Bullet-fast moon rocks carved 2 lunar gorges deeper than the Grand Canyon

[Admin]

The lunar canyons Vallis Schrödinger and Vallis Planck are extraordinarily deep, and scientists now know the valleys were carved by bullet-fast moon rocks.

Bullet-fast moon rocks carved 2 lunar gorges deeper than the Grand Canyon : Read more

 

[m4n8tpr8b]

Interesting article, and the paper it is based on is even more interesting.

Craters have the paradox that they are almost round regardless of the impact angle (well within bounds, the shallowest impact angles do produce oval craters). The basic level explanation has to do with the conservation of momentum an energy: most of the kinetic energy of the impacting object is turned into heat and a shock wave travelling through the impacted body outwards, turning into the kinetic energy of the ejecta (which has orders of magnitude higher mass than the impacting object), much of the moment is carried by a small portion of the ejecta that also has the highest velocity. But more detailed simulations (cited in the paper) show this is a simplification: at shallower impact angles, the original impact point will be at the uprange edge of the eventual crater, and the ejecta will leave in a butterfly pattern, with the fastest ejecta focused along certain directions, and the exact pattern depends on many factors (impact angle and speed, impactor size, surface gravity of the impacted object.)

Even the paper doesn't say so but the ejecta-produced canyons of the Schrödinger Basin still don't resemble any of the simulated patterns from earlier studies, in particular their angle. It's worth more research.

 

[Unclear Engineer]

A couple of thoughts:

First, the velocities stated in the article don't seem particularly high, to me. The muzzle velocity of a typical military rifle round is about 2,200 mph, and the fastest rifle cartridge muzzle velocity is about 2,700 mph. Escape velocity from the Moon is only about 5,100 mph.

A single "bullet" that shot straight through 170 miles of rock would be impossible, though. But that is not what the subject paper is saying happened. The hypothesis of the paper is that streams of rocks were ejected from the impact point along 2 rather narrow directions, and those rocks came down in the two straight lines to make strings of secondary craters. Although that does seem much more plausible than a single, very low angle projectile being able to penetrate so far sideways, the pictures of the resulting canyons look more "plowed through" than a bunch of circles strung closely together. So, I am trying to envision a stream of rocks flying at low angles such that the near ones hit and make craters that are quickly extended on their far sides as additional rocks hit their rims and make additional craters farther from the initial impact site. And so on, for 170 miles in a straight line. Actually 2 straight lines.

That sort of makes sense to me But the narrowness of those 2 streams of rocks diverging from each other by a substantial horizontal angle makes me wonder it those rocks were more related to the original impactor breaking/exploding into 2 pieces, rather than some sort of inhomogeneity in the impacted surface that could have directed the surface ejecta into such tight patterns in 2 directions, as well as making the other observed spread pattern of ejecta.

Even when (if) astronauts get there to take a close look, it is probably going to be long time before humans get to travel distances like 200 miles across broken lunar terrains. So, info may be slow coming.

 

[whoknows]

Are there antipodal maps for the Moon with meaningful data?

Mars might have linked "opposites"
eg :-

"The shield volcano Alba Mons however is almost exactly antipodal to the Hellas Basin."

Are Tharsis Montes and Hellas Basin a result of the same event?

Looking at Mars map: the highest, biggest mountains and their associated highlands are essentially antipodes of the deepest, huge basin. Roughly 180 degrees away, similar latitude except opposite ...

astronomy.stackexchange.com

Interpret that how you will, but it would be interesting to see if there are antipodal formations corresponding with the Schrödinger and Aitken basins? (and separately the Moon's mares)

 

[m4n8tpr8b]

But the narrowness of those 2 streams of rocks diverging from each other by a substantial horizontal angle makes me wonder it those rocks were more related to the original impactor breaking/exploding into 2 pieces, rather than some sort of inhomogeneity in the impacted surface that could have directed the surface ejecta into such tight patterns in 2 directions, as well as making the other observed spread pattern of ejecta.

Are there antipodal maps for the Moon with meaningful data?

Mars might have linked "opposites"
eg :-

"The shield volcano Alba Mons however is almost exactly antipodal to the Hellas Basin."

Are Tharsis Montes and Hellas Basin a result of the same event?

Looking at Mars map: the highest, biggest mountains and their associated highlands are essentially antipodes of the deepest, huge basin. Roughly 180 degrees away, similar latitude except opposite ...

astronomy.stackexchange.com

Interpret that how you will, but it would be interesting to see if there are antipodal formations corresponding with the Schrödinger and Aitken basins? (and separately the Moon's mares)

That sort of makes sense to me But the narrowness of those 2 streams of rocks diverging from each other by a substantial horizontal angle makes me wonder it those rocks were more related to the original impactor breaking/exploding into 2 pieces, rather than some sort of inhomogeneity in the impacted surface that could have directed the surface ejecta into such tight patterns in 2 directions, as well as making the other observed spread pattern of ejecta.

There was no breaking into pieces, and inhomogeneity of the impacted surface also can only have little influence. This was an impact by an object dozens of kilometres across. Even a hundred-metre object would completely melt upon impact, along with a lot of mass of the impacted surface, and the ejecta pattern is produced by shock wave and fluid dynamics. Those two canyons weren't all the ejecta (you can see the ejecta blanket map in the paper), it was just the highest-velocity part of the ejecta.

If you check another paper, cited as source 44 in this paper, you can see several nice diagrams showing the pattern and evolution of ejecta blankets at different impact parameters. At shallower angles, two streams of high-velocity ejecta seem quite common, albeit in those simulations, the angles differ from those for the Schrödinger Basin, so some other factor modified the pattern.

Even when (if) astronauts get there to take a close look, it is probably going to be long time before humans get to travel distances like 200 miles across broken lunar terrains. So, info may be slow coming.

I don't think astronauts are of much use for observations of these canyons.

 

[Unclear Engineer]

I have not read deeper than the cited paper, so don't know details in the paper's references.

So, I am wondering about the posted statement that the impacting material would be "completely melt upon impact".

How does a rubble pile asteroid melt immediately in a homogeneous manner? Or a comet?

Especially if there were substantial amounts of more volatile constituents with less volatile clumps, I can visualize all sorts of non-uniform dispersal patterns. And, with an impactor estimated at dozens of kilometers across, impacting directly at a shallow angle, without interactions with an atmosphere, it seems most likely to me that the first effects would occur on the lower edge and propagate upward through the impactor, perhaps spreading and even somewhat lofting the upper fragments before they reach the surface of the Moon farther along the impactor's initial trajectory.

Actually, it is hard for me to accept a model that simply assumes the impactor instantaneously and uniformly transforms from solid to a liquids before any dispersal. Is that what the paper assumes in its simulations?

 

[m4n8tpr8b]

Interpret that how you will, but it would be interesting to see if there are antipodal formations corresponding with the Schrödinger and Aitken basins? (and separately the Moon's mares)

On Mercury, the Caloris Basin has an antipodal chaos region. Given that the Moon is smaller while the South Pole-Aitken basin is larger, there certainly was an antipodal chaos region. However, don't look for it, because the crater formed when the Moon was very young and several massive impacts followed, blanketing older features in their own ejecta and eroding them with moonquakes.

For the Schrödinger Basin, go here, change Projection to "Lunar Globe (3D)", and type "-75,132.4" into the search field. (You'll see the whole crater from about a height of 500 km.) You'll find the antipodal region by typing in the antipodal coordinates, which are "75,312.4". It's not particularly noteworthy because it is a bunch of old craters filled with younger lava just like neighbouring areas, thus even if there was a chaos regio, it is mostly covered in the lava.

 

[m4n8tpr8b]

I have not read deeper than the cited paper, so don't know details in the paper's references.

So, I am wondering about the posted statement that the impacting material would be "completely melt upon impact".

How does a rubble pile asteroid melt immediately in a homogeneous manner? Or a comet?

By the time it hits a solid body, it doesn't matter what the impactor is composed of - it can be solid iron or it can be a dense cloud of dust, if it has the same mass, and reaches the bottom of the atmosphere at the same speed, the end result is basically the same. Consider the amount of kinetic energy that has to be absorbed and the time in which it has to be absorbed. Asteroids travel at speeds in the range of dozens of kilometres per second. They cannot sustain any structural integrity and will completely melt upon impact in about the time it takes for the asteroid to travel a distance equivalent to its diameter. Even for an impactor as large as necessary to form the Schrödinger Basin, this is just a second or two. It will take several more seconds for the shock wave to travel outwards and excavate the initial crater (which is roughly ten times wider than the impactor, with a volume hundreds of times larger), during which time a lot of impacted material also experiences enough extreme pressure & shear & heat to also melt.

In fact, in vacuum, even fist-sized impactors are enough to produce a plasma "fireball", which is visible by telescopes on Earth as flashes of light. That's how impacts on the Moon have been observed in recent years.

Actually, it is hard for me to accept a model that simply assumes the impactor instantaneously and uniformly transforms from solid to a liquids before any dispersal. Is that what the paper assumes in its simulations?

I didn't say "instantaneous", nor did I say that it is an "assumption". Such simulations are complex 3D simulations that consider all the relevant laws of physics and material properties of both impactor & impacted ground. The melting - in fact, to a good part, vaporization - of material can be seen as a result of the simulations.

 

[Unclear Engineer]

Still, in the end, the results visible on the Moon and in the simulations that try to mimic it are not uniformly distributed. There are those 2 canyons going out in straight lines, plus a more common splash/spray pattern of similar extent. So, there are clearly some dynamic processes that are more complex than impactor-hits-surface-and-melts going on.

I even wonder if "upper" parts of the impactor retained sufficient velocity to escape the Moon's gravity and not impact anywhere. With the moons escape velocity at only 2.4 km/s, it seems like something moving at "dozens of kilometers per second" and striking at a shallow angle would be a good bet for partially escaping back into space. Probably shedding slower moving material under it along its path. Or, paths, if it broke apart during the impact.

While 3D simulations are modeled based on laws of physics, they necessarily contain assumptions about various important parameters, even at the individual finite element level. When those are not known for sure, a variety of possibilities is usually tried.

Modeling is not "truth", but rather an attempt to understand how something observed could have come to exist/occur. There is a tendency for modelers to think they have the right answer when they can at least roughly produce the observed effect with a simulation. But, that has substantial vulnerability to confirmation bias. There are plenty of examples in science of theories that seemed to be supported by evidence being overturned by further analysis showing the same results due to different phenomena.

So, it would be interesting to know how detailed the 3D simulations were with respect to the dynamics of the impactor morphology changes. How do the kinetic energies and momenta of the upper parts of the impactor get changed? By impacting the surface themselves, or by effects from lower impactor parts having already impacted the surface?

And, with the high fraction of orbiting pairs of asteroids, even of pairs stuck together, along with the tidal disruptive forces of encounters with massive bodies like the Moon (and nearby Earth), how are we even sure that there was only one impactor part to begin with?

 

[m4n8tpr8b]

Still, in the end, the results visible on the Moon and in the simulations that try to mimic it are not uniformly distributed.

I never said anything about uniform distribution, in fact, quite the opposite.

So, there are clearly some dynamic processes that are more complex than impactor-hits-surface-and-melts going on.

I never said there weren't. I only countered your idea that the pattern could have been produced by surface features or the impactor breaking apart, which severely underestimates the impact energy and its effects on the impactor & impacted terrain. That is: the impact does much more than break the impactor into pieces.

I even wonder if "upper" parts of the impactor retained sufficient velocity to escape the Moon's gravity and not impact anywhere.

Parts of the impactor: unlikely, again because of the melting/evaporation, and also the direction change. However, you're not that far off, because parts of the blasted-out impacted ground can very well reach escape velocity. In fact, that's how meteors from the Moon and Mars could get to Earth, and we even have identified some small near-Earth asteroids that had to be ejecta from the Moon due to their very Moon-like surface composition (read up on Earth's quasi-satellite Kamo'oalewa, for which we could even identify the crater it came from, and it wasn't even that big of a crater).

Modeling is not "truth", but rather an attempt to understand how something observed could have come to exist/occur.

Modelers are much more aware of this than you are You should really read the paper I suggested.

How do the kinetic energies and momenta of the upper parts of the impactor get changed? By impacting the surface themselves, or by effects from lower impactor parts having already impacted the surface?

That depends on multiple factors, above all the impact angle.

Right upon first contact, several processes start at the same moment: evaporation of both impacting and impacted material and its expansion due to tremendous pressure, shock waves travelling through both at the speeds typical for solid materials (much higher than the speed of sound in air but still much slower than the asteroid's impact speed) and breaking them apart at a microscopic level, elastic compression of the impacted ground (in the case of such a big impact, on the scale of kilometres!) that will eventually lead to a rebound (this is what produces central peaks or rings in larger craters; including the prominent ring still visible in spite of lava fill-up in the Schrödinger Basin); the mixing together of impactor and impacted material; and more. We are talking about the big picture but it is actually a rather complex process.

During the course of the impact, the original material of the impactor will first deform greatly. Exactly how depending on the angle of impact: in a steeper impact, the entire asteroid material gets squished lie a dropped fruit, but in a shallow impact, it might get elongated and the lower to upper parts can progressively impact the ground.

However, progressively, you cannot talk about the original impactor material separately as it will mix with the impacted material, and in fact a good part of this mix will rise above the forming crater in a giant fireball (the one key element of big impacts almost never shown in films & TV shows). Do you know about the iridium that was found in the rock layer separating the Cretaceous and Paleogene (formerly Tertiary) layers around the world and was the first evidence for the asteroid that killed the dinosaurs? That iridium is not in the form of nuggets or dust, it is trace amounts found everywhere in what used to be material similar to ash. It is actual material from the impactor that condensed out of that fireball and got everywhere around Earth through the atmosphere, "contaminating" the fallen-back ejecta and the dust clouds in the atmosphere that caused the decade-long 'nuclear winter'.

And, with the high fraction of orbiting pairs of asteroids, even of pairs stuck together, along with the tidal disruptive forces of encounters with massive bodies like the Moon (and nearby Earth), how are we even sure that there was only one impactor part to begin with?

That's actually half a good point: a contact binary might produce more weird eject patterns. (I recall reading that there were already simulations of such impacts but the one study referenced above did not cover it.) Binary asteroids with larger separation would produce not only more weird ejecta patterns but also non-circular craters, though.

 

[m4n8tpr8b]

This is as good a place as any to talk about how giant impacts in fiction cannot fully show how extreme conditions are.

In Armageddon, a giant asteroid is split into two halves that recede enough in a day to both fly past Earth. Given that gravity between the two halves will slow the separation, how big Earth is, and how its gravity will change the orbit of the two halves, the separating blast would need to give the halves an initial speed in the order of hundreds of metres per second. The adteroid being the size of Texas, even if it had just the density of water, the separating blast would need to be in the order of dozens of billions of megatons. And, of course, even if the asteroid would be a contact binary rather than the weird non-compact but single-body ice dwarf in the movie, you would get a lot of large splinters in the middle in addition to the two big halves, and those would be enough to wipe us out.

In Deep Impact, minutes before impact, the impactor is blown into tiny pieces that harmelssly burn up in the atmosphere. But those tinly pieces would carry the same kinetic energy. Even if the first few hundred pebbles in each square metre burn up, they would clear the way for millions more behind them, and you would still get a crater the same size. Things would be better if the blowing into tiny pieces happened not minutes but days before impact and the cloud of pebbles could expand to say 1,000 km across. But they would still carry all the kinetic energy and deposit that into the atmosphere, along with high-altitude dust, causing severe climatic distruption at the least.

Also in Deep Impact but also in several other films/shows, you have people looking up in the sky in horror as an approaching asteroid starts to burn in the upper atmosphere before impact. In reality, the asteroid would be brighter than the Sun, blinding eyewitnesses and giving them severe burns. (Even the Chelyabinsk meteor caused milder injuries of these kinds).

One thing almost never shown on screen (the only I can recall is in the TV show The Expanse) is that immediately after impact, a giant fireball will rise above the forming crater. This again will be much brighter than the Sun (for several seconds for a large impact), in fact, much worse than before impact: its radiation heat is enough to set anything alive with direct line of sight on fire. (For the Chixculub impact, the affected area extended as far as Florida.) This is the most immediate effect of the impact, arriving before the earthquakes, the airblast, the falling-back ejecta and the secondary fires it starts, and the tsunami (more or less in that order).

In Greenland, people hide from an impact in bunkers. But the earthquake would shatter those bunkers and shake everything inside apart even if not, no way life support systems would keep functioning.

 

[Unclear Engineer]

m4n8tpr8b, I am aware of much that you have posted, including the iridium layer attributed to the Chixculub impact, the intense light/heat flashes from the kinetic energy released from impactors, even if they "burn-up" in the atmosphere before reaching a solid surface, the "pieces of the Moon" in solar orbits, etc.

I have also read the paper that is the subject of the Space.com article, and note that it is based on correlations of parameters from experiments, but does not appear to have been simulation modeled in 3D by the authors or any references.

The paper itself notes conflicting inferences and alternative assumptions. I take it as a good attempt to explain how 2 narrow streams of secondary (?) impactors could have formed the observed canyons.

But, I do not see any discussion of how 2 such tightly focused streams of secondary impactors could have been formed during the impact.

That is what I have been speculating about in my posts here.

And, my speculating seems to bother you, for some reason.

So, I think it is on you to show that this impact is so clearly understood that we fully understand how the two very narrow streams of secondary impactors were formed.

You posted about 3D simulation models. If you are aware of any 3D calculations for this impact event that clearly show results that produce the observed canyons in the observed orientations , depths, lengths and especially widths, I would be interested in reading reports about those specific simulations. It would be especially interesting to see how whatever mechanism(s) involved would not include any asymmetries in the impacted terrain, nor the impactor(s), as you seem to be asserting must be the case.

Frankly, I seriously doubt that the observed results could be the likely outcome of an impactor effectively turning into a molten glob of mixed impactor and surface material simply spraying in a manner unconstrained by any pre-impact parameters of the impactor(s) or terrain impacted. But, if you have some analyses of the internal dynamics of shocked molten blobs making such patterns, please direct me to them.

 

[whoknows]

On Mercury, the Caloris Basin has an antipodal chaos region. Given that the Moon is smaller while the South Pole-Aitken basin is larger, there certainly was an antipodal chaos region. However, don't look for it, because the crater formed when the Moon was very young and several massive impacts followed, blanketing older features in their own ejecta and eroding them with moonquakes.

For the Schrödinger Basin, go here, change Projection to "Lunar Globe (3D)", and type "-75,132.4" into the search field. (You'll see the whole crater from about a height of 500 km.) You'll find the antipodal region by typing in the antipodal coordinates, which are "75,312.4". It's not particularly noteworthy because it is a bunch of old craters filled with younger lava just like neighbouring areas, thus even if there was a chaos regio, it is mostly covered in the lava.

Many thanks for the link, it seems to be a great resource and just what I was looking for. Your first paragraph highlights several points of interest which I am now better armed to look at.

 

[whoknows]

Inputting the coordinates for the Schrödinger Basin and zooming out gives this broader context :-

QuickMap

LROC QuickMap, a powerful map interface to browse Lunar data from NASA/LRO and other missions. Explore the Moon in both 2D and 3D. Developed by Applied Coherent Technology and customized for the LROC team at ASU

quickmap.lroc.asu.edu

Imo (layman) the channels/canyons seem too insignificant and too subtly defined to have been produced by such a major impact event.

 

[m4n8tpr8b]

But, I do not see any discussion of how 2 such tightly focused streams of secondary impactors could have been formed during the impact.

That's because that question is more general and itself just a part of the even more general issue of asymmetric ejecta, and not subject of that particular study, but it is of some of the previous papers referenced in that study. Scientific papers aren't like news articles, giving the full picture, they always build on prior research and assume that the reader either knows those or has the patience to read them if not.

I have repeatedly referred you to one of the papers referenced in the paper on the two canyons in the Schrödinger Basin ejecta blanket. That study is not a simulation specifically meant to reproduce this ejecta pattern in particular, but a general study of the motion of ejecta when you vary a lot of different parameters (impact angle, speed, impactor size, surface gravity). If you had checked that article, you would have seen that ejecta patterns of many different asymmetric shapes are possible, with some of them showing two tightly focused high-velocity parts of the ejecta (while others showing even more complex forms).

I have stated at the very onset that the simulations aren't a perfect match for the specific case of the Schrödinger Basin, thus further research is needed.

That is what I have been speculating about in my posts here.

And, my speculating seems to bother you, for some reason.

There is nothing wrong with speculating, and you should focus on my technical arguments instead of divining my emotional state. I was just trying to explain to you that your first two ideas presented so far don't cut it, and why. To repeat myself, the simulations aren't a perfect match for the specific case of the Schrödinger Basin, thus further research is needed; but that doesn't mean that your guesses for additional factors cannot be ruled out. (I already told that your third idea of a contact binary does have merit.)

Attempting to hammer this home yet another time: a break-up of the asteroid into two parts upon impact or the impacted surface doing some focusing cannot be it because of the magnitude of the velocities, energies, timescales involved.

You think of break-up like an instantaneous event, as if when you throw a rock. But a rupture in a solid body progresses only at Raleigh wave speed at maximum, which is a fraction of the speed of the asteroid, and even if there was a split, the entire duration of the impact is too short for the two parts to gain any distance between them before everything gets evaporated. And whatever the impact parameters, large-scale melting/evaporation is a certainty, due to the magnitude of the kinetic energy that has to be transformed in a very short time.

Focusing by surface features cannot happen because at these scales, the surface is not a rigid body at all. For large impacts, any surface features are destroyed by crater excavation and substrate compression (which,for impacts of this size, can make the initial crater as deep as 50 km before the rebound). Furthermore, I have to repeat that the overwhelming bulk of the ejecta is not from the impactor, but from the impacted surface - the very material you think is doing focusing.

So, again, by any means, keep speculating, but not all ideas have equal merit, and you can come up with better ideas if you get a better understanding of what we already know about impact processes.

 

[m4n8tpr8b]

Imo (layman) the channels/canyons seem too insignificant and too subtly defined to have been produced by such a major impact event.

To address your concerns, I would need to know what you mean by "too insignificant" and "too subtly defined" - for example, what would you think of as significant, by which quality of those features.

For me, at multiple kilometres deep and hundreds of kilometres long, those features are quite significant, in fact I can understand why Unclear Engineer can be so startled at this very strong asymmetry in the ejecta. If you zoom in, between the two big canyons but also to the south of them, you can notice some smaller & shorter depressions/crater chains that point at the basin, and you can also notice some regions where the smooth surface of an old crater bottom or between-craters plain is interrupted by some rugged terrain - large amounts of slower-moving ejecta covering the surface. All in all, a complex ejecta pattern.

Perhaps it's educative if you look at some other ejecta patterns.

Go to (-19.5,265). That's an impact basin with a similar size to Schrödinger, but with pronounced ring structures (formed by seismic waves) surrounding it: Mare Orientale. Zoom out until you see the full disc of the Moon, and you see several crater chains radiating from it. None of them are as deep as Schrödinger's two biggest.

If you go to (-43.35,348.7). You'll see Tycho crater,the youngest large crater. Zoom out until you're at a height ("dist to cursor") of 2,000 km. To the northwest (top left), you'll see a pronounced ejecta line which is of lighter color than the surrounding landscape. If you zoom in on it, you won't see many crater lines associated with it: it has a different color due to different material quality, but some more tens of millions of years of cosmic radiation & solar wind will make them fade away. However, if you move to the root of this ray near the crater, you'll see two crater chains at its edges, shorter and less pronounced than for Schrödinger but still unmistakable.

Next, go to (9.2,339.8). That's another younger crater, Copernicus, but it is on a region that was mostly covered by lavas associated with Mare Imbrium, the second-largest lunar impact basin, thus there are few older craters. You don't see any pronounced rays, on the other hand, you can see the spread of the ejecta rather well. But I want to call your attention to some features to the northeast (top right) and east (right), about one and hald crater diameters from the crater: you see crater chains which aren't ina line radiating from the crater, rather meandering, but are clearly associated with the ejecta blanket.

 

[Unclear Engineer]

I have looked through the paper that is the link for reference 44 of the paper that is the subject of the article, and do not see patterns that look substantially like the canyons in the Schrödinger Basin ejecta blanket.

I'll note that modelling was done for half of the ejecta pattern and assumed to be symmetrical. But, the subject paper of the article finds an inconsistency between the inferred path of the striking object based on (1) the orientation of the eject blanket shape and (2) assumed symmetry of the two canyon angles about the incoming path. So, it is not certain that the canyons are symmetrically angled away from the path of the impactor.

For models of shallow impact angles, there does seem to be a concentration of the ejecta to the side, at the edge of the eject patterns, especially for large impactors. But, those are not in the same sort of orientation as the observed canyons, nor do they look narrowly enough constrained to produce something as narrow as the observed canyons. It is finite element modeling, and is pretty coarse grained compared to the actual lunar observations. But, neither the text nor the figures seem to indicate any explanation for such narrow canyon production.

That modeling also is based on a single, undifferentiated impactor. I am still trying to think about how a rubble pile asteroid would really behave during a low-angle impact. If the asteroid had already been tidally disrupted before impact, so was impacting as a cluster, with variations in timing and impact location, it seems like there could be a lot of complexity to the ejecta field. And perhaps the orientation of the individually struck parts of the surface was already disrupted for some impactors by the initial impacts when the following impacts occurred. At the impact speeds considered, could the forming wall of the initial craters be high enough before the following impactors hit them to substantially alter the overall ejecta pattern?

I am still not seeing a logical reason for such an intense focus of the Schrödinger Basin ejecta into those 2 very straight, very narrow "rays".

I did take a look at -19.5,265 on the Lunar Quickmap, and do see a lot of linear "rays" of small craters that seem to be coming directly from the impact crater. But, there are many, spread over a very wide angle, and as m4n8tpr8b posted, they are not as deep as the 2 from the Schrödinger Basin.

I am guessing that there is something about the resolidification of the impact melt that tends to coalesce the molten rock into streams that then fragment before impact to make strings of craters.

Anyway, thanks to m4n8tpr8b for the link to the Lunar Quickmap. I will probably be using that for a long time.

 

[whoknows]

To address your concerns, I would need to know what you mean by "too insignificant" and "too subtly defined" - for example, what would you think of as significant, by which quality of those features.

For me, at multiple kilometres deep and hundreds of kilometres long, those features are quite significant, in fact I can understand why Unclear Engineer can be so startled at this very strong asymmetry in the ejecta. If you zoom in, between the two big canyons but also to the south of them, you can notice some smaller & shorter depressions/crater chains that point at the basin, and you can also notice some regions where the smooth surface of an old crater bottom or between-craters plain is interrupted by some rugged terrain - large amounts of slower-moving ejecta covering the surface. All in all, a complex ejecta pattern.

Perhaps it's educative if you look at some other ejecta patterns.

Go to (-19.5,265). That's an impact basin with a similar size to Schrödinger, but with pronounced ring structures (formed by seismic waves) surrounding it: Mare Orientale. Zoom out until you see the full disc of the Moon, and you see several crater chains radiating from it. None of them are as deep as Schrödinger's two biggest.

If you go to (-43.35,348.7). You'll see Tycho crater,the youngest large crater. Zoom out until you're at a height ("dist to cursor") of 2,000 km. To the northwest (top left), you'll see a pronounced ejecta line which is of lighter color than the surrounding landscape. If you zoom in on it, you won't see many crater lines associated with it: it has a different color due to different material quality, but some more tens of millions of years of cosmic radiation & solar wind will make them fade away. However, if you move to the root of this ray near the crater, you'll see two crater chains at its edges, shorter and less pronounced than for Schrödinger but still unmistakable.

Next, go to (9.2,339.8). That's another younger crater, Copernicus, but it is on a region that was mostly covered by lavas associated with Mare Imbrium, the second-largest lunar impact basin, thus there are few older craters. You don't see any pronounced rays, on the other hand, you can see the spread of the ejecta rather well. But I want to call your attention to some features to the northeast (top right) and east (right), about one and hald crater diameters from the crater: you see crater chains which aren't ina line radiating from the crater, rather meandering, but are clearly associated with the ejecta blanket.

Many thanks for your input.

re " To address your concerns, I would need to know what you mean by "too insignificant" and "too subtly defined" - for example, what would you think of as significant, by which quality of those features."

I totally agree - I could blame tiredness, a lagging computer and a cat demanding attention - so I will !

re "Imo (layman) the channels/canyons seem too insignificant and too subtly defined to have been produced by such a major impact event."

Wrt " too insignificant", - I meant that in the sense that I thought there might be more evidence of an impact. That they are so significant begs questions for me relating to the former.

I need to re-appraise that after I have looked at your references.

Wrt "too subtly defined", again so.

What I find hard to imagine, focussing particularly on the Vallis Schrödinger, is how over a distance of 170 miles or so, with associated high temperatures and presumably deformation, and loss of velocity, a high speed impactor will maintain its integrity in a way that such a uniform channel might be the result.

 

[m4n8tpr8b]

What I find hard to imagine, focussing particularly on the Vallis Schrödinger, is how over a distance of 170 miles or so, with associated high temperatures and presumably deformation, and loss of velocity, a high speed impactor will maintain its integrity in a way that such a uniform channel might be the result.

I don't have time for a more detailed reply [EDIT: well I did end up writing three paragraphs...], but I'll try to sort this one out for you.

Your feeling about the structural integrity of the impactor is more correct than you think: the impactor was mostly evaporated in the first 2-3 seconds of the impact. The ejecta is not the impactor: it's what the impactor (and the shock wave it launches) blasts out of the ground. For an impact of this size, think of an impactor 15 to 30 km across, digging an initial crater maybe 50 km deep and 300 km across (this will then be flattened to 5% of the original max depth and widened by rebound, lava flows and landslides from the crater rim inward). The blasted-out material has a volume & mass hundreds of times larger than the impactor. (Understanding the origin of the ejecta seemed to be the problem with Unclear Engineer, too.) So the ejecta is not deflected parts of the impactor, but parts of the ground given a high velocity (though still much lower than the impact velocity) by the shock wave travelling through the ground, which was generated by the impact.

This ejecta is partly molten, but partly just crushed rock. What's interesting about this impact is the strong non-uniformity of the ejecta in different directions (anisotropy), as showcased by these canyons. Such non-uniformity can be the result of impact at shallower angles, because the shock wave will give significantly different speed & direction to different parts of the ejecta. The canyons were formed by a part of the ejecta with much higher speed (and higher density) than in other directions, hence they had a lot more energy (note that kinetic energy is proportional to the square of speed). It wasn't formed by a "single piece" but a blob whose parts had slightly different initial speeds, so its progressively faster parts landed progressively more farther away.

If you zoom in, you'll see that the channel is not so uniform after all: in some parts, it's more a chain of oval craters than a continuous channel. This could either be because of non-molten parts in the ejecta or because the molten ejecta clumped into giant "droplets" as it expanded.

 

[Unclear Engineer]

While I don't have an argument with the general concepts described, I do think there is likely more to the impact dynamics than "sometimes it just happens that way".

The focusing of the secondary bombarding objects in two tight streams does not seem to be consistent with other observations of lunar impacts, nor with the 3D simulations.

I do understand that simply splitting a single impactor is not able to result in 2 separate streams that diverge at the observed angles.

But, I think that there could be more than one part to the impactor. And I wonder whether a trailing part or parts could be deflected or cause shock waves in the already raised ejecta to deflect the secondary impactors to be separated at the angle observed while still not scattering them more than is observed.

For instance, if the initial impactor threw up a sheet of ejecta, which was then impacted/penetrated by a second part of the impactor, could that throw the already elevated ejecta material in directions consistent with the observed canyons? That would be a kind of "knock-on" interaction that should be capable of creating the angles of divergence seen between the canyons, because the sheet of ejecta being impacted was not moving at tens of km per second along the path of the impactors.

Maybe some scenarios such as that are worth some additional 3D modeling?

 

[m4n8tpr8b]

While I don't have an argument with the general concepts described, I do think there is likely more to the impact dynamics than "sometimes it just happens that way".

I never said or implied what you put in quotes, in fact, quite the opposite. Further research is needed, the point is to evaluate which additional factors could and could not influence the nature of the ejecta. But, as discussed further below, I think you are getting closer.

The focusing of the secondary bombarding objects in two tight streams does not seem to be consistent with other observations of lunar impacts, nor with the 3D simulations.

I reiterate that you're too categorical on both instances.

Have you looked at the examples of other lunar impacts I have given to @who knows? You'll see examples of other tight streams. In fact, basically all ejecta blankets show strong anisotropy with rays. The canyons radiating from the Schrödinger Basin are special as a matter of degree, not of quality.

You can also see two tight streams of high-speed ejecta (even separated from the rest of the ejecta in their ballistic path) in some of the 3D-simulated scenarios (as well as more complex patterns with more than two such streams). What does not match the two canyons radiating from the Schrödinger Basin is the exact pattern (especially the angle relative to the crater).

But, I think that there could be more than one part to the impactor. And I wonder whether a trailing part or parts could be deflected or cause shock waves in the already raised ejecta to deflect the secondary impactors to be separated at the angle observed while still not scattering them more than is observed.

Yes, you are getting closer to an understanding of what should be looked into. But you are still trying to break it down into the interplay of a very limited number of distinct objects or events, instead of thinking of waves travelling in a continuous medium.

At shallow impact angles, the shock wave is certainly shaped into something more complex than an expanding oval by the subsequent impact of subsequent parts of the impactor. But your earlier scenario of the impact of a contact binary is the only case where you can even approximate that as the subsequent impact of two point objects. More realistically, we can say that there will be a continuous generation of shock waves with changing intensity over the 2-3 second duration of the impactor's demise (in the case of the Schrödinger Basin).

The crater excavation process, that is the launch of the ejecta by the shock wave, will continue on for several more seconds. So the timescales are different; basically no part of the blasted-out ground has yet turned ballistic by the time all of the impactor made contact.

So, instead of some direct association with parts of the impactor, you can think of the ejecta anisotropies as the result of interference patterns emerging in the shock wave. You could then think of possible factors that can produce very pronounced interference patterns.

With the above in mind, both of your original ideas can be adapted for something more realistic. Your contact binary idea was already a good replacement for the earlier asteroid-breaking-in-two hypothesis. Note however that there are more freedoms to explore in simulations if you think of interference patterns: it may be that a contact binary impacting with the two parts at the same time (with the axis through the two parts parallel to the ground and perpendicular to the impact direction) can produce the pattern we need.

As for your surface-feature does-focusing hypothesis, instead of that, inhomogeneities in the material properties of the blasted-out ground (say a large deep lava flow or just the deformed basin rocks of a prior giant impact) could very well cause the shock wave to travel at slightly different speeds in different directions, with a focusing end result.

Both ideas worth studying in additional research, IMO.

 

[Unclear Engineer]

I do see the "canyons" in your lunar location. I note they do not seem to be emanating from the same point in the crater, or as deep as the Schrodinger crater canyons.

I also zoomed out and see what looks like a flat bottomed canyon stretching more horizontally across the frame, roughly at
Lat -34.91305 Lon 331.51362 282.48 m/px

That looks more like a crack filled with lava. What is the cause of that feature?