X Crater: First Class

By Phil Plait | May 9, 2011 6:59 am

When an asteroid or comet impacts a planet, the explosion ejects huge amounts of material, sending it flying in all directions. But there are also plumes of material, long fingers of rock and dust that stream out as well. The boulders and such inside this plume then fall back to the ground, making linear chains of secondary craters. We see lots of these on our Moon, moons in the outer solar system, and Mercury, too.

If these features are long enough, it’s inevitable two chains from two different primary craters would cross somewhere. And it turns out this has been seen… but where?

Well, X marks the spot!

This MESSENGER image of Mercury shows exactly that: two crater chains from two separate impacts crossing over each other (and a third, shorter chain is at the bottom, too). They’re almost exactly perpendicular to each other, which is cool, and the intersection happens to lie in a big, shallow crater about 120 km (72 miles) across that fills this image. Unfortunately, MESSENGER hasn’t been orbiting Mercury long enough to have surveyed the whole planet yet, so I wasn’t able to find the source craters of these two chains.

Interestingly, both chains have elongated craters at their ends, one on the upper left and the other at the top. That indicates a very low-angle impact; anything hitting the ground from an angle above about 10° tends to make a circular crater. However, the one on the left appears to be right on the big crater’s rim, so the elongation may be due to the ground angle changing. The other may be coincidence; both are far too small to have been the source craters for the chains.

I’m not sure there’s any real scientific value in knowing these crater chains intersect or examining the intersection in detail. Still. They’re fun to look at, fun to explore, and they’re just seriously nifty.


Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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More Mercury!
Watermelon planet
Machault by MESSENGER
MESSENGER: Three days out from Mercury
MESSENGER’s family portrait

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (30)

  1. Someone You Know

    I think a stylized version of this, an X with an extra little swoosh at the bottom left, should be part of the logo for any future Mercury-related mission.

  2. That’s dethpicable, y-y-you b-b-b-bad astronomer, you.

  3. Martha

    I wonder if Richard Hoagland or some other writer of lousy science fiction will claim that the X on Mercury is really an artificial structure.

  4. Neal

    For a large-enough impact on a small-enough planet(oid), would it be possible for two plumes from the same impact crater to cross antipodal to the impact point? Or would such an impact melt the planet and leave no craters?

  5. Nemo

    I think we should dig for buried treasure there.

  6. It’s probably a sign from Jeebus.

  7. arcblast

    epic!! it’s a testament to this planet’s violent past… it says the scale is 116 km across, which means that some of these fallout craters could probably be several kilometers across. i can’t imagine how powerful an impact must be that it spews out debris that makes kilometere-wide craters of it’s own! madness!

  8. Gary

    The Truth is Out There…

  9. Pareidolia is subjective, but shrink the photo down to a thumbnail, and I see a pentagram. Interplanetary Devil worship. Masons on Mercury.

    (In Col. Klinck’s voice….) Hoagland!!!!!

  10. Two things I noticed. First, the initial impact crater from the left appears to have impacted on the slope of the large crater… which means it had to come in at a low angle to eject the plume but high enough to get over the large crater’s wall. Also, that same initial impact point as a dot in it. I can only assume that is a smaller more recent impact crater.

    It’s also interesting to me that the secondary craters are so large… most close to the size of the original. Is that attributed to the low gravity of mercury? In fact it seems like the more vertical of the two has a smaller intial impact thn ejecta craters… unless some of those are just random recent impacts.

    Also just something I noticed… the left to right line looks to be the more recent.

  11. @ Buffalodavid:

    Col. Klink. HA!

  12. Of course, now every [anal pore] conspiracy theorist or UFO “enthusiast” is going to use those intersecting crater chains as evidence of some kind of extraterrestrial cover-up. It may seem like I’m being flippant, but I’m not… people have died over these kind of way-out beliefs.

    It’s a scary thought.

  13. toasterhead

    So if my understanding of the Indiana Jones canon is correct, under that intersection should be a series of snake-infested tunnels leading to some sort of talisman necessary to proceed to Act III

  14. Feroxx

    Nono, I don’t think that’s an ‘X’.

    I know an elder sign when I see one…


  15. JJA

    Would that cross be oriented towards the east, by any chance…?

  16. jess tauber

    Its the third smaller line that makes the figure- if it turns out to have a mathematically significant angle to the other two then you have your absolute PROOF that G-D needs a better drafting set.

  17. Rodger T

    arrrrrrrrrrrrr,so that`s where me treasure be buried.

  18. Brian Too

    “Where’s the kaboom? There was supposed to be an earth-shattering kaboom!”

    – Marvin the Martian

    (Doubtless tricked into targeting Mercury by Bugs Bunny)

  19. jcm


  20. Bob

    might the lines be a result of comet/asteroid breaking up before hitting? Kinda like Shoemaker/Levy. Would explain nearly equal crator sizes.

  21. Buzz Parsec


    I think the elongated crater is not the initial impact crater, just the first (or last) of the series of secondary debris hits that formed the chain. Phil notes that it is too small to be the primary crater, which must be off-image to either the left or right. To me it looks like that particular chunk must have been ejected at a very shallow angle, just barely cleared the rim and landed on the down-slope at an even more shallow angle. Remembering from freshman physics, the distance a projectile will fly depends on its initial velocity and the angle to vertical. Maximum distance obtains at a 45 degree angle. The angle of launch is equal to the angle of impact, and since the impact angle is close to horizontal, the impact point has to be closer to the launch point than the impact points for objects ejected with the same velocity but at steeper angles. Since the oblong crater is at the end of the chain, it has to be one of the closer impacts (unless it came from the right at a very very shallow angle, but with much greater velocity than all the other objects), so most likely the primary crater is to the left of the image.

  22. It is an “x”…

    Or a “+”…


  23. CB

    I bet it’s a “+”.

    Because if there’s one thing I learned from Contact, it’s that when the aliens try to communicate with us, it’ll be in the form of math homework. ūüėõ

  24. AshleyCakes

    Ooooh, “Contact!”

  25. Blizno

    6. Angus Says:
    “It‚Äôs probably a sign from Jeebus.”

    Is Angus the only one who sees this for what it really is?
    Rotate the picture a bit counterclockwise (anti-clockwise for those not living in North America) and you get a crucifix. Could it BE more obvious?

    YHWH, billions of years ago, put that crucifix on one of the hardest planets for us to study as a warning. When we have advanced enough to see and recognize this Sign, the Rapture is soon to follow.

  26. Peachy

    Gee. And here I was, thinking that’s where the monolith was buried.

  27. James

    It looks like one of symbols used in cuneiform, the ancient writing of the middle east.

  28. A celestial ‘No Craters’ sign? ūüėČ

    If so, it hasn’t worked! ūüėČ

    Classic image and symbol-oidalia. 8)

  29. Thomas BarSinister

    is it possible, if the object strikes at a shallow enough angle, for it to skip like a flat stone skipping on water, leaving a chain of craters?

  30. Cirquelar

    Examining where they cross could show that stratigraphic relationship between the two (i.e. which one is over the other), thereby inferring their relative age to each other. The two elliptical craters at the ends of the chains may just be a coincidence, but you can see other elliptical-like craters along the chain (though not as pronounced). A crater chain like this may be composed on many fragments impacting at once thereby making a crater look elliptical when in fact its just a bunch of material impacting simultaneously creating a ‘trough’. As for direction, bigger blocks are going to land more proximal to the crater than smaller blocks, but these craters are probably within 1-sigma of their mean diameter along the chain. I might hazard the guess that the crater chains hit top-bottom, then right-left assuming the elliptical craters are globs of tiny ejecta blocks landing at once, while large blocks are spread out and forming somewhat larger craters earlier in the chain. These are cool to study, but distant secondaries on Mars are a bit more informative (and confusing) about their origin and for crater chronologies.


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