The just locked "electric cosmos" thread did have one strand of discussion that I think is worth some further discussion.

landeagle objected to the wet cement and buckets of pellets methods of testing cratering as improper tests of actual lunar conditions.

By the same token, critics of EU/Plasma cosmology often dispute the scaling up of laboratory plasma phenomenon to galactic scales. In addition some similar questions were raised about landeagles page 2 image of a simulated electric cratering.

This does seem to be a serious issue for any laboratory tests designed to simulate phenomenon as they would occur on a much larger scale.

Is the viscosity of wet cement when impacted with an object truly representative of the behavior of the lunar surface when hit with large impactors?

Why can we ... or can't we or how much can we scale up plasma behavior from laboratory to galactic scales?

These sorts of questions seem relevant to both mainstream and ATM astrophysical theories being tested in labs on Earth.

The problem is which parameters determine the phenomena and how they scale with size.

For example, if the morphology of a crater is determined mainly by the kinetic enrgy of the impactor, you can consider flour as a good approximation for regolith in impact cratering experiments.
Of course, assumptions need to be tested.

This is the same reasoning behind engineering tests that use models.

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papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

I touched on this from my own experience with the kind of metalwork that causes the fine particulate dust that he claimed was made by electric arc cratering. I also explained two other methods of of creating the same kind of particulate, both from physical abrasion, and melting the metal while subjecting it to pressurized ejection from the heated area. Abrasion is the method that's specifically mentioned at Clavius.org for the origin of regolith on the moon. In this case, surface soil is ground by loosed boulders from moonquakes. Even the moonquakes themselves will create conditions for regolith powdering on the surface by shaking the dust on the surface to the point where it acts like a viscous liquid, allowing larger material to sink into it over time. The impacts would act to create some amount of regolith when the ejecta is superheated and dispersed, cooling as it falls back to the moon in the form of tectites. Splattered by enough force, it disperses into particles of varying size as it spreads.

The only way where using flour or some other fine particulate in simulations fall short is in the absence of the heating element of impacts. Don't get me wrong, I think its great for simulating the effect, but that's the leg I think landedeagle was trying to stand on with his electric arc cratering. In that case, there is a heat element added and the effects bear some similarity. But when you look at the size of some of the craters that he would attach his electric arc concept to, the arc of energy needed would be unlike anything anyone has ever seen. Its another way of simulating some of the effects, but its no closer to the true nature of cratering causes than the use of flour.

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The last time I felt a warm fuzzy feeling, I was informed by my doctor that it was just gas.

By the way, does any of you ever watch Rough Science?
In the last series, they simulated impact cratering by shooting bullets into sand (you know, for the high kinetic energy).

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papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

Nope, sounds like I missed out on this side of the Pond

I think part of the problem from the other thread is that he was trying to tie the creation of ALL the regolith on the moon to electrical activity, when its more than likely you've got a buncha methods arriving at the end result.

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The last time I felt a warm fuzzy feeling, I was informed by my doctor that it was just gas.

I saw something like that about "killer asteroids". They shot a solid rock with a gun and it disintigrated. Then they shot a pile of smaller rocks - which had little effect. Their point was that if an impending hit from an asteroid involved a "rubble pile" - nukes wouldn't do very much.

Well done Dgruss23. I strongly believe that 'Plasma Cosmology' has many aspects worthy of further consideration and discussion.

I am very (10^23) disappointed that the Top Man, aka The BA, was so quick to ban landedeagle, and I urge him to reconsider. After all, what is the meaning of ATM?

Let's try to get down to specifics, and quit extracting the urine! The behaviour of a number of individuals on the locked thread was utterly disgraceful IMHO. I prefer not to go into detail, but I am very offended.

Landedeagle was new to the board, and quickly subjected to innuendo, sniping, and borderline abuse. This behaviour is unbefitting of this awesome BB.

This is a bit off-topic.
Why don't you go here?

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papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

I have a pretty good real world event I'd like to share.

Quite a few years ago(about 20 years), there was a lightning strike behind my house. It hit a tree, and stripped the bark in really cool candy stripe fashion. You can still see the damage after all these years.

What was real fasinating about this strike is the lighting actually burned a nice trough around the roots. The roots were exposed for about 20 feet. That's a lot of force to produce something like that.

But could this same event I witnessed many moons ago scale up to the point of creating something like the Grand Canyon? It would take an enormous amount of energy to create something that big.

You could (and probably has been done) produce the same effect in a lab given enough power. But does it match real world natural events?

If I were to try and reproduce the same trough effect that I witnessed in a lab on a smaller scale, I would more then likely be able to get the same results, using alot less power. On a larger scale, it becomes trickier. Even if I could re-produce this 'troughing effect' say to 1 mile length and 1 foot deep, does it prove that the theory in question is true? As with any experiment, does it match real world events? I'd say no. Just because you can create an event, doesn't mean it happens like that in the real world.

As far as I know, no natural event has ever been seen, or measured that would account for a massive electrical force that could create craters or canyons. I would think that if this was a true phenomenon, we would have detected it by now.

If we scale up the power necessary to produce craters with electric effects, I would expect the ground to be melted.
Doesn't lighting already melt part of the ground where it strikes, sometimes...? 8-[

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papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

I would say yes. As I mentioned about the roots being exposed in the previous post, the roots no longer had any soil around it. Kind of an awesome and scary display of lightings power.

But to actually create a crater like the one in Arizona? That would have to be one major chunk of current.

edit: spelling.

Fulgarite

Rather than create dust I think lightning is more likely to fuse the ground.

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By asking questions we sometimes get the wrong answers, from wrong answers we learn to ask the right questions.

Modeling a process, IMHO, presupposes an understanding of the underlying processes.

It's not too much of a stretch to assume that phase changes (e.g. melting, vaporization) would occur during planetary-scale collisions. Unless you have good reason to assume that phase changes wouldn't materially affect the outcome, it would seem that a model that includes them (e.g. hypervelocity rail-gun impacts?) would give you a better picture than dropping marbles in a sand pile.

Before jumping to models of questionable validity, should we not make the best use we can of what we can observe in the real world?

Has anybody cataloged the lunar craters? Just looking at them it strikes me that they are predominantly round. Is that an optical illusion? Has anybody looked at the distribution of their eccentricities?

Would a statistical-mechanics approach not yield an expected distribution of masses and transverse velocities at impact? Is there any reason not to expect to see a much larger proportion of highly elliptical craters than we see? What would that say about the mass of the impacting body? Would it almost have to be an electon?!

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Data are plural.

No, even in laboratory impact studies, the craters are predominantly round, even for particles that impact at an angle.

Yeah, I had read as much in other posts here and elsewhere- but I couldn't find the source.

I guess I stumbled over my own stubbornness. When I switched my Google focus from "eccentric" to "round" the first hit out of the chute was a fascinating article concerning the Barringer Meteorite Crater in Aridzona.

In there it is pointed out thatand But, in the same articleand finding a lot ofI'm having trouble visualizing how the "explosion" at the point of impact would fail to carry the momentum of the impact into the crust at an oblique angle- but what if the plasma sheath of ionized air around the meteorite connected the ionosphere to the ground and the resulting arc jumped out ahead of the meteorite just before impact. What if the vaporization of the meteorite was caused primarily by that arc and not "pressure" from the impact?

Hmmm...

'Course all this speculation about the ionospheric connection has no relevance to the lunar case- but in my heart of hearts what I really want to do is tap ionospheric electricity...

Anybody care to speculate what would happen if you established (and were able to control) an ionized conduction path between hither and yon?

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Data are plural.

Think about light entering a medium of higher refractive index--the motion is bent towards the vertical. It's an analogy.
Depends--your head is about 100 volts higher potential than the ground--but a wire held vertically is not going to conduct significant current, nor discharge any significant area.

With "towards" the vertical I have no problem. The analogy may be apt indeed. "To" the vertical, though, sounds like a potential problem.

Interestingly, as I began to look further into this, it turns out that the apparent circularity of the lunar craters didn't go unnoticed by the "mainstreamers" of the early 20th Century. They were trying to fend off a bunch of wild-eyed radical WooWoos (did I use the term correctly?) who were proposing that rocks from the sky were causing the craters when anybody in their right mind knew that they were volcanoes.

Volcanoes make nice round craters. Rocks from the sky should inflict all manner of unsightly scars. We see round craters; ergo, the rocks-in-the-sky guys have rocks in their heads.

"Not so fast", the rockers protest. Think of an impact as a near-instantaneous release of energy- an explosion. We can create explosion models and they make nice round craters; ergo, the volcanologists are old fuddy-duddies and need to get out of the way of those of us who know what we're talking about.

I'm no volcanologist, but I'm still not all that comfortable with the "explosion" bit, either.

Last I heard, melting and vaporization of run-of-the-mill space rocks are highly endothermic processes. We're not talking about reaching a threshold of some kind after which some other process kicks in and releases megatons of potential energy. We're talking very large forces acting over non-zero distances to do enough work to carry out the phase changes very quickly.

Certainly if a suitably massive bolide delivered an off-normal impulse to the moon, conservation of angular momentum dictates that a non-zero net tangential force act to produce a step-function change in the length of the lunar day.

The point of all this is that while an off-axis impact crater may be more circular than one might expect, it still has to produce enough of a net tangential force component to keep the angular momentum people happy. If that didn't result in a departure from circularity of the resulting crater, I'd sure want to know why.

I talked earlier about cataloging "eccentricities". Perhaps that was a little strong. How about "axis-symmetric non-circularies"- a mean-square characterization of a given crater's departure from circularity. There's nothing that says that the complex shock interactioins should produce a simple resultant shape- but it ought to be non-circular.

We've got a vacuum-packed library of all manner of craters right next door on the moon and all kinds of straight-down photography of its content.

Getting back to the spirit of this thread: couldn't we turn a bunch of computers loose characterizing the non-circularity of a large population of them while we carried out hypervelocity impact tests of actual (and/or simulated) asteroidal material and lunar material in the lab? The tests will produce results that could be used to validate computer-generated solutions and a data base of crater non-circularity vs. energy at various impact angles. If simple impacts are all that is happening on the lunar surface, the distribution of non-circularity of the actual craters, the computer predictions, and the lab tests should all match, right?

Obviously, heavy objects fall faster than light ones. No use even running the test, right?

Wouldn't it be ironic if the lunar craters that had to be round enough to satisfy the volcanologists turned out to be too round?! ops:

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Data are plural.

No, but a wire long enough to reach the (conductive) charge layer in the ionosphere that is producing the electric field at the earth's surface sure would!

Assuming that you could throttle it to a usable level- I wonder what it would sound like?

Do you suppose we could ever use enough power to start decreasing the charge to the extent that the average global thunderstorm frequency would drop? Would that be serious?

I wonder what the biological consequences of living in a reduced electric field are? Do you suppose NASA (or whoever) is going to find that they need to supply an electric field along with the artificial gravity on a Mars voyage?

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Data are plural.

Consider the mass of the Earth.
The acceleration that results from this momentum transfer is negligible.


Meteorites have been observed anf filmed.
Has such an electric arc ever been observed (even scaled down)?

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papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

That's why I said "suitably" massive. "Suitable", in this thought experiment, means that it produces measurable and therefore non-negligible effects.

Meteors have been filmed and meteorites have been filmed- but I don't think a meteorite impact had ever been filmed until Shoemaker-Levi 9-- and I'm not sure we were close enough to see enough detail.

Are there not instances of "clear-air lightning" reported? Perhaps those are the "lightning" half of a meteor/lightning pair where the meteorite burned up too high to be detected...

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Data are plural.

Albiet, you're acting nicer, I thought you got banned...

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Feynman
>~~~~<
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.

Religion is a culture of faith; science is a culture of doubt.

spacechip wrote:
Laboratory scale cratering at a variety of angles have been conducted at the Vertical Gun facility at NASA/Ames since the 60's or 70's. What they show is that the craters stay essentially circular for oblique impacts down to about 15 deg. However the ejecta start showing varying patterns at higher angles.

basic description of the Ames Ballistic Range Complex
http://quest.nasa.gov/people/journal...sticrange.html

Also, here is a list of hypervelocity impact facilities:
http://www.fas.harvard.edu/~planets/othershocklabs.html

"Essentially circular" is a long way from immeasurably non-circular...

The moon isn't famous for its atmosphere- but I'll bet I can fire a clod of dirt past its limb close enough to just barely cause a loose grain of lunar soil on top of a hill to roll down the far side of the hill.

Lower the trajectory a little, and I'll bet I can carve a pretty impressive gouge in that same hill with a similar clod fired at the same velocity.

It may well be surprising how quickly the craters caused by subsequent clods fired closer and closer to normal incidence approach circularity- but is there any reason not to expect that you can produce a fairly repeatable continuum of shapes in between?

How would folks who hold to the contrary reconcile their position with the conservation of momentum?

I'll grant that the ejecta may carry away some fraction of the momentum- but how can the distribution of their initial velocities fail to be reflected in the shape of the crater they leave?

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Data are plural.

And what is the likelihood for this to happen with a meteorite?

Don't you think that the shape of the crater might depend on the kinetic energy, rather than on the shape of the meteorite?

What is there to reconcile?

"Some fraction"?
Do you think that the ejecta are like pieces of a jig-saw that fit the shape of the crater?
And why do you say "how can the distribution of their initial velocities fail to be reflected in the shape of the crater they leave?"?
What makes you think that it is not?

In the case of the Earth, "suitably massive" would be the Moon.
What about more common meteorites?

What about the instances where meteorites have been filmed on Earth and no lightning has been observed?

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papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

"Clod" / "Meteorite"... What's the difference?

Why should there be anything other than a uniform distribution of initial velocities?

OK, the existence of the target gravitational potential well will influence the radial component, but there is no obvious reason for the tangential component to be other than random.

Bottom line: I would guess that all angles of incidence are equally likely and the likelihood of it being in any particular band would depend only on the width of the band.

I don't think I said anything about the shape of the meteorite...

I would expect kinetic energy and angle of incidence to be the drivers- modified by the material and, to a lesser extent, the geometric properties of the bolide and the impact surface. The result of a series of simulated impacts should be a distribution of distinct crater shapes that you could compare with the actual lunar distribution.

In hand-waving terms: if you’re going to model an impact as the spherically symmetric decompression of a stationary silk purse at or near the surface (AKA "explosion"), then you are also going to have to model how the decidedly non-spherical sow’s ear that you start with gets into the purse.

My contention is that the processes in the down-stream direction have to be different enough from the upstream processes that the result when the dust settles nearly has to be a somewhat non-circular "rim".

The mass of the ejecta should certainly equal the mass of the “missing” material in the crater plus the mass of the bolide less the excess mass of the compressed material in the crater wall …

...Because I seem to be hearing folks say that you can have excess downstream ejecta from a perfectly circular crater.

I was merely pointing out that if you wanted to "spin up" the moon, you would hit it with oblique impacts- and to the extent that was successful, you would expect to see different crater shapes and ejecta distributions between oblique and normal impacts consistent with the momentum flux.

That's what you would expect if they burn up before they get close enough (or never approach closely enough) to generate breakdown potential in the air gap to the ground.

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Data are plural.

Stepping back from this for a bit and sleeping on it may have helped me look at things from a slightly different perspective...

I guess I have been too focused on the bolide/target interface. Maybe the key to getting the sow's ear into the silk purse is the lee-side ("free") surface of the bolide.

As the bolide decelerates and comes to rest relative to the target there is a reaction force acting over a time interval that transfers the bolide momentum to the target as you would expect. I guess the interesting stuff happens with the mass elements on the lee side of the bolide. Apparently that surface will deform and the deceleration forces acting over the displacement distance do the work needed to establish the initial conditions for the subsequent "explosion". I can see shear forces deforming the bolide and causing it to melt- but I confess that I can't even imagine a mechanism that would cause vaporization...

Ah! Pressure release!

Ok. So the front and back surfaces of the bolide come to rest WRT each other and to the target and then start to rebound. I'll bet that would look a whole lot like an explosion! I'll bet the ejecta would actually go back in the direction from which the bolide came! If that's the case, though, I'd still expect the downstream wall of the crater to at least be thickened- if not measurably displaced.

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Data are plural.

I asked for the likelihood of an impact significantly far from the direction normal to the surface.

Because the distribution of objects in the Solar System is not necessarily uniform.

Even if the initial direction is random, what is the probability for a hit far from the normal to the ground?


What do you mean with "band"?

And how do you know that they have not done it already?

I do not think that this analogy fits actual meteorite impacts.

What makes you think that the "rim" is due to "settled dust"?

You were talking about the shape.

As far as I understand, you expect non-circular craters from oblique impacts.
The point is: why do you expect this?

If the impact is oblique, I expect the distribution of ejecta to reflect this, but I do not expect the crater to be non-circular (for impacts that are violent enough to form a crater).
Why do you expect the shape of the crater to reflect the "obliqueness" of the impact trajectory?

Sorry, but that's what you would expect.
The question is: why do expect this?

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papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

What is the typical speed of a meteorite when it hits the ground?

What is the kinetic energy compared to the energy that holds the material together?

If the kinetic energy is converted into heat, would it be enough to melt it? To vapourize it?
(Compressing a material usually heats it.)

If it vapourizes the meteorite, wouldn't it be a proper explosion?
(Chemical explosives make explosions because the material is converted into gas.)

If there is enough energy to make a crater, would it make any difference if the trajectory was not normal to the surface?
(If it explodes, why would it have a preferential direction?)

If there is enough energy to make a crater, is the size of the crater much larger than the size of the meteorite (making the "obliqueness" of the trajectory irrelevant to the actual shape of the crater)?

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papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

Perhaps you are confusing asteroid impacts with falling objects...

Let me turn the question around. What is the likelihood of a normal impact?

"Normal" incidence means the tangential velocity component is zero. In the absence of atmospheric drag the only force acting is the mutual gravitational attraction of the bolide and the target. That force, by definition, is normal to the tangential directions, so the only way you can wind up with a zero tangential velocity is if you start with one.

Technically, the likelihood of precise normal incidence is zero. The "band" bit comes in when one more properly asks about the likelihood of incidences within such-and-such degrees of normal.

I am sure "they" have looked at impact angle vs. crater shape. All I hear, though are vague pronouncements that the shapes are "roughly" or "essentially" circular.

What I'm not sure of is whether anybody has looked critically at the distribution of departures from circularity on either the simulated or the actual craters.
Am I talking to an artificially intelligent computer program here?

Settling dust, pigs' ears and silk purses are figures of speech! #-o
Aha! Precisely because the ejecta are asymmetrical! Can you propose a mechanism that would create an asymmetrical ejecta distribution without leaving an asymmetrical crater?

Abstract away the bolide and start with dynamite and flat ground. You sure won't get anything asymmetrical with a spherically symmetric explosion!

Would you not have to start with a shallow depression and a mat-shaped charge in a non-horizontal orientation? Would you seriously expect such a blast to leave a round hole?
Yes, I would expect that if the meteorite burned up before it got close enough to the ground, the ionized-air conducting path (think equipotential surface) that it had been generating would terminate and whatever field strength (volts/meter) it had achieved at that point would start to drop. If that field strength were less than breakdown strength there would be no electrical discharge. The same would hold for a secant trajectory whose closest point of approach was higher than the minimum.

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Data are plural.

My vague pronouncement came from Jay Melosh’s 1989 book Impact Cratering, A Geologic Process. He addresses oblique impacts in a few places :
“Although all but the most oblique hypervelocity impacts (&lt;10 deg) produce circular craters, their ejecta blankets have a bilaterally symmetric ‘butterfly wing’ pattern that becomes progressively more marked as the obliquity increases.”
I was hedging a little by saying "essentially".

Apparently only the vertical component of impact velocity (down to 10 deg) is responsible for crater shape. The shock wave in the target stays hemispherical but the energy coupling becomes less efficient at higher angles of impact so that smaller craters are formed. He does say that at the time there was little quantitative understanding of oblique impacts except for laboratory scale experiments at Ames. A recent review on on oblique impacts, which I haven't seen yet, was published in 2000. The full text is only available online via subscription.
http://tinyurl.com/4s24t