I think the Moon watched Bad Universe

By Phil Plait | June 14, 2011 6:30 am

Nature imitates art! Kinda!

I am endlessly fascinated by impact craters. You might think they all look alike, but they don’t. They have different shapes, structures, shading, even (sometimes) colors. And these features can tell us a lot about the object that caused the impact as well as the structure of the surface they hit.

For example, here’s a nifty crater on the Moon as seen by the Lunar Reconnaissance Orbiter:

That image is 500 meters (.3 miles) across, so this is a decent-sized hole [click it to enlunanate]. Note the rubble; that’s a clear indication that the surface of the Moon where the object hit was rocky as opposed to sandy. You only get fractured boulders like that when the impacted surface has some cohesion. Most of the Moon is covered with a layer of dust called regolith, but here, under that powdery surface, was rock.

I’m not a geologist, so that wasn’t the first thing I thought of when I saw this picture. What I did think of was how familiar this crater looked to me. And it didn’t take me long to figure out why…

That’s a picture of me standing at the bottom of a crater I helped make. I didn’t dig it, but I did press the button that detonated the equivalent of 1.5 tons of TNT! I did this for the first episode of "Bad Universe", to simulate what would happen when an asteroid hits the ground. Look how similar the two craters are; there was lots of rubble in our man-made hole, and the resemblance is also striking when you see our crater from a distance:

Note the streaks of debris on the ground around the crater, much like the one on the Moon. It’s cool how well blowing up stuff on Earth can mimic an impact on the Moon.

Interestingly, the desert where we detonated the explosion was part of a well-used explosives range, so the surface was mostly compacted dirt. That doesn’t have the same cohesion as rock, yet the craters are remarkably similar. Clearly impacts are not quite so cut-and-dried as simple explosions on Earth — the Moon has no air to carry a shock wave, for example — but pulling the trigger on a ton or two of TNT does do a good job of simulating the event.

Also? It was hugely awesome to blow that hole. That’s a perk of being a scientist sometimes.

Image credits: NASA/GSFC/Arizona State University; Discovery Channel

Related posts:

A flower bloom on the Moon
Lunar craters, young and old
The extraordinary face of the Moon
The extraordinary back of the Moon


Comments (28)

  1. DennyMo

    See?!? More evidence that this whole “moon” thing is a hoax.

    On a somewhat unrelated note: I thought I’d heard the wackiest conspiracy theories out ther, but then I read this little gem. There are some folks who believe that the Fukushima earthquake was staged, initiated by either a tactical nuclear weapon or a HAARP event (take your pick). The reactors were then further sabotaged by additional tactical nukes that had been pre-placed ostensibly as video monitoring systems. Really? Who comes up with this stuff? Get them on the payroll in Hollywood, these make much better stories than most of the retreads that pass for movies these days…

  2. Mejilan

    Now now, let’s not mock the logically challenged!
    Also, Moon + explosions make for a giddy combination!

  3. Susanne

    Well, not the moon watched it, but the thing hitting the moon certainly was. 😉

  4. Comcast OnDemand has been running commercials with you in it, Phil. They are clips from one of the Universe shows you appeared in (Not your Bad Universe show). Comcast has been promoting that show as an OnDemand selection (of course, I watched it).

    I’m sure if you were looking through the OnDemand menu and saw yourself pop up on the screen you’d be quite proud. I like to say, “Hey, I know that guy.”

  5. dave chamberlin

    If I were a scientist (I’m an idiot instead) I would study blowing things up. What would the shape of a nuclear explosion be in space? It wouldn’t be mushroom, would it be perfectly round with no gravity and then just varying degrees of oblong with slight gravity? Can we make them colored, that would be spiffy. What if we blew up two at once fairly close to each other, what shape would they make. And why can’t we do this at night, right after dark on the fourth of July, what is the harm? Ok, it isn’t science, but what would the ratings be of a TV show called Blowed Up Real Good.

  6. dave chamberlin

    Furthermore, how are we ever going to find out what is in the middle of rocks and stuff in space if we don’t blow them up, and I don’t mean any wimpy crashes that cause dust getting thrown up into space, I mean demolished, enquiring minds want to know. I want to be a Bangologist. I just hope they don’t send me to school in Guantanamo.

  7. Stonez

    I have a major problem with this! How the hell did Phil get to the moon to cause an explosion when we all know no human has ever set foot there…

  8. Pete Jackson

    @6 Stonez: Phil didn’t go to the moon. He just pressed the button.

  9. Magicthize

    “That’s a perk of being a scientist sometimes.”

    So you’re only sometimes a scientist who blows stuff up?

    Or a scientist who sometimes blows stuff up?


  10. CameronSS

    “the Moon has no air to carry a shock wave, for example”

    Would there be vaporized rock from the impact that could have some of the same effects? Or would it get that hot?

  11. bigjohn756

    But don’t Adam and Jamie always tell us not to try this kind of stuff at home, Phil?

  12. Bill


    That’s why he went to the explosives range.


  13. Stonez

    @Pete. I reject your statement and allow my alternative reality to prove true.

  14. YKYBRBATLW * …

    Our cable TV company has the Science Channel and the Oprah Channel next to each other. Yesterday, the Science Channel had a show named “Asteroids”. Right below it on the list was a show called “Dr. Phil”. Guess which Phil came to mind first?

    * You know you’ve been reading “Bad Astronomy” too long when…

  15. DrFlimmer

    @ #5 Dave Chamberlin

    The mushroom is mostly due to air pressure and not directly to gravity. Without air it should be (almost) perfectly spherical.

  16. Sam H

    Given the scale of the picture, if my mental measurements are correct those large boulders near the middle should be up to 20 meters wide!! 😮

    Holy Haleakala.

  17. Sean

    Phil, maybe you should reword that second to last sentence 😉

  18. Nigel Depledge

    The BA said:

    Also? It was hugely awesome to blow that hole. That’s a perk of being a scientist sometimes.

    Darn it, I knew I should have gone for straight Chemistry. Us biological scientists never get to blow stuff up. Although the “playing god” part can be kinda fun.*

    [* Note for the hard of thinking: yes, I’m joking]

  19. nikolatesla

    Um. @DennyMo… Are you one of those gifted and intelligent people that believes all this stuff happening on earth is random? I bet you’re a brilliant atheist too…

  20. @ Sean #19:

    Whew! I’m not the only one with his mind in the gutter!

  21. abadidea

    DennyMo: Ugh, I’ve run into some internet people who believe in the “America intentionally caused the Japanese event with HAARP” piece of crazy. Uhhhh-huh. Someone very close to me (in real life even) believes that same HAARP was used to manipulate global weather patterns to guarantee a sunny day for the Royal Wedding. No, really. Because a pleasant day in May is just so suspicious.

  22. Nigel Depledge

    Abadidea (23) said:

    Because a pleasant day in May is just so suspicious.

    Have you ever visited the UK? Just wondering . . .


  23. Nigel Depledge

    @ nicolatesla (21) –
    Eh? Are you seriously suggesting that the Japanese earthquake was not an earthquake at all, but the result of some nuclear attack?

  24. Nigel Depledge

    On the subject of blowing stuff up, the TV programme Brainiac: Science Abuse seems mostly to be about blowing stuff up. And the demonstrations of liquid O2 were quite interesting (for example, heating a diamond with a blowtorch then plunging it into the LOX and watching it burn).

    They have a segment called “how hard is your thing” where they subject various items to three tests – a ton of bricks, an angle grinder (I think – it might be a different power tool) and a bucket of thermite. Pretty much nothing survives the thermite. But it’s usually very pretty.

    Mmmmm . . . thermite.

  25. Nigel Depledge

    Ken B (16) said:


    Eh? What is this “too long” of which you speak?

  26. Procyan

    Thanks for that explanation, good stuff…suggestion: periodically pick an unusual feature from various locations and give your analysis…There is so little exposition to go along with the myriad images as they accumulate. If you’re so inclined it would really be interesting to get a handle on some of the truly weird and seemingly inexplicable formations found in ice moons, comets, Mars, Venus …and soon I’m sure we will be seeing some facinating pictures from Vesta.


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