By Phil Plait | March 25, 2011 11:20 am

What the heck hit Mars and made this?

[Click to barsoomenate.]

This image is from my favorite Red Planet paparazzo, the HiRISE camera on Mars Reconnaissance Orbiter. It shows three craters, each about 1.5 to 2 km (0.9 to 1.2 miles) across… and they all formed at the same time!

How can I tell? Well, for one thing, if this were a coincidence, with three impacts happening at very different times, then you’d see overlap in the crater rims; the earliest crater would be partially obscured by the later crater, and that in turn by the most recent impact. But that’s not the case here, since the rims aren’t overlaying each other. In fact, the straight walls between them are exactly what you’d expect if you have impact explosions happening simultaneously: the expanding shock waves smack into each other and create a linear feature.

Not only that, but let your eye follow the straight lines between craters up and down, above and below the craters themselves and onto the landscape. You can see that the hellish expanding wall of fire etched itself onto the Martian surface well beyond just the crater rims, and those linear features match the crater wall orientation. I annotated the image here to show you what I mean; the red lines are just outside the linear features.

I can picture what must have happened, millions of years ago over Mars…

An asteroid or perhaps a comet is orbiting the Sun, minding its own business. Most likely it’s a frail body, easily broken apart, but held together by its own gravity. As long as it’s left undisturbed, that is. And what’s that looming ahead? A small planet, but too large to avoid. It grows larger, and larger still… As the object plunges into the thin air of Mars, it breaks up into three similar sized pieces, each perhaps a hundred meters or so across, the size of a football stadium. Moving at the blinding speed of 30 kilometers per second, each of the three pieces hit. Given the crater centers are only about 2 kilometers apart, all three pieces impacted the surface within a fraction of a second of each other.

At essentially the same moment, three fireballs are created, explosions equivalent to the detonations of tens of millions of tons of TNT. Each creates a circular shock wave expanding along the ground, and within a few seconds the shock waves collide. On either side of the center impact, two focused walls of flame and debris are created, blasting up and down in nearly straight lines. The explosions of the two outer impacts expand left and right in near perfect half-circles.

Later, much later, when the area cooled off, what remained is what we see today. Three conjoined craters, the magnitude and fury of their impacts faded by time, but still readable in the landscape. They’re filled with rippling sand dunes now, grains of rust and basalt blown by the ever-present Martian winds. But they’re a reminder of a time, long ago, when, for a few moments, the wind blew much, much harder.

Image credit: NASA/JPL/University of Arizona

Related posts:

Another awesome Martian avalanche
Martian dunes under the microscope
WHAM! Bulls-eye!
Landslide on Mars triggered by an impact?

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

Comments (61)

  1. Mark

    One thing I always find interesting about crater photographs is that they can sometimes have an optical illusion effect – e.g., with this picture, it almost feels as if the craters are coming up from the ground, instead of going down into it. I’m guessing that’s due to the lack of real shadows to give our minds the necessary perspective.

  2. Sam H

    @Mark #1: The curious thing for me is I saw it as it should be seen, meaning that the illusion varies among people. It could even be an indicator of something in our psychology, like the spinning ballerina illusion.


    I’m not a troll, just couldn’t help myself 😉 Spring Break FTW!! :)

  3. I may be way off the mark here but I’m guessing that an event like this would be catastrophic for life on the planet? IF that is the case, could this crater be the reason that no life has been found on Mars?

    I’d appreciate your informed view on my uninformed guesswork!

  4. DrBB

    “and within a few seconds the shock waves collide.”

    Seconds? Woulda thought micro-seconds but maybe my sense of scale is way off. Exceedingly cool image and explanation either way, as was that supernova one.

    @1 Mark: Damnedest thing. I almost always have that problem. Though when it comes to that spinning silhouette whatsits (“Which way is the dancer turning?”) I can pretty well reverse it at will. Not so with craters–they almost always look convex rather than concave to me in photographs and no amount of concentration can force my brain to reverse the impression. BA’s recent series of super-hi-res Luna pix are an exception.

  5. So, a bit like the meteorites that hit Germany around 15 million years ago then. The craters around Nordlingen and Steinheim are believed to have formed simultaneously.

  6. Jose

    @1 Mark: Actually Phil published something about this effect a couple months ago. It has something to do with the shadows and how our brains expect them to be, if you turn the image upside down you’ll see the craters going down instead of coming up, very interesting!!

  7. Jon F

    …that, or it was sandworms. I’ma go with sandworms myself. Big ones. Need lots of Spice.

  8. Lawdog

    We have worm sign.

  9. Don Q

    @1 Mark: I was once looking at the moon directly through a telescope, at a good field of shadowed craters, when all of a sudden, all the craters turned into rounded bumps. With a little concentration, I could get them to swap back and forth between up and down. When I looked at a slightly different area of the moon, the effect was more difficult or impossible.

    In this articles photo, the light is coming from the lower left, not a lighting normally seen in everyday life. It might be interesting to see what happens to the illusion if you rotate the photo so that the light comes from one of the upper quadrants.

    @4 DrBB: Speed of sound on Earth is about 5 seconds per mile or about 3 seconds per kilometer. This would have (sonic) shock waves, starting about 2k apart, meeting in about 3 seconds in an Earth atmosphere, not too much different on Mars. Speed of sound on Mars anyone?

  10. alfaniner

    In the winter that is going to make one hell of a half-pipe!

  11. Chris Winter

    Well, there’s a Web page for that. It says the speed of sound on Mars is 244m/s (801ft/s) at the surface. The page goes through the derivation and gives a great deal of information.

    Oh, the URL? http://www.aerospaceweb.org/question/atmosphere/q0249.shtml

  12. GrogInOhio

    My first thought was reminiscent of one of the rover’s bouncing ball landing crafts. I’m thinking something moving at the speed of crashing meteor, certainly would NOT bounce, but that balloon craft came vividly to mind.

  13. Thea

    I see the craters as concave. In some pictures that have been on this blog, I’ve initially seen some craters as convex, but have always been able to reverse it. The reason for all of this clearly lies in the dark, murky depths of the brain.

  14. There was a physicist at Los Alamos who made headline news some years ago when he reevaluted the Tunguska Blast of 1908 using his own supercomputer program. I do not recall his name but I wonder what he thinks of your scenario..

  15. kikilis

    Musta been a terrible explosion when hitting the atmosphere, to split in three pieces hitting the surface after ~4-5 seconds 2 km apart…

  16. John EB Good

    @8 Don Q: According to these calculations:


    The speed of sound on Mars at what could be considered its «sea level» on a sunny and warm day at -32 C, would be 244,2 m/s which is way slower (almost 30%) than our 343,3 m/s at sea level with a temperature of 15 C.

  17. Rodger T

    I also have the issue of seeing some of the photos as convex rather than concave ,the one that drove me absolute nuts is the recent photo of the farside of the moon,
    I see one 1/2 as concave the other as convex.Can manage to see both halves as normal until I blink and then its all over. lol

    All to do with perspective ,but there a some photos I just cant see as they are meant to be.

  18. Another Eric S

    “As the object plunges into the thin air of Mars, it breaks up into three similar sized pieces, each perhaps a hundred meters or so across, the size of a football stadium.” Or would it be a football field? Just trying to establish perspective between object size : crate size.

  19. Felix

    I thought the explanation was going to be that something bounced causing three successively smaller craters. Would have hit at a very small angle I guess. And even then asteroids aren’t very bouncy!

  20. This is a VERY good argument for why it is a VERY BAD idea to send a team of oil drillers to an asteroid heading for Earth and set off a nuclear warhead inside it!

  21. callcenterhero

    I find it strange that this is a rare occurence.

  22. Mark

    @2 Sam H & @4 DrBB – I’ve seen the dancing ballerina illusion before, I was able to reverse it’s direction almost at will. Sam H – same thing with craters for me, they either appear “in” or “out” (or perhaps “up” or “down”?), but I can’t switch them.

  23. Dave

    Blue angry birds?

  24. DrBB

    @17, @2: Holy crap! I left work, got home, opened this page on my laptop and the instant I saw the image it was in its correct orientation, concave craters and all. Part of the problem was how my brain was interpreting the angle of the ground relative to the camera frame–had that reversed too of course. I think this is maybe the first time I’ve ever got my perception to flip with this kind of image, not that I ever really wasted a huge amount of time trying.

    I must say it’s a much more impressive picture the right way round.

  25. Wayne Robinson

    At first glance, I thought that they were finger prints (look, you can see the imprints of the skin ridges). While obviously not due to the Mutant Star Goat (which would have left hoof prints), perhaps it was due to the Mutant Star Goat Herder?

  26. puppygod

    @8 Don Q: Speed of sound in solids is generally higher than in air. For rock reasonable estimate would be at least 5km/s. I don’t know about martian atmosphere, but note that impact shockwave can be supersonic – though I doubt it would be more than initial relative speed of impactor – around 30km/s tops, probably. So, if we assume that shockwave was somewhere between those two values and craters are 2km apart (1km radius), then shockwaves would clash within 0.2 to 0.03 seconds after impact.

  27. Glidingpig

    Nice pic, but what is that vertical light (white) line thru the crater intersection to the left? was that the blow out of the two shockwaves hitting each other? I do see another half line from the other intersection.

    And FRIDAY, FRIDAY.. oops sorry. I do kinda feel sorry for her, she is only 14 years old. How many of us would like what we did at that age following us forever?

    And they look like the impact was almost vertical, but slightly to the right, as in, threw debris that way. The craters are elongated that direction. (Possibly the other direction, but its off the picture.)

  28. John Baxter
  29. Messier Tidy Upper

    Impressive fireworks there indeed. :-)

    Shortest crater chain ever? 😉

    Where on Mars is this? Checked the source linke and it doesn’t seem to say.

  30. Messier Tidy Upper

    Something similar – although with more widely dispersed fragments – has probably happened on Earth before – see :


    Manicougan crater is just one of a few incl.




    which almost certainly happened together – although *very* widely geographically separated – 215.5 million years ago back in the Triassic period. Perhaps a hitherto unknown large species of Triassic reptile (Homo Dimetrodontis?) made an ill considered attempt to save their world by sending up some sail-backed oil-drillers to blow apart the looming comet /asteroid? 😉

    Or, more likely, the object broke apart early on and high up. Maybe was a binary aseroid or an asteroid with a moon or moons like Sylvia to begin with?

  31. Messier Tidy Upper

    D’oh! Dimetrodon’s :


    lived in the Permian era not the Triassic one! Mea culpa.

    Umm .. would you beleive Homo Coelophysis :


    instead? 😉

    Sylvia is an asteroid with two moons :


    or 87 Sylvia to be exact while asteroid Ida (243 Ida) which is orbited by the small moonlet Dactyl as found by the 1993 Galileo fly-by is another famous example – there are actually quite a few. :-)

  32. Messier Tidy Upper

    @3. Paul Parkinson :

    I may be way off the mark here but I’m guessing that an event like this would be catastrophic for life on the planet? IF that is the case, could this crater be the reason that no life has been found on Mars? I’d appreciate your informed view on my uninformed guesswork!

    I’d say possibly but not necessarily. It depends on the scale and the timing. Life on Earth has survived similar cometary / asteroid impacts although some of them only barely. Life is remarkably tough and resilient. Especially the early microbial type life as we think life on Earth began with extremophiles with life springing up just after the Earth had basically cooled off enough for the surface to be other than molten once the worst of the Late Heavy Bombardment pummeling had eased off.

    If this impact happened very early it might’ve been before Martian life formed (assuming it did) and if this happened very late then Martian life might already have become extinct.

    Plus there are too many questions and uncertainties regarding life on Mars, its possible existence, possible nature and possible duration. There is even the case for life on Mars being around still – albeit just some microscopic lifeforms deep underground. :-)

    Some astrobiologists, so I gather, think that the Viking results are inconclusive and the tests designed to find life may perhaps have inadvertantly killed what they were looking for! 😮

  33. Dermal ridges! I see dermal ridges! That’s a giant footprint! Or toe prints, or something.

    Awesome picture. And I do love the sand dunes running across it.

  34. Wayne Robinson

    Paul Parkinson,

    Don Prothero in ‘Catastrophes’, published just last week, discounts the possibility of planet buster asteroid or comet impacts.

    He also doubts that the 10 km Chicxulub asteroid did in the non-avian dinosaurs, at the K-T extinction, favoring the Indian Deccan Traps volcanos.

    He says the asteroid impact hypothesis only gets an airing because it justifies some research money going to astronomers looking for Earth orbit crossing asteroids, makes great cinema as in that Bruce Willis film and helps to fill a chapter in authors’ of bad popular science books (well, perhaps I made up the last 2, sorry Phil).

  35. Don Q

    @27 Puppygod: “Speed of sound in solids is generally higher than in air.” & “…note that impact shockwave can be supersonic.”

    Yes, but that is why I limited my answer to “sonic” and in “an atmosphere”. The shock-waves in question were the ones that caused the ‘lines’ between the impacts, apparently the result of the collision of airborne particles, rather than sub-surface shock-waves in the rock. So my answer was in response to previous posters thought of “microseconds” (up to 1,000,000 km/sec? not very likely!) versus seconds (the range of sonic shock-waves in a normal atmosphere, just for scale).

    Of course the speed of sound on Mars now, may be quite different from the atmosphere when this collision happened. Other ‘speed of sound’ issues could include the increased atmospheric pressure in the area ahead of the transonic asteroid material. Oh, and the issue of vaporized rock changing the atmospheric density in the area. And of course the temperature changes dramatically with the collision, again changing the speed. Others? Too … many … variables … for … a … short … post. But, the point is, none of these would change it to microseconds.

  36. Superb article and really the photograph is something to remember.But one thing I have doubt.

    @Phil:Looking at the Report published in Chicago Chronicle,”Rowley said that the chance that these craters are randomly so aligned is near zero.” The same question comes to mind also.If the meteor breaks at the atmosphere how come they all fall just beside each other.Seemed like all the three meteors might have come down just side by side or has broken off just after touching ground zero.
    Also if we look closely in the enlarged image of the impact zone,I find some zig zag lines,what could be the reason for that.Also the sides of the crater seems to have eroded at some places and smooth at other places…

  37. VagrantThorn

    While my physics may be a little rusty, I’m pretty confident planetwide disaster would have been averted had they listened to the dolphins.

  38. Radwaste

    Those of you discussing shockwave speed will please note that the same still exists in vacuum, matter being provided by the impinging mass. Those of you fond of studying nuclear weapons know this intimately.

    Air does NOT transmit all impact energy, and in fact it isn’t even required.

  39. Peter B

    Paul Parkinson @ #3 asked: “I may be way off the mark here but I’m guessing that an event like this would be catastrophic for life on the planet? IF that is the case, could this crater be the reason that no life has been found on Mars?”

    I don’t think impacts of this size would have been catastrophic, except in very particular cases. The reason I think that is that these objects would have been much smaller than the rock which hit the Earth at the end of the Cretaceous Period and formed the Chicxulub crater. That rock was probably responsible for the death of large portions of the Earth’s ecosystem, but it certainly wasn’t enough to wipe out life on Earth. Note also that it was the more complex life which suffered most in that impact.

    So I think those impactors could only have been responsible for wiping out life on Mars if the only life on Mars had been directly under those rocks when they struck.

    “I’d appreciate your informed view on my uninformed guesswork!”

    Sorry, but my comments above were little more than uninformed guesswork too.

  40. John Carter

    It kinda looks like a giant, 1951 Vogon Studebaker hit it head on after a wrong turn at the Asteroid (Orange) Belt!

  41. icemith

    I too had my usual perception problem with the image. I more or less just ignore it now, knowing a large proportion of the population see it just as it is:- a concave, dished-in crater. I’ll have another look later.

    As for the impact itself, I feel it was a direct hit, straight in, vertical. (It does happen). This would account for the lack of oval shaped craters. Each piece, roughly the same size, and just happening to be in a triple dead-heat in the race to the planet Mars, impact in line at the same moment. The geometry of the shock waves would create a straight (-ish) line at their own impact in the atmosphere. Consider each of those shock wave as a sphere, then the result would be essentially cancelled out, except at the surface where massive movement of matter would be affected, probably causing a straight valley, one on each side of the central crater.

    There seems to be some slight asymmetry as the two valleys or whatever, are not parallel – an indication of a dynamic event, and not an artifact of something else? Is there any evidence that there may have been a slightly earlier impact of a fourth piece, but obliterated by the craters that we can see? In that case, what would be different? I suppose the ripples we see are the normal dune structure where loose sand is being blown around by the prevailing winds, and not interference patterns that we see in holograms, and Moire patterns, firmly etched in the solid rock.

    Arrrr, wish I hadn’t mentioned dune…. must have been the Spice… sorry, but some others beat me to it, and I couldn’t help myself!


    PS. Looking at that image again, I definitely see the lower left crater as concave, but the lower right is convex. The long valleys are both concave but the central big crater won’t budge from being convex, though there seems to be some dished look to some of the central parts of the three craters. Maybe there IS a big mound at the bottom part of the crater wall area . I can see both effects at the same time, which seems to be an improbability.


  42. I really REALLY wish you would not truncate your RSS feed. Makes reading the full details of these amazing pics a pain! 😉 Please un-truncate?

    Those are some amazing craters.

  43. Filipe

    This one is quite obvious, it was hit face on by a giant evil peanut from outer space.

  44. icemith

    Some hours later, after a good sleep, I can now resolve it as all concave. WOW, and it puts a different perspective on it.

    Except….. what I had resolved to be the two straight, almost parallel “valleys”, are now slight ridges. And I am now at a loss to explain exactly why.

    Anybody offer any explanation? I cannot find or remember seeing any examples for that on Earth.

    And as Filipe @44 above says, the total impact was a giant evil peanut, it would have to have been a three kernel peanut! Having grown peanuts, I know they do exist, like double-yolk eggs, rarish but existing in nature. In space there has to be rarities too, but explaining the mechanics is another thing.


  45. Neal

    Why wouldn’t this have been caused by tidal force dissociation?

  46. Messier Tidy Upper

    @ 31. Messier Tidy Upper :

    Something similar – although with more widely dispersed fragments – has probably happened on Earth before – see : [link snipped]
    Manicougan crater …

    Hmmm… Actually, come to think of it :


    is more like the one I was thinking of with that. 😉

    That’s one – no, *two* – impressive Candian craters! :-)

  47. g leap
  48. Joseph G

    @MTU: Wow! Speaking of giant Canadian holes, (insert your own obscene Canadian celebrity reference here)!

    Srsly, atmospheric breakup isn’t the most plausible mechanism, is it? Shoemaker-Levy was a pretty neat demonstration of tidal disruption and crater chains (well, mushroom-cloud chains, in this case)…

  49. MAC

    That was almost poetic.

  50. icemith

    Phil, I’ve just realised that if the asteroid(s) hit the Moon similtaneously, then your title for this post is mathematically incorrect.

    Shouldn’t it be:- KaBLAM3 (that is, …Cubed. Or at least X3 (…times three)! (I couldn’t make a proper superscript 3 – could not find any way to address the fonts, they are apparently not available in the comment box. I could be wrong, anyone know better?


  51. Capt Tommy

    Really interesting. especally the blast lines. Looking at the Barsoominated picture one can see:

    1. the blast structure seems to indicate the Left hand blastwave was larger, notice the trough gouge is more pronounced. This also indicate that the center rock might have been the largest (as if that matters).

    2. In side to left upper quadrant is a small double crater of the same only newer impact paramiters. Double crater Straight center Wall. Now that is lightning striking in the same place!


    Capt Tommy

  52. Joseph G

    @ 51: Well, if you were on the surface (some distance away, I would hope) watching the collisions, and you were in line with the long axis of the chain, the sound of the three explosions would hit you one at a time, even if the collisions were simultaneous 😀

  53. Berserker

    This is old battle damage. Badlife dodged this salvo, but not the delivery of penetrating masses at 0.9 c. The volcanoes and missing seas are that result, and Mars is no longer infected.

    We see Earth is afflicted. We’ll have to do something about that soon.

  54. David

    It was a hugely Improbable whale.

  55. Matt B.

    I hope we find a set of simultaneous craters in a triangle formation some day. It would be cool to see this in three-part radial symmetry.

  56. icemith

    @ 53.t Joseph G: Yeah, but if you were at right angles to the line of impact, then the sound would be simultaneous, and so would be 4.5db louder. But that is not the problem actually. We are talking about the shockwave produced by the three impacts. They would emit as a hemisphere for each impact, and would soon impinge on each other. On the surface that would manifest itself as a straight line. Extrapolated, that shockwave would form an expanding hemisphere of extra-centric pressure waves in the atmosphere and where they meet another coming the other way, it would result in a straight line on the surface.

    Just what effect it has on the topography I don’t know precisely, but it may create a rill or a ridge, if the compression force was large enough. But would, could, it happen really? I would have thought the effect would have been continuous anyway, not unlike any other effect we see in a fluid, including in the atmosphere. The classic is the cork bobbing in the ocean, as a wave passes by. It is influenced only by the transfer of the energy of the wave through the water, essentially moving in a vertical circle and resting where it was before.

    We’ve all seen the high speed imaging of the effects of that shockwave in the tests of Nuclear explosions even fifty or sixty years ago, destroying buildings and severely flexing trees and the like. I think somehow similar effects on relatively loose ground features such as sand, rocks and soil will be re-distributed by the initial wavefront, but when the effect is effectively cancelled out in the meeting of the two wavefronts, the debris just falls to the surface in a line reminiscent of the straight line boundary. And a valley represents the point of rarefaction in that wavefront where debris falls at the compression point on each side of that lower pressure point. That it ends up being a straight line is a representation of those colliding wavefronts and forms a valley.


  57. Marc

    Has volcanic activity been ruled out completely? We sometimes see volcanic craters that align themselves like this on Earth due to shifts in a hot spot. I’m no geologist, but that seemed like at least something for the more learned to look into and comment on.

  58. reidh

    I think there was much life on mars, and water as well, but the event that produced the asteroids and meteroids etc., I think scoured the shire there, knocked Venus over and Uranus onto is side, gave Jupiter its Red Eye, and Saturn its Rings and maybe Pluto and Charon were/are co conspirators in it. I think earth was on the other side of the Sun at the time and so avoided being demolished like Mars. I mean you don’t has to be a science rocketist to perceive that.


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