Tag Archive | ejecta

A Feathery Treat

Every now and then Moon Zoo produces an image that just needs to be shared. Forum regular kodemunkey found another fresh white crater a while ago. I say another one because the forum contains many examples of these eye-catching recent impacts. And when I say recent I mean these impacts are millions rather than billions of years old. So it’s easy to be a little blasé when yet another one is posted. Until one comes along which hits you between the eyes. We featured one last year. And now we have another – a small unnamed crater on the western edge of Mare Vaporum. Click on the image for a bigger, better view.


Lat: 14.55   Lon: -0.25
M157594937LE / M157594937RE

Here it is in context – one small crater amongst many. The Lunar Reconnaissance Orbiter picked it out and highlighted its symmetrical beauty.

The impact produced some lovely feathery ejecta patterns (which are worth exploring even closer on the NAC images) and a gloriously bumpy and bouldery crater floor. Follow the links above (and this additional resource) for more information on fresh craters or just click on the first image, click again to zoom and sit back and enjoy.

Ejecta Blocking Boulders

All credit for this entry goes to forum regular kodemunkey who wrote this article:

Hello, and welcome to what will hopefully be the first of many IOTW posts from me.

I was exploring the LRO Data using the WMS Browser and I came across Maginus crater.

(Maginus crater, as seen in the WMS browser, latitude -48.992774 longitude -5.149416)

This is what Wikipedia has to say about the crater:

Quote

Maginus is an ancient lunar impact crater located in the southern highlands to the southeast of the prominent crater Tycho. It is a large formation almost three quarters the diameter of Clavius, which lies to the southwest. Just to the north of Maginus is the smaller crater Proctor, and to the southeast is Deluc.

The rim of Maginus is heavily eroded, with impact-formed incisions, and multiple overlapping craters across the eastern side. The wall is broken through in the southeast by Maginus C, a worn crater. Little remains of the original features that formed the rim of Maginus, and it no longer possesses an outer rampart. The floor is relatively flat, with a pair of low central peaks.

The thing about Maginus that interested me at the time was the unnamed crater near Maginus A, as it has a lot of NAC frame coverage. I’m certain that like me you prefer to look at areas with a lot of coverage, if only out of sheer nosiness!

The thing that first caught my eye about the crater was this large, and probably quite deep crack:

The next thing to catch my eye are these huge boulders which are blocking the flow of material down the slope.

These things are quite large, probably at least the size of a house, I wonder where they came from?

Sources and more information:
https://en.wikipedia.org/wiki/Maginus_crater

http://the-moon.wikispaces.com/Maginus

NAC frame: http://wms.lroc.asu.edu/lroc/view_lroc/LRO-L-LROC-2-EDR-V1.0/M175308014LE

Your task, should you choose to accept it (even if you don’t ) is to try and figure out how the boulders came to be in their present positions.

Ejecta Blocking Boulder

On the floor of Al-Bakri crater lies an approximately 100 foot diameter crater with a very unusual feature that may have interfered with its impact ejecta pattern.

ACT-REACT map NAC photo strip

You can see the open wedge area (no ejecta) caused from a strategically placed boulder near its rim.  Here is what Moon Zoo Team member Irene Antonenko ( IreneAnt ) has to say:

” This is really interesting because the boulder really shouldn’t affect the placement of the ejecta all that much. When the crater is being formed, ejecta is being thrown out from closer to the centre, so the boulder would be too far away to affect the ejection of material. And, when the material lands, it is thought to land from above (not sideways), so again, the boulder shouldn’t affect the emplacement of ejecta material. “

There may be some tells as one looks around the crater floor for clues that may help solve this mystery.  Our ejecta blocking boulder appears to have been sitting at that location for quite some time. There does not appear to be any boulder tracks like the one below from a boulder that probably rolled down from the rim of Al-Bakri crater south of our mystery boulder.

If you look at the other boulders in the area you will see that they appear to be white (high albedo). The ejecta blocking boulder is darker and appears to be the black sheep of the boulder community. This anomaly may be resolved if one considers that the darker color of the boulder may be due to it being covered with a dusting of fine ejecta particles from the impact.

It appears that the major force of the impact, as Irene stated above, moved up and over the boulder not affecting or having little affect on its placement. However, there does seem to be a lateral surface flow of ejecta that hit the boulder. The boulder then acted like a nozzle/guide that created the unique ejecta- free wedge design out from the crater. There is also a possibility that crater excavation moved our mystery boulder up to its present position while blocking the ejecta along the way.

The old boulder may have staked its claim to that spot first and was not willing to give it up even with the more recent arrival of a claim jumping impactor.  What are your thoughts?


Tom128 is a regular contributor on the Moon Zoo forum.

Crater Chain Boulevard

This is a very busy section for crater chains/secondary impacts near the Lunar North Pole at 72.51 N, 121.37 W

Act-React Quick Map

The impact formation at top right is especially interesting:

It is somewhat of a mystery to me on how it formed.  You can see what appears to be an ejecta blanket that perhaps moved in a W-E direction giving the surface a sculpted and scraped appearance.  That would be fine except for the line of craters that have made a chain of impacts on the left edge of this formation that would seem to have come in from a N-S or S-N direction.  Notice there is no surface ejecta sculpting to the left of this chain.

What are your thoughts?


Tom128 is a regular contributor to the Moon Zoo forum

Absorb yourself in Tycho

Appropriately named after one of the most colourful characters in astronomy, Tycho Brahe, Tycho is one of the most prominent craters on the Moon with its large, bright ray system dominating the southern hemisphere. Tycho is 85 km (53 miles) in diameter and is a relatively young crater at 108 million years old. Because it is young the rays have not been degraded and dulled by meteorite and micrometeorite impacts and still have a high albedo. So extensive are the rays that samples of impact melt glass thrown out by the impact that created Tycho were collected by the Apollo 17 astronauts from the Taurus Littrow region 2,000 km away. Tycho and it’s rays are most spectacular when viewed at full Moon when the Sun is overhead.


image: jules

The Lunar Reconaissance Orbiter Wide Angled Camera gives us a very different view of Tycho. Here we see the well preserved terraced crater walls and central mountains which are just visible in binoculars. So fresh are the features in Tycho that it is the perfect place to study the mechanics of how an impact crater forms.

click for high res version from NASA.

And here’s a close up of the rugged crater floor.

LROC

More information and another close up picture in this LROC News System article.

The NAC images of Tycho are well worth a tour. There are many NAC images of the crater floor – search on Lat -43, Long -11. Here are a few to start with:
M102230053LE
M114031031LE
M129369888LE

Enjoy! You may be some time!


Jules is a volunteer moderator for the Moon Zoo forum

L shaped dark ejecta

This week I found an image posted by ElisabethB which I think is worth another look.
It’s bright crater with dark L shaped ejecta.


http://www.moonzoo.org/examine/AMZ40013wv
Latitude: -2.69124°
Longitude: 342.478°
Sun Angle: -88.47°

As the crater is not very well placed here, it’s much better to take a look at the strip.

Do we have any more L shaped ejecta patterns?

Are they common?

How did this form?

The LROC strip can be found here http://wms.lroc.asu.edu/lroc/view_lroc/LRO-L-LROC-2-EDR-V1.0/M104634241LE and the crater is near to the top left.

Here is the forum thread with more comments.


Thomas J is a volunteer Moderator for the Moon Zoo forum

Another Look into Daguerre Crater with LROC

LROC Image

Apollo 16 Image

.

In April of 1972 the Apollo 16 CSM Casper piloted by Thomas K. Mattingly orbited the Moon while Commander John W. Young and LM Orion pilot Charles M. Duke landed in the Descartes region and conducted three EVAs on the lunar surface.

Apollo 16 CSM

Onboard the CSM was a sophisticated array of cameras that photographed the lunar surface during the 64 orbits.  The panoramic photograph AS16-4511 (P) top right shows a 2 km crater near the western edge of Daguerre crater, 11.53 S, 33.11 E.  I marked the WMS Image Map photo strip M121993376RE area in green, shown below and a LROC photograph of the crater is shown above, top left.

Here is a short summary about the crater from, “APOLLO OVER THE MOON: A VIEW FROM ORBIT (NASA SP-362)” on page 118:

“It shows the striking bilateral symmetry of the rays of a small (2-km diameter) crater in the floor of the large crater Daguerre in Mare Nectaris. Continuous areas and narrow filaments of light-gray ejecta extend from the crater across the dark mare surface through 270°, but are entirely absent in the southern 90° sector. Within the crater, dark material occurs on the southern crater wall while the remaining walls are bright. (The reader may wonder about the material whose reflectivity cannot be observed because it lies in shadow on the east wall of this crater. Until the area is observed under high Sun conditions, we are forced to make the simplifying assumption that it is bright because most of the materials visible elsewhere in the walls are bright.) This crater probably resulted from the impact of a projectile traveling from south to north along an oblique trajectory. Its pattern of ejecta distribution is similar to that of small craters produced by the impact of missiles along oblique trajectories at the White Sands Missile Range, N. Mex. Some observers postulate that the dark material is a talus deposit of mare material that has fallen into the crater.-H.J.M.  Another geological explanation is that the unusual pattern may be due to an intrinsic characteristic of the local terrain, probably an abrupt lateral change in the composition of the bedrock within the area that was excavated. F.E.-B. ”

As a side note, Harold J. Masursky and  Farouk EL-Baz were both geologists who worked with the Apollo program.  Those familiar with the astronaut biographies will find many references to Farouk El-Baz.

Taking a second look at the crater with LROC, we can now see which of the two geologists was correct with a stunning picture of the dark material spreading out in a ray pattern and also cascading over the crater wall towards the crater floor.

Here is an initial analysis made by MZ team member IreneAnt about the crater and its apparent oblique impact:

“If you look carefully at the LROC image, you can see an ejecta herring bone pattern in the dark wedge portion outside the crater. I think this is good evidence that this dark wedge is ejecta. You can also see from the LROC image, that this dark wedge matches up very well with a layer of dark material in the crater wall. So, there isn’t really a missing section of ejecta here, it’s just a different colour; in the black area, you hit and excavated black material, while in the light areas, you hit and excavated light material.  So, it seems that Farouk El-Baz was right and the ejecta pattern may have been caused by variations in the pre-impact target.

The thing that I find really interesting here is the implication for low angled impacts. From the Apollo images it seems clear that there is a section of the ejecta deposit that is missing, thus indicating a low angled impact. However, when you look at the higher resolution LROC image, you can see that there is, in fact, dark ejecta in the “missing” section, so this is not a low-angled impact. So, the two images tell very different stories. This casts a doubt on all “low-angle” impact craters identified based on missing ejecta sections. It may just be that higher resolution data is needed to see some ejecta of a different composition.”

Irene continues her analysis of the crater talking more about the lateral shift in the lunar material from lighter to darker:

“These kinds of horizontal variations are more common on the Moon than was originally thought. This is what my research revolves around. What probably happened here is that a small mare flow was confined by topography (hills and such) or was just too small to flow very far (think how a little bit of milk spilled on a flat table will only flow so far). Another possibility is that this is a pyroclastic deposit. Sometimes volcanoes can explode like a shaken bottle of pop. When this happens, drops of lava cool as they fly from the vent and land on the ground as glass beads. These kinds of deposits stay near the source vent, since glass beads don’t flow as well as liquid lava does. One final possibility is that this is a pond of impact melt from the Daguerre impact event. Impact melt would have been confined the same way as a lava flow.”

Irene presents very interesting information on the dark colored ejecta and iron:

http://clients.teksavvy.com/~iant/Various/InDaguerreFeO.jpg

“You can learn a bit more by looking at the composition of the material in and around the crater. In this image, you can see the iron content (calculated using data from the Clementine mission) overlain on a Lunar Orbiter image of this exact crater. The colours represent various iron contents (in Weight % FeO), as identified by the colour bar on the right. The shading represents topography through the use of shadows (sun is shining from the right). You can see that most of Daguerre’s floor has relatively high iron content (greens and yellows), while the rim of Daguerre (top right of the image) is relatively low in iron (blues). Our LROC crater seems to have excavated mostly material that is less iron-rich (light and dark blues), except for the wedge of high iron (greens and yellows) at the bottom of the crater. This high iron wedge corresponds exactly to the dark ejecta section you can see on the LROc image.”

I marked the wedge section with white lines and circled the approximate outer rim of the crater. The white rectangle in the crater indicates no iron content.

“If you zoom in, you can see that the iron-rich wedge at the bottom of the image extends into the crater interior. Remember that only parts of the crater interior are in shadow. To get a feel for the extent of the entire crater, complete in your mind the circle that is suggested by the right edge of the shadow section. Then you will see that the green wedge does indeed extend inside the crater. It is possible that the iron data is registering the land slide of dark material that we can see down the crater wall in the LROC image.

There is a high likelihood that the dark layer, which was the source of the ejecta that created this iron-rich wedge, is basalt. It is also possible that it may be a pyroclastic deposit, where the glass beads re-crystallized into basalt-type minerals after they solidified. The dark ejecta wedge, is expected have the same composition as this source layer.

The lighter ejecta material is highland material. It is lighter in color because of its lower iron content. It was emplaced when this impact crater excavated either sections of Daguerre’s crater wall and slump terraces or some pre-existing highland ejecta from an older and large crater. There’s not enough information here right now to tell which of these was excavated by our LROC crater, though. Lots more work to be done!”

I would like to thank Irene for taking the time out from her busy schedule to make this outstanding analysis of the crater. Forum moderator Jules and I also had some fun with a speculative comparison of the crater using the photographs of Apollo 16 and LROC.


Tom128 is a regular contributor to the Moon Zoo Forum
Irene Antonenko is a Moon Zoo Team member