APOD: Messier Craters in Stereo (2013 Jun 08)

APOD Robot · Post by **APOD Robot** » Sat Jun 08, 2013 4:10 am

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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Beyond · Post by **Beyond** » Sat Jun 08, 2013 4:22 am

Well, to me... they don't look any messier than any of the other craters.

Hated · Post by **Hated** » Sat Jun 08, 2013 5:18 am

Listen, I cant believe you all call yourselves Astronomers, and believe that all of these craters here are from ONE impact. It is very obvious to me indeed there was a fast moving object that struck the moon moving from left to right. it is very clear to me that that object Bounced and only resulted in the two elongated areas. Then it is clear that another object that was far smaller impacter the area to the right in a near vertical manner, creating the rounded impact crater.

FLPhotoCatcher · Post by **FLPhotoCatcher** » Sat Jun 08, 2013 6:25 am

According to the skyandtelescope link (http://www.skyandtelescope.com/observin ... 04151.html) "A grazing impact (1° to 5°) of a projectile coming from the east excavated Messier... and another part of the projectile ricocheted downrange to form Messier A..."
So... one projectile going nearly horizontal caused both craters? I can't see that happening, since they are so close together - the impactor would have skipped out of the first crater and gone much farther before impacting again. Also, it would have fractured and lost mass after making the crater on the left. It seems to me that a more reasonable scenario would be that they were created by two impactors that were orbiting each other when they made a grazing impact, one impact more horizontal than the other.

Boomer12k · Post by **Boomer12k** » Sat Jun 08, 2013 9:46 am

The terminology is incorrect...this is a 3D picture...you use 3D glasses...."Stereo" is where you have TWO pictures and you use either a "Stereo" Viewer of one picture for each eye, or you Cross your eyes to blend the two pictures together....when you use two pictures to make a 3d picture it is still not called "stereo"...that is the other technique...this finish product you have here is 3D....

This is 3D....it says so on my Red/Blue Glasses......"3D Glasses"!!!! Not stereo glasses.

Hope someone gets it right next time....

Other than that it is an interesting picture. Thanks.

:---[===] *

JohnD · Post by **JohnD** » Sat Jun 08, 2013 10:06 am

Hated,
I hope you aren't living up to your name, and are not just teasing us!

Common sense and statistics tell us that the angle of impact is almost never vertical. It will follow a normal distribution, with the mean about 45 degrees, so that vertical impacts and grazing impacts are right out on the limbs of the curve and very rare. Yet the vast majority of craters are circular. It has been confirmed by experiment that the crater from a high speed impact is circular, and remains so as the angle of impact goes oblique, down to very low impact angles, less than 10 degrees.
See: http://www.annualreviews.org/doi/abs/10 ... Code=earth
And: http://www.impact-structures.com/unders ... -approach/

To explain the coincidence of two similar craters adjacent to one another, a 'bounce' is most unlikely.
See: http://adsabs.harvard.edu/full/1978LPSC....9.3843G
More likely is that this represents a single body that has split into two, possibly under tidal stresses. The best and most recent example was the Shoemaker-Levy comet that turned into a 'string of pearls' and caused a series of impacts on Jupiter. The seperation would depend on how soon before impact the split occurred, and the strength of the gravity field that the object was falling into.

John

Willy · Post by **Willy** » Sat Jun 08, 2013 10:10 am

Great videos:

Click to play embedded YouTube video.

See http://www.youtube.com/watch?v=gV8joAJ85y0 for Additional Notes from the video's author.

Their author, John Moore, has made many more videos like these using images from LROC.

FLPhotoCatcher · Post by **FLPhotoCatcher** » Sat Jun 08, 2013 10:31 am

Stereo view of the Messier Craters I made from the original pics. To view, cross eyes. Click for larger photo.
http://www.flickr.com/photos/mattmerritt/8984558885/

: Click to view full size image

neufer · Post by **neufer** » Sat Jun 08, 2013 11:56 am

FLPhotoCatcher wrote:
Stereo view of the Messier Craters I made from the original pics.
To view, cross eyes.
Click to view full size image

Chris Peterson · Post by **Chris Peterson** » Sat Jun 08, 2013 2:15 pm

Boomer12k wrote:The terminology is incorrect...this is a 3D picture...you use 3D glasses...."Stereo" is where you have TWO pictures and you use either a "Stereo" Viewer of one picture for each eye, or you Cross your eyes to blend the two pictures together....when you use two pictures to make a 3d picture it is still not called "stereo"...that is the other technique...this finish product you have here is 3D....

This is 3D....it says so on my Red/Blue Glasses......"3D Glasses"!!!! Not stereo glasses.

No, the terminology is exactly correct. A stereo image is one in which you have two images and a system for directing one to each eye. It doesn't matter if the images are physically separated, isolated by polarized light, isolated by different color filters (an anaglyph, as in today's APOD), or any other such system. These are not true 3D images, merely limited simulations of a 3D view that fool our brain.

True 3D images contain much more information. Examples include holograms and those made on 3D computer displays, which allow you to move your head around and see the scene from different views.

Colloquially, they are all called "3D", but only the latter truly are. So-called 3D movies aren't- they are stereo, just like today's APOD.

rstevenson · Post by **rstevenson** » Sat Jun 08, 2013 4:14 pm

I'm finding it difficult to accept that both craters could come from two pieces of a formerly single object, with the impacts therefore happening within seconds of each other at virtually the same angle of incidence. Why? Because the crater shapes are so different. The left crater looks like a glancing blow, as described for a low-angle hit. The right crater looks like a somewhat more vertical blow, giving a nearly circular crater along with some of the excavated material flowing out to the right.

Sure, that would mean a coincidence, with the two craters being so close to each other and with very similar orbital parameters, as evidenced by the bright rays off to the right of both of them. But coincidence does not equal impossible. And I think it's clear that the angle of incidence is different for the two impactors.

Or perhaps there were three impactors? The flow out to the right of the right crater could be all that remains visible of the second crater produced by the split first object. Then the third impactor, perhaps at a much later date, hit virtually in the same spot, producing the round crater and covering up part of the crater below it.

Rob

Beyond · Post by **Beyond** » Sat Jun 08, 2013 4:35 pm

Sounds good to me, Rob... but then, what do i know

Chris Peterson · Post by **Chris Peterson** » Sat Jun 08, 2013 4:43 pm

rstevenson wrote:I'm finding it difficult to accept that both craters could come from two pieces of a formerly single object, with the impacts therefore happening within seconds of each other at virtually the same angle of incidence. Why? Because the crater shapes are so different. The left crater looks like a glancing blow, as described for a low-angle hit. The right crater looks like a somewhat more vertical blow, giving a nearly circular crater along with some of the excavated material flowing out to the right.

It is quite dangerous to use the shape of a crater to infer much of anything about an impactor. The nature of a hypersonic impact results in a hemispherical release of energy, meaning that craters are ideally round, but are often distorted somewhat by the nonisotropic nature of the medium they are in. The exception is very shallow impact angles- less than 10°, which can produce elongated craters. But the dynamics are complex, and two nearly identical collisions could produce very different looking craters.

It is also worth keeping in mind that a large percentage of impactors are probably loosely bound rubble piles, so even with a "single" impactor, what actually creates craters in a chain can be very different from hole to hole. And, tidal stress shortly before impact can break a body into two or more chunks moving in almost, but not quite identical paths... quite a feasible way to produce a crater chain.

Statistically, all of the indicators that this pair of craters was formed by a single event far outweigh the possibility that they are unrelated.

FLPhotoCatcher · Post by **FLPhotoCatcher** » Sat Jun 08, 2013 8:15 pm

Chris Peterson wrote:
rstevenson wrote:I'm finding it difficult to accept that both craters could come from two pieces of a formerly single object, with the impacts therefore happening within seconds of each other at virtually the same angle of incidence. Why? Because the crater shapes are so different. The left crater looks like a glancing blow, as described for a low-angle hit. The right crater looks like a somewhat more vertical blow, giving a nearly circular crater along with some of the excavated material flowing out to the right.
It is quite dangerous to use the shape of a crater to infer much of anything about an impactor. The nature of a hypersonic impact results in a hemispherical release of energy, meaning that craters are ideally round, but are often distorted somewhat by the nonisotropic nature of the medium they are in. The exception is very shallow impact angles- less than 10°, which can produce elongated craters. But the dynamics are complex, and two nearly identical collisions could produce very different looking craters.

It is also worth keeping in mind that a large percentage of impactors are probably loosely bound rubble piles, so even with a "single" impactor, what actually creates craters in a chain can be very different from hole to hole. And, tidal stress shortly before impact can break a body into two or more chunks moving in almost, but not quite identical paths... quite a feasible way to produce a crater chain.

Statistically, all of the indicators that this pair of craters was formed by a single event far outweigh the possibility that they are unrelated.

I have to agree with rstevenson. If tidal stress shortly before impact broke the impactor in two, the angle of impact would be almost identical, so the craters should be more similar in shape. It's really the right crater, and the idea that a single impactor caused both craters by skipping once off the surface that I have a 'problem' with... It does appear that there are two different craters on the right - one deeper, more recent one over an older, more elongated one. I realize the 3D photo makes the craters look deeper than they really are, but still...

Chris Peterson · Post by **Chris Peterson** » Sat Jun 08, 2013 11:13 pm

FLPhotoCatcher wrote:I have to agree with rstevenson. If tidal stress shortly before impact broke the impactor in two, the angle of impact would be almost identical, so the craters should be more similar in shape.

That's the flaw in your reasoning.

It's really the right crater, and the idea that a single impactor caused both craters by skipping once off the surface that I have a 'problem' with... It does appear that there are two different craters on the right - one deeper, more recent one over an older, more elongated one. I realize the 3D photo makes the craters look deeper than they really are, but still...

I don't think there are superimposed craters here. But what it means when an impactor "skips" is very different that the image most of us probably have in mind from skipping a stone across dirt or water. With a single impactor, the part that comes into contact with the surface completely vaporizes; what "skips" is the upper part, which creates a second impact, down path, before the shock wave moving up into it from below can destroy it.

JohnD · Post by **JohnD** » Sun Jun 09, 2013 10:28 am

Hated wrote: It is the impact on the right that has an obviously newer single smaller near vertical impact.

hated,
I hope you followed up the links I posted for you above, on the incident angle of impactors, points that were kindly confirmed by Chris.

Al hypervelocity impact craters are circulaer, until the angle of incidence is less than about 10 degrees.
Thus, an explantion that involves the Messiers being simultaneous could be that the oval crater was a smaller fragment.

However, I refreshed my memory by referring to an excellent book, Planetary Geology, a collection of black and white photographs taken by probes and telescopes before 1979, with discussions by a group of that included the late Prof.John Guest of UCL, Prof.Paul Butterworth, now of Washington State U., Dr.John Murray of the Open University and William O'Donnel, now I think at Raytheon Labs, Santa Barbara. I reference the authors as this is an obscure book, not a paper. Their discussion of Messier concludes by saying that "double and multiple craters have been produced in the laboratory by impacting projectiles into sand at angles from 2^o to 7^o from the horizontal".

I can't find a reference to such lab.studies, but this paper http://articles.adsabs.harvard.edu//ful ... 1.000.html says "On planets without significant atmospheres, this change [retention of energy by the impactor] in enregy partitioning at very low angles (<10^o) is expressed by downrange ricochet impacts ("sibling" craters) that increase in distance from the primary with decreasing impact angle." This statement is backed by a reference, Schultz PH , Gault DE. (1991) Lunar & Planet.SCi XXII, 1195-1196, which is a conference proceedings book, not avalable online.

The Ames Vertical Gun Range could be a source for such studies, but I read that it could not fire at an angle less than 15^o, so there may be no data for angle as low as we would wish.

This page shows a strikingly similar crater to Messier, on Mars but without a 'sibling' crater:
http://cintos.org/SaginawManifold/Obliq ... index.html
and you may like to compare with the lunar crater caused by crashing a Saturn IVB booster into the Moon, at an oblique angle:
http://www.nasa.gov/mission_pages/LRO/m ... 4sivb.html
The booster did not 'skip' across the moon's surface.

John

PS If you want a really ENORMOUS elongated crater, try Orcus Patera on Mars, 130kms long. Good picture from ESA at http://www.esa.int/Our_Activities/Space ... ted_crater
and if APOD posted that, we could have a good argument about origins. My bet is it's a crater chain. J.

Hated · Post by **Hated** » Tue Jun 11, 2013 9:58 pm

I must say, when I saw you all banned me for a day simply because I raised questions and put forth an alternative theory that you claim was NOT scientific Norm. I was in the middle of drinking some milk with an Oreo cookie, and I laughed so hard at the obvious close mindedness of it all, that milk actually came out my nose.

Lets see....Once upon a time Man KNEW the Earth was flat, then someone had a theory that it was round

Without exploring theory we can never gain knowledge.

I also love how you simply deleted what I had said

To find the Truth, you must go Beyond

rstevenson · Post by **rstevenson** » Wed Jun 12, 2013 1:25 am

Hated wrote:Without exploring theory we can never gain knowledge.

That depends a lot on who is doing the exploring. It sure wouldn't cause any great increase in the sum of human knowledge if I explored some of the bigger unknowns in cosmology.

At any rate, there are many forums on the web in which alternative ideas can be discussed. This forum choses not to be one of those places. Seems simple enough, and not really anything to cause milk-snorting.

Rob

geckzilla · Post by **geckzilla** » Wed Jun 12, 2013 2:07 am

I also only put the ban up so you would get the message. Normally I simply PM new users to inform them of the rules. That being said, it's also inappropriate to discuss moderator actions in public. So please, either stop now or make a forum account so that I may converse with you in private.

Edit: and please read the rules before posting. - bystander

Beyond · Post by **Beyond** » Wed Jun 12, 2013 2:53 am

rstevenson wrote:milk-snorting

Milk-snorting

That must be quite a MOOving experience

Starship Asterisk*