Lunar Florescent sources

[Drifter]

Just a quick enquiry ... was strolling the lunar surface on Iroc and bumped into this area of florescence on the lunar surface.

Any thoughts anyone? (Co-ordinates at bottom of screenshot if you want to get better definition from original website).

Was struggling to see clear heavy impact crater that would account for the wide spread of surface debris?

Didn't think it was image flare - not expert on that so could be wrong - but noticed on RHS there appears to be traces of surface debris scatter?
It almost seems like someone threw a very low velocity ‘flour bomb’ at the surface of the Moon?🤨

Have there been mineral studies done on these areas of exceptional lunar florescence? ... I tapped the phrase into SGL’s Search ... but surprisingly it came up with ‘no results’??

[Merlin66]

This may be of interest to you:

https://www.cloudynights.com/topic/579760-moon-my-work-with-sct-925-and-asi178mc/

and the very informative Website Selenology Today

https://digilander.libero.it/glrgroup/

Edited April 5, 2021 by Merlin66
added info

[Drifter]

Interesting photos Merlin66 .... Cheers for responding. Wish the minerals on the moon were as coloured as the ones on Earth! - maybe some are and we see the Moon more in shades of black and white from Earth because of atmosphere and refraction?
.... I wonder if the gases and liquids trapped in Earth’s atmosphere were chemically responsible for influencing the multispectral qualities of Earth’s minerals?

I guess an astro-geologist with a spectral analyser might throw light on the mineral content of the flare impact points on the Moon that interest me. Some seem to display characteristics of photo-luminescence. Wonder if the history of crashed objects on the Moon, human, alien or meteor/asteroid has scattered either radio-active dust over the surface? - or a host of naturally florescent minerals similar to those found on Earth?

Edited April 6, 2021 by Drifter

[Barry Fitz-Gerald]

This is a small (approximately 50m diameter) very fresh impact crater. The impactor struck the floor of the large crater Theophilus in an area where iron rich, low albedo (dark) impact melt dominates the surface. The impact excavated material which has a lower iron abundance and a higher plagioclase feldspar content, which is typical of the lunar highlands. This plagioclase rich material is not only bright due to its content (it is a light coloured mineral) but it is also bright as it is optically immature - it has not been exposed to space weathering which darkens and eventually obliterates bright crater rays. So the brightness of this crater's ejecta is a result of the composition of the excavated material and the youth of the crater itself. All the boulders visible to the west (left) of the crater are not associated with the impact crater and have probably eroded from the small mound they are lying on - if you explore the floor of Theophilus further you will se lots of examples of such rocky mounds. The crater itself would have excavated some boulders but not the the large amount visible in the image. The crater has also formed on a slightly inclined surface which dips from SE to NW producing a slightly asymmetric pattern in the ejecta with a concentration in the downhill direction (towards the NW or upper left of image).

I do not think there is anything exotic going on here such as mineral fluorescence, just normal lunar impact processes and illumination of highly immature, plagioclase feldspar rich ejecta. If you use the LRO Quickmap site and encounter an unusual feature try toggling through the various options for illumination incidence in the LROC-NAC menu on the left hand side of the screen, this will show the same feature under different lighting conditions and angles. 

[Drifter]

On 09/04/2021 at 16:34, Barry Fitz-Gerald said:

This plagioclase rich material is not only bright due to its content (it is a light coloured mineral) but it is also bright as it is optically immature - it has not been exposed to space weathering which darkens and eventually obliterates bright crater rays.

Thanks for that explanation, Barry ... and the tip  below flipping through the LROC illumination options. 

 Any idea roughly how long it would take this space weathering to obliterate the bright crater? - Wonder what chemical processes might to going on with lunar weathering?   ... Is it solar ray damage coupled with moisture/gas driven out of the lunar rocks+soil ... hanging trapped in a very thin surface atmosphere mixed with dust?

Quote

If you use the LRO Quickmap site and encounter an unusual feature try toggling through the various options for illumination incidence in the LROC-NAC menu on the left hand side of the screen, this will show the same feature under different lighting conditions and angles. 

 

[Barry Fitz-Gerald]

Space weathering takes the form of meteorite and micrometeorite bombardment which occurs constantly and shatters and effectively 'sandblasts' everything on the surface, from boulders down to the smallest particle. Returned lunar samples revealed that even the smallest particles in the soil had miniature craters on them called 'zap pits' Radiation also damages rocks exposed on the  surface as energetic solar and cosmic rays penetrate the minerals in the rocks and cause damage on the atomic/molecular scale. The net effect is that a rock on the lunar surface will be reduced to fine grained dust in a few 10's to 100's of millions of years depending on size. Larger boulders get broken down relatively quickly - well, still in the 100's of millions of years - because they are bigger targets for meteorites to hit. So, the astronauts footprints will not last forever, and if you intend visiting the Moon to see them I would suggest you do not leave it longer than about 10 million years. As well as being broken down the radiation damage caused the surface to darken due to changes induced in the iron bearing minerals in the rocks, so a bright ray around a fresh crater will eventually - after several million years  - become so darkened that it blends in with the background and becomes invisible. This process can be used to produce a relative dating sequence for craters, so young ones such as Copernicus and Tycho have rays but older ones such as Eratosthenes do not have a visible ray system. The exception to this rule is when the crater excavates intrinsically bright subsurface rock (as are found in the lunar highlands) in which case even after eons of space weathering the ray may still be visible against the generally darker surface , these are called compositional rays. Lichtenberg is an example of a crater with compositional rays.The lunar atmosphere is so tenuous that I suspect it plays no part in space weathering, and as far as I know any chemical processes as such would play an insignificant role in surface erosion. The dust produced by space weathering builds up and will eventually bury surface rocks, and when this happens the rate of breakdown drops as the rocks become shielded from micrometeorites and cosmic rays.

 

Cheers, Barry.

 

[Drifter]

On 11/04/2021 at 15:24, Barry Fitz-Gerald said:

Space weathering takes the form of meteorite and micrometeorite bombardment which occurs constantly and shatters and effectively 'sandblasts' everything on the surface, from boulders down to the smallest particle. Returned lunar samples revealed that even the smallest particles in the soil had miniature craters on them called 'zap pits' Radiation also damages rocks exposed on the  surface as energetic solar and cosmic rays penetrate the minerals in the rocks and cause damage on the atomic/molecular scale. The net effect is that a rock on the lunar surface will be reduced to fine grained dust in a few 10's to 100's of millions of years depending on size. Larger boulders get broken down relatively quickly - well, still in the 100's of millions of years - because they are bigger targets for meteorites to hit.

That clarifies things nicely.

With that comprehensively answering pretty much all my questions about this plagioclase material ... I was wondering, while you are in the ‘room’ B ... if you have any thoughts on this other meteor/lunar surface weathering observation I am interested in?

 

 

On 11/04/2021 at 15:24, Barry Fitz-Gerald said:

So, the astronauts footprints will not last forever, and if you intend visiting the Moon to see them I would suggest you do not leave it longer than about 10 million years.

😁🤔  It’s not on my bucket list of priorities in ‘The Universe Tour’ ... if ever I escape Earth’s atmosphere and get to the Moon ... I’ll be heading here:

On 11/04/2021 at 15:24, Barry Fitz-Gerald said:

The lunar atmosphere is so tenuous that I suspect it plays no part in space weathering, and as far as I know any chemical processes as such would play an insignificant role in surface erosion. The dust produced by space weathering builds up and will eventually bury surface rocks, and when this happens the rate of breakdown drops as the rocks become shielded from micrometeorites and cosmic rays.

I’m trying to promote a new school of thought that is open to the possibility meteor strikes near volcanic craters on the moon might puncture lava tubes full of water+more acidic condensates trapped in reservoirs below the lunar surface (as detected in large quantities by satellite probes scanning underground lunar reservoirs in recent years). I like the idea these liquids slowly oozing from a meteor puncture point ... might have caused either surface or subsurface erosion at a time the Moon had a more significant atmosphere as volcanic activity subsided during it’s history. Certain rilles seem to give the impression they might have been chemically etched by this process ... especially more acidic volcanic condensate seepage ... a bi-product of the liquefaction of rocks or magma rising up out of the core.

This inner etching  (see pic below-apologies for blur ... pic of a pic) down from the Aristarchus crater - might be such surface erosion ... or sub surface acidic ‘dissolving’ of substrate followed by collapse of surface volcanic dust to create a smooth pronounce channel that runs away from a puncture source (downhill) dissolving to nothing:

.... these rille channels all over our Solar System show little or no sign of piles of cooled lava at the end? - it’s very unlikely it all disappears so neatly into the Mares (what do you think, B?) .... High rates of sublimation caused by weak atmospheres might explain the lack of extensive surface erosion on the moon .... compared to Mars ... but I like the idea of this type of surface erosion causing breakdown, condensation on the surface when conditions allow - especially around the borders of the cooler poles during the lunar cycle.

Edited April 13, 2021 by Drifter

[Drifter]

On 04/04/2021 at 15:35, Merlin66 said:

This may be of interest to you:

https://www.cloudynights.com/topic/579760-moon-my-work-with-sct-925-and-asi178mc/

Seeing as Barry F-G nailed a very decent answer to the plagioclase scattering ....

Just a quick comment on  a couple of surface ‘oddities’ which caught my eye in the Cloudy Nights link Merlin66 posted?

If you scroll to p.4  post #83 .. the OP Easybob95 has dropped in a colour enhanced picture titled ‘An other mosaic’ which shows roughly in the middle a black line I initially thought was an ‘artefact’ on the photo, then got slightly interested thinking it was a ‘cliff edge’?! False alarm - not seismic heave or crust cracking!

Thinking aloud ... The b/w image above it suggests a rille labelled near Ptolemee crater with a ‘hard’ edge casting a shadow ... Is it a bit unusual a rille casting such a pronounced dark line on an image?? ... unless the edge has dropped? 

Also, this jumped out from the top left corner ... which I magnified as a screen shot:

In the centre is a ‘bouncing bomb’ scar of impacts in a line ... any thoughts how this neat continuous alignment is formed?
... presumably from one event?

 

[Barry Fitz-Gerald]

Stu,

Sorry to disappoint but sinuous rilles are volcanic features, no need to invoke the flow of water which has never existed in liquid form on the moon as it would immediately sublimate in the vacuum of space.  Water is present but in amounts so small that it would require industrial processes to release it from the hydrated minerals which contain it or the regolith in permanently shadowed craters.

Sinuous rilles were formed by flowing liquid, but this was basaltic lava at high temperature (1,200 degrees C) and very low viscosity - comparable viscosity to engine oil. Basalts are the commonest rock in the solar system, these lunar basalts have have a low silicon content and as viscosity increases with silicon content, these are particularly runny.  In the remote past the moon also erupted a more magnesium enriched basalt lava called a Komatiite which was even runnier, not far off the viscosity of water.  Similar lavas erupted on the early Earth when the planetary heat-flow was much greater than today and can be found as Pre-Cambrian rocks in South Africa. The upshot is that these basaltic lavas could flow turbulently, which allowed them to thermally erode downwards into the surface to and create an incised channel, with the sinuosity a consequence of their low viscosity. Some rilles may have developed a roof of chilled lava over the top, producing a lava tube through which the lava flowed and eventually emptied out leaving a hollow tube - examples of these are widespread on the Earth and are known as lava tubes. These may offer potential benign sites for future lunar bases.

Most sinuous rilles disappear into the maria as the lavas they carried spread out and in many cases drowned their own channels as the lava level continued to rise. When a smaller rille is nested inside a larger one, such as in the example you show (Schroter's Valley) this indicates a high volume initial outflow of lava which carved the main channel followed by a final very much reduced flow that formed the smaller channel during the waning phases on the volcanic activity.

The straight line in the second photo is The Straight Wall or Rupes Recta - looks steep but is not, just a shadow effect. It represents a fault where the terrain on the west side has subsided relative to that on the east. The crater chain in the third is the Davy crater chain (Davy being the large crater at the eastern end of the chain) and you are correct - it formed in a single event. This happened when a tidally disrupted asteroid struck the surface with the fragments arranged in 'line astern' , impacting simultaneously. The small craters have patterns in their ejecta that show that they formed as the same time, with the impactors arriving from the west. The fragment that formed Davy was the largest. The impactor would have been similar to Comet Comet Shoemaker–Levy 9 which struck Jupiter in 1992 but on a much smaller scale. This was originally thought to be a line of volcanic craters stretched out along a fissure, but the crater morphology is 100% impact. Multiple impacts are far more frequent on the moon than was previously thought and can be identified by common ejecta blankets .

 

Cheers, Barry.

 

 

 

 

 

[Drifter]

On 13/04/2021 at 17:52, Barry Fitz-Gerald said:

Sorry to disappoint but sinuous rilles are volcanic features, no need to invoke the flow of water which has never existed in liquid form on the moon as it would immediately sublimate in the vacuum of space.  Water is present but in amounts so small that it would require industrial processes to release it from the hydrated minerals which contain it or the regolith in permanently shadowed craters.

Thanks for that mine of information on my conundrum. It’s definitely a theory I can live with! Appreciate you taking the time. 
Just a quick comment on the above paragraph .... my erosion idea was based around the time most volcanic activity had died down .... when an atmosphere created by volcanic emissions still lingered for millions of years greatly reducing the effects of sublimation we see today. Where winds, like the storms that rip the surface of Mars ... eroded ejected matter into smooth sandy particulates that blew to form the smoothed contours of many rilles.

I had more an idea of v. acidic/corrosive liquids - as found in lakes around some volcanoes on Earth .... burning  away/ dissolving ejecta to create quite significant erosion features in a relatively short time - yet be evaporating away at the end of the rille without trace or colouration(?) .... or working subsurface (little affected by later sublimation).

I noticed most rilles, especially Schroter's Valley seem to have a ‘spring head’ that almost invariable arises from a significant asteroid/meteor impact near a volcanic crater .... Do you agree these ruptures likely created ‘leakage’ that formed the rille? - an impact in close proximity where lava tubes would be found in abundance below the surface? .... the question remaining ... at the time of these impacts, were these volcanoes still active enough to create the Komatite you mentioned ... in the SV case for long enough to cut a Valley the depth and breadth of that seen today. Unless we set up a Colony here and do a detailed study of SV, I guess we will never know the exact era the rille was cut, the date of the huge impact and when volcanic activity ceased.

Presumably many of these lava tubes on the Moon still contain large reservoirs of subsurface water (unaffected by sublimation) - let’s hope I am wrong and it’s drinkable or easily purified ... a Moon Evian or Moon Volvic water(other brands will also be available from our Lunar stockists as Lunar Tourism increases), an essential resource to sustain long term Lunar Colonisation Projects.

My view is we should be practicing survival on the hostile Moon first - at this site of great interest ... also another site near the Lunar Poles - honing those skills - before taking the huge huge step attempting long term, more risky, Martian Colonisation and exploration. Surely best to learn to ‘walk’ before ‘running’ to Mars and likely sacrificing wasted lives on a Project that might seriously set back desire for further forays to distant worlds?

On 13/04/2021 at 17:52, Barry Fitz-Gerald said:

Sinuous rilles were formed by flowing liquid, but this was basaltic lava at high temperature (1,200 degrees C) and very low viscosity - comparable viscosity to engine oil. Basalts are the commonest rock in the solar system, these lunar basalts have have a low silicon content and as viscosity increases with silicon content, these are particularly runny.  In the remote past the moon also erupted a more magnesium enriched basalt lava called a Komatiite which was even runnier, not far off the viscosity of water. 

I like the idea you present of this magnesium-enriched Komatite having the viscosity of water and disappearing into the Mares ... because it seriously bothered me how lava had the weight and power and heat to cut a serious channel in Schroter’s Valley in particular .... cooling as lava does over the hundreds of miles travelled .... yet not leave any trace of serious pile up along the edges, twists and turns .... or especially at the end of it’s journey ... just the impression of something that either evaporated or dissolved into the substrate. 

Does Komatite always do this ... on Earth and on the Moon? It’s very clean and tidy stuff, I must say! .... 

** V. interesting you mentioned Komatite being very magnesium-enriched with the viscosity of water ... I never rolled with the idea Earth’s water came from the Asteroid Belt - there has never been any evidence of these water delivery impacts showering the Earth or the Moon - for me personally it’s a ridiculous idea that perpetuates today when there appears to be no evidence in our historical record in 5,000+ years Humanity has recorded such events and disasters ... and nor has has our geology record.

I believe - after reading an interesting paper on the liquefaction of rocks that shows water is a serious bi-product in the chemical reactions going on and magnesium is also produced in large amounts during this process -  it ties in nicely, when you calculate the % amount of magnesium in sea water - that it is pretty obvious that Earth’s water was created almost solely by volcanic processes and the retention of Earth’s water by a stable atmosphere and our Moon’s unique gravitational dynamic and fixed orbit. To many it’s the secret why Earth’s water was retained, collected it’s mineral salts - whilst the moon’s gravity and tides drove our cyclic weather systems etc.
It’s a System so brilliant, it hardly seems likely it could have happened naturally by accident to create 5 billion years of stability to let our Evolution happen!🤔

It makes sense to me volcanism along tectonic plates etc, though more limited today, continues to generate significant water which sees sea levels rising slowly - while landmasses heave and drop, and ice melts periodically .... It puzzles me why climate scientists get their knickers in the twist it’s all man’s fault we are drowning .... when it is largely due to these natural forces clearly beyond our control.
Human stupidity says ban the combustion engine .... when scientific logic says .... it’s cheaper and more effective to move to higher ground! If I publicise this fact before Environmentalists like Greta, I might be burnt as a ‘heretic’ like DT .... under her piercing gaze! 
Are people happy Volcanism creates significant amounts of water? On other planets and Moons too  in our Solar System for billions of years... for the duration volcanism thrived .... It’s a nice idea Mars was probably a failed Earth 1.0 Eden Project that had to be abandoned. Our Moon being the key why Earth 2.0 was such a great success. So successful as a tourist destination - it now attracts different civilisations from all over the Galaxy ... and probably beyond!😆
 

How do you feel about this ocean production idea? ... I’m surprised it’s not common currency?

On 13/04/2021 at 17:52, Barry Fitz-Gerald said:

This happened when a tidally disrupted asteroid struck the surface with the fragments arranged in 'line astern' , impacting simultaneously. The small craters have patterns in their ejecta that show that they formed as the same time, with the impactors arriving from the west.

Considering the number of impacts speckling the Moon through it’s history - (and we must thank it’s role in sparing Earth and our Evolution from more than one major extinction ... and maybe even a couple of minor ones!) .... Do you have an explanation  why most impact craters seem to show the Moon being struck at a 90° angle to the horizon?

You would think that meteors/asteroids/ice blocks from the Asteroid Belt would leave scarring, impacts, dents, scratches and scrapes at all angles imaginable .... yet we see ~ 90+++ odd % looking like ~90° angle strike.  .... Does the Moon’s gravity exert such a huge force on small rocks travelling at such a fast velocity? Tear-drop impacts seem very rare .... any ideas why?

I‘ll make that my last question, B F-G ... if this is taking up too much of your precious time!

Cheers. 
Jon aka Drifter.

Edited April 16, 2021 by Drifter

[Barry Fitz-Gerald]

Meteors and Asteroids strike the lunar surface at all angles ranging from 90 degrees to grazing impacts. However due to their velocity which can be from say 12 to 75kms per second the effect is not like throwing a large rock at a hard surface. During the impact shockwaves are generated wich pass into the surface and through the impactor. This occurs in such a short timescale that it caused the impactor to be melted and vapourised in what is effect an explosion from a point, with no effect being carried over from the impactors trajectory. This symmetrical 'explosion'  results in a circular impact crater in almost all impacts. It is only at angles of about 35 degrees and lower that we can see any asymmetry introduced by the impact angle, and this only shows up in the ejecta pattern which develops unique patterns in the ejecta called Zones of Avoidance where little to no debris ends up striking the surface. These Zones of Avoidance because of the processes that take place in the impact process occur on the side of the crater from which the impactor arrived. So for example Tycho formed by a low angle impact from the SW, Copernicus a low angle impact from the South, and the far side crater Jackson an impact from the NW. Grazing impacts lower than say 5 degrees are much rarer and result in craters such as Messier and Messier A where the impactor breaks up on contact with the surface and can cause one elongate crater at the point of impact and others, further 'downrange' where the fragments impact.

 

Cheers, Barry.

 

 

[Drifter]

Thanks for that ... I will check out those impacts you mentioned.

Have just been watching the Icelandic, St Vincent and Mount Etna eruptions and am beginning to have doubts if enough water is being produced as a bi-product of volcanic activity ... unless it’s vaporising largely unseen in some types of eruption ... or is wrapped up in some way to keeping pyroclast and other liquified systems flowing.

Here’s an interesting eruption I bumped into this morning showing a different pH extreme which I thought might possibly cause a different type of erosion on our Moon.

Whether the level of acidity is enough to dissolve lunar substrate at the rate required? ... just throwing a few ideas around .. to see what sticks.🙃

 

[Drifter]

Just thought it worth dropping these rather stunning images of Messier and Messier A you mentioned ....

http://lroc.sese.asu.edu/posts/1136

Guessing the traces of fluorescence give a further confirmation from which direction the object arrived? .... showing a gradation in temperature melt across the crater?

 

 

[Barry Fitz-Gerald]

Yes, those are pretty impressive images - but the interpretation given by the LROC team is not the correct one I suspect. They show two impacts making up Messier A (the bottom image in your post) which they have called Impact 1 and Impact 2, with Impact 1 supposedly an older crater that already existed and was partially obliterated by Impact 2. Have a look at the image that goes with this post, it is taken from the LRO Quickmap page with the LRO Diviner Nighttime Soil Temperature layer enabled, where red is warm and yellows cooler.  The temperature differences are related to the 'rockiness' of the surface as larger rocks retain their heat longer into the lunar night than finer grained material.

You can see that the impactor arrived from the lower right and was heading towards top left. The first impact at a very low angle of about 5 degrees produced the elongate crater Messier (the top image in your post). As it formed, ejecta was thrown out to either side to produce the 'butterfly wing' pattern we see visually in the telescope. Little ejecta went downrange - that is in the direction of travel - a characteristic of very low angle impacts. The 'butterfly wings' show up in the Nighttime Soil Temperature overlay as red patches either side of the crater (yellow arrows), this being a result of the ejecta being 'rockier near the crater rim, which you can actually see in the image in your post. The impactor itself underwent a process called 'decapitation' where the upper part sheared off (as the lower part decelerated catastrophically as it contacted the surface) and continued down range, whilst the lower part formed the crater Messier. The bit that sheared off then struck the surface again - having lost none of its pre-impact velocity to form what is labeled as Impact 2. But as the angle of impact was so low, the sheared off bit itself now sheared apart and formed a second crater - Impact 1 at the same time. You can see the evidence for this in the Nighttime Soil Temperature image as Impacts 1 and 2 have their own separate 'butterfly patterns' of ejecta (blue and white arrows) which are clearly visible either side of the craters. Now, if Impact 1 was a pre-existing crater it would not have a 'butterfly pattern' but it clearly does, so these two craters formed simultaneously. The argument for Impact 1 being older, is that it looks subdued and does not have a sharp rim like a fresh crater - well that can be explained by the fact that it was formed not only by impact processes but also as part of the impactor slid along the surface in the downrange direction - so not a straightforwards explosion type process. Impact 1 crater is also draped in large quantities of impact melt ejected downrange from the Impact 2 crater, which has blanketed the surface  and produced the subdued topography we see. These features can be seen in other close binary impacts such as Birt and BIrt A and Thebit A and Thebit L.  A bit more info can be found on the Lunar and Planetary Institute link below

 

https://www.lpi.usra.edu/meetings/lpsc2013/eposter/1916.pdf

 

I am not sure what you mean by fluorescence, but the impact melt would probably be at more or less the same temperature and any gradations in brightness would be a result of varying illumination across the image - maybe?

 

Hope this makes sense.

 

Cheers, Barry.

[Drifter]

I feel the plagioclase variations you mentioned earlier in your OP might be giving important information relating to the heat generated on impact .... the mineral composition of the impacter creating a distinctive chemical signature formed by nuclear fusion/fission(?)- then cooling.

I like the idea the plagioclase is showing not only the point of first contact ... but also a rather detailed barometric gradation of temperature impact friction across both Messier+ Messier A impact sites .... rather than varying illumination across the image.

If you temporarily roll with the idea of temperature variation across the impact site being also an indicator of direction ... tying in with the debris/scatter/groove observations from the Berlin paper you dropped ... Could Messier (which shows less convincing evidence of ejecta direction being the same as Messier A - slight lower right to left impact) .... be a slight upper left to right deep ‘graze event’ ? ... possibly a very solid object - large heavy fast moving - that didn’t land ... but bounced like a pebble on a pond creating plagioclase ‘glow’ where it first hit?

I like your idea of Messier A being one event with a fragmentation .... but if you look closer at the Impact 1+2 sites in the more detailed photo I dropped... particularly the lumpy debris to the left of both craters .... if you draw an imaginary circle around both holes and a line to this ‘after dump’ ... you can see there is a slight difference in angle between the two -suggesting possibly two separate objects on slightly different trajectories? ... maybe LROC called Messier A correctly as two events? ....What do you think?

 

 

 

 

[Barry Fitz-Gerald]

The composition of the ejecta blanket is related to the rocks present at the impact site, as it is these that are shattered, melted and vapourised. These processes will clearly alter the minerals in the rocks (by shock effects and heating) and change their physical state, but the temperatures involved are in the 1000's of degrees not the millions required by fission/fusion nuclear reactions. So nothing is made in these impact events beyond that produced by heat and shock.

Also, plagioclase will only be present in the ejecta blanket of a crater if there is plagioclase present in the rocks at the impact site - it is not formed during an impact. So for instance the Messier/Messier A impactor struck a mare which consisted of a basalt lavas lying on top of more basalt lavas - and the ejecta contains material which is of a basaltic composition. If the crater had formed on a mare surface which overlay a different rock, say of a highland composition, then this would potentially be excavated and end up in the ejecta provided the crater was deep enough.

Not sure about what you are saying about the direction of the impactor that formed Messier, but if you look at your image you can see that just outside the eastern (right) rim there is an area with little or no ejecta - this is called a Zone of Avoidance (ZoA) and is typically found in low angle impact craters and forms in the up-range direction - i.e the direction the impactor came from. Outside the western rim a stream of impact melt can be seen on the surface - and impact melt is primarily ejected down-range (direction of travel of the impactor) in low angle impacts. So Messier was caused by an impactor traveling from east to west (red arrow attached image).  You are correct in that it was a grazing impact, but as I mentioned above it is likely that part of the impactor formed Messier whilst the upper part which did not contact the surface sheared off and formed Messier A.  Any glow you see in the image is fresh (not subjected to extensive space weathering) fragmented basaltic ejecta - no plagioclase- sorry!

As for the difference in angles between Messier and the two parts of Messier A - a number of experiments have been done investigating low angle impact dynamics and what was found was that if an impactor broke apart on first contact with the surface then the bits that came off continued down-range at pretty much the same velocity, but the azimuth direction was not preserved - so the fragments would deviate from the original direction of travel. This is consistent with what we see in the Messier group. So in my (humble) opinion Drifter, Messier A formed in a single event. And I did not want to mention this for fear of over complicating things - but if you look at your image of Messier A you will see that the crater marked Impact 2 has pinches (yellow arrows attached image) in the northern and southern rim - makes the outline look like a Remembrance Day poppy. This indicates that this crater is in fact composed of 2 almost overlapping craters that formed simultaneously (have a look at Fig.2b in this paper https://www.hou.usra.edu/meetings/lpsc2018/pdf/2938.pdf) - so there were at least 3 impacts (and a bit of sliding along the surface) not two.

Must go for a lie down now.

 

Cheers, Barry.

 

 

 

[Drifter]

Firstly …. Apologies Barry for the delayed reply … busy week … and needed more time to study the information you presented before throwing the following ideas in the mix.

On 28/04/2021 at 18:30, Barry Fitz-Gerald said:

The composition of the ejecta blanket is related to the rocks present at the impact site, as it is these that are shattered, melted and vapourised. These processes will clearly alter the minerals in the rocks (by shock effects and heating) and change their physical state, but the temperatures involved are in the 1000's of degrees not the millions required by fission/fusion nuclear reactions. So nothing is made in these impact events beyond that produced by heat and shock.

Could some luminous lunar impacts from observation suggest from the very spiky scatter effects -that an explosion has taken place on the surface? - quite nuclear in intensity? …. not just a dull thump, debris flying up in the air and flopping down in the local area?

…. I’m getting an uneasy feeling luminescent effects might not be just disturbed terrain minerals … but the result of a combined explosion on the surface where the mineral composition of the meteorite is essential to generate the heat necessary to form such melt scatter patterns that travel extreme distances.

When temperatures reach a critical level as atoms smash into each other, surely chemical composition of the incoming object is just as important as the substrate to create a fresh ‘luminous’ deposit in some cases? ….
With water now being recognised as present close to the lunar surface … this might be providing the oxygen needed to illuminate and catalyse some of these reactions … maybe some of these chain reactions are more ‘nuclear’ and intense than some people imagine?

Here’s one that lit up the surface - as bright as the Pole Star in intensity … and estimated to be just 1.4 metres in diameter. 
http://www.bbc.co.uk/news/science-environment-26325934

The interesting information here is this event lasted 8 seconds … the Chelyabinsk meteor was estimated as originally 19 metres in diameter exploding with a force estimated 500,000 tonnes of TNT sending a shock wave that circled the World twice. 

I wonder if you’re keen to roll with the idea the luminosity in the Messian craters indicates direction of first contact of an incoming object causing melt luminosity ‘scrape’? …. I like the idea Messier was a West to East ‘bouncing bomb skimmer’ … the v.light melt you pointed out …. being brief incoming burn … followed by a phase of intense hot luminosity friction burn ‘melt’ … the hard roundish meteor just having it’s rough edges broken off as it’s surface was cooled from West to East gouging out a scar before leaving the ‘scene’ as it bounced … either to land downstream somewhere … or as lift off damage appears v. minimal on the RHS of the crater … with just minor subsidence cracking of the Eastern edge …. maybe this large object ‘bounced’, didn’t explode or fragment and escaped the moon’s gravity - continuing it’s journey through Space? -  Is that possible?

If you apply this same idea to the two impacts of  Messier A …. the position of your yellow arrows on that photo plus the raised borders of both craters confirm the angle of both impacts were very different to Messier - I’m happy with the idea Impact 1 came first and the butterfly indent at the arrows you marked shows the trajectory was possible ~20° different to Impact 2 …. the melt burn ‘fluorescence’ of that impact confirming (probably to me only!) it’s direction being the opposite of Messier - East to West - showing hot on the RHS fading to cooler on the LHS …. as the boulder fragmented - without exploding - buried deep and threw a cover over the earlier crater.

Is this a theoretical scenario you see having elements with a certain logic?🤔

Edited May 8, 2021 by Drifter

[Drifter]

I wonder what % of modern day impacts are producing spiked scattering explosions?

Here’s a 2013 impact that illuminated for just 1 second in this video report linked to a NASA investigation.

 

[Barry Fitz-Gerald]

Hello again!

In reply to your first point, an impact event on the lunar surface will approximate an explosion as the kinetic energy of the impactor is released almost instantaneously - that is why most craters are round and only extremely low angle impacts producing elongate craters . As I noted above even with an impactor arriving at cosmic velocities varying from 14kms/sec up to 75kms/sec the energy released is still only in the thousands of degrees C and whilst this will vapourise, melt and shatter the target rock (an the impactor) the temperatures will NOT be in the several millions required for any form of nuclear reaction. Vapourised minerals will be reduced to their component atoms and molecules but these will not have sufficient energy to do anything other than bounce off each other - there will be no nuclear reactions. The tiny amount of water present in the lunar rocks is mostly locked up in mineral structures and will play little to no part in reactions. If any survives the impact it may re-combine in the minerals that form from in the cooling melt - but I would guess most would be dissociated into hydrogen and oxygen or lost to space. When the vapourised rock and impact melt cool and solidify you get - well rock of a similar composition you do not get any exotic products. If you melt basalt rock and let it cool you get basalt rock - might not be the same as the initial rock as it will have solidified under different conditions of pressure/cooling rate/gas pressure and so on - but it will still be basically a basalt.

Impacts into the lunar surface involve high velocities (and kinetic energy) even in the case of the slowest impactors, so the release of energy will be instantaneous and produce an explosion like result. The ejection of debris will therefore always occur at high velocities - the ejecta will not just flop out of the transient cavity, it will leave at high speed and at a relatively high angle. As the impact process proceeds the energy of ejection declines and the last ejecta to leave the crater will just have enough energy to clear the rim and form the proximal ejecta blanket - but a crater forming impact is not like throwing a stone at the ground - the energy involved is a different order of magnitude.

The composition of an impactor will have an effect on the impact dynamics as they will vary from cometary (rubble pile type), stony, stony iron to iron - which just reflects the composition the what is flying around in the solar system in the form of meteors and other space rocks - BUT - if the kinetic energy involved in the impact is the same, on impact you will get the same size crater and ejecta as it is the energy released that does the work and not the composition of the impactor. The kinetic energy of a body is 1/2mv² so the mass is relevant - a lower mass impactor (say rock) having less kinetic energy than a high mass impactor (iron) if the velocity is the same. There is some evidence to suggest that at lower impact velocities (14kms/sec and lower) that part of impactor may survive in highly fragmented form and end up concentrated in the central peaks of some craters such as Copernicus, where concentrations of olivine, a mineral common in meteors was found to be present. This is a theoretical point of view based on simulations.

As for Messier and Messier A - I appreciate you hypothesis, but all the evidence from crater morphology, ejecta distrbution, melt distribution and theoretical considerations based on laboratory simulations indicates that these craters formed by a low angle impact from the east with the impactor fragmenting at first contact (producing Messier), and with the fragments produced impacting in the downrange direction (producing Messier A). From my study of the crater group - nothing else makes sense, but don't let that put you off - I never take anyone;s word for anything!

As far as what %age of modern impacts are producing craters with ejecta blankets and rays (not sure what spiked scattering explosions means) the dynamics of impacts are the same today as they were 4.5 billion years ago - it is only the rate and number of impacts that has declined (with maybe a few blips on the way) to the rate observed today, due to the planets hoovering up all the rocky debris or it being ejected from the Solar System. So the same size/composition meteor traveling at the same velocity would have produce identical craters in the past as the present.

 

Cheers, Barry.

 

 

 

[Drifter]

Hi Barry … firstly thanks for your very comprehensive, interesting and informative answer - and apologies for my delayed reply - (rewrites, a little research + a family issue problem+ distraction that took precedent over this SGL discussion unfortunately).

On 14/05/2021 at 08:38, Barry Fitz-Gerald said:

As for Messier and Messier A - I appreciate you hypothesis, but all the evidence from crater morphology, ejecta distrbution, melt distribution and theoretical considerations based on laboratory simulations indicates that these craters formed by a low angle impact from the east with the impactor fragmenting at first contact (producing Messier), and with the fragments produced impacting in the downrange direction (producing Messier A). From my study of the crater group - nothing else makes sense, but don't let that put you off - I never take anyone;s word for anything!

Glad you don’t mind me pitching a few ideas - speculating on what might be creating the fluorescence? Ignore my ramblings below if evidence shows they make no sense!

From the scatter patters in the two photos dropped into the discussion May 8th … Tycho looks like an exceptional surface explosion …. blasting fluorescent traces thousands of miles. (Nothing ‘exotic’ … just composites consistent with the elements present!). 
On Earth we get intense burning - like an oxy acetylene torch effect at the pressurised front end of meteors entering the Earth’s moisture-laden atmosphere - prolonged by low angle trajectories. I gather the Chelyabinsk meteor glowed white hot before explosively fragmenting creating a shockwave with the energy intensity of a number of hydrogen bombs - Could the presence of water detected recently by lunar probes be the catalytic source that caused Tycho to explode so violently? - and create other ‘flashlight’ impact events on the Moon? 

Aristarchus crater observations(see Wikipedia - sorry, link copy not working in SGL?) support this idea - it shows the brightest albedo reflections and many examples of transient lunar phenomena - also chemical trace composites consistent with ruptured dead volcanoes, lava tubes flooded with water condensates and gases trapped by consistent rock liquefaction. Maybe the nearby ancient Herodotus crater is not an impact as billed by Wikipedia? … but the volcanic source of the lava that scientists claim eroded Schroter's Valley?

I can imagine subsurface water trapped by the last bubbling of volcanoes dying on the Moon - maybe seeping through to the surface or being released more rapidly in a gush by meteor impacts to create the thin atmospheric haze we see in some lunar photos at certain times in the lunar cycle.

I like to think when the Moon in ancient times had a thicker atmosphere than it has today, lunar winds blew with some force across the surface and eroded the ‘rounded sand particles’ astronauts have sampled …. and spiralled sublimating water vapours to gather and condense around the lunar Poles forming the frozen lunar lake pockets some speculate still exist … like they do on Mars.

[Why plan ambitious manned missions to Mars when research around Aristarchus, the Cobra’s Eye, Schroter’s Valley etc … drilling for water and exploring frozen lunar lakes for Life is a more logical step at this time?]

Looking again closely at the Messier ‘graze’ photo with your graphic inclusions(post April 28th) … I’m struggling to see significant ‘Melt’ where you indicated … couldn’t this be happily incoming brief heat from a ‘pebble bouncer’ travelling West => East? …

Is it wise to just ignore the ‘fluorescence’ … because it definitely looks like a ‘heat marker’ indicating direction of ‘incoming’  … then cooling - showing a fade in fluorescent material production as the object leaves it’s fleeting scar … the right hand eastern lip being only lightly compressed falling back and cracking slightly as the object takes off into Space … or lands further east?

As I mentioned earlier - with Messier A … it’s fluorescent marker also shows the incoming angle … this time from East => West . The 1st impact - showing a 15/20° difference in trajectory … but also East => West … having it’s fluorescent ‘burn’ buried by the debris of the secondary strike.

Doesn’t this scenario fit slightly better with the observations seen? … as it incorporates the all important fluorescent markers?

 

 

 

 

[Barry Fitz-Gerald]

Hello again!

Here are some replies to your previous posts:

You said:  'From the scatter patters in the two photos dropped into the discussion May 8th … Tycho looks like an exceptional surface explosion …. blasting fluorescent traces thousands of miles. (Nothing ‘exotic’ … just composites consistent with the elements present!). 
On Earth we get intense burning - like an oxy acetylene torch effect at the pressurised front end of meteors entering the Earth’s moisture-laden atmosphere - prolonged by low angle trajectories. I gather the Chelyabinsk meteor glowed white hot before explosively fragmenting creating a shock wave with the energy intensity of a number of hydrogen bombs - Could the presence of water detected recently by lunar probes be the catalytic source that caused Tycho to explode so violently? - and create other ‘flashlight’ impact events on the Moon?' 

Answer: The impact that created Tycho did eject rock and impact melt over distances of some 5000kms where it landed on the lunar far side just to the south of the crater d'Alembert - a journey that took about 2 hours. The Tycho impact was however probably no different in terms of violence to other impacts of a similar scale, and its ejecta is only conspicuous because it is relatively young. You use the term 'fluorescent traces' - but the bright rays and ejecta blanket are only bright because they are composed of fresh fragmented rock (with lots of exposed crystalline surfaces) which reflects the sunlight more strongly than the underlying space weathered surface (fluorescent materials re-emit previously absorbed light). In time most bright rays and ejecta fade due to space weathering and become invisible. If you took a few builders sacs of granite chippings and dumped them on the mare surface they would probably be glaringly bright in comparison to the space weathered surface beneath. Given a few tens or hundreds of million years they would gradually darken under the influence of micrometeorite impacts and the solar wind/cosmic rays to become far less conspicuous.

Water is present on the moon with ice (probably quite a lot) detected at the poles in permanently shadowed craters, and water has been detected even on the sunlit part lunar surface (100 to 400parts per million) but this would probably play no part in the cratering process itself as the temperatures generated during the impact are hot enough to melt rock - let alone water. Water is also present in lunar rocks - up to several hundred parts per million in some lunar glasses - so the moon is far from dry, but water is unlikely to have been present in sufficient amounts to form any standing bodies or flows. Water content is an important factor in the way lava's form and how they erupt - but impact cratering is a very extreme process and water is only likely to affect it if present in large amounts (such as on Earth or Mars maybe).

Any impactor traveling at cosmic velocities of 12kms/sec and upwards would produce a flash of visible light on striking the lunar or any other surface it struck. In the case of the moon, with no effectively atmosphere there would be no heat or shock generated until the moment of contact.

 

You said: 'Aristarchus crater observations(see Wikipedia - sorry, link copy not working in SGL?) support this idea - it shows the brightest albedo reflections and many examples of transient lunar phenomena - also chemical trace composites consistent with ruptured dead volcanoes, lava tubes flooded with water condensates and gases trapped by consistent rock liquefaction. Maybe the nearby ancient Herodotus crater is not an impact as billed by Wikipedia? … but the volcanic source of the lava that scientists claim eroded Schroter's Valley?'

Answer: The Aristachus area is draped in volcanic glasses which are responsible for the  the high albedo of the area, also Aristarchus itself is a young impact crater that has excavated a lot of intrinsically bright rocks and this is present in its ejecta. There is nothing to suggest Herodotus is anything other than an old impact crater, and Schroter's Valley appears to have formed as the result of a 'Fire Fountain' type eruption. This was centered on the 'Cobra's Head' the crater like depression which was probably the site of a lava lake, with the lava then flowing out to form the rille. There is no indication of water being involved in any way beyond the very small amounts being present in the volcanic glass beads that drape the Aristarchus Plateau surface. The only liquid rock present was probably in the form of lava. The plateau is underlain by a prominent Thorium anomaly, the presence of which accounts for the level of volcanism due to heat generated by radioactive decay.

 

You said: ' I like to think when the Moon in ancient times had a thicker atmosphere than it has today, lunar winds blew with some force across the surface and eroded the ‘rounded sand particles’ astronauts have sampled …. and spiralled sublimating water vapours to gather and condense around the lunar Poles forming the frozen lunar lake pockets some speculate still exist … like they do on Mars. '

Answer: There was some speculation that during the intense volcanic lunar episodes that a sort of temporary atmosphere might form, and also during the major basin forming impacts it is possible that something similar could have happened. But any gaseous atmosphere would I guess quickly dissipate due to the low gravity and stripping by the intense solar radiation - the moon has no global protective magnetosphere to protect it from such radiation. I am not aware of any ‘rounded sand particles’ recovered by Apollo, there were the green and orange glass beads from the Apollo 15 and 17 sites, but these glass beads are the result of Fire Fountain eruptions where the fine mist of super hot lava droplets chill rapidly in the vacuum of space and fell back onto the surface. So surface erosion by winds - unless those winds were the result of the movement of vapour in a temporary volcanic or impact generated atmosphere - is not something I am aware of being a factor in lunar history.

 

You said: 'Looking again closely at the Messier ‘graze’ photo with your graphic inclusions(post April 28th) … I’m struggling to see significant ‘Melt’ where you indicated … couldn’t this be happily incoming brief heat from a ‘pebble bouncer’ traveling West => East? … '

 

Answer: The melt is the very smooth surfaced material immediately to the west of the rim of Messier - this is the down-range side which is typical of low angle impacts - in this case from east to west, not the other way.

 

Here is a cartoon of the Messier impact - Messier on the right, Messier A on the left. Red arrows show the direction of the impactor(s) - from the east towards the west. The first impact created Messier and produced rays to the north and south and ejected melt onto the surface to the west of the rim. The impactor broke up and headed west at a slightly different angle to form Messier A - this type of offset in trajectory has been seen in experiments. This second impact formed the 2 'Comet Ray' rays to the west, with the sections of the  rays closest to Messier A being obscured by impact melt thrown out of the crater(s) along the original direction of travel. This is the most consistent explanation for what we see I think.

 

Regards, Barry.

 

 

[Drifter]

 

Thanks for your informative reply … which threw up a few conundrums, delayed my reply(which I’ve had to split in two- following shortly) …. and had me going back to your earlier comments which have flipped my viewpoint slightly … caused a few rewrites and a rethink or two over the last week!

Tackling the Messier Affair in this first post … I now see why the consensus is that Messier is East=>West. … with the very low angle trajectory I felt the slight melt/groove could easily have been a Western arrival and a Zone of Avoidance at the Eastern side caused by ‘bounce’ …. but the LH lip is slightly raised either side of the melt groove suggesting push from the East. The butterfly spread flagged up a ‘bouncer’ … but the traditional ‘profile scarring’ convinced me you were right and best follow the consensus opinion on this one!

I still feel the brighter reflective materials in both Messier and Messier A are an indication of a reaction between the composites of the meteor, the substrate, gases and most likely moisture sublimating from sources underground pushed to the edge of the groove where it might be in a high enough concentration and hotly reactive to leave these ‘fluorescent’ traces. If it was just ‘fresh throw up’ would it be showing a gradient of brightness with a build up to high albedo intensity at the western end exit where most of the ‘melt’ often is? … Interesting if this catalysed  it’s creation - a combination of low angle, meteor/substrate+sublimating gases/water/hydoxy burn … plus piezo-electric sparking if certain crystalline particles are present?

I like the idea Messier having similarities to an oxy-acetylene welder running a mig arc over the surface spraying fine dust fallout along the way and leaving a badly melted slaggy deposit! That sounds good to me.

I also like the idea that ‘reflective deposits’ in meteor craters are related to angle of incidence and direction  … BUT this created a major problem for me with relation to Messier A that initially I couldn’t figure … the problem was that the reflective material is on the Eastern side of Impact 2 - yet melt debris from Impacts 1+2 and ray scatter data indicated in your latest graphic plus the Nighttime Soil Temperature data as shown in your April 25th post shows clearly Messier A seems to be consistently an East=> West event too.

The clue to sorting this reflective anomaly conundrum/inconsistancy came from this extract you posted April 28th … 

“As for the difference in angles between Messier and the two parts of Messier A - a number of experiments have been done investigating low angle impact dynamics and what was found was that if an impactor broke apart on first contact with the surface then the bits that came off continued down-range at pretty much the same velocity, but the azimuth direction was not preserved - so the fragments would deviate from the original direction of travel. This is consistent with what we see in the Messier group. So in my (humble) opinion Drifter, Messier A formed in a single event. And I did not want to mention this for fear of over complicating things - but if you look at your image of Messier A you will see that the crater marked Impact 2 has pinches (yellow arrows attached image) in the northern and southern rim - makes the outline look like a Remembrance Day poppy. This indicates that this crater is in fact composed of 2 almost overlapping craters that formed simultaneously - so there were at least 3 impacts (and a bit of sliding along the surface) not two.”

 

3 impacts agreed - but only the earlier ones partly buried to the left showing the elongated ray ejecta flying westwards plus (VERY!) lumpy melt fragments … the third impact to the right of your yellow arrows which we can agree hit later - seems to have been a slightly larger boulder … but check this idea …  possible coming from West =>East leaving the reflective burn gradation on the Eastern side, ?? … note: greatly pushing up the Right Hand lip of Messier A and throwing a moderate pile of dust eastwards - if you look at all the dust sources you helpfully posted in this discussion. This greatly raised lip wouldn’t have been present if ALL 3 projectiles came ‘bearing gifts’ from the East.

Does that roll with what you can see?

Sadly, in conclusion, I think there is a slight problem with your June 6th statement:

“Here is a cartoon of the Messier impact - Messier on the right, Messier A on the left. Red arrows show the direction of the impactor(s) - from the east towards the west. The first impact created Messier and produced rays to the north and south and ejected melt onto the surface to the west of the rim. The impactor broke up and headed west at a slightly different angle to form Messier A - this type of offset in trajectory has been seen in experiments. This second impact formed the 2 'Comet Ray' rays to the west, with the sections of the  rays closest to Messier A being obscured by impact melt thrown out of the crater(s) along the original direction of travel. This is the most consistent explanation for what we see I think.”

Sorry, but I see a few flaws in the logic of this explanation.

1) What made Messier fragment and deviate to form Messier A Impacts 1+2 (but not 3) … when the exit wound is clean and consistent - with no deviation scarring? 
Is it at all possible the Messier meteor remained intact - lost some edge debris and bounced back out into Space?

2) The 2 long ‘rays’ to the west of Messier A show two further angles of deviation from Messier, is this really likely at the speed this was travelling to cut this clean groove with little end resistence? Yes, I get possible deviation from fragmentation, but …. see 3.

3) The objects creating the identical 2 long rays were on a different trajectory and indicate they were similar in size … but why are the crater widths roughly the same as Messier, possibly wider? … Is this really consistent with it being 2 large fragments from Messier??

Struggling with that idea, tbh.

Weighing in with my gut feeling + conclusion - Agreed Messier was an East =>West fly by -  or landed downline somewhere. Agreed Messier A … 3 impacts … But  2 E=>W,  … the last one W=>East.

Why? … because note: the right hand side of Impact 2 shows a very pushed up rim … and there are good traces of scatter from it’s edge, particularly to the south - which wouldn’t happen at all if all projectiles came from the East. It’s visible in the photos + scatter patterns in posts you made April 25th, 28th and June 6th.

Pt 2 on Tycho, rilles, Herodotus etc following shortly.

 

 

Edited June 14, 2021 by Drifter
Addition

[Barry Fitz-Gerald]

Well, I think we may have to agree to disagree on the previous discussions and the interpretations we each have of the impact mechanics of Messier and Messier A!  But 'Vive la difference' as we say in Dorset.

There is an extensive literature on impact cratering, a lot of it technical but also a lot that is accessible to the likes of us - and if a paper appears too complicated I suggest you just skip to the conclusion which will summarise the contents.

Here are some useful links to papers that are Open Source and available on-line and cover many of the the topics discussed above:

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/j.1945-5100.2011.01246.x   - covers low angle impacts, bit technical but check out diagrams and conclusions. .

https://meetingorganizer.copernicus.org/EPSC2010/EPSC2010-73.pdf  - ditto. The author has written extensively on the transition from circular to elliptical craters, also a bit technical but check out diagrams and conclusions.

https://www.osti.gov/pages/servlets/purl/1321817  - relates to the formation of the Imbrium basin - figures at the end are relevant to offset azimuthal trajectories. Original paper was in Nature some time ago.

http://www.psrd.hawaii.edu/Sept04/LunarRays.html - summarises a 2004 paper by Hawke and others on crater rays.

Unfortunately not all research papers are open source, but an increasing number are becoming so which is useful. Finding stuff on specific areas such as Messier is tricky, but there are some references out there, you just have to hunt for them.

This last one is an excellent paper on ejecta which is quite accessible and should be of interest:

https://www.academia.edu/20837861/Impact_ejecta_emplacement_on_terrestrial_planets -  this research benefits from having terrestrial impact craters and deposits to provide a 'ground truth' which can be applied elswhere in the Solar System, such as the Moon.

...........................if you find anything in it about fluorescence, let me know!

 

Cheers, Barry.

 

Oh, nearly forgot this from the Lunar and Planetary Institute - you can download the whole book (Traces of Catastrophe) which is excellent: https://www.lpi.usra.edu/publications/books/CB-954/CB-954.intro.html

 

 

 

[Drifter]

Thanks for those links … I’ll check them out.

So you didn’t see anything in the right hand raised lip (and some scatter debris) of the Messier A group to suggest the 3rd projectile in the 3 you mentioned possibly travelled from West=>East?

[Barry Fitz-Gerald]

No, I see nothing in any of the images to lead me to conclude otherwise to what I have already outlined above - everything is consistent with the E-W impact/fragmentation scenario.

The diagram attached shows a cross section of Messier A produced using the Line Tool in Quickmap - please note the extreme vertical exaggeration, the real crater is very shallow compared to its length. This shows the the eastern rim is depressed relative to the western rim in A, a combination that is diagnostic of low angle impacts with the lower rim indicating the direction the impactor arrived from and the higher rim indicating the direction the impactor was heading towards. This is seen in very many low angle impact craters, many of which look perfectly circular in plan-form (please see: The shape and appearance of craters formed by oblique impact on the Moon and Venus by Herrick, et.al (2003) :.https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/j.1945-5100.2003.tb00001.x )

The surface to the west of A is scoured by fragmented material that left the crater along a horizontal trajectory, and in effective contact with the surface. This scoured surface was then draped in impact melt and ejecta from the forming crater. This process is covered in detail in Elbeshausen, D., K. et.al.(2013), The transition from circular to elliptical impact craters. JOURNAL OF GEOPHYSICAL RESEARCH: PLANETS, VOL. 118, 1–15 (see Fig.2).  The models in this study are idealised computer generated scenarios, and real impacts are far messier (no pun intended) - but the parallels are compelling and persuasive.

If an impact had occurred from the west, the western rim would be depressed relative to the eastern, and there would be evidence of ejecta/melt traveling east - of which there is none. It is all going west.

 

 

In the case of Messier A, the observations and theoretical work are all in agreement as far as I am concerned.

I appreciate your desire to come up with alternatives, I do it all the time.

 

 

Barry.