The impact of my time at Barringer Crater (AKA Meteor Crater)

I spent the last week touring Meteor Crater in Arizona. It was a unique opportunity sponsored by LPI that gave us unprecedented access to meteor crater to aid in our understanding of impact cratering processes. It began with 3 days of touring the crater followed by 4 days of investigating a particular problem.

This was lead by the lead scientist at Meteor Crater and the head scientist at LPI (the Lunar and Planetary Institute).

Introduction to Meteor Crater

trail guide
We toured along the east rim then back along the west rim to view the crater from a different perspective. Then we traveling into the crater itself and explored the crater floor (making our way up slightly to view a piece of the crater wall up close; available in Guide book, D. Kring, 2017).

We toured along the east rim then back again along the west rim viewing the crater from two different perspectives. On the second day we explored the interior of the crater. The beauty of Meteor Crater lies in its location and how well preserved it is.

Think about the Grand Canyon. It’s only ~150 km away from Meteor Crater, and in fact they both lie on the Colorado Plateau which means the geologic layers are the same (at least before impact).

mc cp
The Grand Canyon and Meteor Crater lie on the Colorado Plateau (the ~edge is drawn in red). Therefore, the geologic layering that exists is the same for both.

You may have already learned that the Grand Canyon is like a picture through time. Cosmos, a Space Time Odyssey illustrated this with an nice animation that separates each layer to highlight how each different layer has a different history for how it formed.
02463f7fe

 

gc mc layers
The Grand Canyon layering compared to the section effected by meteor crater (Moenkopi, Kaibab, and Coconino). From Meteor Crater Guide book, ch2 by D. Kring, 2017).

Meteor Crater penetrated through to the top 3 or four layers, Moenkopi, Kaibab, and Coconino. You can learn more about these in D. Kring’s guidebook (2017), but they each speak to a different environment by which they form. Coconino likely formed by sand dunes. Kaibab formed when Arizona was covered by a sea of varying depths (with fossils). Moenkopi formed during a time of a flood plain, similar to the Florida Everglades.

IMG_20181007_135208
Kaibab Limestone with fossils (exposed by an ejected boulder ~10m in size).

What happens when impacted is that the impactor (~30m in size) penetrates ~30m below the surface releasing large amounts shock pressures into the ground that rebound into the meteorite.

shock
From Kring 2017 guidebook

It acts like poking a pen through paper. The paper breaks and the ring bends back. In fact, they bend back over one another, folding. The result is that the lowest layer is folded on top of the other layers inverse to how they are normally layered. The diagram below shows the “fold hinge” having been mostly blown out in ejecta while the Moenkopi remains. However, overtime, this hinge is eroded (as well as the upper layer) and it becomes more difficult to see.

impact overturn
From Kring 2017 Guidebook

This overturned rim consists of a part of the blanket of ejecta that extends outside the crater.

fg
A Geologic cross section to summarize the crater geology.

This overturn is idealized. Sections eroded. Some shear; sections of Kaibab are missing between Coconino and Moenkopi because it slid outward further into the ejecta blanket. Furthermore, Kring suggests there were likely two other types of ejecta. A base-surge unit of the finest particles thrown up by as ejecta that is the last to fall and coat the rim and ejecta. This unit is known to exist from atomic bomb testing that formed craters. The other unit, which actually was the target of our research project, was known as Fall-out or Fall back ejecta.

Research Project: Fallback ejecta at the west rim

Fallback material is a layer of debris that is deposited over the overturned ejecta/rim. Kring describes its radial extent as unknown in the field book, but in person he made it seem as though its radial extent would be minimal. He described it as highly shocked material that is shot nearly straight up into the air before falling back down. This suggests that the layer it produces should be a mix of material, rather than distinctly inverted layers of the original target rock (see figure below). The idea that it goes straight up suggests it can’t extend too far out (without further modification).

 

fallback
Example of Fallback ejecta consisting of a mix of materials

Our research objective of this trip was to investigate region of possible fallback material by mapping its extent and identifying key characteristics within it. This means looking for key things like moankopi above the two layers (when it should be below) or evidence of high impact pressures with things like shocked Coconino.

Note, a previous version of this blog went into more detail about the project. I regret that decision. The blog wasn’t meant to expose too many details about the project, especially with the potential for publication. I have a habit of discussing my research openly, and I realize this is a unique situation that deserved more discretion.

General Thoughts and Take Away

I wish I had a clearer idea of what to expect going into this. The first 3 days or so are introduction. The next day is an applied field project to expose us to the area and investigating a problem. We measured ejected boulders to calculate their velocities. Then we moved on to this project, but the transition went from being guided to self ran. There wasn’t a clear distinction that, hey, from here on out you’re guiding yourself. That lead to a bit of confusion at the start, and even Kring blowing up at us, even going so far as to call us “by far the worst group of students I’ve ever had,” after telling us we were picked for this very competitive school because were believed to be the best of the best. That bothered me and several others. That isn’t how you teach. That isn’t how you motivate. What’s worse, I have to ask myself do I really want to talk about this here? Because, I could risk throwing away my chance to get another field school sponsored by Kring or LPI. At the same time, the thought that I’d be willing to work with someone who would treat me this way makes me feel…pathetic.

SAMSUNG
The group picture I tried to take and failed because a certain someone was too eager to check their own camera.

Note, images of Meteor crater are not to be reproduced for professional use. Images must legally be obtained by contacting Meteor Crater enterprises.

Advertisements

A minor setback in finishing up manuscript, now fixed.

Issues with results

Last Friday was one of many deadlines for which I was set to have a new draft of my manuscript (of my masters research) to my adviser, Dr. Catherine Neish. I was set back by a problem with my newest results that I noticed as I was discussing (i.e. writing) about them. To recap, I have measured crater morphometry (diameters, depths) using SARTopo, a low resolution topography on Titan. Then I compared it to Catherines stereo results (of higher topography) to ensure the low resolution data was reliable. I then replicated her results because the methodology of the measurements were different. Hers being an average of the entire 2D regions. While mine are averages of individual profiles (up to 8). Obviously, these results would differ, especially if there are fluctuations in the topography. However, I noticed that one of my crater measurements was significantly lower than Catherine’s.

Troubleshooting

At first, I assumed it was differences in the methodology. After all, the point of me doing this was because we feared they would be different, but I studied it closer by looking at the 8 individual measurements I took to make sure the lower result was just a matter of averaging lower areas. This wasn’t the case though. Every profile was significantly lower depths which didn’t add up. It ended up being a simple problem. I was weighting scaled images. As in, I used black and white images  where the white region was the max height and black the min height. This will not give precise measurements and will skew the data.

All in all, it wasn’t that off, but for Shikoku it was. That meant I had to go back extracted precise text file matrices of the data. I had another issue in this process where I was using the wrong file for Shikoku to extract the data. Stereo files vs radar images have different resolutions. That’s how I was differentiating them. Except, Shikoku had several 1404m resolution files; this wasn’t the case for the others. I started to use the wrong one. I don’t think this was the problem originally because I used an image already made (by Catherine I assume). Still, the problem is now resolved.

Results

These updates and fixes have significantly improved my results. Before, they all lied below or within error of SARTopo, but some of them disagreed with Catherine’s results. Now they are more in line. That is, Foresti and Hano are unnaturally low compared to SARtopo (~110 and 70m respectively). This has been explained before; there is a problem in the stereo processing where it likely doesn’t have enough representative features in the radar images to identify a difference in the two. Before, Hano was comparable to SARTopo, and I figured Catherine’s results were just because there was significant variance in the topography (some very low and very high) regions. Although, this isn’t what I find. Its around 50-70m in each profile, never reaching 100.

All the others lie slightly above SARTopo results, but they lie well within the margins of error. The highest are observed with Soi and Shikoku (+80 and +90m respectively). All in all, this is the result we were looking for. The results are slightly higher because SARTopo does average the results downward. Dr. Livio Tornabene actually made a point to point this out in my Thesis notes where he pointed out a paper that proved this was happening on Mars with two different topography sources. This is something I’m adding to the manuscript because it is relevant, and they actually take terrain to floor depths too.

Despite being slightly lower, they lie within the error, so these results can be considered reliable. Here is a plot of the values. Neish stereo results with a square, H18 results with triangle, and SARTopo with circle. The 6 stereo craters are color coded along with corresponding SARTopo. If there is no stereo, the SARTopo values are left grey. One last thing I want to point out is that every stereo measurement (save Forseti, which is not reliable) is higher using my (H18) method. This is what I expected. Neish and others used an averaging of a region of floor and rims, but we used peaks. Therefore, you’d expect the highest points in Neish and others to be lower, or at least I did.

stereo depth 10.18
Titan Crater Depths measured with SARTopo and stereo from Neish and from H18 (this work). turquoise is Ksa, green Santorini, yellow Shikoku, orange is Soi, and the blue ones are Hano (light) and Forseti (dark).

 

Other news and closing thoughts

I hope to have the manuscript sent to Catherine by Friday. Next week I will be gone to go to the meteor crater field camp. As far as future work goes, I’ve emailed McMaster about working with them to do some tests on the production of long chain polymers in a cold wet environment like Titan’s. I may end up emailing Dr. Britney Schmidts student at GA Tech about modeling impurities in a freezing water melt lens, but I have a meeting with a few people in that group tomorrow. I’ll begin my inquiry there.

The new normal: White House press briefings continue to get shorter and more infrequent

This is not a research update. This is a long facebook post I decided to turn into a short blog post. I have very strong beliefs, but usually I try to let the reporters do the reporting. Except this time, they’re not reporting enough about something they should be.

There was only one White House press briefing in September. This is not normal, yet no one is talking about it. I first heard about it in a brief segment on NPR’s Politics podcast. Except even there, there was no real coverage. Rather, it was one reporter expressing her surprise (in a sentence or two) at the lack of interest. I don’t like to rely on CNN as my source here (even though we’re dealing with a simple fact) just because people on the will be more likely to dismiss its importance from mere association (a success of Trump’s targeting them as biased). Unfortunately, they’re the only ones talking about it. That speaks to how little press it’s getting.

Bush briefings were on average 32 minutes. Obama’s 70 minutes. Trumps began about on par with Bush’s (~25-30 minutes). By June of 2017, the Washington Post said the Trump briefings were getting shorter and more infrequent. While this was technically true, CNN made the point that this only holds true compared to Obama. As I’ve already mentioned, Bush’s were the same length.
However, that has changed. They have been getting consecutively shorter and more infrequent since January 2018. The length has decreased, on average, 3 minutes each month as of June 2018. That’s ~15 minute briefings.
WHPB
From Washington Post
Fast forward to now and we’re down to one briefing last month. This isn’t normal, and these are a crucial part of our right to be informed. Furthermore, it represents a growing lack of transparency that exists in the Trump administration and their attempts to stifle the free press. This shouldn’t just fade into the background. It deserves to be reported.