Starship Asterisk*

Messier Craters in Stereo

Explanation: Many bright nebulae and star clusters in planet Earth's sky are associated with the name of astronomer Charles Messier, from his famous 18th century catalog. His name is also given to these two large and remarkable craters on the Moon. Standouts in the dark, smooth lunar Sea of Fertility or Mare Fecunditatis, Messier (left) and Messier A have dimensions of 15 by 8 and 16 by 11 kilometers respectively. Their elongated shapes are explained by an extremely shallow-angle trajectory followed by the impactor, moving left to right, that gouged out the craters. The shallow impact also resulted in two bright rays of material extending along the surface to the right, beyond the picture. Intended to be viewed with red/blue glasses (red for the left eye), this striking stereo picture of the crater pair was recently created from high resolution scans of two images (AS11-42-6304, AS11-42-6305) taken during the Apollo 11 mission to the moon.

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Ahhh....great 3d repeat... and looks great in 3D too...even the 3d full moon... nice and round, and bulging forward...nice effect.

Very interesting set of craters...sort of a "2 in 1" shot.... or is it 2 & 1/2 in 1 ??


I was able to finally get out for the first time this year and get a shot of the moon...
In case you might have missed my post...check here.
http://asterisk.apod.com/viewtopic.php?f=8&t=34817

Hope it is OK to do that...

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Who stole my red-green glasses? Can't find them.

Craine wrote:Who stole my red-green glasses? Can't find them. :(

Here's the image broken into a crossed-eye stereo pair, which I generally find preferable to anaglyphs (and which doesn't require any glasses).

Thanks for the stereo pair, Chris, just what I needed!

As a geologist with a strongly dominant eye and therefore little stereoscopic vision:
a. I have never had the slightest problem in seeing aerial photos as three dimensional
b. Anaglyphs are annoying and utterly useless

The crater on the right seems flat bottomed. Why is that?

As we see the picture, I think the impactor's trajectory was Right to Left and not the opposite as you write. Thank you

tetrodehead wrote:The crater on the right seems flat bottomed. Why is that?

Infill after the impact. Likely from Magma. The left crater also shares this flattened bottom feature at what appears to be the same level so Magma infill could be likely

Seems to me ther ought to be allot of meteorites or asteroid chuncks on the Moon,,,,,


:---(===) *

Constantopoulos wrote:As we see the picture, I think the impactor's trajectory was Right to Left and not the opposite as you write. Thank you

No. The APOD is looking downwards and southwards (or south up, or upside down, if you prefer).

The two bright rays mentioned in the explanation, are clearly visible on a good, wider image of this pair, extending to the west, which is to the right in the APOD, or to the left, here: http://lroc.sese.asu.edu/news/uploads/L ... ntext2.png

Boomer12k wrote:Seems to me ther ought to be allot of meteorites or asteroid chuncks on the Moon,,,,,

With no atmosphere to slow them down, most impactors will simply vaporize. Most of the "chunks" are dust sized.

First the kudos! I love APOD and set it as my home page on just about every computer I have to use on a regular basis. Now the caveat, I'm very uneducated in astronomy and physics.

I'm curious about the craters, perhaps more accurately about what made them. If the hypothesis is a shallow angel resulting in a skip and then landing (like we've all done as kids at a lake with rocks) is there any data on the size/mass and relative speed of the impact such that this particular crater pattern results? If the crater on the left is 15 km long then the gap between the two looks to be 10 km or less.

I guess I'm a bit surprised that the first could be made and then be able to make the crater to the right so close. To make the second crater I would think the object would need to have a lot of kinetic energy still present but if that were the case would expect the distance between the craters to be much larger or the second one a smaller carter, perhaps with the remains of the object still visible.

Has anyone done the math on that?

Nitpicker wrote:

Constantopoulos wrote:As we see the picture, I think the impactor's trajectory was Right to Left and not the opposite as you write. Thank you

No. We are looking downwards and southwards (or south up, if you prefer). The two bright rays mentioned in the explanation, are clearly visible on a good, wider image of this pair, extending to the west, which is to the right in this APOD, or to the left, here:

Click to view full size image

http://lroc.sese.asu.edu/news/uploads/L ... ntext2.png

This confuses me. Which direction of travel is assumed for the image you provided. I would think it has to be right to left in your picture (south toward the top). Is that right?

The APOD is South up (or upside down to most people). The LROC image I linked to is North up (or right way up to most people). The trajectory of the object forming the craters was from East to West. The bright rays extend to the West.

Steve Dutch wrote:As a geologist with a strongly dominant eye and therefore little stereoscopic vision:
a. I have never had the slightest problem in seeing aerial photos as three dimensional
b. Anaglyphs are annoying and utterly useless

As a person with two eyes of more or less the same quality, my observation/opinion is that the anaglyph gives a much greater sense of depth than either of the source images alone. Indeed, it seems to me that the sense of depth is significantly over exaggerated in the anaglyph, compared with the analytical reality (based on quoted crater sizes and depths).

The cross-eyed stereo pair provided by Chris, does not seem quite so exaggerated to me, but I can't be too sure. I can't study these for too long without giving myself a headache.

Just to provide yet another orientation to confuse matters, here is one of my images of the Moon, with East up, showing nicely the two bright rays heading westward (downward in my image) from Messier A. It also shows all six landing sites of the Apollo missions, which you can only just read in this version reduced for upload. You can see that the Apollo 11 site and the Messier region are both close to the lunar equator, which confirms that Apollo 11 orbited equatorially.
Edit: and of course, when we refer to East and West on the Moon, since 1961 at least, East on the Moon is West in the sky and West on the Moon is East in the Sky. So Mare Orientale (Eastern Sea), named in 1906, is on the Western limb of the Moon. Clear as moon mud, no?

Heh, I was just reading about Mare Orientale last night. It's surrounded by an interesting crater that we can't quite see.

Nitpicker wrote:

Constantopoulos wrote:As we see the picture, I think the impactor's trajectory was Right to Left and not the opposite as you write. Thank you

No. The APOD is looking downwards and southwards (or south up, or upside down, if you prefer).

The two bright rays mentioned in the explanation, are clearly visible on a good, wider image of this pair, extending to the west, which is to the right in the APOD, or to the left, here:

Click to view full size image

http://lroc.sese.asu.edu/news/uploads/L ... ntext2.png

First, thank you for dealing with my question. I am a civil engineer who has dealt with impacts on the ground. YOUR picture with impactor travelling from right of screen to the left is COMPATIBLE with mechanics. The APOD picture is not: the direction (first contact points) to (deep part) is the displacement vector of the impactor.
Constantopoulos@otenet.gr

Constantopoulos wrote:First, thank you for dealing with my question. I am a civil engineer who has dealt with impacts on the ground. YOUR picture with impactor travelling from right of screen to the left is COMPATIBLE with mechanics. The APOD picture is not: the direction (first contact points) to (deep part) is the displacement vector of the impactor.

You have experience with hypervelocity impacts? These can be generated experimentally with exotic instrumentation, but otherwise the only such impacts on Earth are from meteors, and we have no examples where the meteor was observed prior to impact.

The cratering caused by such impacts is complex and may be counter-intuitive. The direction of debris, shape of crater, slumping, and other features may not provide much evidence of the angle and direction of impact.

BMAONE23 wrote:

tetrodehead wrote:The crater on the right seems flat bottomed. Why is that?

Infill after the impact. Likely from Magma. The left crater also shares this flattened bottom feature at what appears to be the same level so Magma infill could be likely

Possible, but unlikely for such small impacts. Craters of this size have flat bottoms simply because there is a limit to how deep a crater can be without gravity leveling the floor.

Constantopoulos wrote:

Nitpicker wrote:

Constantopoulos wrote:As we see the picture, I think the impactor's trajectory was Right to Left and not the opposite as you write. Thank you

No. The APOD is looking downwards and southwards (or south up, or upside down, if you prefer).

The two bright rays mentioned in the explanation, are clearly visible on a good, wider image of this pair, extending to the west, which is to the right in the APOD, or to the left, here:
http://lroc.sese.asu.edu/news/uploads/L ... ntext2.png

First, thank you for dealing with my question. I am a civil engineer who has dealt with impacts on the ground. YOUR picture with impactor travelling from right of screen to the left is COMPATIBLE with mechanics. The APOD picture is not: the direction (first contact points) to (deep part) is the displacement vector of the impactor.
Constantopoulos@otenet.gr

Given that the main differences between the APOD image(s) and the LROC image I linked to, are only the orientation, the field of view and the lighting (morning vs afternoon sun), I don't understand how you can conclude that one is compatible with the mechanics and the other not. (I am a mechanical engineer who works mainly as a civil engineer, but I have never studied hypervelocity impacts in any detail.) I estimate that the side slope of Messier on the incoming side is roughly 60%, but I am quite prepared to accept Chris' s comments, that this evidence is not directly related to the trajectory of the impactor.

jmh wrote:First the kudos! I love APOD and set it as my home page on just about every computer I have to use on a regular basis. Now the caveat, I'm very uneducated in astronomy and physics.

I'm curious about the craters, perhaps more accurately about what made them. If the hypothesis is a shallow angel resulting in a skip and then landing (like we've all done as kids at a lake with rocks) is there any data on the size/mass and relative speed of the impact such that this particular crater pattern results? If the crater on the left is 15 km long then the gap between the two looks to be 10 km or less.

I guess I'm a bit surprised that the first could be made and then be able to make the crater to the right so close. To make the second crater I would think the object would need to have a lot of kinetic energy still present but if that were the case would expect the distance between the craters to be much larger or the second one a smaller carter, perhaps with the remains of the object still visible.

Has anyone done the math on that?

Hello JMH

I am not an authority in these matters but have an idea of the cause of the two impacts. That is; a single large rock breaking into two parts upon experiencing the gravity of the moon and prior to impact. Comet Shoemaker-Levy 9 prior to impacting with Jupiter is an example of my thought with regards to these impact craters. It seems the most logical answer as to two craters so close together of nearly equal size and angle. I am someone who has gazed at the sky, never studied it. Slightly disappointed your question was not addressed by some of the trained professionals viewing this APOD. To use your caveat, I'm very uneducated in astronomy and physics, too.

I am always pleased and amazed when one of the regular posters addresses and answers one of my questions. Your post certainty caught my attention and I feel my answer is correct and hope it fits with what you were asking.

Bill

BillBixby wrote:I am not an authority in these matters but have an idea of the cause of the two impacts. That is; a single large rock breaking into two parts upon experiencing the gravity of the moon and prior to impact.

I agree. A tidally disrupted impactor seems much more plausible than some kind of skip.

Looking at the paper that is mentioned in the "that gouged out the craters" link, which I've just found here:
http://articles.adsabs.harvard.edu//ful ... 3.000.html

... it seems to me that there is a very wide range of possible crater shapes formed by shallow-angle impactors. And there are quite a few double-lobed comets and asteroids out there, that may or may not break up prior to impact. I'm not sure I'm prepared to say that a tidally disrupted impactor "seems much more plausible" than a single, oddly-shaped impactor.