moon. If it had been hit it would have been totally vaporized (whatever didn't add a micrometer's thickness of plating onto the NS's surface) and the gas given a kinetic kick which would have spread it all over the Orion arm. Earth would have been flash burned, it and all the other planets would probably be wanderers in the galaxy, and the sun would be planetless. This isn't any small chunk of iron we're talking here - it is a mass rivalling or perhaps bigger than that of the sun come to visit us. It's gravitational effects alone would be devastating.