Exposing PseudoAstronomy

February 18, 2014

Most Craters Look the Same


Introduction

This blog post is about minutia. But, it’s a topic near and dear to me because it’s been my research focus since late 2007: Impact craters.

On December 10, 2013, Robert Morningstar – brought back onto Coast to Coast after appearing on their JFK conspiracy episode – made a claim about impact craters that is simply, completely, 100%, wrong. But, it’s one that I’ve seen made before, so here we go with the minutia blog post.

The Claim

Morningstar made the statement starting at 32:32 into the third hour of the program, and the text below is quoted through 34:38.

I saw one thing that really intrigued me, it looked like a crater with a uh, arrowhead in it, and the crater was called “Weird Crater*.” …

What’s weird about Weird Crater* is that triangle, uh that I saw in the thumbnail, is formed by the impact of three meteors all of the same diameter.

{George Noory: Isn’t that strange.}

That is not a-really possible. And this is a really strange phenomenon on the moon, it’s called the “doublet craters.” Around– surrounding the moon, there are double craters, uh, that appear regularly — dot-dot, dot-dot, dot-dot — you know? And they’re both the same size. It’s not possible. What is possible is artillery [laughs] in my estimation, in my view. … That makes two craters of the same size. But, to think that three meteors in the same diameter could hit one zone, in one crater, uh and the doublet phenomenon, tells me that not everything is right with the interpretation of uh, of the selenologists.

*Note: According to the USGS index of IAU-approved names, there is no such crater. I looked through all crater names beginning with “W” and the closest I found was Wyld and Wildt. There is nothing that has “rd” together that starts with “W” so either he is making this up, or the crater is not officially named that so I cannot locate it to examine it. While this is somewhat interesting, it is not actually relevant to the rest of this, though.

Double Craters and Crater Clusters and Crater Chains

To say “he’s wrong” would make this blog post short. And these days, unlike what my high school English teachers remember, I am much more verbose than that.

First off, there are at least three theoretical reasons why you would expect “doublet” or triplet craters or even chains of impact craters (I’m just dealing with impact craters here, not other forms like chains of pit craters).

The first theoretical reason is that you have a binary or trinary asteroid that strikes a surface. Or a weak asteroid that was pulled apart from an earlier pass – or just before impact – by tidal forces and strikes the surface. This is expected, and we know that many smaller asteroids are very weak – the “rubble pile” model has come into favor these days that posits that many asteroids are actually re-assembled after previous breakups. This means that they will be pretty weakly held together, and a close pass by a larger gravitational body can rip it apart.

Which brings me to the first-part-b theoretical reason – more evidence than a reason – for why you expect to see chains of craters: Bodies are ripped apart soon before impact and strike the surface like a shot-gun. Don’t think this is possible? What if Comet Shoemaker-Levy 9 had impacted a moon instead of Jupiter, and soon after its breakup rather than a few orbits later? You would get a crater chain. We see these all the time on satellites of the outer planets, such as in the example below from Ganymede.

Crater chain on Ganymede.

Crater chain on Ganymede.

The second reason we would expect it is the phenomenon of secondary craters: Craters formed from the ejecta blocks of a primary crater that go off and form their own craters. These most often occur in clusters and clumps and chains. One need look no further than the area around the young and large Copernicus crater on the moon to see examples of these.

Third is that it can easily happen by coincidence on older parts of the moon or any other object that’s already heavily cratered. I spent literally 10 seconds just now and found this region of the moon which shows several craters of very roughly the same size, some of them right next to each other.

So, right there, three reasons and plenty of examples of why you would expect – and we do see – craters appearing in pairs or groups right next to each other.

Craters of the Same Size

Another part of Morningstar’s claim is that the craters look to be the same size, which means they’re artillery fire. Sigh. This points to a profound ignorance of the cratering process in general. There’s not really a more polite way to say it.

We graph crater populations most often in what’s called a “size-frequency distribution,” which is basically a log-log plot that puts crater diameter on the x-axis and number of craters on the y-axis. It’s often binned in SQRT(2)*D diameter bins, such that one bin might go from 2-2.8 km, then 2.8-4 km, then 4-5.7 km, then 5.7-8 km, etc. The reason is that on this kind of plot, crater populations tend to follow a straight line, starting in the top left and going to the bottom right. Bill Hartmann, one of the founders of the field, has probably the easiest public-access explanation of this. Or, you can go to the intro of my thesis, section 1.4.3, pages 16-18.

What this means in simplest terms is that there are more small craters than large craters. Many, many more small than large craters. From my thesis work, there are about 11,000 craters larger than 20 km on Mars. 48,000 larger than 5 km. 78,000 larger than 3 km. 385,000 larger than 1 km. If you go just 50 meters smaller, there are another 40,000 craters on Mars, almost as many craters in that 0.95-1.00 km range as the entire number of craters >5 km put together. (No comparable database exists – yet – for the Moon.)

That boils down to, as I said, Morningstar is apparently ignorant of the cratering process and craters in general. Not only do you expect to find many craters of the same size (in the Mars case, nearly 50,000 just in a 50-meter-diameter spread), but it would be weird if they weren’t like that.

“Okay,” you may say, “but that’s observational. It could still be artillery fire because you’re just talking about what you have observed after that fire.”

Except that’s not the case: Asteroids form impact craters. Probably >90% of the impact craters in the inner solar system. So, we can look at their size-frequency distributions” and – hey! – they match those of craters. I’ll repeat: What we think causes impact craters (mainly asteroids) matches the size distribution of the craters themselves. As opposed to artillery.

Final Thoughts

Coast to Coast AM guests often say things that are just completely wrong. I often just shake my head. Earlier today, I was listening to an interview David Sereda gave, and almost literally nothing he said was true (I did a two-part podcast series on him — part 1 and part 2). In those cases, it’s so hard to know where to start, that I simply don’t.

I don’t know much more than the average skeptic about the JFK assassination conspiracy. So, when Morningstar spent just a few minutes out of a three-hour interview saying things that were completely wrong about craters, well, I pounced.

16 Comments »

  1. So let me guess: this was another case of a guy connecting the dots… wrong!

    Comment by Rick K. — February 18, 2014 @ 10:39 am | Reply

    • It’s rather like all the people who saw the snow in Atlanta and decided that it ‘must’ be artificial, because they were unfamiliar with the real thing.

      Comment by Graham — February 18, 2014 @ 8:02 pm | Reply

      • Ignorance breeds many a-conspiracy.

        Comment by Stuart Robbins — February 18, 2014 @ 11:41 pm

      • Stuart, your comment about ignorance reminded me of a sci-fi short story I read many years ago (Long enough ago I cannot remember the title or author, but i’m guessing it dated from no later than the 60s). In it the Earth is peaceful and pastoral and the overwhelming majority of the population is telepathic, what one knows, all know. The small (less than 15 individuals) portion of the population that does not have the telepathic facility has been given the make work task of looking after the library that holds all human knowlege gained before the rise of the telepaths, who disdain such knowlege as ‘irrelevant’.

        Then, unexpectedly a brilliant comet (I feel the author should have chosen a supernova.) appears in the night sky, and the telepathic part of the human race is seized by a massive panic attack, what one fears, all fear….

        The staff of the library are given the obligatory gloat, before they get down to caming down one of the telepaths and, with the aid of an astronomy text show that the light in the sky, is neither new or threatening.

        In my darker moments, this is where I fear the internet is taking the human race, the ‘fake snow’ saga does nothing to disabuse me of this notion.

        Keep up the good work.

        Comment by Graham — February 19, 2014 @ 7:23 pm

  2. The Messier pair are odd looking – although they’re side by side, they’re different shapes. They also have a pair of streaks going off to the west, like the tails of a comet. Do you think they were formed at the same time? Can you comment on them? http://bit.ly/1mrmDLt

    Comment by Trekker — February 18, 2014 @ 10:46 am | Reply

    • I disagree with the uncited Wikipedia entry that the less elongated crater (Messier A) would have been caused by a “rebound” of the impactor that formed the first. To create the impact, you have to have a huge energy release that’s initiated by the impactor striking the surface. All that kinetic energy goes into making the impact and destroying most of the impactor. It’s hard to see how you’d get Messier if the impactor rebounded and made Messier A.

      Rather, to me this looks like a low-angle binary impactor. It was probably a single object that got pulled apart just 100s of meters on a close earlier pass and then struck the moon at an angle of around 5° or less. One formed Messier A, the other Messier. The ejecta going perpendicular to the long axis of the crater is typical of elliptical craters. Two elliptical craters that close together on such young terrain likely points to them having formed at the same time, and interfering ejecta curtains could explain the streak of ejecta “behind” Messier A.

      Comment by Stuart Robbins — February 18, 2014 @ 11:18 am | Reply

      • I’m not sure from what you wrote as to which direction the impactor would have come – was it left to right or vice versa?

        Comment by Trekker — February 18, 2014 @ 2:24 pm

      • It’s really hard to say since I’m not a modeler. To me, it looks more likely they came from the west, so Messier A formed just before Messier. The impactor would burrow into the surface towards the east, vaporizing, and releasing jets of material behind it while the other impactor had a slightly smaller impact angle. But, don’t take my word for that.

        Comment by Stuart Robbins — February 18, 2014 @ 4:19 pm

      • Indeed, appearances can be deceiving. I too disagree with the uncited Wikipedia entry — especially after enhancing a QuickMap screen capture of the entire region around Messier and Messier A and after using the QuickMap line tool to look at elevation plots along various lines across Messier and Messier A and then across each individually in order to confirm my suspicions that we are really seeing three separate impact events which by coincidence impacted the moon in roughly the same location.

        Messier A looks like a pair of overlapping double impact craters which might have been created by a single object which was torn into two roughly identical sized objects by lunar tidal forces just before impact, with the west crater being created a few seconds before the creation of the overlapping east crater. But this is not the case since Messier A’s west crater rim is more eroded than Messier A’s the east crater rim. Thus Messier A’s west crater is a separate and older event in comparison to the event which created Messier A’s overlapping east crater. This is further substantiated by the fact that the interior of Messier A’s west crater is more eroded and by the fact that relatively small later impacts are seen within Messier A’s west crater but not within Messier A’s overlapping east crater. From an albedo standpoint, Messier A’s overlapping east crater appears to be a considerably younger crater which also features a lot of downward interior slope movement and a combination of a melt pond and debris accumulation on the crater floor. The interior slope movement has exposed a lot of high albedo interior crater wall features, similar to what we see at Copernicus. Furthermore, the depth of Messier A’s overlapping east crater is considerably deeper than the apparent floor of Messier A’s east crater. And this is, visually, were we also see an optical illusion since the human mind interprets both of the similarly sized yet overlapping craters as apparently having the same depth. Yet the QuickMap line tool elevation profile across Messier A’s two overlapping craters reveals that all of Messier A’s east crater slopes down towards the much deeper crater floor of the overlapping east crater impact. Finally, note that a close examination of the crater rims of the two craters which make up Messier A reveal that the the older west crater rim has an elliptical shape whereas the younger east crater rim has a considerably more circular shape.

        Let’s now look a Messier. Messier, to the east of the double crater forming Messier A, appears to be approximately the same age as the east crater of Messier A. Note that the impact which formed Messier obviously was created by an object which had a low inclination relative to the lunar surface. This alone further suggests that the impact which created Messier is unrelated to the two separate impacts which created the overlapping craters of Messier A. Finally, note that the alignment of the major axis of the Messier crater, although close, is not aligned with an axis drawn between the centers of the double craters of Messier A.

        If my theory holds water, then it now stands that the double crater of Messier A and the crater of Messier actually represent three completely unrelated impact events. Messier A’s east crater and Messier appear to have been created at nearly the same time in the lunar past. But which one of these two relatively fresh looking craters was created last? As Stuart points out, grazing impacts create a characteristic fan pattern perpendicular to the direction of impact. The fact that the fan pattern emanating from Messier remains whereas any ray pattern from the east crater of Messier A is lacking would seem to suggest that Messier is perhaps younger by a few to several tens of thousands of years.

        So now the only thing to explain are the pair of prominent rays emanating westward from Messier A. One might think that these two prominent rays were created by the grazing impact of Messier. But I would suggest that the crater excavated by the much older impact of the object which formed the west crater of Messier A created a ready made path for the subsequent impact which created the east crater of Messier A to create the pair of rays emanating eastward from the older west crater of Messier A. Basically, I suggest that the later impact which created the east crater of Messier A blew off the western rim of the older west crater and scattered the debris westward to create the two prominent rays. One might argue that the grazing impact which created Messier might have blown off the tops of the crater walls of the Messier A double crater. But the problem with this is twofold. First, the crater rim and in particular the east half of Messier A’s east crater is still crisply defined. Second, the east side of Messier A’s east crater actually is higher in elevation relative to everything westward.

        Comment by GoneToPlaid — February 19, 2014 @ 1:35 am

      • Oops! Corrected paragraph follows. Corrections are in ALL CAPS.

        Messier A looks like a pair of overlapping double impact craters which might have been created by a single object which was torn into two roughly identical sized objects by lunar tidal forces just before impact, with the west crater being created a few seconds before the creation of the overlapping east crater. But this is not the case since Messier A’s west crater rim is more eroded than Messier A’s the east crater rim. Thus Messier A’s west crater is a separate and older event in comparison to the event which created Messier A’s overlapping east crater. This is further substantiated by the fact that the interior of Messier A’s west crater is more eroded and by the fact that relatively small later impacts are seen within Messier A’s west crater but not within Messier A’s overlapping east crater. From an albedo standpoint, Messier A’s overlapping east crater appears to be a considerably younger crater which also features a lot of downward interior slope movement and a combination of a melt pond and debris accumulation on the crater floor. The interior slope movement has exposed a lot of high albedo interior crater wall features, similar to what we see at Copernicus. Furthermore, the depth of Messier A’s overlapping east crater is considerably deeper than the apparent floor of Messier A’s WEST crater. And this is, visually, were we also see an optical illusion since the human mind interprets both of the similarly sized yet overlapping craters as apparently having the same depth. Yet the QuickMap line tool elevation profile across Messier A’s two overlapping craters reveals that all of Messier A’s WEST crater slopes down towards the much deeper crater floor of MESSIER A’S overlapping east crater impact. Finally, note that a close examination of the crater rims of the two craters which make up Messier A reveal that the the older west crater rim has an elliptical shape whereas the younger east crater rim has a considerably more circular shape.

        Comment by GoneToPlaid — February 19, 2014 @ 1:42 am

      • Now we just need someone to model it.

        Comment by Stuart Robbins — February 19, 2014 @ 1:45 am

  3. Morningstar was also dead wrong that night about the crashed spacecraft. I blogged it and again I thank ‘Trekker’ for correcting my first draft.

    http://dorkmission.blogspot.com/2013/12/robert-morningstar-on-c2c-last-night.html

    Comment by expat — February 18, 2014 @ 10:54 am | Reply

  4. Thank you for the detailed reply, GoneToPlaid. I appreciate it.

    Comment by Trekker — February 20, 2014 @ 4:48 pm | Reply

  5. A good and clear presentation. Thank you, Doctor Robbins.

    Comment by Jennifer — June 2, 2014 @ 6:40 am | Reply

  6. what about the depth of craters being same??

    Comment by mooncrraters — September 3, 2016 @ 3:59 pm | Reply

    • They’re not. We’ve known this for decades.

      Comment by Stuart Robbins — September 3, 2016 @ 4:00 pm | Reply


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