Amazing close-ups of comet Hartley 2!

By Phil Plait | November 4, 2010 9:37 am

Just an hour ago as I write this, the NASA spacecraft EPOXI passed just 700 km from the nucleus of comet Hartley 2! The flyby was successful, and it took incredible images of the comet’s solid heart:


Wow! These images are in order of approach (left to right, top to bottom), as EPOXI flew by. We knew from ground-based radar that the nucleus wasn’t round, but these pictures clearly show it to be shaped like a peanut. That’s not too surprising; this shape is common in asteroids and comet nuclei. But what detail! You can see the surface is irregular and contoured. There’s a groove of some sort on the left side, and what might be an impact crater or pit on the very left tip.

And those bright streamers of light? Those are jets of gas shooting away from the comet, formed when frozen material on the comet surface gets heated by the Sun, expands, and shoots away!

Amazing. And very lovely.

Here’s the fourth image a bit bigger:


Looking more carefully, weird things pop up. The round ends of the nucleus are bumpy and rough, indicating material is loosely aggregated there. But the waist looks smooth! There also appear to be bands of material circling the round ends separating the waist from the tips. You can also see what looks like a large boulder or spire of ice on the right side of the smooth section, poking up into the Sun. That’s a testament to the weak gravity of the comet; the nucleus is only about 2.2 km (1.4 miles) across, so there’s not much mass there. That piece jutting up is probably about a hundred or so meters high.

[UPDATE to note that there will be a live press conference at 20:00 UT (16:00 Eastern US time) where scientists will discuss these images. You can watch it live on NASA TV and on JPL’s Ustream channel. Also, Emily Lakdawalla has written her thoughts on the comet on her blog, too.]

And mind you, these are not the highest-resolution images! These are medium-res; even better ones will be coming soon. Trust me, as soon as they’re available I’ll have them here. I want to add that this part of the mission is a bonus; the mission was extended after the Deep Impact part back in 2005. Renamed EPOXI, it has gone on to do some amazing work in characterizing how we look for extrasolar planets. It was a very smart decision to continue this mission, and now we have these images and data, a whole new comet to investigate and understand.

Congratulations to the EPOXI team for a successful and amazing cometary encounter!

MORE ABOUT: comet, EPOXI, Hartley 2

Comments (122)

  1. Daniel

    That’s just awesome!

  2. Liam Bradey

    Hi Phil, brilliant piece. And so quickly written! The pictures are truly jaw-dropping. And how wonderful that the whole world is able to view them, just under an hour after they were taken 13 million miles away. Saw the impact crater on the left tip straight away too. As always, fantastic work.

  3. That very smooth looking band around the waist seems weird. With the rest of the surfacelooking as rough as it does, the contrast is remarkable.

    Any idea what is next instore for this valliant researcher? Will it be deep space oblivion or something more fitting for this knowledge gatherer?

  4. Wow, that’s amazing they could get that close and take such a great picture!

  5. Looks like a turkey drumstick for the gods.

  6. Tom

    Very cool! I can’t wait to see more images from this.
    They got a much better view than I did from my backyard. —



  7. J. D. Mack

    Totally fake. There are no stars in these photos!

    Nah, just kidding. These images are awesome! Can’t wait for more.

  8. The waist reminds me of Chang & Eng Bunker’s abdominal connection…
    A Siamese Twin Comet!
    What surprises me is the lateral size of the waist. The ends must have solid protuberances in there that are holding them apart. Or perhaps there’s a smaller rock in there that’s covered by the looser dusty material. Great photos!

  9. James Morasco

    That’s got to be the biggest fried drumstick I have ever seen.

    Now I’m hungry.

    Thanks Phil.

  10. Nick

    Why is the peanut shape common among asteroids and comets? Does it have something to do with “centrifugal force” of the comet/asteroid’s rotation?

  11. Sir Craig

    Wait a minute – where are all the crystal spires and structures? This looks nothing like the comet from Armageddon! I call fake! Like J.D. Mack asks: Where are the stars?!? This is nothing more than a liberal attempt to get us to spend more money on useless space projects!

    [/conspiracy loon rant]

    Seriously, these are very cool pics, and I cannot wait for the higher resolution ones. Even if there aren’t any crystalline structures…

  12. Messier Tidy Upper

    Wow BA, you & Emily Lakdawalla have both been lightning fast getting these posts up! 😉

    I’ve only just finished watching the event via NASA TV online.

    Well done – & my congratulations & thanks to the Deep Impact / EPOXI team too. Superluminous (beyond merely brilliant) work y’all. :-)

    Looks like a chicken drumstick or a bone I’d give my dog (if raw of course NEVER give cooked bones to them!) to me. 😉

  13. Mike Sperry

    could the smooth center area be due to centrifugal force moving loose surface material away from the center? judging by the sequence of images, it looks like it’s tumbling end-over-end. with the low mass creating a very small amount of gravity, even that slow of a tumble would be enough to cause material to migrate away from the center.

  14. Messier Tidy Upper

    BTW. Emily Lakdawalla’s blog post on this is here :

    for comparison, extra, etc .. if that’s okay to post as well. Hope it is, my apologies & please delete if not. I’m unsure of the right netiquette here..

  15. What kind of destruction are we talking about, if this H-2 hit central Texas , for instance .

  16. Tim

    I’m amazed at the work involved to get a tiny little craft within 700 Km’s of a small (relatively) Comet.

    I’d really like to know more about the smooth middle. That strikes me as odd. Odd and fascinating.

  17. Ray

    I wonder if the way to think about it is that the rocky ‘ends’ are the highlands, and the reason the waist is so smooth is that this is the gravitational ‘lowlands’ that the looser material has settled into if things get disturbed. Just like a mountain on earth has the rocky parts up top, and the sandy debris near the bottom. Even in that low gravity where the smaller debris floats around a bit before settling it just takes longer to get to the lowlands, but it eventually gets there.

  18. Pshaw

    The middle portion of the comet isn’t really smooth. It just LOOKS smooth. That’s exactly the way you would expect it to look if NASA was photoshopping the image to hide evidence of an alien civilization living on the central regions of this comet.

  19. Grand Lunar

    I’m surprised how similar to an asteroid Hartley 2 appears!
    And to think these are medium-res! I wonder what details high-res can reveal.

    I wonder if a Plymouth Rock mission can reach a comet like this…

  20. Oscar Ferro

    Wow indeed! I never imagined that a cometary nucleus could be imaged in such detail. I always thought that it would be shrouded in its own emanations.

  21. Calli Arcale

    Ray — that reminds me very much of what we saw in the “saddle” of 433 Eros when NEAR visited. Material slumped downhill into the saddle. It wasn’t this smooth, though, I don’t think. I can’t wait for the high res pics to get a better look!

  22. katyfrog

    Very cool thanks for the Pics

  23. Messier Tidy Upper

    @15. Tim :

    I’d really like to know more about the smooth middle.

    See how bone shaped it is esp. in those first two close-approach shots?

    Well it must have been chewed by a GIANT space dog mustn’t it! Its the only explanation – the *only* one I tellz ya! 😉

    Let’s just hope it doesn’t want to play ball with our planet! 😉

    … Unless could it be the skeletal, vacuum mummified corpse of a starwhale instead? 😉


    PS. Just seen you’ve already linked Emily Lakdawalla’s blog post on this too which I’ve got on a comment now awaiting moderation. Ooops. [Sheepish.]

    Sorry I’m about three-quarters asleep here now – 3 a.m. in my timezone.

    PPS. The Discovery launch countdown clock is now at T- 1 day, 2 hours, 35 minutes & 55 seconds with a 60% chance of acceptable weather conditions in case anyone’s curious. :-)

  24. Bubba

    What are the dimensions of this nucleus?

  25. Les Doerfler

    I think it looks quite a bit like the Satellite Of Love from MST3K. I’m awaiting comment from Deep 13.

  26. … small step for man….thank you nasa & epoxi team!! breathtaking pics!

  27. Jason

    Very cool images.
    @18 I would guess that the overall density of the gas jets is extremely low, even right at the surface. Its just the total amount and distance that make it seem so thick to observers on Earth.
    Also, is there any data on just how Fast the gas in the jets is moving or any way of determing that from the data that was received?
    And on a related note how much Thrust is applied?
    I am guessing

  28. kurt_eh

    It’s a bowling pin! 😉

  29. Messier Tidy Upper

    @24. Bubba asks :

    What are the dimensions of this nucleus?

    I’m pretty sure they said its the smallest comet seen up close so far.

    Something like 10-20 football fields in size if I heard and recall right? They did say but, well, I was half asleep then and more than that now so could well be mistaken.

  30. BigBob

    Beautiful images. Emily describes what she thinks is a ‘contact binary’ where “Gravel and dust has flowed into the weird gravitational region between the two lobes, filling it almost as though it were a liquid”. That would explain the dramatic surface texture difference between the lobe ends and the connecting neck. Also the dumbell shape. I guess a mathematician could analyse the shape and model it’s formation to confirm/deny that it could have formed that way. Science eh?!

  31. jpsIII

    I’m honored to be able to view these images; they could only be imagined at the time I was growing up immersed in sci fi. I still might opt for the crystalline-palace real estate, if any is still available. Great job.

  32. Messier Tidy Upper

    This :

    may help with the size comparison for Hartley-2 although it doesn’t (yet) have this latest seen-up-close comet.

    The BA also discussed that :

    visited asteroids & comets to scale comparison chart of Emily Lakdawalla’s too. :-)


    Netiquette~wise : more links and comments are good, right?

  33. EdS

    The abrupt edge of the smooth area certainly looks depositional. Does it make any sense to consider that it originally was not there – that the two ends were/are pulled apart, perhaps slowly, in some way, and that the deposition is extremely low-density and unconsolidated?

    It will be really helpful when we know what its rotation is.

  34. natalie

    Thanks so much! Beautiful and fascinating.

  35. Pete Jackson

    As is often the case, the background in these photos is kept black so as to look nice. Unfortunately, this loses information (which is why astronomers would always use negatives to display images when I was a student; a gray background on a negative looks nicer than a gray background on a positive). But if you download and play with your favorite photo analysis tool to brighten the background, you will find gas jets shooting out the middle of the nucleus as well.

    And yes, #7 and #11, perhaps then you might even see stars!

    Thanks, Phil, for bringing these to us and in so timely a way.

  36. Bryan D

    That drumstick shape is pretty strange, it it because of melting and refreezing?

  37. AJ in CA

    I remember first hearing about the upcoming EPOXI fly-by and thinking “That’s weird, I don’t remember hearing about the launch of this EPOXI thing.” Of course then I looked it up and found out about Deep Impact and DIXI (this comet roundevouz) and EPOCh (the extrasolar planet work that the probe was doing while waiting for the rendevouz).
    Maybe I’m just cynical, but I found this to be even more exciting and amazing then these comet images! I mean NASA (and U of M) took a device that wasn’t even in earth orbit, that had finished its (already difficult) mission, and went and planned and accomplished two MORE with it, one of which wasn’t even anything like what it was designed for! This is Apollo-13-crew-return-caliber inventiveness, IMHO. Who says government agencies can’t be efficient? 😀 Seriously, this should be front page news on every American newspaper. Big ups to all the folks at NASA and U of M!

  38. Walter

    How is it that those streamers jet in all directions and not away from the sun? They also appear to be light sources themselves, not what I’d expect from “ice” being sublimated from the heat of uni-directional sunlight.

  39. Douglas Troy

    Amazing photos, can’t wait for the hi-res stuff, but I have to admit, I never thought it would have looked so strange; that smooth region in the middle just looks out of place.

  40. Major Mark

    Wow, V’Ger let itself go…

  41. AJ in CA

    @38 Walter: I could be wrong, but I believe they’re coming straight out simply because there’s no force causing them to bend. The solar wind is extremely tenuous, (keep in mind these visible jets are only maybe several hundred meters long), so it probably takes a bit more time for the jets to get swept up into the cometary tail.

    As for the jets appearing to glow, I think that’s just because they’re composed of water, ice crystals and vapor (like a white cloud directly illuminated by the sun) and they’re contrasting with the crust of the comet, which is typically a very dark, carbonaceous material.

    Anyway, it’s most beautiful tuber-shaped thing I’ve ever seen 😛

  42. John

    I would venture the idea that the smooth middle section comes from the heat generated from the impcat of two smaller comets that begin to cool as the forces of gravity/centrifigal pulled the two apart.

  43. Nekura

    Why is the “peanut” shape so common? I would have though that random accretion would be uniform, creating roughly spherical objects.

  44. scott

    amazing saw it wed. night east to west in the horizon i’m in nh saw it earlier in the year also just amazing

  45. Keith Bowden

    I’m with Emily… the “ridges” around the “smooth” central portion have me fascinated. And what would this thing look like closer to the sun with the plumes in full bloom? I’m simply amazed. (Or to put it another way, “I’ll be superamalgamated!”)

  46. BJN

    Cool! Space Drumstick, nom nom.

  47. Smart1

    Amazing pictures!!! looks like God’s weapon

  48. Jeff

    these are insanely good images, including even the volatile jetting activity

  49. Matt

    The idea that the comet’s rotation would send material to the edges doesn’t work for 2 reasons. 1) the comet would have had to form and then start rotating. An impact could change it’s rotation, but that would pretty much knock all that loose material off. 2) The waist of the comet is still downslope from the knobby ends, so the material would slide toward the middle. If the rotation provided enough of a centrifugal effect to move material out to the ends, it wouldn’t stop there, it would leave the comet entirely. The contact binary idea makes a lot more sense. The rough ends of the comet are solid, and the waist is actually the loose material, which has settled into the gap between the original two bodies.

  50. Robet Gurskey

    > (Or to put it another way, “I’ll be superamalgamated!”)

    A Doc Savage reference, very good. I’m sure Lester Dent would be truly amazed by these photographs.

  51. 30. BigBob Says: “Emily describes what she thinks is a ‘contact binary’ where “Gravel and dust has flowed into the weird gravitational region between the two lobes, filling it almost as though it were a liquid”.

    This would make sense. The nucleus probably fractured in two at some point in its past but the two halves were still bound gravitationally, and fine dust could run “downhill” into the crack, slowly forcing the two halves apart. The two bands on the edges of the smooth area would be the original fracture line.

    This is fascinating!

    – Jack

  52. Captn Tommy

    It sure would be great if we could follow one of these to perihelos and see if the two ends pulled apart even for a few ‘Hours?’under the solar G influence, even though the separation might not be more than inches.

    This is from the touching binary comet remark in Emily’s Blog in PS site.
    (Read that post via the BA’s hotlink.)

    #48 Ken
    Emily mentioned the concentric ‘rings’ in the lobes, and processes to form them; compression and tension.

    compression: those lovely jets are excerting a force (see Newton, Issac). This seems to be longitudinal/axial (from the Pictures) for the most part. Vector Force over millions of years would probably couse some physical shaping to a relativly soft object (ice ball).

    tension: The sun has a pretty good pull and the dumbell shape, I might venture a guess, aligns heavy side toward the sun on its low pass. But you would have to do some fancy calculations to varify that. Again this is force over millions of years.

    think about it :)

  53. JohnW

    Wow! It looks like a sea anemone. Or maybe Cthulhu’s dumbbell (gotta keep those biceps from getting flabby).

  54. Wicked. Cool.

    @35. Pete: so I used my favorite photo analysis tool to brighten the background, I think you can see the jets spray area a bit more but the pixelation gets rather distracting….can’t wait for the real high-res images to come in!! (See for yourself:

    Comets are shaped like peanuts… they must be the solar system’s packing material. (Those things get everywhere!)

  55. Thomas Williams

    These are amazing and truly jaw dropping pictures. The EPOXI team has done an incredible job bringing these photos.

    Inspired by Matt, my best estimation is, that the waist consisting of loose substance could very well be mud or dust, creating the smooth shape of the waist by the gravity between the two major bodies. Looking closer at the small white asteroid body (possibly ice) circling the lower waist, its presence seems to create disturbances on the surface right beneath it presumably because of gravitation.

    A muddy substance could be explained by gasses in the form of fluids (because of the cold environment) mixed with dust. A fluid/icy surface might reflect the heat of the sun enough to avoid boiling, while a rough surface (as seen on the major bodies) would absorb the heat and melt the gasses inside the bodies with an almost explosive effect, when the surface temperatures rises.

    If the substance forming the waist consisted of dry dust alone, the shape would possibly have a surface shaped much more like the moon surface (assuming, that the comet body is occasionally hit by dust and tiny rocks). However, if the waist consisted of fluids alone, the heating of the sun would easily create much more violent waves on the surface?

  56. SordidEuphemism

    Looks like the whale-seeker from Star Trek.

  57. Thomas Siefert

    I for one welcome our peanut overlords…

  58. Koji

    I saw a similar piece in my KFC bucket the other day. I wish I had taken a picture of it. In fact it had a brownish color. Why is this black and white?

  59. Keith Bowden

    @50 Smart1 – Don’t you mean “Hammer of God“? [Arthur C. Clarke, 1993] 😉

    @57 JohnW – “Cthulhu’s Dumbell” – sounds like a great name for a band!

  60. khalse

    It looks like a poop that’s about to go Super-Saiyan.

  61. HP

    I’ve been thinking about this all day, and I just realized what those streaming jets remind me of: The sparkly exhaust from Flash Gordon’s rocketship in the old serials from the 1930s!

    I was looking forward to seeing these images, but I thought they’d be scientifically interesting but not nearly so dramatic. Comets hurling through space leaving a trail of sparks! This is straight outta Gernsback.

  62. @BaybeeTeaze♡ღ

    it looks like a giant bone
    ღRip HumbertoTorresღ

  63. owlbear1

    Way to spend my tax dollars!!

    Thank you!

  64. Neil

    Like another commenter above, I think it looks like a giant extra-terrestrial bowling pin tumbling through space. What I want to know is…where’s the bowling ball?!? Better keep watching the skies…

  65. Tom

    @69: “Where’s the bowling ball?!?”

    Hiding in the clouds of Neptune.

  66. Sean McCorkle

    It looks like what I pictured for the Musk Dogs’ Gristleship in Alastair Reynolds’ “Pushing Ice”, although not quite as ugly and missing bits of bone. The streamers only add to the effect: engines and thrusters!

  67. aaron wenger

    Years ago (1968) I wrote my thesis under Armand Delsemme on a high vac, low temp. try at constructing gas hydrates like Delsemme postulated might be found in comets. I was amazed at how the surface of the comet at this scale mimics the same surface structure that we saw on the gas hydrates at much, much smaller scale. Truly amazing pictures. I am saddened by the fact that my old mentor is now blind and cannot enjoy these last few comet missions visually.

  68. This is unbelievable!

    I love Emily’s contact binary theory. If it holds true, that means that we are looking at not one, but TWO tiny worlds, orbiting each other, connected by a natural bridge! Like two islands connected by a sandbar, BUT IN SPACE! If that’s not mind-blowing enough, it has geysers spewing gas into the void!

    When I woke up this morning, the idea of such a natural “contact binary” object in space was ridiculous. Now I’ve seen a picture of one.

    Thank you yet again, Science!

  69. Awesome post as usual. Could you explain to me where in the solar system this spacecraft actually is? I have looked around, but cannot find anything on that. Thank you!!!!

  70. ScottDogg

    I think it looks more like a shoe (viewed from beneath) than a peanut! I was actually making a joke that I’d see an image of a foot in one of the close-up images of Hartley 2 before I saw them, because I remember seeing an image of a hand in one of the images of Wild 2 taken by the Stardust spacecraft. It looks like I was right!

  71. Brian

    Incredible images and not even high res. I can’t wait for the high resolution images to come on line.

  72. Monkey

    Is it a perspective thing, or do those ejection plumes seem to be shooting out at different directions?

    Not sure if ejection plume is a phrase to cause astronomers to cringe….but im late for work and its all I got!

  73. Comet with a corset

  74. Anchor

    “But the waist looks smooth!”

    Indeed! I think that we’re looking at a ‘contact binary’ wherein the slight but constant grinding action over eons of time produces a grist of dust between the two bodies. The mantle of dust preferentially builds up and accumulates there and we see a smooth-surfaced “waist” between the two bodies that wiggle slightly with respect to each other.

    Also, the surface of the ‘bulbs’ that appear most active in jetting out gas look very much like certain parts of Temple 1, with what appear to be tall spikey spires. I hope that the EPOXI team is able to extract more detail out of these images to see those…

    This has been a beautiful encounter – looking forward to much more as the EPOXI team combs out all the data! An absolutely magnificent job!

  75. Oli

    @77. Monkey: They eject material in random directions, but the gas is then blown away by the solar wind. The bigger stuff (mainly dust) isn’t blown away so easily follows a more curved trajectory, following the comet’s orbit. That’s also why comets can have multiple tails.

  76. By the way – NASA has issued a call for proposals to collect possible further mission ideas for DI/EPOXI/?? once the calibration after the Hartley flyby is complete. This extension used most of the remaining delta-V, but orbit planners and their software are getting cleverer all the time.

  77. Brenna Toblan

    Hey Phil, my Physics students have a few questions:

    1. What are the odds of a person getting hit by a meteorite?
    2. How many meteorites actually survive to strike the surface of the earth every year, out of all that reach the atmosphere?
    3. What are the odds of an extinction-size event in the next hundred years?


  78. VJBinCT

    Holy cannoli! That’s what it really looks like.

  79. It’s not what it looks like. That pair of lions sits on a huge CUBIC BASE that’s painted black. There’s a lot more UNDER IT than there is showing. Also. We’re looking through a window glass taking this photo, and you can see someone standing next to the window at the left. ETs took this photo. I’m working at clarifying the details in this photo. Check out my wall at FB.

  80. It’s not what it looks like. That lit up canary sits on a huge CUBIC BASE that’s non-reflective black. There’s a lot more UNDER IT than there is showing. Also.

  81. dj

    it’s too bad they didn’t get photos when it grazed the atmosphere in early 1986. the orange & green sheets of flame across the small end were spectacular!

  82. TerraHertz

    Walter said: “How is it that those streamers jet in all directions and not away from the sun? They also appear to be light sources themselves, not what I’d expect from “ice” being sublimated from the heat of uni-directional sunlight.”

    Congratulations! One person here using their own eyes, instead of dogma.
    The answer is that they are not ‘jets’ of water from sublimating ice. They are corona point discharges, between the body of the (highly charged) comet, and the surrounding plasma environment. Thus the brightest points are the surface spots where the ion streams impinge on the comet surface. Also, why the ‘jets’ are much more linear than you’d expect from water molecules flying off in all directions.

    Notice that the points of origin do not correlate at all with the areas of solar illumination. Instead they are from ‘pointy bits’ – exactly as expected with an electrical discharge process.
    It’s a pity these images don’t indicate the direction of motion of the comet, solar wind direction, and sun (illumination) direction. The discharge orientations will be a complex function of highest points on the comet, and nearest distance to undisturbed local space charge- ie the solar wind. Mostly unrelated to heating by sunlight.

    Anyone interested in reading more, just google ‘electric universe’. Paradigm shift time.

    For instance, the findings of OH radicals near comets is not due to water being emitted then broken down by solar UV. It’s due to oxygen being electro-sputtered off the comet surface, then combining with H+ ions in the solar wind.

    It’s amazing, how doggedly the existing ‘outgassing icy comets’ paradigm hangs on despite so much contrary evidence.

    How can anyone look at those pictures, and NOT immediately recognize corona point discharges? Sigh. I suppose most people have never worked with high voltage systems, especially in vacuum, so they have an excuse. But still, NASA… it’s really sad.

  83. quinn

    wow. These photos will make a huge IMPACT.

    Now. If you’ll all excuse me, i’m off to ruin someone else’s comment thread.


  84. John Ennis

    It looks like a highly eroded remnant piece of layered media of a peanut shape. Note the planer areas at the contacts between the ends and waist. The waist being finer-grained material as compared to the coarser, agglomeration knobby deflating ends. In this case a piece of an ice mass from some larger mass.

  85. Anchor

    It’s remarkable that the nucleus subtended AT MOST only about 9.8 arc minutes ( 0.16 degree) from the point of view of the spacecraft at the time of the its closest approach. But it wasn’t displayed broadside to the spacecraft at the time, so that the angular size was substantially less than even this.

    If we were on board, it would have looked like a bowling pin with an apparent length less than a third the diameter of our Moon as seen from Earth. Imagine a real 15-inch bowling pin seen from over 438 feet or 146 yards away. It would been like looking at a pin separated from your position by the length of at least 1.5 football fields!

    Viva precision telescopic cameras!

  86. Anon

    Well observed [38. Walter].

  87. Luke Reid

    Has to be in the top 50 photographs of all time! Bravo!

  88. DaveZx3

    It has a very artificial appearance with design elements all over the place. The diameter at the “waist area” can’t be more than 600 to 700 feet given the overall length of a quarter of a mile plus. There could simply not be enough gravity in such small mass to influence the smoothness of this area. IMHO It looks like a piece of some artificial structure which broke off at some point and has been battered in outer space ever since. Look forward to the high res photos.

  89. The waist looks distinctly like what one would expect to see if the starting point for the structure had been a larger object that was composed of layers of differing matter. Exactly like the structure we see here on this planet. Ergo, stratification; a core of rough material, followed by a thick layer of dust and then finished with another, outer layer, of rough material. In which case I wonder if this was once a part of a much larger object, that has been hit and broken into smaller pieces.

  90. Alsee

    Considering that this was a bonus extended mission I think NASA should have leaned more heavily on the risk/reward ratio. Imagine if they had aimed for a 70km flyby, or even a 7km flyby? The high res photos would get ten or a hundred times better detail!

  91. @92. : I would think it makes sense that the side of the comet getting the most direct sunlight would have the most energetic geysers, and that these would show up as very bright regions in a CCD image from a spacecraft’s cameras (set to give the “right” amount of exposure in visible light at that speed of passing.) I would also think that the geysers would be emitting streams of highly-reflective icy particles strongly enough that they would overcome the force of the solar wind at first for quite some distance, before settling into a cloud around the nucleus due to gravity (the coma?) and THEN being blown back into the comet’s signature tail once far enough away from the nucleus for the solar wind’s force to take over. This is my super-basic knowledge of space physics and comet behavior, and I’m sure there’s a lot more math and homework assignments involved, but it seems to make sense to me.

    I’m sure there’s electrical forces at play as well between the surface of the comet and the particles of the coma and the solar wind and all that, but not to the extent that you say we are seeing in the images above. :/

  92. One possible reason for the knobby rings around the waist might be that the dust layer insulates any surface activity beneath the dust, so the rings could be fumaroles forming right at the limit of where they CAN form. The roughness of the outgassing regions reminds me of the deepwater chimneys that form around hot water “smokers” (which seems analogous to what is going on here). In that sense, the boulder-like things (including the white monolith) could be the litter of chimneys formed from less volatile substances during venting episodes.

    Very much looking forward to what the corrected HRI images may tell us!

  93. ali

    this is not a comet.please nasa ,be honest.this is an artificiel structure.

  94. Anchor

    There’s nothing artificial in this object. It’s a comet nucleus. Its structure CAN be explained.

    One good scenario is that it is the result of a gradual merger between two icy rubble-pile-like bodies that were once in mutual orbit around each other – a binary. Episodic jetting of volatiles from them over billions of years gradually braked their orbital velocity and robbed them of their mutual angular momentum until they made contact (a so-called ‘contact binary’). Jetting since then continued to spin-down the tumbling rate to its current 18-hour period. Meanwhile, continued outgassing frees dust particles, some proportion of which are not ejected at escape velocity. Some of this material will loiter near the nucleus and settle back to the surface, preferentially accumulating near the comet’s center of mass near the contact point between the two original bodies.

    Episodic perturbations experienced by the nucleus (such as can be delivered by tidal forces exerted by close flybies lof Jupiter over its long history, which in fact has occured most recently in 1971 when it passed only 0.09 AU or 13.4 million km of Jupiter) can also have contributed to the apearance of the smooth mantle girdling the ‘waist’ by slightly jostling the two bodies with respect to one another, a dynamic action that can have ground material at their point of contact or otherwise redistributed material there in such a way as to prefentially sort objects according to size, burying larger objects like boulders while lifting small pebbles and dust particles to the surface.

    The apparent annular boundaries of that waist region may not be any more mysterious than a relatively smooth and straight shoreline on a beach. Those may simply be the places where the boulders begin to peek up their heads out of the dusty mantle.

    Read Emily Lakdawalla’s excellent interpretation on the link Phil provides: there she points out striking similarities between this comet nucleus’ topography and texture and other bodies (both in comets AND an asteroid – Itokawa) which have been visited by spacecraft. If Hartley 2 is ‘artificial’, consistency demands that ALL of these must be too. Yet few suggested they were when those images came out. Something that vaguely resembles a blunt bowling pin comes along and suddenly its got to be a piece of a UFO or something. Sheesh.

    If anyone sees this comet nucleus as an artificial structure, they must with equal conviction deny that nature is capable of producing a limitless number of examples of order out of chaotic conditions. You might as well consider the symmetry exhibited in snowflakes as exhibiting evidence of artificial origin.

    Science fiction stories are fun and may even exercise the imagination, but such an imagination is no match for an objective scientific attitude.

  95. Messier Tidy Upper

    @24. Bubba Says:

    What are the dimensions of this nucleus?

    Well, according to the updated wikipedia page for Comet Hartley 2 :

    Its diameter is estimated to be 1.2 to 1.6 kilometres (0.75 to 0.99 mi). … Observation by the Spitzer Space Telescope in August 2008 showed the comet nucleus to have a radius of 0.57 ± 0.08 kilometres (0.35 ± 0.050 mi) and a low albedo of 0.028.

    Hmm … Two different figures from the same source I see. Not sure if that helps or not.

    Mind you, its an irregular object so I’m not sure how their measuring there & whether that’s length or breadth. Or whether the DeepImpact fly-by has changed these figures significantly.

    Source for this to be linked separately to avoid moderation delay on this answer – but wikipedia Hartley 2 anyhow. :-)

  96. Messier Tidy Upper
  97. TerraHertz

    Studying the shape, and trying to imagine how it came to be that way, I can only make one observation that seems possibly worthwhile.

    It’s been suggested the body may consist of two prior bodies, come to rest against each other with the smooth waist then forming by infilling with smaller dislodged particles.

    Note the larger of the two lobe ends is resting on its long axis against the other end. This is not the minimum energy configuration. In effect it is ‘balanced on its end’. This geometry clearly could be maintained while the two bodies were orbiting each other closely (tidal lock), but once they touched, would it still be stable?

    It seems quite an interesting question.

    @102 J Major. And you’re very sure of that, so no need to try the search I suggested and read for a while, right? You do understand that electrostatic force is 10^36 times more powerful than gravity? (Based on Proton charge/mass; it’s even more for Electrons.)
    We humans intuitively ignore electrostatics, because we live in an environment in which electrostatic differentials rarely build up higher than a few KV, and even terrestrial lightning is relatively small change compared to what electrostatics can really do.
    But in space it’s very different. Low density plasmas exhibit some very strange behavior and charge on the whole, does NOT cancel out.

    Btw, for all the people assuming the ‘jets’ are from the brightly sunlit areas, pay more attention. Observe the overall lighting and shadow of the body, work out the illumination direction from that. Now, what are the very bright areas at the base of the ‘jets’? You realize some of those areas are actually in full shadow, but nonetheless they are still bright?
    Not just bright, but so bright they saturated the imager? (assuming the images haven’t been level-adjusted to hell by NASA, but I suppose that’s not a safe assumption.)

  98. paolo

    sembra che i gas emessi dalla parte rivolta al sole , ricadano in parte sulla parte centrale , determinando la tipica erosione della parte centrale.
    seems that the gas emitted from the part facing the sun, fall in part on the center, causing the typical erosion of the middle

  99. TerraHertz

    Wait… Is Hartley2 tumbling end over end? And how fast?
    If it is, then the two lumpy end bodies might NOT be touching at all, even now. They could be still locked in relatively stable tidal phase. The precise rate of tumble would answer this – is it exactly what would result in the two end masses having the separation they do?

    In which case the smooth ‘waist’ may not be solid at all, but effectively a dusty ‘liquid’, who’s shape is determined by the gravity gradient between the two solid end bodies.

    This would even allow the end bodies to still be rocking relative to each other slightly, though the dust ‘liquid’ would be providing some damping. But not much, since with such low gravity its density and viscosity would be very slight.

    This might explain why that bright, tall ‘spire’ thing just happens to be at the boundary of the waist and one of the end bodies. A large object, that got caught in the ‘liquid dust’ and because it had higher density than the dust it ended up ‘settling’ out till it rested on one of the solid end bits. Where it is now.

  100. Messier Tidy Upper

    Also see the NASA mission page for EPOXI here :

    & via typing ‘Hartley 2 size & dimensions’ into the NASA site search engine :

    Comet Hartley 2

    … Nucleus size (estimated): About 2.2 kilometers (1.4 miles) long Nucleus mass: Roughly 280 million metric tons
    Nucleus rotation period: About 18 hours


    & an closest approach image complete with scale bar showing that lengthways, Comet Hartley 2 measures 1.25 miles or 2 kilometers.

    So there you go! :-)

    [Assuming this passes moderation, can’t see any reason why it wouldn’t.]

  101. Messier Tidy Upper

    D’oh! Forgot to add the link to the last source there – the close approach with yellow ruler one – which is here :

  102. Messier Tidy Upper

    @24. Bubba : (One last time!)

    The NASA website – linked separately above & currently awaiting moderation – has a search engine and typing ‘Hartley 2 size & dimensions’ proffers a number of web-pages which give a size for the nucleus of about one and a half miles (just under) or 2 km long. :-)

  103. mharratsc

    Aren’t they supposed to be pointing Fermi at this comet as it goes by?

    Here’s a prediction: It will be generating copious x-rays. It also has a large radio signature.

    That will confirm the ‘Electric Comet’ model, and melt (pun intended) the dirty iceball/icy dirtball comet model.

    C’mon folks.. the same plasma physics that give us the plasma thrusters we’re using on these spacecraft are *also in effect on the bodies that we study!*

    Why is this so hard to absorb??

    Well- other than the 90 year old solar paradigm bequeathed to us by Eddington…

    Seriously- a 90 year old book sets the stage for our 21st Century observations of the physical forces at work in our solar system… very sad.

    IEEE Plasma Cosmology FTW~~

  104. TerraHertz

    “Why is this so hard to absorb??”
    Because almost no university courses in plasma physics exist, so very very few professionals have any understanding of it at all. Even most physicists don’t know plasma physics, and as for astronomers… ‘trapped magnetic field lines’ my arse.

    Also, because there’s nothing in our terrestrial environment that provides any direct experience with and thus intuitive understanding of plasma processes. Takes thousands of dollars worth of equipment before you can even create a contained environment in which to play with low pressure plasmas.

    Who’s even heard of Birkelund currents, and double layer charge barriers?

  105. MG

    Are high resolution images available yet? You said you’d update when they were, but I don’t see an update yet… Did we forget, or is NASA still just holding them close to the chest, as it were?


  106. Wayworld

    The comet pictures are amazing but I was waiting for the amazing announcement that EPOXI DISCOVERS THAT COMET IS AN ALIEN BASE!

    I couldn’t wait another 50 years so I enhanced what shots NASA has provided. See the comet as you may never see it from NASA.


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