Barry Fitz-Gerald

I like a good mystery, but I have to admit that this one has me slightly puzzled.  The Apollo 15 Metric and Panoramic cameras imaged the far side crater Paracelsus C, and it is now imaged in high resolution by LRO with the images available at the LRO Quickmap site hosted by the University of Arizona. Features in the image were identified and described in a 2016 Journal of Space Exploration article entitled  Image Analysis of Unusual Structures on the Far Side of the Moon in the Crater Paracelsus C by M.J. Carlotto and others (open source availability). Whilst I am not in complete agreement with their conclusions, I thought it worth bringing attention to the features discussed as they are interesting to say the least and I would like to hear some views on what they might represent.

The attached image is from taken from the LRO Quickmap NAC coverage of Paracelsus C and show a cluster of quasi angular apparently solid three dimensional structures on the southern crater floor. They appear to be partially buried by regolith, and indeed seem to lie within an apron of material that has slumped down off the southern crater wall. As can be seen they appear at first glance to be large slabs of rock, but the largest is some 70m long (the inset image of a Boeing 747-100 adds a touch of scale), whilst the others show a degree of angularity and the presence of straight line features that are at odds with the general run of the mill population of lunar boulders. Of course their composition is unknown, but if they are part of the normal lunar suite of rocks such as basalts or anorthosites (this is in highland terrain and so possibly dominated by the latter), then it is hard for me to understand how a 70m long slab of such rock with limited tensile strength could maintain its structural integrity and remain in one piece, especially if it originated higher up on the crater wall/rim. Of course this image is showing only one aspect of illumination and others, but other images with differing illumination angles and directions are available via the Quickmap site. Also such large blocks are big targets and would naturally be fragmented by meteorite/micrometeorite bombardment, but there is little in the way of spallation debris surrounding them.

So, if there is a structural engineer, igneous petrologist or someone who knows a thing or two about growing 70m long plagioclase crystals out there - please have a look and if possible offer an opinion.

Regards, Barry.

'Still a bit puzzled why Messier A impact craters appear to be deeper and wider than the Messier crater - when what created them was fragments from Messier - travelling at a reduced velocity and a fraction of the mass?'

I think you are not alone there, and it is such a strange 'one off' that there is little to compare it with, and the differences in the crater outlines certainly are a conundrum that I do not have the answer too.  That's why alternative interpretations like yours are always worth discussing because it forces you to look at things again in a fresh light. It's easy to accept the standard interpretation - but more interesting to question it. So when you say ' I’m happy for all these impacts to be unrelated … and Messier to have bounced back out into Space!' I would be daft to rule this out as a possibility, because you could very well be correct!

Cheers, Barry.

You are right, the pesky Zone of Aviodance is difficult to see in this case, but have a look at the Apollo 11 image attached - you can see subtle ridges marked with white arrows which are the edge of the Messier A Zone of Avoidance. The deposits shown with the grey arrow probably came from Messier A during the late stage of crater formation when ejecta did end up being thrown out towards the east - so even though they are called Zones of Avoidance you do get some ejecta in there in many cases. Cauchy is a good example of a crater with a ZoA but where you will find ejecta within it. In the pic the red arrows show the ridges that mark the edge of the ZoA as is the case with Messier A, but if you zoom in you can still see stuff there which was flung out of the crater during the final stages of crater formation. Even though Cauchy is pretty circular the ZoA shows it was a low angle impact crater.

The ZoA in Messier A is also obscured by all the impact melt that came out of Messier which forms the smooth puddle between the two. The fact that the Messier A craters are more rounded than Messier would suggest that the impact angle was not as shallow in the case of Messier A - which could be seen as a weakness in my version, but have a look at Fig.2 in https://www.osti.gov/pages/servlets/purl/1321817    - you can see an elongate ragged crater on the up-range side and a smaller rounder one, slightly offset downrange. But of course this is the result of a lab experiment so extending the interpretation to larger more complex scenarios is not a precise one - but a reasonable guide.  But it leaves some wiggle room for alternatives!

Cheers, Barry.

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.

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

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.

1 hour ago, Stu said:

Sounds good Barry. The only thing I would say is that you will not properly be seeing the granulation  low powers, just the overall mottling of the surface and variations in density over the disk.

By using a setup that works at high powers you can really see much more detail in the active regions and also the granulation gets much more like tiny open cells. I say this not as any form of criticism, I’m just quite passionate about WL solar and want to encourage people to get the most out of the views.

That is probably very true - my solar viewing tends to be quite quick and not too detailed, so have never pushed the magnification up very high - but for a wide field view it works fine. I keep my higher power aspirations aimed at the moon.

I use a Startravel 120 with a Baader Solar Film filter (DIY) and a Baader Solar Continuum Filter, the views are very good, faculae, sunspots and granulation all sharply defined with good contrast. I have not used high powers preferring to see the complete disc in one FOV. 

I do not know if this is the same thing, but on a number of occasions I have seen a very bright point like flash somewhere in the region of mag -5 or brighter in various parts of the sky. A second or two later there is a repeat flash, at a slightly different position, but less bright sometimes followed by other much dimmer ones again displaced from the original location. I have got my bino's onto the part of the relevant part of the sky a couple of times and I have seen a feint point of light moving from the position of the original flash, and again with the occasional further but dimmer flashes occurring.  I am guessing that this is a satellite - not a geostationary one as it is clearly moving - that presents a broad surface or solar panel to the sunlight at the point where the bright flash is seen. Why we see only a few flashes might be down to the configuration of the satellite, how it is rotating, viewing angle and so on - but I am satisfied that they represent man made space litter.

I used to get quite excited at seeing a satellite when I first started observing in the 1960's as they were pretty infrequent - the other night I saw 3 simultaneously in the field of view of my 10x56 binos.   I did not get excited, but I did sigh a little.

Barry.

De Vico A is older (probably Nectarian in age so about 3.85 billion yrs) than Rimae Sirsalis which formed later and cut across the older terrain including the ancient craters. De Vico AA appears to be younger than Rimae Sirsalis as has been noted, as the rim interrupts the southern margin of the rille.  Rimae Sirsalis is however older than the lavas that fill Oceanus Procellarum, as these lavas have flooded the rille beyond Sirsalis K.

Rima Sirsalis is a 'graben' where two parallel faults develop and the ground in between them collapses downwards to form a linear trough. It is thought that these faults converge as you go deeper into the crust until at some point they may meet at depth, as a result the sides of the 'graben' are not vertical but are moderate slopes. One school of thought has them developing above vertical sheets of magma ascending towards the surface (dykes or dikes) where the upwards pressure cracks the rocks above to produce the faults that bound the graben on either side. An alternative hypothesis is that they form as a result of tensional forces where the crust is being stretched (such as around the margins of the mare) and the faults are produces as a result of that stretching. There is a magnetic anomaly associated with Rima Sirsalis, the only lunar magnetic anomaly associated with a graben which is notable. There is little evidence of surface volcanism along the length of Rima Sirsalis to suggest there is a dyke underneath - and the area is crossed by many other graben that may have formed due to the presence of the Orientale Basin - so maybe a tectonic origin is more plausible?  Sinuous rilles are thought to form partially as collapsed lava tubes, but they also formed open channels as the extremely hot turbulent lava cut downwards into the pre-existing lunar surface.

Cheers, Barry.

Even impacts that occur at fairly low angles end up producing circular craters as has already been said - the analogy with ripples in water is a good one as the shockwaves  do all the hard work of excavating the crater. At angles below about 35 degrees however the ejecta blanket starts becoming asymmetric, with a V shaped gap appearing in the up-range direction (where the impactor came from) this is called a Zone of Avoidance. The far side craters Ohm and Jackson are very good examples of this type of ejecta distribution. At lower angles a similar zone develops in the down-range direction, and at even lower angles most of the ejecta goes out sideways to produce a 'butterfly wing' type ejecta pattern with little or no ejecta in the up-range or down-range direction.  Messier is an example of this type of distribution.  However during low angle impacts (about 35 degrees and lower) to begin with ejecta leaves the crater preferentially in the down-range direction. During crater formation, and where the impactor arrives at a high angle (45 degrees and above), the ejecta leaves the crater in the form of a conical ejecta curtain - rather like a wide ice cream cone with the point of the cone at the impact site. At low angles however this 'cone' is initially tipped over towards the down-range direction - so the early ejecta is concentrated in this direction. As the crater forming process continues this 'cone' tips back towards the upright position - meaning that the ejecta is no longer preferentially sent down-range but ends up leaving the crater more symmetrically.  At the same time the crater transient cavity which may have started off being elongated along the direcrtion of travel of the impactor  becomes circular as the impactor penetrates the surface and crater excavation efficiency increases. In this way the initially elongate crater is consumed by a growing and more symmetrical circular transient crater cavity and the initially asymmetric ejecta is over-printed by the later more symmetric ejecta. So despite being very rapid, the impact cratering process can evolve in the seconds it takes place and both the crater outline and ejecta pattern can evolve from asymmetric to symmetric.

Dawes is a super example of this where the attached Clementine UVVIS Colour Ratio map shows the early ejecta as a yellow fan distributed to the west - which is the down-range direction, the impactor having arrived from the east as shown by the red arrow. The fainter circular blue halo is the ejecta produced later in the impact process when the ejecta cone was more upright resulting in a more symmetrical distribution. The cross section shows that the eastern rim is lower than the western one - a common feature of low angle impacts of this sort where the up-range rim is depressed relative to the down-range one.  The SELENE image of Dawes shows it to be fairly circular, so if the ejecta was invisible due to age and space weathering the evidence of the low angle impact would be difficult to spot.

Probably the best known lunar crater Copernicus is another example of a low angle impact - this time the impactor trajectory was south to north, but the crater is pretty circular. You can however see evidence for the low angle impact in the ejecta pattern which is far from symmetrical. There are a few other whopper craters the size of Copernicus that resulted from low angle impacts (Arzachel and Cardanus for example) where the impactors came from the the north or south but resulted in circular craters - so arrived at high angles relative to the plane of the ecliptic. Maybe these impactors arrived from the Oort cloud as opposed form stuff orbiting in the plane of the ecliptic.

To leave an elongate crater the impact angle would probably have to be well below 10 degrees, and at these angles cratering efficiency is much lower compared to higher angles. Again the best example of this is Messier - Schiller is often though of as being an elongate low angle impact crater, but this is probably not the case and it was formed by the impact of a train of debris from a tidally disrupted rubble pile type asteroid of comet (à la Shoemaker–Levy 9).

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.

I would agree with Vlaiv, they do not look like any artificial satellites that I have seen, which all appear as point sources with no structure - well to my eyes at least. Your objects have structure, the pair group look like slightly crumpled spheres illuminated from the top right and with the opposite side in shadow, whilst the elongate object looks like a partially eaten sausage (there is a less savoury analogy - but I will not use that one) but also appears to be illuminated from the same source as the pair. Both groups show what appears to be intrinsic colour - a shade of brown/orange but with one of the pair slightly darker. These factors suggest they are relatively nearby objects and nothing at high or orbital altitudes. The shape of the objects appears to remain consistent in each image so they do not appear to be aircraft strobe or navigation lights smeared out by the effect of camera movement. The interpretation of the white 'object' as being an optical artefact is quite plausible, but it appears to be keeping station relative to the brown objects in successive frames, so could be a real (maybe point source) object but with the image distorted by the camera lens into the shape you have captured. One obvious interpretation is that they are deflated or partially deflated balloons, which can appear quite unusual when seen at distance. But for balloons drifting on the wind they appear to be keeping station quite accurately and not tumbling as balloons tend to do when buffeted by the winds - which leads on the the question, do you remember if the wind direction on the night was the same as the direction of travel indicated in the different frames?

Anyway, the short answer is I haven't got a clue what you captured in those images, and everyone loves a mystery - don't they? 

Do you have any higher resolution copies?

Cheers, Barry.

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.

These features are Dark Halo Craters (DHC's) - and they form where an impact excavates darker, usually mare type basalts or pyroclastic deposits from beneath a lighter surface. In this case the surface is dominated by Copernicus ejecta rich in light highland rock (a plagioclase feldspar rich rock called anorthosite which is intrinsically bright - see The Genesis Rock found on the Apollo 15 mission) and a small impact has penetrated this and produced its own ejecta blanket of a much darker nature, probably composed of pulverized mare basalts from an underlying mare surface. DHC's are good probes of the lunar surface and can reveal the underlying rock types in their dark ejecta blankets. They were used to identify many areas of 'cryptomare', ancient mare type deposits buried beneath younger, lighter smooth plains within the highland areas, showing that volcanism was taking place very early in lunar history.

Cheers, Barry.

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.

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.

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.

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.

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. 

Just remembered - it was also sold under the brand name Sky Rover in the far east, so maybe a few turned up in Australia (https://www.astronomyalive.com.au/product/sky-rover-ult-130-ed-glass-130mm-triplet-super-apo-refractor-telescope/)

The later iterations of all these Kunming Optical scopes turn up under different badges - as do most non top end telescopes so it seems. You are correct about re-sale value however, probably not as good as a 'branded' scope, but if it performs well it could have anything written on the dew shield as far as I am concerned.

This looks identical in every way - including the case - to telescopes that were sold under the OSTARA name in the UK. They appeared in the most unusual outlets and also in on-line vendor ad's.  I strongly suspect they are made by the same Chinese company that supplied the Orion Eon's and the Altair Astro Wave 130 that was reviewed in Sky at Night in 2013 as they appear superficially to be identical apart from the badge on the dewshield. Of course these suppliers can specify what specs they require from the manufactures such as glass, number of baffles and so on and so the clones sold under different names may have a different spec. Whether this is a lower spec or not I do not know, but what I can say is that I have one of the Ostara 130's and it is a rather nice telescope which provides excellent views - so no complaints there. It also cost (second hand) considerably less than a 'premium' brand leaving spare cash to invest in a couple or three decent eyepieces. There was a review of an OSTARA 115mm Apo on this forum some time ago which was quite positive, but I have never seen anything written on the 130mm version but assume it would be of the same quality.

Cheers, Barry.

Dorchester in Dorset? If so send me a PM - I am also in Dorchester!