WHAM! Bulls-eye!

By Phil Plait | July 30, 2010 7:06 am

I have a Martian mystery for you today, and one that is writ quite large and dramatically. It seems weird at first, then simple next, but when you dig deeper — literally — things get very weird indeed.

It all starts with an out-of-control awesome picture that honestly made me reel back and say "Wow!"

I present to you out-of-control awesome:



Click the pic to embiggen. This unnamed crater is about 700 meters (roughly half a mile) across, and sits in the northern mid-latitudes region of Mars. It’s interesting, isn’t it? The multiple concentric bowls of the crater are trying to tell us something, but what?

My first thought, also mentioned on the HiRISE blog, is that this is a coincidental double impact: the big terraced crater was the original impact, then a later, second object impacted almost exactly in the center of the older one, hitting the bulls-eye like William Tell splitting an arrow.

The topography seems to support that; the inner crater has a raised rim, as you might expect from a second impact, and that would be hard to explain in a single impact. The terracing — shelf-like structures sortof like an upside-down wedding cake layering — is seen sometimes when an impactor smacks into layered ground. Imagine a layer of dirt on top of ice on top of rocks: each layer reacts differently to the impact, leaving the circular, concentric shelves in the crater bowl.

Note too that the central crater doesn’t look exactly centered, supporting a second impact.

Case closed… but wait, Your Honor! We have a surprise witness!

This picture is actually part of a much larger region which provides some context:


You can see the extensive ejecta blanket (excavated material laid down from the impact ) around the crater now, which is nifty. But note the smaller crater to the lower right (indicated by the arrow): it looks a lot like the bigger crater! There’s a shallow bowl with a deeper crater almost but not quite in the center. There’s no terracing, but it’s a smaller impact and wouldn’t have dug so deeply into the surface.

hirise_bullseye2So what gives? If all we had here was the big crater, I might believe the coincidence of a nearly perfect second impact bullseye inside it. But two of them? Right next to each other?

It seems unlikely, to say the least. And I thought I had an explanation for it… which I’ll give you. But note: I chatted for a few minutes with Alfred McEwen, the Principle Investigator of the HiRISE camera (which took the image), and he told me things still aren’t quite as they seem. Keep that in mind while I describe my thought…

My idea is/was this: both of those craters were single impact events. The terrain itself must explain the weird structures; there must be several layers of material with different solidity. In the lower right crater, the softer surface material deformed and splashed back, forming a shallow bowl. Underneath it is a stronger material, forming the raised rim central crater that’s slightly off-center. The fact that’s it’s not centered may be due to sloping in the surface, or that the surface layer isn’t constant in thickness across the surface. Perhaps there is stronger material to the left which resisted the impact pressure, leaving the inner crater off-center once the event was over.

This explains the big crater too. The outer bowl is shallow. Inside that is a raised rim, as you’d expect from a stronger material. The impactor was big enough to dig below even that layer to a third, deeper and even more resilient layer, leaving a beautiful raised rim. It’s not centered either, again perhaps due to the layers being irregular in thickness or to different material strengths in the layers themselves.

Finally, in the context image, you can see lots of shallow smaller craters. Again, I think this shows the top layer is something soft like ice, which leaves those barely visible bowls behind after smaller impacts.

Tadaa! Done.

But wait! Not so done. As Alfred pointed out to me, note that the second crater is actually sitting on the ejecta blanket from the first one (which is how we know that the smaller crater impact occurred after the bigger one). Since it’s on top of that material, the ground underneath the impact would’ve been different than the ground into which the original impactor hit. The other shallow craters are all sitting in that material as well. So we can’t simply state that the terrain was similar to the original event because the original impact changed the surface structure.

Also, the detail of the structure is difficult to interpret. Turns out that at this latitude glaciation is common, and that tends to screw up details, changing the way things look. Interestingly, the rim of the innermost crater in the big crater looks pretty fresh, too, like it happened after the original event, supporting the William Tell idea that a second asteroid impact hit right in the middle of the previously excavated crater.

Finally, in the top image, look at the floor just outside that innermost crater. See the two crescent-shaped lobes at 1 and 2 o’clock? Those may be slumped material from the walls of the crater. If a second impact happened in the center of a pre-existing crater, you’d get some disturbance of the material, including debris flowing down from the walls.

So what do we conclude?

This place is a mess. That’s what I conclude. Alfred said my idea that layered terrain explains most everything has some merit, but so does the idea that a second impactor did the deed. We simply can’t tell.

If you think I’m having fun figuring this out, then dingdingding! I am. Because it is fun. This is good old-fashioned sleuthing, detective work on the scale of a city block. When we look at pictures like these we get evidence of a crime scene, perhaps millions of years old — talk about a cold case! — but still fresh enough that we can puzzle out what happened. The big crater is the main clue, drawing our attention, but the second, smaller crater may be a smoking gun, the surprise evidence that just might make everything else make sense.

It’s CSI Mars. But in this case it’s not some procedural drama on TV. It’s real, it’s huge, and it’s sitting there on another world for everyone to see. All you need to do is go there and look.

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: crater, HiRISE, Mars

Comments (105)

  1. Matt T

    hitting the bulls-eye like William Tell splitting an arrow
    Er, is this an exceptionally clever meta-analogy? You’re putting one arrow-marksmanship story on top of another, just like the double impact craters….?

    Oh, and my scientific explanation for the phenomenon in these photos is… um, I have no smegging clue. Therefore it must be aliens. (Jesus/pyramids/homeopathy/space teapots/etc)

  2. One object that broke into four pieces traveling close, but not quite, together?

  3. Sion

    Wowzers. The lower smaller crater looks as though it formed in regular rock, but the bigger outer crater doesn’t look like normal rock to me – the crater walls appear to have ‘scales’ – maybe a permafrost layer? I think you are right about a single impactor, and the resulting landform is probably due to the way the kinetic energy dispersed through the different layers. The smaller crater could be due to an impact through two differently responding layers, but just not the same two layers as the big crater, i.e., instead of permafrost-and-rock it punched into looser ejecta-and-ages old permafrost?

  4. Ross Cunniff

    Perhaps there is a subsurface layer of liquid water – the impacts penetrate *almost* to the layer, leaving the rock above that layer fractured. Some time after the impact, water starts to ooze up through the cracks, and then sublimates, progressing to a steam explosion. So, perhaps a “volcanic” caldera inside an impact crater.

    An alternate idea is a subsurface layer of carbon dioxide ice. Similar process but triggered by heat of the impact taking a little bit of time to reach the layer and trigger explosive sublimation.

  5. ChazInMT

    Check grammer in third paragraph up from bottom, should be has instead of as…Has some merit… Then delete ME! (well this entry…you being Phil & all, you might have a way to just, Delete Me…my wife might go for that, but my son would be upset.)

  6. Messier Tidy Upper

    Spectacular & fascinating. :-)

    But it’s giving me this strong urge to throw a giant dart at it.

    They’ve gotta name this the Bulls-eye crater surely! ;-)

  7. Brian Schlosser

    Is it me or does the even smaller crater at the 1 o’clock position (of the big crater) seem to have something funky going on at its center too? Looking at the full res image on the HiRISE site, its hard to tell for sure, but it looks to me to have the same crater-in-crater feature…

  8. Richie

    Yeaahh…sorry. Was testing the giant death-ray and had some calibration errors with the beam. First shot went way off target. Next one had beam confinement issues.

    I’ve got the bugs worked now though, so I’ll stop messing with you.

  9. Big Al

    OK, I’m going to make my guess. Unless it’s an artifact caused by the lighting, the floor of the central crater seems to slope down toward the shadowed side. Could the central crater be a collapse feature? If the initial impact is in permafrost, the impact would have transferred heat into the substrata, and allowed frozen water to drain out of it, creating a void that the center of the crater later collapsed into.

  10. @Matt T,

    As Zapp Brannigan once said: “If we can hit that bull’s-eye, the rest of the dominoes will fall like a house of cards…Checkmate.”

  11. daver

    The center does seem to resemble a sink hole… except that it has a raised ring around it.

    Could a center peak have had that circumference and then most of it collapsed into a void?

    Or could a central ‘peak’ at impact have been so large that it separated from the ground and became a secondary impactor? I’m thinking of something like what happens when a droplet of water hits the surface of water.


    Please note that I just googled for that.

  12. Mike

    Uhh, just in case you haven’t got it from previous posts, the “split the arrow” story was not William Tell, but rather Robin Hood.

    William Tell shot an apple off his son’s head.

  13. Jeff

    It is almost certainly terracing. It looks too much like it to be otherwise

  14. ASFalcon13

    Cool subject, but it hurts to look at those pictures…I can’t seem to get my brain to see it as a crater instead of a dome (like what you describe here: http://www.badastronomy.com/bad/misc/hoagland/glassworm.html). I’ve tried rotating the photos, but no luck :(

  15. To my untrained eye, I would question your conclusion that the smaller crater happened AFTER the large crater. It appears to me, that the smaller crater would have created some ‘radial ejecta lines’ as is very evident from the larger crater. These lines dominate nearly the entire image. This seems to indicate that the smaller impact actually occurred first as the larger impact erased the smaller impact’s radial lines.

    Secondly, the smaller crater seems to be somewhat ‘filled in’ with the ejecta of the larger impact. This would explain why it looks shallower, and less terraced. It also would support why the smaller impact crater looks ‘softer’ than the large crater; because the hard edges were jostled when the large impact occurred, and the ejecta further blanketed the site. This is very similar to how the countryside looks after a soft powdery snow.

  16. Mandy Q

    I think that Mars was hit by the great nipple asteroid discovered by the late Dr. McTiterington. Just sayin’ :)

  17. How come there is pitting (for lack of technical term) on the main surface and on the outer ring of the big crater, but in the center ring of the big crater.
    I wonder if sink holes are possible on Mars? I mean if the center region was a sink hole that happened later, would that explain why the pitted surface has smoothed out and hasn’t had time to regain its pittedness. Maybe? She said without any actual scientific background.

  18. Here are a few things I noticed that haven’t been addressed yet…

    - There is some phenomenal patterned ground in the large version of the first image, on the outer crater walls and ejecta blanket. This suggests to me freeze-thaw cycles acting after the hypothetical first impact. But the outer crater’s floor and the inner crater are without that awesomely cool snakeskin patterning, suggesting that they’re younger than the outer crater. I think that would support this being a double-impact event.

    - Again in the first image, the inner crater looks not only off-center but distinctly elongated. (Impactor coming in from the left of the image?) I think that would also support a double-impact for that crater.

    Neither of those observations shed any light on the crater to the SE in the context image, I think. Might it be some kind of secondary cratering event?

  19. danish

    Two pieces of the same meteor on nearly direct impact (vs oblique) in multi layered terrain.

  20. Andrew

    Could it be a VOLCANO ???

    Forget about meteors. One volcano, large eruption, followed by small eruption. Similiar, smaller feature = another place the lava erupted.

    Feel free to educate me if I am clearly demonstrating ignorance.


    volcanoes = molten rock

    how about a geyser effect where depleting gas pressures cause smaller flows, 3 cycles? Multiple /stratified sources of magma?

  22. mariana

    I would have thought a second impact in the middle of the first would be far too coincidental…the odds must be heavily against such a bulleyes impact even if the meteorite broke up shortly before the sudden stop at the end of its trip. ??

  23. Ky

    Rotate the photos 90 degrees CCW so they’ll make sense to our human brains.

  24. Chas, PE SE

    Another explanation for the off-centerdness of the almost concentric craters is that the impactor was traveling at an angle to the surface, not coming straight in. The forces would have vector components, for one, and the crater-in-the-second layer would be some distance downtrack.
    Also, an ejecta blanket from the first impact would not be all that thick — only a few meters at most, less than the thickness of a piece of paper compared to the original layer of soil –relatively

  25. Loose, thick surface layer that compacts after a shock wave?
    It’s funny, the closeup of the smaller crater keeps “inverting” to my eye, looking like a fried egg.

  26. Fabian

    Could it be a comet impact with a larger leading mass and smaller trailing material?

  27. It’s CSI Mars.

    In that case, all will be resolved (snicker), if you just…wait for it…ENHANCE!

  28. T. Stubb Fudpucker

    Sodom and Gomorrah, nuked.

  29. Dr. Bergeron

    Wow is right.

    It looks to me like a single impact event. I imagine that 1) the terrain of the impact would have to be quite porus, and/or 2) the makeup of whatever impacted there turned to liquid instead of sublimating into the atmosphere and leeched into the terrain, causing the compaction and/or dissolving of of the terrain (think powered sugar).

    It also has the look of the remnants of a small liquid body. Perhaps what we’re seeing in the concentric rings of this crater is a freeze/thaw/evaporation cycle of a liquid mass as the planet rotated.

  30. A Dalek about to exterminate a fried egg?

  31. fernly

    In the embiggened closeup, the ejecta blanket with its snakeskin (or fish-scale) pattern is just fascinating. Note also that in a narrow ring along the circular crest of the crater there are many points of mini-slumps where small pockets of material have sagged down. To the lay eye this sure looks like a big ka-floomp! of a wet slurry that then drained and dried, but I’m sure a real areologist would see other possibilities.

    Undeniably the smaller skirt surrounding the inner crater has a much finer texture with lots of boulders, and all the way around its margin you can see where this more powdery texture is partly covering and softening the shape of the fish-scales. Which strongly suggests that the fish-scale pattern pre-dates the smaller blanket.

    Now the question would be: how long would the fish-scale pattern take to form? For this to be a single event, the scaly pattern would have to form as the material fell, and the central skirt would have to be thrown higher and fall down upon it. (Seems like a stretch.) If you suppose two events, then the first one forms the sloppy blanket that can take any amount of time to dry into fish-scales, and the second event comes along and overlays it.

  32. Whoa! I wonder if they are going to make an anaglyph for this crater!

    If the “cookie-like” mesa and other depressions anaglyphs were impressive… I can´t wait to see this one!

  33. I have one of those on my elbow. Should I see a doctor?

  34. It looks to me like there is fairly clear evidence of two different layers of material.

    The surface layer is a fine grained material, like a silt or clay, with some adhesion in the particles. The sort of tiled or scaled texture looks like a dried mud flat., with raised surfaces divided by cracks (unlike artic polygons which are low surfaces surrounded by pebble ridges) This texture extends down into the outer crater which suggests that the texture formed after the surface formed. There are also no surface rocks or boulders in this area.

    The lower layer appears to be a coarser material, like sand or fine gravel. This material does not adhere to itself and so does not form a textured surface. It does appear to flow or slump relatively easily. Look at the scalloped edges of the inner sides of the middle ridge, the material seems to have flowed like sand. Notice also that this layer also contains larger stones and boulders scattered over its surface.

    It looks to me as though a single impacter struck a two layered terrain. A fine silt over a coarser sand gravel and boulder layer.

    This would be a pretty exciting find, since on earth that is the kind of layering that you might expect to see on an ocean or sea bottom. Especially one near a major river delta.

  35. bamed

    Looks like a sink hole in the center of the big crater.

  36. Flying saucer prints. The big one is the mothership.

  37. This is exactly the kind of fun that the “Universe is only 6,000 years old/God Did It” crowd is missing. I don’t find it amazing looking at that image and thinking “God did it. Ok, that one’s explained. Next!” Instead, going through all the possible explanations and getting closer and closer to the truth using only our intellect is extremely amazing. Seriously. We’re able to look at a photo (and some other evidence) and pretty much deduce what happened millions of years ago? That might be so common in science that it’s taken for granted, but it truly is an amazing thing to behold.

  38. Richard

    It looks sort of like Islands that forms when pockets of volcanism moves at the bed of the seas (except that there’s only two real ‘outflows’).

    If I would guess, which I obviously have to do because it’s just such a nice image, the big thing caused by a meteor impact resulted in warm liquids being released from first the center of the crater before the underground drifted away, causing the next outflow to be where the second Eye is located.

    As I have never seen island trays linked to impacts in other instances, I of course think my guess is completely wrong.

  39. Joseph @ 15: I agree that the top layer (seen in surroundings and the floor of the 1st level of the two craters) is a permafrost layer with freeze-thaw cycle patterns. This also means that it would be a rather soft layer. The next two layers don’t have that pattern, suggesting harder and yet harder rock. The wall of the 2nd level crater is subjected to the freeze-thaw heaving and could easily explain the two land-slides, me thinks.
    Intriguing post, Phil.
    Cheers, Regner

  40. Marty

    I was going to say what bamed said. Single impact, later sinkhole. IOW, there’s a hollow space somewhere under there. Must be where the secret city was. ;)

  41. I strongly doubt the sinkhole idea. The inner crater has a raised rim. Sinkholes have sharp edges with no rim. Also, there’s an ejecta blanket around the inner crater as well. Look at the super-high-res version to see.

  42. Also, the terracing and layering in the surface are pretty certain. It’s the details that’re baffling!

  43. Marty

    The ejecta for the “inner crater” looks a lot like erosion after the sinkhole…sank. Hard to tell without elevation details, of course.

  44. Michal

    I’m with Tailspin in his early comment. Looks like the comet/asteroid picked up a tailing object on its journey to Mars that was far enough behind the initial impact to leave its own crater.

    Or, and this is probably the sillier theory, the object that impacted had a high density core such as lead, surrounded by a lower density material such as ice. Though I’m pretty sure that would just leave a single, large crater rather than the layered craters we see in the image.

  45. Tbird49er

    I think Doc Bergerone has it best (or closest). Looks like the “frozen” wave I get when I toss a rock in mud of semi-soft consistency. It looks more like a wave frozen before dissipating on the top shelf of ejecta. Would fit the angular impact, ejecta pattern, and the curious “sink hole’ appearance of the central impact point. Also would explain the smaller companion crater. Fun to conjecture, no?!

  46. Clearly, this was the work of an alien intelligence, trying to baffle and confound our scientists.

    Since the “Face on Mars” (Cydonia) was covered up by NASA as just an interesting play of light combined with human imagination, the aliens are looking to make real faces on the Martian surface.

    These, “holes within holes” are attempts at making eyes. If the hole within the hole is offset, the eye was just made to look in one direction.

    For other faces, look to the Galle Crater on Mars.

    Really, this Science stuff is pretty simple once let your imagination run wild.

  47. Cladinator

    Could the wind somehow build a seemingly normal crater to look like the above images? Its interesting to think about what the wind conditions could potentially do to the terrain.

  48. alfaniner

    You mean, for once a scientist is truly baffled?!?

  49. Phil,
    Check out this similar crater posted on the HiRISE site about a month ago. They list it as a ‘squishy impact crater’. It looks like the ground was more squishy so you have ripples instead of distinct bowls. Neat!


  50. Martin CT

    So here’s another interpretation. There was a single impact, but the impactor was structured: a dense iron core and a less dense outer shell. What you see as multiple rings is just the “image” of the impactor!

  51. Torbjörn Larsson, OM

    My guess would be that it is likely a post-impact modified crater, which can look like anything. That explains why it is a (at least locally) non-unique feature, perhaps better than the impact modification theory.

    Also, I would guess that the bulls-eye impact theory have 5 strikes against it:

    * Two impacts instead of one is less likely. Post-impact modification _will_ happen.

    * Two sets of two impactors: less likelier.

    * The two sets next to each other: even less likelier.

    * The problem of no inner impact ejecta in the craters adds much to the complexity of the theory. Granted, some say there is ejecta as BA, some don’t as of yet.

    * And, for my money the perhaps largest problem: the lighting condition isn’t too good, but the inner feature of the larger crater doesn’t look symmetrical in the embiggened picture. I get an ellipticity of ~ 0.15.

    Post-impact modification may work towards asymmetry on existing features instead of introducing it pristinely, but it doesn’t look like that was what happened.

    Now, impacts, where a typical high-speed impactor affects an area 20 times larger, will most often become circularized by the area increase. I.e. ellipticity from non-vertical impact angles is swamped by the feature size increase. It will take a _very_ angled impact (IIRC, more than 75-80 degrees impact angle) to make an ellipse of note. See how circular the large crater is!

    So not only would that be rare (but not the most unlikely here, see above), but I’ll bet it would be very hard or impossible to put that geometry inside an existing crater with walls, as here. Too bad I don’t have access to the 3D geometry.

  52. Matt T

    @TechyDad (38) & alfaniner (45)
    I don’t know who said it first, but this reminds me of the classic saying: “the sound of true scientific progress isn’t a genius shouting ‘eureka!’, but a hard-working researcher muttering ‘what the f—???’”.

    @TechDad (10)
    Ughhhhhhhhhhhh (<— exasperated Kif sigh)

  53. Radwaste

    If I was going to kill a planet eons ago, I’d arrive at a substantial fraction of lightspeed with a hundred-ton iron mass in the hold, release it and then brake. Later, I’d come back and note the damage, and the resulting volcano the locals call Olympus Mons.

    Fun to think about, although exceedingly unlikely and unresearched!

  54. John Paradox

    Naw, it’s just an ad….

  55. I’d need to see the topography, but it looks unlikely that the inner structures are second impacts based upon the depth/diameter ratio. It looks too deep.

  56. Denver Astronomer

    It’s a long shot – but could this be a case of a meteor that broke into several fragments and impacted in two groups, each group having at least two fragments striking the planet over a period long enough for the rotation of the planet to offset the impact)?

    Actually, I may have to shoot down my own theory – the offsets look to be on opposite sides of the two craters.

  57. ShaneC

    One should always investigate one’s principles. One never knows, do one? (apologies to Fats)

  58. QUICK!!! Someone queue Richard Hoagland!

  59. Captn Tommy

    Have You ever dropped something into semi-solid slush?

    1. with the correct consistancy you can get ripple waves that freeze (the outside wave and the middle wave). You will notice that the immediate aera around the center crater is clear i.e. this is the rock layer under the Ice/Mud layer that was “liquified” and pushed away.

    2. If you study the dynamic waves at the crest outside of the outer wall, especially on the Left side of the the crater, these indicate flow back, I have the same structures on the outside of my pond where the ground is subsiding due to sand base under a topsoil top. the 1 and 2 o’clock colapses could also be subsiding of a viscuss medium.

    3. In the big picture, notice the polygon on every surface outside the center area which shows no polygoning. Polygoning usually means a dry former mudlike substance. No polygoning = rock in this case.

    My conclusion… One strike on a ice/mud glacier type surface in a VERY cold environment liquifying I/M layer to a certain distance Creating the ripples and the melted icecream ejecta blanket on top of which the rock rays were laid. The same goes for the small guy.

    The risks are many, and the chances slim… But …Oh the songs they will sing of us in the Hall of Heroes! – Kor, Dahar Master.

    Captn Tommy

  60. Zucchi

    Confound it. We’ll just have to go there and check it out on foot.

  61. Derek

    Giant chicken pecks. If you look at the top right edge of the entire large image (the one that shows both craters), you’ll see three big foot prints. You might have to adjust your contrast to see them, but they are there.

  62. Joseph

    Reading through your description of the impact site and why it is so interesting, I kept thinking of the Dr. Horrible line:
    “And sometimes there’s a third, even deeper level, and that one is the same as the top surface one. Like with pie.”

  63. Just a small question after observing the entire topology. Could this indicate that the surface was a muddy surface which I would think would move like the features indicate. Also the telltale dried cracking around the two outer crater might indicate that a liquid was present. This would suggest that maybe the impact caused that liquid to evaporate and cause the surface to crack like a dried mud puddle.

  64. gopher65

    It looks to me like the ground collapsed sometime after the impact. Perhaps there are lavatubes in the area, deep enough to have survived the impact almost intact, but just close enough to the surface to have collapsed as the impact happened.

  65. You mention unlikely astronomical events, and don’t list Hoag’s Object? I’ll bet the scientists who first looked at the Hubble version of this sat stunned for a minute when they saw that little object in the upper left corner! What are the odds of that happening?


  66. Buzz Mega

    If the smaller one hit after the larger ejecta blanket had settled, then how come no small ejecta field on top of that? The larger diameter shelf of the smaller crater is textured with the same pattern as the ejecta blanket of its surroundings, suggesting that its ejecta blanket is buried beneath the still falling blanket of the larger one.

    I think they were two chunks from the same original object. Split early high up in a denser atmosphere than today’s. Coming in at the same angle, hence the same sort of symmetry clues. Perhaps made of a slushy cometary material to begin with.

    The stratified crust was a first thought by many, and stratification itself suggests interesting earlier processes.

  67. Steve Huntwork

    Both of the craters were obviously created from single impacts.

    Next question: What physical properties of the layers would be needed to form this result? Personally, I see layers of ice…

    I agree, this is a very important scientific finding.

  68. daver

    @53 @Matt T

    I think it was Isaac Asimov.

    “The most exciting phrase to hear in science, the one that heralds new discoveries, is not Eureka! (I found it!) but rather, ‘hmm… that’s funny…’”
    - Isaac Asimov

    Or maybe not?


  69. Boomer

    How about splashing? I’ve seen super slo-mo footage of water droplets landing on water. When the intial drop hits the water, a smaller droplet is pushed back up and into the air. That second droplet then comes back down and lands on the water, which then ejects yet a smaller droplet into the air. Could this happen on a larger scale, but with solid matter?

  70. The asymmetrical aspects of these craters is more likely due to low incoming angle of the impactor.

  71. JamesR

    This is great.
    I guess a lot about such features. Guessing is what sharpens our minds and makes us think.
    My guess.
    Single impact.
    Not solid rock but some type of consolidated soil rock mix with maybe a water component.
    High angle like Torborn I figure 75-80 degrees
    Also Notice that from 4 oclock to 12 oclock outside of the distinct crater area a broken surface area coincidentallly opposite of about where the impact came from. That would be the direction the energy from the impact would take. My guess is that the impact came about at 1-2 oclock.

    I guess we’ll find out when we put a rover down and can get real time info.

  72. réalta fuar

    Torbjorn Larsson is almost certainly on the right track. The energy of even small impactors like these is too great for the impact material to make much of a difference on the final shape of the crater. The ejecta blanket of the big crater is also much too thin (maybe a meter or two or less) at the location of the smaller crater to be very relevant (depth of the smaller crater is probably 10 meters or so.). So most likely post-impact modification. I like the idea of subsurface ice being involved though the smaller crater’s depth argues against that. I suspect will actually not be really hard to model once impact experts and other geo types get to work on it. They do seem to be unique (so far) which is of course what makes them interesting, but Mars has lots of interesting stuff happening on it’s surface. An idea of the ages (or at least relative ages) would help.

  73. Robert

    The hexagonal patterning of the upper layer suggests an icy matrix to me. What do we know about the behavior of an impactor striking a surface like this? It seems that ice undergoing a violent phase transformation might either permit a substantial fraction of the impacting body to reach the underlying rocky layer or perhaps the shock wave in the vaporized ice body might be enough to do the trick.

    Or something, something, something else and then ta da!

  74. 24601

    I’d love to see someone with the setup to fire a small projectile into a slab of clay covered by a layer of fine silt, such as you’d find at the sea floor or the bottom of a lake, and see if the same pattern results.

  75. acommenter

    Looks like a classic case of pseudomamma to me.

  76. enlightenism

    It’s been mentioned once already but I’m seeing a dome structure. Makes a lot more sense and you don’t need a William Tell/Robin Hood impactor(s) scenario. Topography! We need Topography!

  77. Sean McD

    Wow, the detail is awesome in the embiggened image. It’s definitely a double impact though, and seasons apart too judging from the moisture cycling in the ejecta from the first/outer ring and the walls of the terrace. The newer inner crater ejecta has none of the dry lake bed, scaled look to it. Also, the inner crater has a heart shape, indicating an oblique strike and its ejecta also has this faintly in the bottom of the big crater to match and its slightly off center. Cool.

  78. Phaedrus

    I saw the first picture and thought, “Hey, that’s pretty cool!”

    Then I saw the context picture and burst out laughing with glee. This is the type of science that gets my brain giddy. Thanks for posting this! Now all we need is someone to write a clever sci-fi story explaining how it was formed, or perhaps something even more clever. My theory: aliens landed in the center of the pre-existing crater and their ship bounced. ;)

  79. Phil K

    Here’s another possibility to consider, inspired by the SL-9 impact on Jupiter. Suppose some gravity gradient (tidal) effect caused a small comet to break up into two pieces in nearly the same trajectory. Then the big one hits, followed shortly after by the small one following nearly the same trajectory.

    This appeared at a high latitude? Well, at high latitudes the surface isn’t moving eastward as rapidly due to planetary rotation as at a low latitude.

    Again, just a quick guess, but one I haven’t seen yet.

  80. Strahlungsamt

    The Superfluous Nipple on Mars.

    And you Mars was just a pretty face.

  81. Nullius in Verba

    The location of the crater rim is determined by the point at which the shock waves go sub-sonic. The hemispherical shock wave moving outwards bounces off the upper surface, and the release of pressure this causes smashes up the rock and flings it out. Once the shock wave has dissipated to the point where the rocks can transmit it as an elastic wave, crater excavation stops and you get the crater rim.

    To have several crater rims therefore implies that there were several shock waves, with different energies. One possibility is reflection of the downward hemispherical wave off a deeper layer of rock. Another is reflections internal to the complex flows and density changes resulting from the impact itself. Another possibility, as noted, is different layers of rock with different speeds of sound.

    Ring craters are not all that uncommon. Mare Orientale on the moon is another good example.

  82. xreid

    When I saw these pictures I had a similar thought when you mentioned that the terrain may have had different layers, except in my mind it was the striking object that may have had different layers. Imagine something with a dense core (like iron?), surrounded by a less dense outer layer (rock?). Would it leave a multi-depth crater? Could such an object exist?

  83. matt

    in the ‘much larger region’ is there not a 3rd witness, much smaller than the 2nd witness, above the right side of the large crater, basically tangent to it?

  84. Michael Kameka

    I completely agree with @15, @J.R. and @67, @Buzz Mega…the smaller DOME ‘Scout’ was the first on site, and evidence of it’s arrival was covered up by the much larger ‘Mother Ship’. (that’s what they look like…saucers)

  85. at 10. TechyDad Says:

    As Zapp Brannigan once said: “If we can hit that bull’s-eye, the rest of the dominoes will fall like a house of cards…Checkmate.”

    In point of fact
    Hit that bull’s-eye, the rest of the dominoes will fall like a house of cards…Check,mate..
    the extra one’s a bogie :-)

  86. Sion

    Perhaps Phil can let me know if I’m correct or not on this, but I don’t think that any assymetry we see in the shape of the crater is due to impact angle, as a lot of people are proposing. I was taught that the impact angle is largely irrelevant and that no matter what angle the impact occurs at, a near-circular crater will be formed. Ejecta may be a different matter, but the crater will be round.

  87. Space Bear

    Looks like a coupla nipples to match the pretty Martian face.

  88. John

    Its quite clear that aliens used a large bomb and then dug a cave entrance in the centre softer rock in order to move underground when the atmosphere began to become inhospitable. Simples.

  89. Broken in two or more parts by the gravitational force.

  90. scibermuse

    My first question was where is the light coming from?

    Look at the wide area around these two bizarre features: There are several impressions that appear to be eroded/filled-in craters. That indicates that the light is coming from the RIGHT, most likely, and therefore these are RAISED features, which solves double/triple concentric conundrums, but makes these items possibly even more mysterious!

  91. Shelgeyr

    Perhaps the problem lies in the immediate common assumption that these are “impact” craters. I suggest that the evidence points to them being far more likely EDM (Electric Discharge Machining) scars. Still completely natural phenomena, with no aliens required.

  92. Robert Carnegie

    I want to say that the top layer is, for instance, sand, and the big impact just splashed some sand around, and then the small impact just had a little more sand to punch through. But I’m sure this has problems, such as, even Martian sand is liable to be blown around… how about gravel? I could practise in the driveway when I get home?

  93. scibermuse, the light very clearly comes from the left. Look at the central crater. Notice that the left side of the crater is in shadow and the right side in light.

  94. If I look hard at the top lh corner of the major crater image and allow my eye to drift round clockwise I see an inward spiralling – imagination?

  95. Jonny

    @Shelgeyr – I was wondering when someone would mention EDM actions being involved and while I don’t disagree I have to ask a rather obvious question -

    Could these crater formations be the combined effect of EDM and an impact?

    Under EU theory electrical discharge events could occur when a small meteor or other foreign object carrying a different charge potential enters the electrical atmosphere of a larger body, although such a discharge would likely ‘blast away’ most of that incoming object it is entirely possible that if large enough to start with at least some portion of the object would survive the discharge and continue on to impact the surface.

    The object causes the discharge that produces the first crater/scar via EDM and then the remains of that object impact the center of the EDM crater/scar afterwards causing the ‘bullseye’ effect.

    I know I have seen many meteors here on Earth produce what seem like electrical discharge effects as they approach the surface(typically in the form of a bright flash often accompanied by power or internet disruptions in the area), it doesn’t seem to be a far stretch to assume that a meteor would act similarly on Mars.

    Of course it could be solely the result of an impact or multiple impacts or solely the result of multiple electrical discharges originating at those locations, but to me it seems far simpler and more logical to say it’s both.

    But now I’m probably going to piss off both conventional and EU theorists, lol.

  96. KD_in_KC

    I’m no physicist or geologist, but when I see it I see (much like the smaller sister @ 5 o’clock, this was a single impact into a soft top layer hiding something underneath that could rapidly change from a solid to a liquid or gaseous state with the correct amount of heat.

    1) Impact by an Iron projectile just hot enough to make the surrounding are flash melt / boil / suffer massive steam explosion.

    2) Said steam compression is released through impact hole and underground laterally melting other solid material causing instability of the above lying material and a convex raising of the surrounding area. (Think underground nuclear bomb testing ala – http://en.wikipedia.org/wiki/File:NTS_test_preparation2.jpg , with less energy)

    3) Ground instability caused surrounding areas to collapse into the now vacant area where the solid use to be.

    Viola – three different craters with the same phenomena. Underground frozen lake perhaps?

    Being from Missouri, understanding that my great state essentially is sitting on top of a ginormous limestone cave system with water, I can see this happening. (I understand that this is pretty much what the author says, but since the crater is only a half mile across at the top, and the ejecta blanket would launch mostly up, the out, arcing the impact area for the 2nd impact wouldn’t extremely different than before the initial impact.

    But that’s just my uninformed opinion, I could be (and most likely am) wrong.

  97. Markus

    I don’t see a problem with the fact that the small crater sits on the ejecta of the bigger impact. Ejecta blankets really aren’t that terribly thick, and compared to the more compact ground they’re sitting on they’re also somewhat fluffy. The object that caused the smaller crater should have had no trouble penetrating all that and getting to the original soil underneath with its layering look tendency, giving it similar characteristics to its bigger neighbor albeit on a smaller scale.

  98. pecafresh

    looks like a couple nuclear bombs went off.. the little one is the second bomb in its early stages

  99. 77Jack

    How come all these meteors seem to hit the surface at 90 degrees? If they’re flying in from space shouldn’t they be hitting at an angle? And if they’re hitting the surface at an angle then why do all these craters look like almost perfect circles? I mean even the “ejecta” is in a uniform circular pattern.

  100. John

    Gravity causes them to impact this way


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