Mars scar

By Phil Plait | March 28, 2011 7:00 am

Speaking of weird impact craters on Mars…

Mars Express is a European Space Agency orbiter that’s been snapping away at the Red Planet since late 2003. In August 2010 it took this picture of a bizarre feature on Mars:

[Click to impactenate.]

I would’ve thought this was a canyon of some sort, but in fact it’s an elongated crater! Most likely some large object broke up as it entered the atmosphere of Mars, striking the surface at a low angle and creating a series of craters that merged to form this strange thing. Unlike the triple crater I mentioned last time, this one is pretty frakkin’ big: it’s 78 kilometers (almost 50 miles!) long, 10 km (6 miles) wide at one end and 25 km (15.5 miles) wide at the other. Whatever hit here was pretty big, certainly over a kilometer across before it broke up. Probably several.

In the high-resolution image you can clearly see a blanket of material surrounding the site, created as material ejected from the impact settled down. The narrow end of the crater seems to be perched right on the edge of a small cliff, and that’s too much of a coincidence; it must have formed by the impact itself.

Mars Express has a stereo camera as well, allowing 3D elevation images to be made. Check this out:

Wow, that really gives you a sense of what happened here. The impact must have been tremendous — something like that happening on Earth now would be a near-extinction level event! At the top right, just inside the crater wall, you can see material that has slumped back down in a landslide kilometers across. The flow of ejected material can be seen as well.

One thing I can’t quite figure out: was the impact left-to-right or right-to-left? Looking at the edges and the ejecta blanket, I think I could argue convincingly either way. And interestingly there’s another elongated crater to the northwest of this one, too. They’re almost perfectly aligned, implying strongly they’re associated with each other.

[UPDATE: Regular BABloggee Ivan Simic points out to me that in the full 3D image there are small impact marks to the right of the big one. These look like secondary impacts — probably from material ejected from the first impact — and they have their narrow ends pointing toward the big impact, as you’d expect from something hitting at an extremely shallow angle. I am now leaning toward the impact direction going from the narrow to the wider end of the scar; that is, right-to-left in the top picture (reversed in the 3D one). Come to think of it, the narrow end has a sharp rim, and the wider end is less well-defined, again consistent with a narrow-to-wider impact direction.]

The more I look at Mars, the cooler it gets. All kinds of weird stuff happened there, and we have literally only begun to scratch at the surface.

Related posts:

Phobos is, like, totally groovy
More *incredible* Phobos imagery
Hebes Chasma
Glacier on Mars?

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: crater, Mars, Mars Express

Comments (50)

Links to this Post

  1. Kijk nou, ook Mars heeft een litteken | Astroblogs | March 28, 2011
  1. Just waiting for someone to claim it’s a footprint. 😀

  2. Sir Chaos

    To me as a complete ignoramus it looks more like a scratch – as if something grazed the surface and then flew on. Or maybe as if it hit at such a shallow angle that it was deflected…

    Well, ideas like these are probably why this sort of thing is best left to professionals.

  3. @Steve: It’s irrefutable proof that enormous Disney dwarfs once lived on Mars!

  4. Gary Ansorge

    In the second picture, the gouge to the right looks like the broken off handle of a spade, which implies there was a big chunk of something moving to the right, shedding pieces along the way.

    Gary 7

  5. Jason Dick

    My guess is that the impact direction has very little to do with the shape of the crater. I suspect that the shape of the crater has more to do with the size of the various pieces of the impacting object. The single crater impacts I’ve seen seem to provide very little information as to the direction of the impact (though granted, I haven’t looked at nearly as many craters as you have, Phil!).

  6. Blizno

    In the last picture it looks like some of the tremendous momentum of the object moving at an angle to the ground was transmitted to the debris. My mind’s eye can imagine a huge sheet of material sliding in the direction of the impact. The “cliff” might be where the sheet stopped moving.

  7. Joseph

    Not a footprint.

    Obviously it is a landing cradle for a ginormous spaceship.

    Simply weathered by time.

    P.S. – Interesting note, Spell-check says ‘ginormous’ is a word!

  8. Steve H

    It almost looks like a bounce. Or like a stone skipping. and impacting again to the NW… Like Sir Chaos, however, I’ll leave it to the Pros.

  9. Guysmiley

    I thought it didn’t matter the angle of the impact, craters were always circular? Or is that only when above some certain impact velocity?

  10. Jeff

    you made an excellent observation that this came in at a low angle to merge into this groove. The theme is that today, unlike the past, the images have such great resolution we can actually infer in detail PROCESSES that are occuring.

    When I was in college, they had so little in terms of planetary astronomy it is revolutionary today.

  11. RAF

    Just imagine being at a “safe” distance away to witness such an event as it happened.

  12. JMS

    I find this hard to understand. At the speed that space debris usually impacts, the instant that the object hits the ground it explodes. That is why you don’t really see craters like this on earth or on the moon. No matter how shallow the angle of impact, the craters always end up as circles.

    I’d like to see this recreated at Nasa’s supergun facility.

  13. Sam H

    This is interesting (and even better than last week’s), but there’s almost certainly vertical exaggeration applied to the oblique view, right?

    And holy crap, there’s ANOTHER double impact crater in the same freakin’ image!! 😮

  14. A.

    I thought it looked small when I saw the picture… then I read “78 km”. Jesus!

  15. Wouldn’t the “fat” end of the elongated crater be the initial point of impact (meaning that the impact happened from left to right in the first image, right to left in the 3d image below)? If the object were in one piece, the first place it hit would get the brunt of the force. If the object had broken into pieces when it hit, then the largest piece would hit first, followed by smaller pieces. It seems to me that the crater sort of “points” in the direction of the object’s travel like an arrowhead.

  16. Just now looked at the linked image showing both impacts. So, how do you end up with two elongated craters like that? I’m guessing something big breaking in two, then both pieces breaking into several smaller pieces, causing a sort of overlapping buckshot effect. Something like that?

  17. So I’m curious, what’s the right-to-left theory here? Would it imply a sort of… “skipping” event? That seems unlikely with the forces involved. To me it seems it would have come in left-to-right and as more of the object impacted, the crater would have become deeper and wider as it is in the image. Kind of how you’d throw a rock in a sandbox at maybe a 33 degree angle or less… except with much more energy and explosion. Plus the crater appears to flatten toward the right which makes it seem as though debri was ejected in that direction.

    Just to make sure everyone knows, I’m talking about the second image’s orientation.

  18. ozprof

    So now we know where the Enterprise REALLY came down!! :-)

  19. RMC

    Just used Google Earth to superimpose the picture over my home city, and the results are… absolutely jawdropping…

  20. crf
  21. Delta

    Phil I think you might be jumping to conclusions about the impact forming the cliff. If you look on the elevation map, showing the other impact scar, it looks like it is part of an escarpment that goes off to the north east.

    Correlation does not equate to causation ; )

  22. Chet Twarog

    Would these impacts have blasted Mars rocks into space with some meteorites impacting Earth, Venus, and/or Mercury?

  23. Tim G

    What is the cliff that Phil is talking about?

  24. Joseph G

    Headline reminded me of a song I remember singing along with as a kid. Sorry to take up space, but I just can’t resist 😀

    Marz Barz
    words & music © by Jan Harmon 1984-86

    The Martians invited us up for tea
    We will arrive at a quarter past three
    They’ll fly us to Mars with a Martian named Marge
    And they’ll take us to their house in their Mars Barge

    Marz Barz eat ‘em in your cars bars
    better than Atari starry Sagitary-arrs bars
    Screen stahs eat them in your Cahs Bahs

    They will be serving us Marzipan
    Campbell’s Marzmallow soup from a can
    Orange Marzmalade over marzcaroni stars
    Marzachino cherries and Marz Barz


    Then to the theater we will go
    We will be seeing Marz-cell Marz-ceau
    Marzcello Marztriani will strum his guitars
    and we’ll have a few Marztinis in Marz Barz


    Then we’ll go strolling though the canals
    We’ll watch Marz mongooses in their corrals
    We’ll watch marzupials hop metearrz
    And over there’s a couple of Marz Barz


    Then we will tell them we must be off
    We’ll say adios and Marzeltov
    And as we depart we’ll see the canalis
    And the ruby luminary of the Marz Barialis


    Now maybe tomorrow they’ll visit me
    I’ll serve them their favorite galactical tea
    Hydrogencicles and Pickled cigars
    Cosmologic lollipops and Hippopotamarz Bars


  25. Joseph G

    Wow, those are some gorgeous data. Kudos to the Mars Express team!

    I wonder, could Mars once have had a third small moon? Perhaps in an eccentric orbit with a rather low Perigee (er, Periareion)? If so, will Phobos one day create a similar gouge?

  26. phdnk

    I agree that the impact direction has little to do with the crater’s shape. However, the ejected material can provide a clue. It seems to me that the blanket is skewed towards the wide end of the crater. So I suggest the debris fell from right to left (in the first image).

    We can also see individual craters overlap. The one at the wide end has apparently formed after the biggest crater. The piece which has done the wide end crater flew higher and therefore traveled further and hit later.

  27. Joseph G

    @23 Tim G: I think he’s talking about the diagonal escarpment you can see in the upper right of the top image and the upper left of the lower image. I’m not sure how an impact would create such a thing, though.

  28. Arthur Maruyama

    @ RAF (#11):
    I suspect that the only safe place to have had observed this impact was from high Martian orbit. :)

    For simplicity sake let me call the multi-impact crater pictured above “Crater A” and the second multi-impact crater that BA mentioned “Crater B.”

    I’m no planetary astrophysicist, but I suspect that crater B is considerably older than Crater A. Crater B shares the smoother bottom that the majority of the craters in the area have while Crater A does not, suggesting that Crater B was likely part of the Late Heavy Bombardment phase that ended about 3.6 billion years ago (so as a non-specific answer @ crf [#20]: younger than that).

    Considering the amount of energy that must be expended in order to excavate a crater, it seems unlikely to me that Crater A was formed in the main by a single body that “skipped” across the surface of Mars. Remember that the body that forms an impact crater is much smaller than the crater itself, and that the kinetic energy of the impact largely destroys that body. For example: the mile-across Meteor Crater in Arizona is thought to have been formed by a meteorite that was about 150 feet across, and while traces and chunks of it have been found the majority of the meteorite apparently was vaporized in the impact.

  29. Ray

    Thats not an impact crater. Its stripmining. Aliens came to Mars and scooped up a bunch of Mars’ most valuable commodity. I’m not sure what they did with all that dirt but it must have been really important.

  30. DrBB

    @21. Delta Says:
    March 28th, 2011 at 10:20 am
    Phil I think you might be jumping to conclusions about the impact forming the cliff. If you look on the elevation map, showing the other impact scar, it looks like it is part of an escarpment that goes off to the north east.


    I was about to post that too. Much clearer in the linked image, the cliff seems to be a much larger structure with its own continuity not something caused by this impact. Almost looks as if the impactor was traveling at such a low angle that it caught the lip of the cliff as the first point of impact. That seems a little more plausible than the second interpretation that sprang to mind, which is that it was traveling the opposite direction, also at an exceedingly low angle, and lost contact with the ground where the cliff dropped away, then impacted again further out, creating the other elongated crater that’s visible in the linked image. Probably I’ve seen too many Road Runner cartoons…..

  31. Truly Anomalous

    Joseph said:

    “I wonder, could Mars once have had a third small moon? Perhaps in an eccentric orbit with a rather low Perigee (er, Periareion)?

    Possibly; this is a good explanation for this crater, though not the only one: could also have been produced by a very oblique asteroid/cometary impact.

    “If so, will Phobos one day create a similar gouge?”

    Yes, in several tens of millions of years probably. It’s decaying orbit will be quite circular, with a smaller and smaller radius…

  32. Christoph C

    I’m by no means an expert in any of this, but I believe it could have been a glance for the right to left. I would bet a buffalo nickel that the remaining pieces of the meteor are off the cliff. On the right side of the crevice the hills in the crater are a sign that there was hard impact, from what little I know. I’m willing to bet that the rest of the crater is from the meteor pushed through the rest and fell off the edgeof the cliff.

  33. Arthur Maruyama

    @30. Ray:
    Obviously they used a long trowel–you can see the impression made by the handle in the lower-right in the second picture that BA posted above.

    As to what happened to the dirt: duh, Phobos and Deimos. 😉

  34. Torbjörn Larsson, OM

    Likely the largest pieces hit the ground first on account of larger radius during shallow impact making the row, everything else equal. That makes the narrow end the last, and explains the plowed material seen in the bottom figure.

    They’re almost perfectly aligned,

    What are you smoking, it seems nifty strong!? Rulers gives ~ 60 deg to ~ 70 deg ellipse long axis alignment to the W-E axis.

  35. Messier Tidy Upper

    @18. ozprof : “So now we know where the Enterprise REALLY came down!!”

    LOL. :-)

    But *which* Enterprise are you meaning? 😉

    This one? :

    Or this one? :

    Or maybe even this one :

    perhaps? 😉

  36. timebinder

    It’s Big Man’s footprint.

  37. mattstronomyfan

    Is it just me, or do the darker regions in the lowest areas of this crater appear to have cracks? It reminds me of when a mud puddle dries up and forms large cracks.

  38. So the USMC only taught me how to do this with field artillery, but the principle ought to be the same. On a low-angle shot the crater will be elongated, widening in the direction of travel, with ejecta beyond and to the side of the point of impact that narrows as the angle of impact decreases. In other words, left-to-right in the second picture.

  39. mfumbesi

    78Km long, 78km long, man it would take your breath away to stand on one end and look…… to the other side. I wonder how deep is it. From the pictures I would guess around 8km deep, man I would love to go there.

  40. Anchor

    Oblique or low-angle trajectory of impactors with relatively high tensile or material strength (such as an iron-nickel asteroid) would be much more likely to avoid disintegration via tidal forces before atmospheric entry or after entry into the atmosphere, especially in shallow trajectories where the dynamic stresses build up much more gradually than steep trajectories.

    The form of this impact feature strongly suggests it traveled from the narrow end and plowed toward the fat end (right to left in the top image). Low-angle impact simulations bear this geometry out: when an impactor first makes contact with the surface, only a relatively small portion is sheared off, but the rest of the impactor is bouyed for a time by the energy released beneath it. But it continues to lose energy and gradually plows out a widening ‘channel’ until its bulk is consumed. The fact that one sees smaller elongated scars that are aligned with the main feature’s exclusively beyond the fat end (and no evidence of such beyond the narrow end) indicates secondary or briefly surviving impactor debris being cast forward from the main impact.

    This is hardly new to impact science: one can see prominent twin rays extending beyond the famed lunar crater pair Messier and Messier A, located in Mare Fecunditatis. If you have a six-inch or larger telescope, have a look at it! Or look at the images in this well-illustrated Wikipedia article:

    One popular interpretation is that a shallow-angle strike by an impactor produced the highly-elongated Messier, and that at least part of it rebounded to create the complex form of Messier A (possibly with an initial gouge produced by one mass followed ‘almost immediately’ by another portion that came down onto the foot of the secondary gouge after it was lofted into a slightly higher ‘hop’) casting glassy material in jets further down-range to produce the twin rays.

    But another fascinating feature of this complex are rays extending in narrow ‘wings’ perpendicular to the long axis of the main elongated Messier (which is also the brighter of the two in terms of albedo, indicating that it was almost certainly created with higher impact energy than its down-stream companion Messier A was).

    The Mars analogs which Phil has featured in the last few days also have such perpendicular ejecta ‘wings’ – except this much larger one shown here (captured by Mars Express released last year) has a LOBATE terminus indicating fluid flow, stronglysuggesting the presence of a substantial reservoir of subsurface water ice – an unmistakably Martian habit and ubiquitous on Mars. You can see such lobate forms around a number of the larger circular craters in the same image.

  41. Nigel Depledge

    Guysmiley (9) said:

    I thought it didn’t matter the angle of the impact, craters were always circular? Or is that only when above some certain impact velocity?

    You are right. This is how we are able to deduce that the impactor fragmented before it hit. The pieces hit close enough together that the impacts did not form separate overlapping craters, but instead one elongated feature, as the individual craters merged.

  42. Kevin B

    Looks strikingly similar to the impact crater caused by a high speed crash of a jet at a low angle. Left to right seems most likely — especially with the evidence of the secondary impacts to the right. Great photo! Would love to see the associated craters.

  43. Capt Tommy

    I beieve that at an angle of less the 5 degrees the meteor would creat a scar such as this, again like a skidding stone across a pond. I recall seeing this on Discovery Channel… Or reading it in Astronomy. The mud flop ejecta would indicate this guess. (I’d say Hypothosis, but my references are sketchy though a a low angle skipping stone in water is a good analogy to a very fast low angle skipping rock and hard ground)

    Irregardless isn’t it interesting that there is another similar scar so close… See my observation on yesterday’s triple hit.

  44. Very cool! Though my favourite martian feature is still the smiley face…

  45. Doug

    Looking at the first image, I got the classic in-and-out optical illusion. That is, it did not look like an elongated crater, but a big plateau! Like a giant loaf . . of something. Thankfully, the 3-D rendering is much less ambiguous!

  46. Andrew W

    If this crater is the result of the angle of impact rather than the shape of the impactor, and given that the vast majority of craters are round, do we conclude that the impactor was moving very, very, fast, like well above solar escape velocity?

  47. Shaun

    Looks like the Noahs Ark site.

  48. lurker_above

    Lieutenant Worf: “It’s as though some great force just scooped all the machine elements off the face of the planet. “

  49. daos

    very cool. so what happened to the pieces? can related impact craters be found downrange? or did it all just disintegrate on impact..


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