Messier Craters in Stereo (2009 Dec 11)

[APOD Robot]

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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[dwain0]

I enjoyed the images of Messier and Messier A today. But I didn't understand why the empactor path was described as left to right until I examined the link http://www.skyandtelescope.com/observin ... 04151.html

In 3304151.html it is clear that the empactors' path is as described, but on the APOD page it appears to be right to left.

[geckzilla]

Both descriptions are correct, though. The article you've linked shows the craters rotated 180 degrees from the APOD's orientation.

[markjaffemd]

Can anyone tell me where is the object now that impacted the moon to make these craters? Thanks

[BMAONE23]

Given this image I would say it likely that the impactor either disintegrated upon impact and left the two light toned streamers from Messier A toward the left or grazed in both locations and bounded farther away. (most likely disintegrated upon impact)

[bystander]

Given this image I would say it likely that the impactor either disintegrated upon impact and left the two light toned streamers from Messier A toward the left or grazed in both locations and bounded farther away. (most likely disintegrated upon impact)

Personally, I think it was two separate impactors. Regardless, there is a third option. The impactor(s) could be buried in the crater(s). But I agree with BMAONE23, most likely disintegrated.

[peter_from_nyc]

I notice that the bottom of the left crater is "flat".

Can that be because it hit a different density layer of the moon, so it did not penetrate evenly as a spherical imprint?

Is it the same depth as the crater on the right, which would confirm that there are a bunch of shells/bands of different densities? (I'm not a geologist.)

[ta152h0]

That would be cool if Apophis hit the moon.Sitting on my favorite bench having a cold one..

[BMAONE23]

Given this image I would say it likely that the impactor either disintegrated upon impact and left the two light toned streamers from Messier A toward the left or grazed in both locations and bounded farther away. (most likely disintegrated upon impact)

Personally, I think it was two separate impactors. Regardless, there is a third option. The impactor(s) could be buried in the crater(s). But I agree with BMAONE23, most likely disintegrated.

I agree that the two craters appear to have been hit at separate angles of attack. Messier is a glancing hit while Messier A is more a directly hit circular crater, though Messier A also shows an artifact of an earlier glancing blow. I would think that the impactor that created Messier gave a slight additional glance off at Messier A loc and was followed by a second impactor that created the more circular Messier A feature

[bystander]

I agree that the two craters appear to have been hit at separate angles of attack. Messier is a glancing hit while Messier A is more a directly hit circular crater, though Messier A also shows an artifact of an earlier glancing blow. I would think that the impactor that created Messier gave a slight additional glance off at Messier A loc and was followed by a second impactor that created the more circular Messier A feature

From the Sky and Telescope article Messier on the Moon referenced in the APOD:

Surprisingly, not much changes until the impact angle is less than 45° (measured from horizontal). But at shallower angles the crater becomes increasingly elongated in the direction of motion, and portions of the projectile ricochet and gouge out a series of small pits downrange from the main crater. As the impact angle changes, the ejecta and rays undergo even more pronounced changes than the craters do. When the impact angle is less than 15°, the ejecta pattern becomes elongated in the downrange direction and a "forbidden zone," where no ejecta appears, develops in the uprange direction. For grazing impacts of just a few degrees, the rays go sideways only, producing a butterfly-wing pattern. Amazingly, examples of all of these exotic ejecta patterns can be found on the Moon, Mars, and Venus.
...
The really remarkable fact about Messier and Messier A is that the scientists Gault and Wedekind were able to beautifully mimic every one of the pair's weird features in laboratory impact experiments. A grazing impact (1° to 5°) of a projectile coming from the east excavated Messier (explaining its elongated shape and classic butterfly-wing ejecta pattern) and another part of the projectile ricocheted downrange to form Messier A and its long rays. Bigger craters formed obliquely too — look closely at Proclus, Kepler, Tycho, and even Mare Crisium. Maybe, on the Moon at least, truth really is stranger than fiction.

The unusual shapes of the craters Messier and Messier A are well seen in this CCD image by Florida amateur Maurizio Di Sciullo. North is toward the upper right. (Rotated 180 from APOD)

Messier_Messier_A_close_m.jpg (9.57 KiB) Viewed 3096 times

You can see the butterfly ejecta around Messier and the elongated ejecta pattern downrange of Messier A.

[ebow]

This is one of the few stereo images I've seen where the 3D effect really "pops" for me! Usually I get only a vague impression of 3D; maybe it's the relatively close vantage point from which the source images were taken.