Pothead discovers worlds largest impact crater

[Turtle]

I love threads like this one.

...

Non-Impact Bounce: An object entering the atmosphere creates a huge pressure wave ahead of itself. The energy needed to create this wave is usually what overcomes the object and destroys it. Imagine that the object survives the pressure wave (Survivable Construction) but gets low enough to complicate the whole thing with a Ground Effect with the pressure wave bouncing off the surface of the planet. So the object never actually touches the earth even as it scars it. The ground effect echo slows the object, but also pushes it back up and away from the earth. The object might skip like a rock on the surface of a lake in this ground effect before finally slowing enough to make impact. Just like skipping a stone it would need a very low angle of impact.

 

Food for thought.

 

Bill

 

 

Mmmm....tastes like chicken! :D Not just like skipping a stone though. :) :eek: Here's a bit I think helps support my continuing claim of no skip, no plough, no bounce, no hop, no nothing but kaboom!

 

Atmospheric entry has no significant influence on the shape, energy, or momentum of impactors with a mass that is much larger than the mass of the atmosphere displaced during penetration.

...

This equation applies for impacts into solid rock targets

where gravity is the predominant arresting influence in crater

growth, which is the case for all terrestrial impacts larger than

a couple of hundred meters in diameter...

http://www.lpl.arizona.edu/~marcus/CollinsEtAl2005.pdf

 

For all intents and purposes, any meteor forming a crater is a bomb, not a rock on a pond. :) That's all I got. :) :doh:

 

On a side note, here's the largest iron meteorite ever found: >> Hoba meteorite

[TheBigDog]

I know that we already covered the fact that the moon having no atmosphere makes a totally different beast, but I love the splash-zone around this crater, and as it is on my desktop wallpaper I often ponder exactly what the impact was like to cause it.

 

I call it the Butterfly Crater.

 

Bill

[Turtle]

I know that we already covered the fact that the moon having no atmosphere makes a totally different beast, but I love the splash-zone around this crater, and as it is on my desktop wallpaper I often ponder exactly what the impact was like to cause it.

 

I call it the Butterfly Crater.

 

Bill

 

Is it this one perhaps? Proclus (crater) - Wikipedia, the free encyclopedia

The crater has a notable ray system that extends for a distance of over 600 kilometers. The rays display an asymmetry of form, with the most prominent being rays to the northwest, north-northeast, and northeast. There is an arc with no ejecta to the southwest. These features suggest an oblique impact at a low angle...

 

If it's not the exact one, the type of impact appears similar. Could be the melt on the lower portion came after the ray-maker and covered some over too. :( ;) :coffee_n_pc: :D :hihi:

[CraigD]

Meteor-Earth collision simulation programs are complicated, but some rough approximations, done using a few simple data and formulas, can give us an intuitive feel for the subject.

 

Typical rock melts at about 1500 K, and vaporizes (boils) at about 3500. Pure iron has slightly higher melting point and a lower boiling point. Typical rock has a specific heat of about [math]850 \,\mbox{J kg}^{-1}\mbox{K}^{-1}[/math]

 

Via the formula for kinetic energy, [math]E=\frac12 M V^2[/math], then, we have that a meteor with a speed of greater than about 2500 m/s that converts all of its kinetic energy to heat will be vaporized.

 

A typical meteor has an impact speed of about 20000 m/s. The least speed it can have is given by the formula for gravitational potential energy, [math]E= u M \left( \frac1{r_0} - \frac1{d} \right)[/math], where [math]r_0[/math] is the radius of the Earth, [math]d[/math] the initial distance of the meteor, effectively infinity, [math]u[/math] Earth’s standard gravitational parameter, and [math]M[/math] the meteor’s mass. Via the kinetic energy formula, this calculates to about 11000 m/s.

 

So, we have that the minimum impact speed is about 4 times what’s necessary to vaporize the impactor. A logical question, then, is why do any meteorites remain intact? The explanation is that a smaller meteorite has a larger frontal area to mass ratio than a larger one, so experiences greater acceleration due to air resistance. Too small, and it’s vaporized by the conversion of its kinetic energy to heat due to acceleration due to air resistance, too large, and the entire meteorite will vaporize, either partially and explosively before striking the surface, or vaporizing itself and the Earth’s crust it contacts into a spreading “rock gass” fireball.

 

We’re far from a precise formula, but what we have is a rough prediction that only a fairly small range of initial masses of meteorites can remain intact, permitting the possibility of gouging, burrowing, skipping, or other novel behavior. From the catalog of intact meteorite finds, I suspect the largest possible intact meteorite is one with a final radius of about 2 m, and a mass of about 100000 kg, a bit larger than the largest known meteorite, the Hoba meteorite.

[Moontanman]

Meteor-Earth collision simulation programs are complicated, but some rough approximations, done using a few simple data and formulas, can give us an intuitive feel for the subject.

 

Typical rock melts at about 1500 K, and vaporizes (boils) at about 3500. Pure iron has slightly higher melting point and a lower boiling point. Typical rock has a specific heat of about [math]850 ,mbox{J kg}^{-1}mbox{K}^{-1}[/math]

 

Via the formula for kinetic energy, [math]E=frac12 M V^2[/math], then, we have that a meteor with a speed of greater than about 2500 m/s that converts all of its kinetic energy to heat will be vaporized.

 

A typical meteor has an impact speed of about 20000 m/s. The least speed it can have is given by the formula for gravitational potential energy, [math]E= u M left( frac1{r_0} - frac1{d} right)[/math], where [math]r_0[/math] is the radius of the Earth, [math]d[/math] the initial distance of the meteor, effectively infinity, [math]u[/math] Earth’s standard gravitational parameter, and [math]M[/math] the meteor’s mass. Via the kinetic energy formula, this calculates to about 11000 m/s.

 

So, we have that the minimum impact speed is about 4 times what’s necessary to vaporize the impactor. A logical question, then, is why do any meteorites remain intact? The explanation is that a smaller meteorite has a larger frontal area to mass ratio than a larger one, so experiences greater acceleration due to air resistance. Too small, and it’s vaporized by the conversion of its kinetic energy to heat due to acceleration due to air resistance, too large, and the entire meteorite will vaporize, either partially and explosively before striking the surface, or vaporizing itself and the Earth’s crust it contacts into a spreading “rock gass” fireball.

 

We’re far from a precise formula, but what we have is a rough prediction that only a fairly small range of initial masses of meteorites can remain intact, permitting the possibility of gouging, burrowing, skipping, or other novel behavior. From the catalog of intact meteorite finds, I suspect the largest possible intact meteorite is one with a final radius of about 2 m, and a mass of about 100000 kg, a bit larger than the largest known meteorite, the Hoba meteorite.

 

You are not saying a meteor larger than 2m will vaporise are you? I mean even if you are right about the heat of reentry at some point the meteor will be traveling to fast for the entire thing to even get hot much less vaporise. Rock meteors probably tend to explode up to a certain size and after that they would have to be to big and traveling to fast to transfer the heat of reentry significantly to the meteor. an iron nickle body would be even less likely to vaporise above a certain size. I can imagine a body say 20 miles in diameter hitting the earth at 10 to 20 miles a second the atmosphere is about 20 miles thick I predict the body would indeed impact the earth as a solid mass and vaporise as it's kinetic energy was transformed into heat as it hit the solid earth not the atmosphere. The energy released would be many orders of magnitude greater than all the nuclear devices on the planet detonated at once.

[Turtle]

Meteor-Earth collision simulation programs are complicated, but some rough approximations, done using a few simple data and formulas, can give us an intuitive feel for the subject.

 

Have you tried this one? >> http://www.lpl.arizona.edu/impacteffects/ It accompanies the report that Modest put up and that I have referenced.

 

We’re far from a precise formula, but what we have is a rough prediction that only a fairly small range of initial masses of meteorites can remain intact, permitting the possibility of gouging, burrowing, skipping, or other novel behavior. From the catalog of intact meteorite finds, I suspect the largest possible intact meteorite is one with a final radius of about 2 m, and a mass of about 100000 kg, a bit larger than the largest known meteorite, the Hoba meteorite.

 

I don't buy skipping or gouging as you, Jack, Lauri, et al have suggested. I note there is no crater at the Hoba meteorite, and from reading that report that I keep mentioning, I gather the Hoba (and other large intact meteorites) actually slow to the point where they simply reach terminal velocity and, well...drop like a rock.

 

Sign me 'Still Not Convinced',

:coffee_n_pc:

 

PS What 'other novel behavior' have you got in mind there? :hihi:

[CraigD]

You are not saying a meteor larger than 2m will vaporise are you?

I estimating too coarsely and with too few factors to give precise numbers, but in short, I’m saying what happens to a meteor or meteorite falls into 3 main classes, determined primarily by mass:

• Small bodies convert all of their kinetic energy into heat, transforming from a single solid body into gas and dust before hitting the ground.
  
• Large bodies reach the ground farily intact and cool (except for a small amount of their outer layers), having been largely unaffected by the atmosphere, where the sudden conversion of their kinetic energy into heat from a change in speed of roughly 20000 m/s to zero in a fraction of a second to (for very large, eg: 20+ km diameter) a few seconds transforms them and the Earth rock they strike into a hot gas. Some serious and well-simulated models suggest that events such as these have occurred half a dozen times or so in the past 3.8 billion years, resulting in global catastrophies in which the oceans are vaporized and the Earth’s entire surface incinerated down to hot bedrock
  
• ”just right” bodies, such as the Hoba meteorite, and various smaller ones, some of which make the news when they hole roofs and vehicle sheet metal, do neither of the above, and strike the ground/ocean/unfortunate dwelling/vehicle intact.
  

I mean even if you are right about the heat of reentry at some point the meteor will be traveling to fast for the entire thing to even get hot much less vaporise. …

Correct. Very big meteorites essentially ignore the atmosphere. They don’t ignore the ground, however, so the ultimate effect is the same – kinetic energy converted into heat several times greater than needed to boil/vaporize the entire meteorite, with the excess vaporizing the Earth in the area of the strike.

 

Note that I’ve not attempted to address the many complicating details, such as the original kinetic energy that’s transformed not into heat, but into more kinetic energy in the form of “splash” material thrown high into or even outside of the atmosphere. I’ve been attempting to just get a preliminary, order-of-magnitude estimate to see if a giant, intact meteorite scenario such as the one Jack described is physically plausible – or, in the classification scheme above, if a “big three mile wide iron ball” can be a “just right” body capable of any sort of striking, skipping, gouging, or whatever.

 

My preliminary conclusion is that this can’t happen. Even tweaking the numbers slightly by assuming the impactor is a ball or pure tungsten, melting point 5930 K rather than the 3500 used in my estimates, a big meteorite is going to transform from solid to gas on initial impact, so rather than any bouncing like a ball, gouging like a plow, or burrowing like a bullet, it’s going to “splat” like a (superhot) paintball

 

 

Have you tried this one? >> http://www.lpl.arizona.edu/impacteffects/ It accompanies the report that Modest put up and that I have referenced.

I have. It’s very cool. I’m gratified that its “The minimum impact velocity on Earth is 11 km/s” hint matches my rough estimate.

 

It’s a complicated program, though, with some 25 pages of empirical table-rich text just summarizing it in plain English. Even with its source code in hand, I imagine it would take days to understand, hence my attempt to take a simpler look at the physics in terms of energy only.

I don't buy skipping or gouging as you, Jack, Lauri, et al have suggested.

I don’t buy it, either.

 

I can imagine a “glancing impact” scenario where a large (100+ km diameter) body struck the earth and ejected nearly its original mass into space. I can, with an exercise of imagination, imagine a very weird large body that behaved essentially artificially, jetting steam, using aerodynamics, etc. to make a sort of “sort landing” involving lots of skipping and gouging, but find it hard to imagine such an object existing other than as the result of advanced engineering. While the “how could you make it?” question is an interesting one, it’s not relevant, I think, to a thread about naturally occurring meteorites.

 

What I don’t want to do with any of my “estimating the plausible” posting is discourage anyone from getting outside and looking for geological evidence of meteorite impacts. I’m actually contemplating a sort of “science dream vacation” involving a phoned ahead visit to the NY State Museum in Albany, then some rough hiking and informed sightseeing on Panther Mountain, to get some hands-on experience with the more visible clues of an impact crater, such as creekbed fracture patterns, actually look like. Right now, if someone were to drag me off into the woods and show me what they thought was an undiscovered crater site, I wouldn’t have much of an idea what to actually look for, or tell anyone to look for. :umno:

 

Being married, though, it’s a tough sell of a vacation plan. :) “Let’s go to upstate New York and climb mountains to look at cracks in creekbeds” comes out a lot less attractive than “let’s go to the beach and drink shaved ice wine coolers”. :)

[Turtle]

I have.[tried the impact calculator] It’s very cool. I’m gratified that its “The minimum impact velocity on Earth is 11 km/s” hint matches my rough estimate.

 

I noticed your 'hit' too, and took a smidge of gratification myself. :D

 

It’s a complicated program, though, with some 25 pages of empirical table-rich text just summarizing it in plain English.

...

What I don’t want to do with any of my “estimating the plausible” posting is discourage anyone from getting outside and looking for geological evidence of meteorite impacts.

 

The program itself is quite simple to use I think. The user enters only 6 parameters (distance from impact, meteor density, diameter, speed, angle of entry, & target material) and the program describes the result. I agree on your description of the report, but what I don't want to do, is discourage anyone from reading complicated material. I don't concern myself with not understanding everything in such cases, rather I just plunge in. :) ;)

 

I’m actually contemplating a sort of “science dream vacation” involving a phoned ahead visit to the NY State Museum in Albany, then some rough hiking and informed sightseeing on Panther Mountain, to get some hands-on experience with the more visible clues of an impact crater, such as creekbed fracture patterns, actually look like. Right now, if someone were to drag me off into the woods and show me what they thought was an undiscovered crater site, I wouldn’t have much of an idea what to actually look for, or tell anyone to look for. :)

 

Being married, though, it’s a tough sell of a vacation plan. :( “Let’s go to upstate New York and climb mountains to look at cracks in creekbeds” comes out a lot less attractive than “let’s go to the beach and drink shaved ice wine coolers”. ;)

 

Cracked creek beds & shaved-ice wine coolers? ;) I'm all for field work, and boy would I like to put my boots on the ground down in Chihuahua. :umno:

 

On the matter of other impact scenarios, one not mentioned yet is the impactor so large that it causes anti-podal focusing and rips up Earth on the opposite side from the strike. (search for Dr. Mark Boslow, Sandia Labs impact physicist) I think I cover that in this thread: >>http://hypography.com/forums/astronomy-cosmology/9072-craters-earth-other-planets.html

 

Here's a bit on finding impact sites by amateurs: >> Astroseti.org : How to discover asteroid impacts

 

A bit on ocean impact clues: >> http://www.nytimes.com/2006/11/14/science/14WAVE.html?_r=2&ref=science&oref=slogin&oref=slogin

 

:)

[Jack Hughett]

Correct. Very big meteorites essentially ignore the atmosphere. They don’t ignore the ground, however, so the ultimate effect is the same – kinetic energy converted into heat several times greater than needed to boil/vaporize the entire meteorite, with the excess vaporizing the Earth in the area of the strike.

 

Hey CraigD,:shade:

Is it possible that in the case of a large iron meteorite that maybe even the mass of the ground isn't enough to vaporize the object. I have even wondered if one could possibly penetrate the crust and on into the mantle. The average thickness of the crust ranges only between 20 and 120 km. An iron meteorite could penetrate this in a matter of seconds. So instead of always being splattered by impacts the earth simply swallows them up.

 

I personally feel that the only way to get a center peak in a crater is from ground penetration.

 

Jack

[TheBigDog]

Your logic is flawless, Craig, but I wonder about taking such an empirical approach. Note the thread on hot water freezing faster than cold water, could there be counterintuitive elements at play with regard to the melting and explosion of objects entering the atmosphere?

 

Bill

[Michaelangelica]

Earth Scars - Interactive Map - National Geographic Magazine

[bigfatpothead]

I am sorry I missed most of this as it was happening!

I have been on the road doing comedy for a bit and was pleasantly surprised that someone is with me on this, even though it's reverse of what I theorized it is nonetheless acceptable to me.

 

One thing I want some physics guy to answer is why are the valley edges so perfectly serated, with equidistant spacing between identical serations.

It looks like something sharp, jagged and round, rolled through the valley, zoom in on the valley and follow it from the impact point in a north east direction and count the serations, you will see the symmetry, zoom way in and you can see a cemetary!

 

 

Bigfatpothead

DOT COM

 

Hey again Modest,

 

Off subject but my son claims he's the king of modesty.

 

 

"However, you're looking at this a bit backwards I think."

 

The story of my life!

 

By the way that is a fun program for figuring impacts, but it seems to be designed strictly for circular impacts. Once you get below 45 degrees the dynamics doesn't change. It maintains that the impact is circular in shape, or did I miss something in the calculation?

 

As far as finding shocked quartz and spherules. They may be extremely hard to find and is it possible that they may not even exist with this impact. The dynamics would be totally different from what we think of a "normal" impact.

With this (ok I'll use it) "alleged" impact zone being over 100 miles long, and the first point of contact with the earth being considered more of a grazing instead of a direct strike, would the pressures be the same?

 

Jack

[Turtle]

I am sorry I missed most of this as it was happening!

I have been on the road doing comedy for a bit and was pleasantly surprised that someone is with me on this, even though it's reverse of what I theorized it is nonetheless acceptable to me.

 

One thing I want some physics guy to answer is why are the valley edges so perfectly serated, with equidistant spacing between identical serations.

It looks like something sharp, jagged and round, rolled through the valley, zoom in on the valley and follow it from the impact point in a north east direction and count the serations, you will see the symmetry, zoom way in and you can see a cemetery!

 

 

Bigfatpothead

DOT COM

 

:phones: The forms result from erosion and if you measure them accurately they are not equidistant. Again, (and again, and again...) no colliding space-rock 'rolls' or 'scrapes' on that scale. Put that idea to rest in that cemetary. :phones:

[charles brough]

I saw a NOVA science program a year or two ago about the comet that hit Siberia. One important point in the program was that it came in at a sharp angle. They could tell from the different directions the burned trees had been flattened down.

 

I tried to see the links, but none of them came up, so I have no picture of this much more immense event. I assume it was hundreds of millions of years ago if a reality.

[modest]

It was the:

 

Tunguska event - Wikipedia, the free encyclopedia

 

~modest

[Michaelangelica]

you are not the only one

two recently in Australia

Aussie finds meteorite crater on Google Earth | COSMOS magazine

Googling geologist identifies possible meteorite crater out the back of Bourke | theage.com.au

and

Sudden impact: Google unearths rare meteorite crater - Technology - smh.com.au

[simcha]

shalom everyone!

... As an interesting side-topic:

Has anyone been to "Crater-National-Monument" in Arizona ??

I was there! I saw it!

It's about 40,000 years old, roughly a kilometer wide in diameter, and about a third of a klm. deep ! ... i didn't go down into it, but i walked along its perimeter.

I was so impressed and awe-insipred,... that when i was leaving on the only access road in and out, (hhmm/hmmm/hmmm), i wasn't paying attention,... &

i slamed into a "speed-limit-sign" and it flew over the top of my car !

(... no, of course i didn't report it. ... are u on drugs ?!?)

... If i recall, it was in the spring of '87 ...

Simcha.