Vesta's odd bottom

By Phil Plait | September 17, 2011 7:00 am

Man, Vesta is weird.

It’s a 500 km (300 mile) wide asteroid, the second biggest, so its gravity should be strong enough to crush it into a sphere. But it’s not a ball; it’s lumpy and stretched out and, weirdest of all, has an enormous circular depression at its south pole which flattens that entire hemisphere of the little world.

Here’s a recent image taken by the Dawn spacecraft, looking down on Vesta’s strange southern region:

[Click to envestanate.]

You can tell it’s not round! It’s like looking up at a pancake held over your head. The Sun angle is such that the left hand side of the rock is in darkness, which actually helps with giving the image some relief and perspective.

My first assumption is that something really big hit Vesta a long time ago, carving out that basin. Central peaks are common in events like that, smack dab in the middle of the crater (like the gorgeous mountain in the Moon’s Tycho crater), and we see one here, too — that dark spot in the middle, more obvious in an earlier image from Dawn. It’s huge, many kilometers across, but like the asteroid itself it’s weird: it’s really round and smooth, not jagged and sharp like most central peaks. I was at first surprised to find out some scientists are wondering if the basin was from an impact (the usual suspect) or if it were due to some internal process… but then, looking again at the basin and mound, they’re strange enough that maybe sometimes you need to think a little differently.

In a few months, Dawn will drop in from its current 2700 km orbit down to just a few hundred kilometers. When it does, the sharpness of these images will improve dramatically. I hope we get enough information to solve some of the questions about this rock (some detailed commentary on the geology of Vesta has been posted at the DLR website). We have samples of Vesta thanks to meteorites we think came from collisions to the asteroid, so having images and other data to investigate it up close and tie in what we know from the samples will improve our knowledge of this world immensely.

Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Related posts:

Vesta’s double whammy
Vesta in breathtaking detail
Dawn of a new Vesta

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: Dawn, Vesta

Comments (55)

  1. Chief

    you forgot to add “hit” Vesta.

    This is what I thought as well. I wonder how fluid the whole sphere became as the ripples look like a water ripples. Kinda cool.

    Wonder how much gold and other rare elements are inside.

  2. SkyGazer

    After reading that headline after a week about Berlusconi and his “appraisal” of Mrs. Merkel´s behind, this article proved to be a breath of fresh air.

  3. Chris

    Vesta’s got no booty!

  4. Trippy! 😉

    Reminds me of fossil ripple marks in sedimentary rocks and slightly in the spiral around the pole there of the south polar ice cap on Mars.

    Weirdest looking asteroid terrain yet. :-)

    @1. Chief : Wonder how much gold and other rare elements are inside.

    I’m guessing there’s plenty of iridium! 😉

  5. See :


    for info and examples of geological ripple marks.

    Plus check out this JPL youtube animation :

    of Vesta which is pretty impressive too & comes with a good commentary. :-)

  6. Nemo

    Phil, how can you not comment on the smiley face?

  7. The ellipsoidal (egg-like) shape of Vesta reminds me quite a bit of the ice dwarf Haumea :

    & of Achernar – the most rotationally flattened star :

    Except that Vesta is dark lunar grey where Haumea is icy white and Achernar blue-hot.

    For comparison with the spiral around the Martian south pole see :

    which also shows the underlying rock spiral as wellas the polar (dry &water mixed) ice in the inset image.

  8. Digital Atheist

    The Smiley face has got no eyes. hmmmm… I wonder if it could be an incomplete billboard add for The Hitchhiker’s Guide to the Galaxy? Maybe they got interrupted while creating it and had to bug out before they were seen.


  9. Chief

    re 4. Messier Tidy Upper: I’m guessing there’s plenty of iridium.

    But no mass extinctions.

  10. Chris

    @ Nemo
    LOL now I can’t stop seeing the smiley face

  11. BJM

    RE: “The Smiley face has got no eyes.”

    Unless it’s a frog smiley face with two eyes bulging out the top.

  12. Brett

    Obvious reason:

    “That’s no moon asteroid!”

  13. I can’t see the smiley face. :-(

    Wikipedia has updated its Vesta page btw. complete with a good scale comparison with Lutetia, Mathilde and several other asterods we’ve flown spacecraft by. :-)

    (Click on my name for Vesta’s wiki-page.)

    According to that, Vesta spins in 5.342 hours – whatever that translates into minutes and seconds~wise. 5 hours 34 minutes 20 secs maybe or am I missing something?

    Would that be enough to make it rotationally flattened – more ellipsoidal than spherical – does anyone know and care to enlighten us please?

    @9. Chief S: “re 4. Messier Tidy Upper: I’m guessing there’s plenty of iridium.”

    Me too – but, alas, on checking to confirm this I coukldn’t find any mention of it in the sources found so far. :-(

    Vesta’s got an unusal lava surface though and is the source of the “Howardite–Eucrite–Diogenite” (HED) achondrite meteorites which have iron and manganese in them if that’s any help.

  14. Chris

    @14 Messier
    Tilt your head about 90 degrees to the left. Right in the middle is the smiley face :-)

  15. ethanol

    The more I look at this the more I can’t make sense of it, particularly the shading. Indeed if the right side of the craters are shadowed then the left side of the mountain should be, but comparing to other pictures it looks like the shadow is more on the TOP of the mountain. Apparently it has some sharp circular depression on the top that I can’t see in other pictures but my eyes still can’t make any sense of it. In general the shading for this whole picture looks weird, fake even. Has it undergone some sort of contrast processing to accentuate the ripples I wonder?

  16. Naked Bunny with a Whip

    It’s like looking up at a pancake held over your head.

    It must take you ages to eat breakfast.

  17. Robin Byron

    This particular photo reminds me of the outer surface of an abalone shell. That comes from spending a good percentage of your life in and around the ocean, I suppose.

  18. Holy Smokes! All these years, we could only dream of seeing asteroids so close up. I knew there’d be surprises. (Now, if one of them turns out to be a perfect cylinder, and its mass indicates it’s hollow ….)

  19. Elgarak

    It’s possible this asteroid is not entirely stable.

  20. Johnlt

    How do we know it is the south pole ?

  21. Duane

    It’s obvious what happened: God dropped it on the floor, called “three second rule!” picked it up and put it back in the pan.

    Serious question: What would gravity feel like walking around the edge of the flat spot? Would you feel it weaken / strengthen as you walked to different places (assuming you could actually walk there)? It seems like two people standing on different sides of it would perceive each other as standing at an odd angle.


  22. Chief

    re 15: Chris

    Oh great, now I can’t get the stay puft marshmallow man out of the picture… (or the martian from 5 million years to earth)

    With the comments, does this mean that the Dawn spacecraft has the ability to determine the elemental makeup of the body, ie laser spectro analysis or something.

  23. Infinite123Lifer

    This is a link Messier Tidy Upper provided above.

    Although this is a spectacular image it does not show the “equatorial banding”(i do not know if that is even close to correct on terminology) on Vesta. I cant get over the ripple marks which were described.

    On this articles picture (the flat pancake, Vesta’s odd bottom) there are the obvious ripple marks (of which Iam not sure what kind they are, I am still investigating), but if you look at Vesta from a different angle at the start of the link above from the first about 2 seconds to roughly 18-20 seconds there is like this incredible band of distinct equatorial “ripple marks?”, “gravitational squishing?” which covers almost about 1/3 of the entire surface in the center of the comet and then disappears as you head towards the poles.

    I count about 4 distinct “troughs”; the bottom equatorial band being the widest and slimming as they go up (from the youtube, DLR thingy portal). The band goes all the way around Vesta until it reaches that huge crater section and it appears that these bands stop.

    I am wondering if those distinct “bands????” are the results of the object trying to squish itself into a sphere and that because where the huge crater lies that equals missing mass, which means that perhaps it is not heavy enough to compact itself on that one side where the huge crater is.

    Actually now that I look at it again…..@ 25 seconds it appears that Vesta is missing a large portion of itself in the upper right hand corner, however I cannot tell if that is just from a lack of light or if it is actually “severely disfigured” on that side. Also, at about 1:54 into the Vesta show, it shows the (temp maybe, or core density, (I am still checking that)) and it appears from these images that perhaps Vesta is not missing a large portion of itself.

    Anyways, I just thought that those large equatorial bands were perhaps from Vesta’s attempt to squish itself. And if one side of Vesta is “really really”more massive than the other that the “ripple markes” in “Vesta’s bottom” could perhaps be some evidence of “squishing”. (oh man, I godda do some work on the lingo here)

    All in all it appears Vesta has some serious density issues…@21 Duane, perhaps God dropped it on its head one time to many.

  24. Infinite123Lifer

    I think the structure of Vesta’s strange crater is the result from a collision which left a crater and simultaneously created higher density material at the impact site. Over time Vesta’s gravity tried to squish it (as seen possibly in its equatorial region) but was unable to because it does not have quite enough mass. So this odd shaped basin or bottom formed from an object “just having enough mass and density to form a sphere, as it was doing, but not form one after losing enough mass in a colossal collision”, so in other words it got clipped during an important transitioning phase from an elipse type object to a sphere type object. Possibly, something smashed it pretty good just when it was about to “grow up” and become a nice sphere, leaving it at an awkward stage and injured on its way to becoming a sphere.

    Its my best intuitive guess is all.

    Volcanoes on Vesta?….I wonder if it is harder for an object to squish itself into a sphere gravitationally if it is cooled or solid from the inside out. I doubt it, you would think having a liquid core (though the same weight as if possibly solid) it would obviously be more malleable and able to form into a sphere.

    I do not think Vesta has a liquid core,(I am taking it that that implies that I am saying it does not have volcanic activity) due to the rigid and distinct banding at its equator. It appears to actually be just squishing itself. Or maybe it bumped something just right and scraped it away (I doubt that)…the mystery continues I suppose.

    Ok, also,the color images which I questioned as temp or density are probably not temp, since the surface temp is probably pretty uniform. Density, might be a little harder to discern I’am guessing. And I read that they are just different pictures of the different color spectrum put together.

    Thank you for your patience.

  25. lqd

    Why haven’t you posted about the new Space Launch System NASA announced, or about the impending UARS satellite breakup that the media is scared stiff about? I’ve been dying to hear your thoughts on those topics.

  26. Infinite123Lifer

    Or perhaps Vesta was once a much larger body. After an impact the less dense outer core blew off and the resulting Vesta was left to cool and harden. Having little time to “sphere itself” before it cooled (if it was semi-molten) and being comprised of different densities some areas cooled much quicker than other areas resulting in its odd shape with irregular patterns of banding.

    —On a funny note here—

    This is from the DLR Portal:

    “The latest 3D images, which show the whole asteroid, make something very clear – Vesta holds quite a number of challenges for the scientists on the Dawn team. “For example, we can see a very large impact crater in the south polar region, the likes of which we have never seen before,” emphasises Jaumann.”

    At first I thought they meant “JaaMan! We found something new “the likes of which we have never seen before”” but actually Prof. Dr. Ralf Jaumann is a person. :) :) :)

    JaaMan! Vesta is strange.

  27. Joseph G

    Does anyone know where I can get msyelf up to speed on this asteroid? I mean, I’ve read tons about Mars, but I’m sort of a Vestal virgin 😛

    Seriously though, one thing I wonder about dwarf planets like this is whether they ever had volcanic activity. Is heat from radioactive decay or tidal stress necessary for volcanism, or was there some stage in the early solar system when bodies like Vesta were still mostly molten? I know the moon once had volcanism, but according to the giant impact hypothesis, it would have formed from a cloud of molten debris no matter when whatever hit us hit us (and no matter how solid it was). Is there a minimum size cutoff for bodies to experience volcanism?

  28. Infinite123Lifer

    For #28. Joseph G. In the original article Phil posted if you click on “has been posted at the DLR website)” it will take you to the geology of Vesta.

  29. Joseph G

    @25 infiniteifer: Jah Rasta! Kiss me neck but I n’ I puppalick di beenie sinting lik a yabba and she got nah batty! It bex mi, yah nuh see?

    Edit: Wait, did you mean “jah” as in “yes” in German?
    I just thougt of that 😛

  30. Joseph G

    #29 @infinite123lifer: D’oh! I totally missed that. Thanks!

  31. Georgijs P

    Should’t the object be at least 800km wide to be crushed into a sphere? This might explain the reason to why Vesta isn’t a sphere. It was written in Wikipedia though so it could be wrong.

  32. This looks like a CG render. Notice in the full size image that the edges of craters are pixellated and blurry while the shadows within the craters are fairly sharp. This is a modelling error that happens when your texture is in a lower resolution than your renderer.

    I’m not sure this is a photograph.

  33. Joseph G

    @ Noel: Not sure if I’m looking at the same thing, but I think that might just be a compression artifact. Lossy compression methods always seem to leave more visible artifacts where color changes are slight. Actually, I think they may have just been a bit too aggressive with the compression slider when they saved that thing as a jpeg for the website 😛

  34. Steve Morrison

    @22: Have you seen this recent Straight Dope column about what it would be like to walk on a cubical world?

    As for the missing eyes, I suspect the smiley was just typed by some galactic newbie who left out the colon.

  35. @ Joseph: Look at the two larger craters to the left of and slightly below the peak. the colour of the asteroid itself is pixellated, yet the shadows are not. Then there are smaller craters all around that area where the lighting is on the wrong side.

  36. Infinite123Lifer

    This is in the NASA article when you click to envestanate:

    “Scientists are discussing whether the circular structure that covers most of this image originated by a collision with another asteroid, or by internal processes early in the asteroid’s history.”

    I am very new to this stuff, but that is plain-fully obvious.

    I take it that the DLR website clip of Vesta is completely CG?
    Is the picture of “Vesta’s odd bottom” slightly CG meaning a real picture but CG’d up?

    I know that the Hubble pictures go through a process before being released, however the photo that gives you the most “actual, factual” evidence should be the one that is released? should it not? It is hard to discern something from a fake….2 say the least.

    So the equatorial banding in the DLR website might not even exist?
    What a possible bummer.

    At least in Geology I know what I am looking at is a real picture…
    (that was below the belt, but well inside the Kuiper) :) I still Love the Universe!

    The ripples mentioned in the original article are still interesting.

    @32… Just thinking about the 800km to compress to a sphere…
    I would think it would have mostly to do with density rather size. Density of the material in relation to its surface area.

  37. Joseph G

    @35 Noel: Are you looking at the full-size image linked on the site? The compression artifacts are gone there, but yeah, I can see how the shadows do look oddly sharp.
    I just figured that this was caused by Vesta’s greater distance from the sun.

  38. Infinite123Lifer

    @35…If this picture is altered from its original and like you said

    “Then there are smaller craters all around that area where the lighting is on the wrong side.”

    I guess that would be obvious that it has been severely altered.
    But like the HB moon landing photographs and how they talked about the shadows.

    Vesta would reflect its own light and if the picture was taken over the course of “????more than 1 or 2 seconds???” (i have no idea how long of an exposure) could Vesta be reflecting some of its own light be the culprit? Or because of exposure time the shadows shift and when they put the image together…ahhh…. I suppose the light source is all coming from the same place, the Sun, (I got that right, maybe)

    i voluntarily digress.

  39. Joseph G

    Ooh, teh Wiki answered my question – Vesta IS thought to have had a molten, convective mantle at some point. Also, there’s a great animation in that entry, made from Dawn images.

  40. JMW

    @6 Nemo and @13 Brett…

    It’s not the Death Star. It’s the Happy Star.

  41. Ian

    I’m wondering if it was a very gentle impact. Instead of going *smash* you got more of a gentle *smoosh*, which would explain why everything’s so smooth.

    Especially if Vesta was very soft (mostly molten?) at the time. It reminds me nothing so much as a ball of clay gently pressed against a table.


  42. David in England

    @Ian: Coinciding with your *smoosh*, I wondered from the lateral lines if Vesta had met a larger object at say 20deg, slowly rolled up the larger object, but with enough inertia to leave the larger body’s gravity.

    If as you suggest, Vesta was still squishy, the larger object would be the clay table, and any mountain range on the larger object might cause the lateral lines, as well as serve to “flip” Vesta away…

    Just guessing, of course.

  43. @ 39 Infinite123Lifer
    “I guess that would be obvious that it has been severely altered.
    But like the HB moon landing photographs and how they talked about the shadows.”

    I’ve never seen a moon landing photograph that looked fake. All the previous vesta images look fine too, but there can’t possibly be any surface of vesta that is within the line of sight of these craters I’m looking at. Yes, Vesta reflects its own light, but I’m sure it can’t reflect that light into a recession in the surface. Another wierd thing is that all the craters on the right side while still pixelated, look fine as far as lighting goes, but as soon as you get to the right side you get craters that are being lit from the left and from the bottom. One large crater to the left and slightly above the peak has its darkest area at the top, but there’s one of those super-crisp shadows coming from the right. The Nasa site claims this to be a photograph from Dawn’s framing camera, but these lighting inconsistencies make that impossible.

  44. Infinite123Lifer

    I was trying to state that “some” people thought that the pictures of the Moon Landing were faked because of the way that the shadows were not parallel to one another, meaning there were actually 2 different light sources. We know that Earth cast a large amount of light on the moon, meaning “there were” 2 different sources of light. I wonder how much scattering light there could be out there. If Vesta was within range of another lightsource…? Jupiter? I know space is big and this is probably unlikely,but probabilities can be a funny thing.

    That is interesting. The shadows are not consistent with one source of lighting…unless there is some serious natural causes going on here.

    Noel said:
    “The Nasa site claims this to be a photograph from Dawn’s framing camera, but these lighting inconsistencies make that impossible.”

    I am wearied of NASA being said to contradict itself. Conflicting evidence is awkward. I know humans work there. These humans are supposed to be dually attentive to authenticity and the pursuit of truth, and I am sure a high majority of them are? Inconsistencies are part of the nature of what they do though, (there will always be inconsistencies with human based observation…(like mine, major) theirs minor, minute, pico-perhaps) but this is all very complicatedly put together, there are many aspects to the arrival of “just a photograph”, I am pretty positive of that. They say its a real photograph from Dawn’s framing camera and maybe it is with some touch up is all.

    I ll get to the bottom of this Vesta’s bottom.
    I am sure it is harmless.

  45. I’m not trying to make NASA look like they’re faking something. I have no doubt that Dawn is up there taking pictures of Vesta, and there are some really good shots, with none of these problems I’m pointing out. My guess is a communications error between whoever produces/recieves the images and whoever updates the website. Maybe someone actually made a model, and somehow the website guy got the wrong message and thought it was a photograph.

  46. Steve Brown

    Is that circular feature at the precise south pole?

    If so, has anyone shown this to Greg Bear?

    Reality stranger than fiction? You bet!

    Best wishes.

  47. Infinite123Lifer

    Noel, indubitably.

  48. Ganzy

    Scenario 1:

    Something big, hit Vesta head on. The resulting shockwave, from the point of impact, shattered everything before it as it propogated through Vesta. The energy of this travelling shockwave diminished as it headed towards Vesta’s equator/centre.

    The weakened shockwave ‘uniformly’ passes through both Vesta’s equator and centre. As the weakened shockwave progresses through and towards the concave limits of Vesta’s opposite interior, it becomes increasingly magnified (like radio waves
    hitting a satellite dish)

    This magnified lesser shockwave is then reflected back towards the shockwaves point of origin.

    Again, this lesser shockwave loses energy as it heads towards and across Vesta’s equator.

    As the reflected lesser shockwave re-crosses the equatorial boundary of Vesta on it’s return journey to it’s original pont of origin, it again starts to become magnified.

    Although diminished, this increasingly magnified ‘weaker’ shockfront races towards the focii of it’s original point of entry through the now shattered remnants of Vesta’s ‘south pole’.

    Even though the shattered material the shockwave is now passing through causes an overall damping effect on the shock wave itself, there is still enough energy contained within this diminished shockwave for it to try and punch its way out of Vesta’s surface.

    This it does, but quickly dispates leaving the large dome shaped protrtusion in the centre of the depression. If the original impactor had been much smaller, Vesta’s geology would have quickly absorbed and reflected locally the resultant shockwave, leaving a sharp/spiky central protrusion much like tycho’s.

    Scenario 2:

    Vesta used to be peanut shaped, much like hayakutake. If this Vesta peanut was spinning quickly on an axis central and perpendicular to it’s length, then centrifugal force would likely have concentrated heavier elements in one or other of Vesta’s ‘lobes’. At some point in time something slammed into one of Vestas lobes. This impact imparted enough energy to slow Vesta down enough for Gravity to overcome the centrifugal force and sphericalize Vesta. Ultimatetely Vesta became heated by impact energy, spherical and ‘Hardened’ before the heavier elements could migrate and find a common centre. This leads to a Vesta that is imbalanced and therefore denser and heavier on one side than the other. A small impactor slams into the ‘lighter’ less dense side of Vesta upsetting the weaker hemisphere’s structural ability to hold itself up, and it succumbs to the gravitational attraction of the denser other hemisphere and collapses.

    I don’t like scenario 2.

    Interested to hear the official outcome of this tale.

  49. Peter B

    Johnlt @ #21 asked: “How do we know it is the south pole ?”

    Well, us ordinary folk know this because NASA tells us.

    NASA knows because of the conventions of the Solar System: if viewed from below the ecliptic (the plane of the Earth’s orbit around the Sun), if a planet or asteroid is rotating on its axis in the same direction as the Earth, then we’re looking at its south pole.

    In other words, if Vesta rotates in the same direction as the Earth, then its south pole will be below the plane of its orbit, the same as it is for the Earth. If, on the other hand, it rotates in the opposite direction to the Earth, then its south pole will be above the plane of its orbit.

  50. Peter B

    MTU @ #14 said: “According to that, Vesta spins in 5.342 hours – whatever that translates into minutes and seconds~wise. 5 hours 34 minutes 20 secs maybe or am I missing something?”

    You’re missing something.

    In this case the decimal expansion is exactly that: decimal. So it’s 342/1000 of an hour, or 0.342 * 60 minutes. In other words, a little over a third of an hour.

    That means the length of the “day” is 5 hours 20 minutes 31.2 seconds.

    Does that make sense?

  51. ethanol and others: I think this is a composite of several framing-camera images, possibly overlaid on the new shape model. The object in the middle of the southern-hemisphere crater is a peak that sticks out; it ought to be shadowed on the left side, like the rest of Vesta, but it’s not.

    Vesta is now in a relatively low orbit and its images don’t cover the whole asteroid. It makes sense that one would be pasted together from several images.

  52. Stu Young

    Simple. Vesta is an ancient, nuclear-pulse propelled spaceship. The flattened “bottom” is where the nuclear pulse units were detonated. 😉

  53. Damn it, now I’ve got that “Bunny with a pancake on its head” image in my mind.

  54. reidh

    more pictures than that!


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