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.

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