CometWatch 14 February – flyby special

Four image montage of Comet 67P/Churyumov-Gerasimenko comprising images taken on 14 February 2015 at 04:32 GMT from a distance of 35.0 km. The image scale is 3.0 m/pixel and each frame measures 3.0 km across. The view focuses Hatmehit, the large depression on the comet’s small lobe. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Four image montage of Comet 67P/Churyumov-Gerasimenko comprising images taken on 14 February 2015 at 04:32 GMT from a distance of 35.0 km. The image scale is 3.0 m/pixel and each frame measures 3.0 km across. The view focuses Hatmehit, the large depression on the comet’s small lobe.
Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

On Saturday, Rosetta passed within just 6 km of the surface of Comet 67P/Churyumov-Gerasimenko in the first dedicated close flyby of the mission. The closest approach took place at 12:41 UT over the Imhotep region on the comet’s large lobe.

Four sets of NAVCAM images taken on 14 February were downlinked from the spacecraft yesterday and we are delighted to be able to share all four with you here today.

As usual, we present either a mosaic of montage of each image, noting that at the closest distances the combined effect of the rotation of the comet and the movement of the spacecraft between the first and last image being taken is particularly large, resulting in difficulties in creating an accurate mosaic. The montages have been tweaked in Lightroom for global intensity/contrast, but we have not made any local adjustment of e.g. ghosts/vignetting or other local intensity mismatches; the mosaic has been adjusted to fix boundary intensity mismatches. The individual frames are also provided here [as a zip file] to check features and to offer you the chance to create your own mosaics.

Four image mosaic of Comet 67P/Churyumov-Gerasimenko comprising images taken on 14 February at 14:15 GMT from a distance of 8.9 km from the surface. The image scale is 0.76 m/pixel and the mosaic measures 1.35×1.37  km across. The image focuses on the stunning features of the Imhotep region, on the comet’s large lobe. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0 Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Four image mosaic of Comet 67P/Churyumov-Gerasimenko comprising images taken on 14 February at 14:15 GMT from a distance of 8.9 km from the surface. The image scale is 0.76 m/pixel and the mosaic measures 1.35×1.37 km across. The image focuses on the stunning features of the Imhotep region, on the comet’s large lobe.
Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Four image montage of Comet 67P/Churyumov-Gerasimenko comprising images taken on 14 February 2015 at 10:15 GMT from a distance of 12.6 km from the comet centre (about 10.6 km from the surface).  For the comet centre distance, the image scale is 1.1 m/pixel and each frame measures 1.1 km across. In this orientation the view is across the ‘back’ of the large comet lobe, with the ‘neck’ and the small comet lobe towards the top of the image. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Four image montage of Comet 67P/Churyumov-Gerasimenko comprising images taken on 14 February 2015 at 10:15 GMT from a distance of 12.6 km from the comet centre (about 10.6 km from the surface). For the comet centre distance, the image scale is 1.1 m/pixel and each frame measures 1.1 km across. In this orientation the view is across the ‘back’ of the large comet lobe, with the ‘neck’ and the small comet lobe towards the top of the image.
Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

The closest images, taken shortly before (right) and after (above) the point of closest approach respectively, provide stunning details of the contrasting terrains that we have seen so far on the comet. Particularly notable in the image set taken at 14:15 UT (above) is the long, layered and fractured exposed surface at the lower left.

Towards the centre of the frame the faint outline of raised near-circular objects with smooth floors can be seen. In the same image, several angular blocks appear to jut out from beneath the surface. Boulders, ranging in size from a few metres to a few tens of metres, lie scattered across the whole surface of the comet. Here, in Imhotep, we see boulder Cheops towards the top centre of the mosaic.

Four image montage of Comet 67P/Churyumov-Gerasimenko comprising images taken on 14 February 2015 at 19:42 GMT from a distance of 31.6 km form the comet centre. The image scale is 2.7 m/pixel and each frame measures 2.8 km across. Rosetta’s parting shot following the close flyby features the comet’s small lobe at the top of the image, with the larger lobe in the lower portion of the image set. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Four image montage of Comet 67P/Churyumov-Gerasimenko comprising images taken on 14 February 2015 at 19:42 GMT from a distance of 31.6 km form the comet centre. The image scale is 2.7 m/pixel and each frame measures 2.8 km across. Rosetta’s parting shot following the close flyby features the comet’s small lobe at the top of the image, with the larger lobe in the lower portion of the image set.
Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

During the flyby, the spacecraft passed through “zero phase” angle – i.e. with the Sun exactly behind the spacecraft – offering extremely good illumination conditions. As well as providing the opportunity to take close-up high-resolution images of the comet surface, flybys like this also allow Rosetta’s instruments to sample the innermost parts of the comet’s atmosphere, or coma, to better understand the connection between the source of the observed activity and the wider coma.

Rosetta is now moving out for a far view of the comet – it will reach a distance of about 255 km from the comet centre tomorrow.

Download the 16 individual frames comprising the four montages/mosaic here, as a zip file.






  • DavidW says:

    That's so good Emily, thank you

  • Gerald says:

    Thanks a lot, for providing these great images!
    Glad, that the flyby worked as scheduled.

  • Phil Stooke says:

    Amazing pictures, especially the Imhotep set. Thanks!

  • Daniel says:

    The layers in the ~9km A frame are quite striking., although even at this distance you'd still like to have the magic TV show "zoom&enhance" function to take a closer look.
    There is a suspicious smudge at 740x 270y (with 0,0 in upper left corner) in the T1029_C frame, a close encounter with a dust particle?

    As an aside, any images that were taken at or close to the "zero phase" part of the flyby could give you a view of Rosetta's shadow cast on 67p. In essence an indirect self-portrait.

    • Harvey says:

      At 1AU, tye angular size of the sub is about 0.5 degrees, about 0.01 radian, around half that at 67P, say ~5mR

      If we take Rosetta as 3m across (ok, the solar panels are longer) at 6km, that is 0.5mR as seen from 67P.

      So I don't think the shadow will be any more than a very diffuse darker blob on a non uniform, very dark surface, and quite probably not observable?
      (The diffraction limit is much lower; it's the non point source sun that causes the problemz.)

      • Daniel says:

        Oh right, you are actually quite right in that, Rosetta was not close enough. Assuming I didn't make any errors in my quick maths check (which isn't a safe assumption) then you'd get something like a ~30m diffuse shadow cast on 67p. I'm afraid don't have an intuitive understanding on how visible that would make it but that's a very large area to spread it out on. The solar panels would have an apparent size larger than the sun disk I think? But only in one dimension either way.

        It just goes to show the problem with assumptions, thanks for pointing it out.

        • Harvey says:

          Well I was right it's a diffuse blob, but wrong about its observability; impressive demonstration of the OSIRIS dynamic range.

  • Kevin says:

    Thanks for these detailed images, the 14:15 mosaic shows some amazing layering details on the plateau (left - mid/bottom) and the dust further up.

  • dave says:

    Great images Emily,

    The pictures of the Imhotep region, from 8.9 meters on the 14th, has such a lot of detail, and from this angle it is much easier to see the topography, the larger circular raised feature at bottom left of the picture has always been difficult to make out, as the other pictures have been more or less overhead.
    Now with this picture we can see how high it is above the plain and the stratified nature of the structure, looking as if deposited at different intervals. There is also splendid detail of many other features all over Imotep.
    eg - Dare iI say it? it looks like rock, maybe we need a different definition of rock for low gravity, low vacuums.
    It does not look like dirty ice however and can anyone really believe that the hard surface is as thin as a sheet of paper from this picture, I don't think so.
    We also get to see some filled cups at the center of the image.
    On earth we might see this in boiling mud or I suppose from a cooling volcano source, But here this type of type of cup feature cannot fill with a liquid ices, as at the low pressure we will expect it to sublimate.
    I don't believe its just filled with dust, as the dust seems to move around and you therefore do not expect it to lie with such a flat surface as if water in a cup, you would expect it to be disturbed and maybe some blown out of the cup leaving humps of dust around the crater rim.
    Looking forward to any alternative views as to how these features have come about

    • Harvey says:

      i think in looking at pictures of 67P and trying to understand what is going on, the first thing you need to do is *completely suppress* any idea comparison to earth bound features.
      The conditions are so *radically* different, extremely low gravity, low pressure, hard UV exposure, cyclic heating, solar wind exposure when further out, etc, that the processes operating bear virtually no resemblance at all to those on earth.
      So visual comparisons are likely to do nothing but misslead. What it 'looks like' on earth is almost completely meaningless; you have to try and think ab-initio, from processes that do operate on 67P.

      • Sovereign Slave says:

        @ Harvey..."you have to try and think ab-initio, from processes that do operate on 67P."

        Fine Harvey, challenge accepted. In all of the speculations (and statements of fact) about sublimation accounting for the jets we see, one thing continues to strike me as inexcusable. Where are the references to actual lab experiments backing up the sublimation claims? We keep hearing about reputable pier reviewed papers alone being the gold standard when considering the relevancy of scientific propositions, but they’re not. The gold standard is replicable lab experiments. Take for example the paper for comet jets based on sublimation that’s often referred to which proposes a possible hypothesis for them ( It’s fine and reasonable to speculate about how something might happen. But that’s not science, that’s just speculation. In science, you take your speculation (hypothesis) and you develop experiments to test your hypothesis. Yet the authors of that paper didn’t do this, and as far as I can tell, no one else has undertaken a single lab experiment to test the hypothesis that sublimation can create the dust jets observed on P67. Even a very simple test of taking frozen volatiles, putting them in a sealed chamber, subjecting them to enough heat to fully sublimate, then measuring the amount of pressure increase and buildup would at least lend some kind of experimental reality to the sublimation theory. Is there enough pressure to blow dust at supersonic (or however you refer to speed in a vacuum) speeds or not? Which volatiles (or combination of volatiles) create the most pressure? When you add radiation to the heat does it create more pressure? Does speed of sublimation affect pressure? On and on. You don't have to replicate every condition on the comet to at least get some kind of scientific base line for what is being advocated. And perhaps someone has done this, but I’ve not seen anyone refer to it in this blog. And if not, WHY? It’s basic science. Anyway, if sublimation theory for comets has never advanced past the best educated guess stage, it has little to no true scientific standing, and deserves to be questioned with the highest degree of skepticism instead of being fully accepted with open arms and repeated as the de facto mantra/story that really explains comets and their behavior, much less their origins. So my suggestion is for all the sublimater's out their to run a few experiments before taking a hard line stand, or if that's been done already, to start backing up your talk with references to some basic science.

        • Kamal Lodaya says:

          Sovereign slave: Why don't these beautiful pictures evoke any curiosity in you? The reason is that there is no "electric geology". Since you have presupposed that the comet has been formed from the inner planets a few thousand years ago, you can always say this is like Earth and that is like Mars and keep quiet about new features like the goosebumps, because that is for planetary and space scientists to develop and you to borrow once it has been developed. The electric theory only has to postulate.

          • Sovereign Slave says:

            Kamal, nothing in my post above says anything about EU theory, which is after all, just a theory, though I think a more compelling one than is generally recognized by mainstream. My point above is this: for a theory like sublimation to be so strongly advocated, scientific protocol requires that there should have been a fairly extensive body of laboratory experiments recreating the required conditions for sublimation to take place on a comet (approximate at least) and that the results of these experiments show that comet sublimation as an explanation is at least possible. There are a huge number of unsubstantiated assumptions regarding comet sublimation theory and coma jet activity in particular. Recreating pressurized outgassing (various volatile gases mixed with a high proportion of dust) and having it escape through a hole in various materials that approximate assumed cometary materials would not be that difficult, and could quickly and no doubt easily demonstrate if sublimation is a viable comet theory or not. Yet as far as I can tell, not one single scientist has done this. And until it is done, sublimation theory is just abstract guess work and not based on science, and science which could easily be undertaken at that. Why it hasn’t been done is another question, but it seems exceedingly odd if it hasn’t been done. So again, if these type experiments have been done, please refer to them. If they haven’t been done, what is the basis for being so certain about sublimation, besides “What else could it be?” Also, I’d be interested to know from originalJohn or any other EU advocate what laboratory experiments have been done supporting EU theory around electrical sputtering accounting for what is being found in the coma.

      • dave says:

        Hi Harvey,
        I agree we can be fooled by just going by the photos, but that's all we've got in a lot of instances.
        Also your comment certainly applies if the comet was made slowly out in the cold reaches of the solar system.

        However its possible and its been suggested on the blog on several different occasions, with several different explanations, that the comet may have had a cataclysmic birth. This could be as a collision on a planetary body, or maybe an explosion from a planetary body or sun, or even as an an explosive discharge event on to some body.
        I know electric birth is not ok for you, so if we confine ourselves non electric sources then there are still a couple of other mechanisms.
        If we take our own moon as an example its said to be the result of a large collision of some type with earth. this cant be the only example of large collisions in our solar system.

        If this type of birth formed this comet then your comments may not apply. It could be possible in this type of cataclysmic event that much of the original source could of formed in a reasonable gravity and who knows maybe even an atmosphere.
        It may be at this stage we need to keep all of our mind and our imagination open, because it just maybe that our observations are more real than we realize.

        There has been plenty of unexpected data from the instruments all the way through this project, maybe its trying to tell us something.


        • Harvey says:

          The comet has a density near 0.5g/cc.
          It emits far more water than can be explained by any other mechanism, and the D/H ratio in that water is totally different to that in the solar wind. So the comet must be the source of the water, and given its temperature, must contain ice.
          These facts- and they are quite simply unarguable facts - confirmed times over, appear to be completely inconsistent with a 'cataclysmic' origin.
          Please don't bother with 'combustion', it's just too silly to be worth the time.

          • originalJohn says:

            " given its temperature must contain ice"
            An unarguable fact Harvey? Afraid not. An unarguable piece of flawed logic.

            "confirmed times over"
            Quite simply false. It has never been confirmed that any comet nucleus, including this one, contains ice.

            Pretty silly really, believing that so much water could be produced from nothing and then retaining such faith in the face of repeated lack of evidence. Worth the time. I don't think so.

            Now, combustion. Is it silly that all the reactants are there. And how silly is it that all the products are there. So it must be silly that the activation energy isn't there. But no, it is there, in abundance. And it can't be silly that it easily accounts for the quantity of water, regardless of D/H ratio. And not at all silly that it requires no ice, when no ice has been found.

            So which is the silliest idea? Ice sublimation or combustion. Let the readers decide.

          • THOMAS says:

            "given its temperature, must contain ice"

            On the contrary, Harvey. The first VIRTIS temperature data to be released showed an average surface temperature which was a huge "20 - 30°C higher" than predicted by the dirty snowball model. Nothing whatever in the temperature data indicates the comet "must contain ice" at all. Or perhaps I've missed something.

          • Lucas says:

            Any experiments on this? For the jet speed for example?
            I haven't found anything on the subjest... so still it's all speculation for 150 year old theory...

      • Kamal Lodaya says:

        Dave: Your views are coloured by hypothesized past events, which is why they are hard to take seriously. I have no idea how the comet was formed, violently or not. It seems reasonable to suppose that it has been going round the Sun for a very large number of orbits, and we are not viewing it at a very special point of time very close to its origin. This is the point of difference.

        You believe (without evidence) that these violent events happened only a few thousand years ago, this comet might have been part of Earth then. When someone says that things are different out in space, or that what looks like rock may not be rock, your beliefs force you to say that everything on the comet may be Earth-like, and things which look like rocks may be rocks. When someone talks about sublimation, you feel forced to add a response saying that no evidence of ice has been seen on the comet.

        The point about the Rosetta and Philae pictures (and other data) is that they are bringing in so much new information, and like many others, I revel in trying to understand all the new stuff, and not in plugging some pet theory of my own.

        • dave says:

          Hi Kamal,

          My point was, we can not take for granted that the comet was formed as the standard model says.
          There is plenty of evidence for collisions in our solar system, just take the explanation of our own moon as an example.
          I am not saying I believe any of these specific incidences as the birth of the comet.
          What I am saying is, this comet has defied many predictions, so people should open their minds and say why? and if the std model does not quite fit is there some other way that the comet could of formed? At least think about it.
          All I said to illustrate was that if this is a shard from some previous collision then it is not fair to rule out stratified rock because it can not form in low vacuum, low gravity, low heat in space - Perhaps it was not formed as the std model tells us hence that's why nothing makes any sense.
          That means we have to look at all our assumptions and test them against the data.
          For instance there appears to be a lot of stratified material on the comet, If its not rock , that's fine, but in that case how did it form, how was it deposited. If its a deposit of dirty ice, how did it get there.
          I don,t know the answers to any of these problems, nor do I understand why the existing model for comet birth is so sacrosanct, that we are not supposed to question it. This is the closest we have ever been to a comet and there has been a mountain of measurements made, so if we don't question the model that was made with scant evidence all that time ago with out all this data. When will we question it?

          • THOMAS says:

            @ Kamal Lodaya

            As for your assertion that “you believe (*without evidence*) that these violent events happened only a few thousand years ago”, I beg to differ as regards the supposed lack of evidence. If you knew a little more about the EU model, you would know that quite apart from its intrinsic scientific content, it also rests on the undisputed fact that many different primitive civilizations all around the world, with no possibility of having communicated between them, have left oral traditions and rock carvings portraying exactly the same events of warring gods in the sky hurling thunderbolts at each other. In Homer’s Iliad, the two main deities who take an extremely active and violent part in the battle for Troy are named Mars and Venus and these two planets, which no normal modern man can now even identify in the night sky, played a strangely dominant role in the daytime memories of our distant ancestors all around the world. As for the objective evidence for catastrophic upheavals on Earth in the not-so-distant past, I recommend the reading of Immanuel Velikovsky’s “Earth in Upheaval”, which presents a vast body of well-attested paleontological, archeological and geological evidence to suggest catastrophic events of extreme violence in the history of modern man.

            I repeat that I never believe anything “without evidence”, which is why I insist on believing the evidence of my eyes. As for the body of anthropological, literary, archeological, geological and paleontological evidence which tends to support a world-vision based on EU-style catastrophism rather than on standard theory Lyell gradualism, please do not claim it doesn’t even exist. It does. You will be perfectly free, once you have read up on it, to then deny its relevance in support of the EU model if you wish.

          • Kamal Lodaya says:

            Dave: Why can't we have sublimation and other mechanisms, maybe occurring at different frequency levels? Why can't we have stretch theory, as suggested by some on this blog? The answers to these questions will be fought over in research papers once people have access to all the data, and over years we will come to an understanding of how what you call "the standard model" is to be refined. It would be good if we understand comet birth from 67P, but I would not be surprised if we do not learn anything new on this question. From the pictures we are seeing now let us try to understand what is going on there now, because that is strange enough and requires all our effort.

        • THOMAS says:

          @ Kamal Lodaya

          I am actually the one who originally expressed most of these ideas. I say this not to rob Dave of any credit which may be due to him but simply to set the record straight and not leave Dave with the burden of having to defend ideas which he does not necessarily share with me...

        • THOMAS says:

          @ Kamal Lodaya

          Regarding the substance of your comments, I will simply reply that I have always preferred to believe what my eyes are telling me rather than what I take to be a falsified theory is telling me to believe. When something on 67P looks identical to rock formations observed in many places on Earth or Mars, down to the tiniest detail, I find it impossible to believe I’m actually looking at cleverly disguised ice. And “when someone talks about sublimation”, I certainly don’t “feel forced to add a response saying that no evidence of ice has been seen on the comet”. When I and others state that “no evidence of ice has been *seen* on the comet”, we are simply stating the facts as they have actually been announced by the mission researchers themselves. It is objectively true that not a single tiny scrap of ice has yet been observed on the comet surface. What is irrational about putting credence in these observations?

          • Sovereign Slave says:

            Can't help but consider the irony that if something did reveal itself as looking like ice, I can't help but imagine that the sublimation folks wouldn't immediately declare that as clear evidence of ice. Also ironic that what obviously appears to LOOK like dust on the comet, EVERYONE seems to agree is dust, yet what obviously looks like rock, can't be rock. So if you believe in the sublimation theory, what looks like ice is ice, what looks like dust is dust, but what looks like rock is definitely not rock. Hmm

          • Kamal Lodaya says:

            Thomas: Sometimes the EU proponents talk about logic, and when flaws in their arguments are pointed out, they retreat to saying we will only believe what we directly see.

            There is a picture called "Icy alcoves?" which has been put out by ESA researchers. When this was pointed out, the response on this blog was: "So even if it is ice, and therefore it would be sublimating, it is insignificant to power the activity we see."

            I do not know the basis of that last clause, but I assume you are looking for icy oceans of some kind as the only possible evidence of sublimation. Yes, no one has seen icy oceans on the surface of 67P.

            Does this mean that the "dirty snowball" theory has been refuted and sublimation is ruled out? I think not.

            I don't have a problem with electrical activity happening on the comet. It is just that I don't see it.

  • Walter Van den Broeck says:

    I propose to integrate in each picture a blue car and the Golden Gate bridge in order to have a more intuïtive sense of the dimensions of the comet's landscape. These human artefacts should be toggable by a mouse click.

  • Bill Harris says:

    OMG. It's full of stars. Little wonder, then, that the Goosebumps have a ratio of 1:2:3 ... :n

    @ Rosetta Blog: "Rosetta is now moving out for a far view of the comet – it will reach a distance of about 255 km from the comet centre tomorrow."

    Good opportunity for a long exposure wide angle image of the inner coma... 🙂


    • Kamal Lodaya says:

      Bill: The scarps in Imhotep point to subsidence happening on the plain because of evacuation(s) happening on the right hand side. This may also match the scarps observed in Hapi. Do we have more evidence of such scarps due to subsidence?

  • Ivano says:

    Che spettacolo! Ma quanto carburante ha ancora Rosetta?

  • Sepp von der Olm says:

    Any sign of our friend Philae ?

    • Robin Sherman says:

      A great set of images Emily, thank you. Thank you to the NAVCAM Team as well.

      The hope was that a reasonably close up view from a different angle might reveal Phillae's hiding place. The only one of the 4 mosaics with a view of the landing area, is the one from 35Km. This is further out than the images we have seen where Phillae might be visible, so the chances of a definite visual identification are very, very slim.

      It is a view from a slightly different angle though, and includes the first touchdown site, Agilkia and a view of Phillae's journey almost from above, so I thought I would take a closer look anyway. No Phillae, but a candidate for the spot where Phillae grazed the comet with one foot after 46 minutes of her first bounce, might be visible. I would recommend viewing this video by Flug, made using flight data from Rosetta and Phillae together with Matthias Malmer's 3D shape model, in conjunction with the three images below.

      Extra conjecture, speculation, guesses, errors etc. are in the descriptions accompanying the images. I should stress that the flightpaths shown in the last image are not calculated, accurate or intended to be real, they are just to help visualise and aid understanding of the events of 12th Nov last year.

      • Robin Sherman says:


        Ignore the second image, that is not Malmer's Mount. I have just seen Thomas's mosaic below and have clearly been confused by the overlap of images. The green oval is still correct though.

    • Klaus Neumann says:

      You will wait in vain on any sign of Philae on those prictutes taken from a distance from which one pixel is about two to three meters in sqare. Philae is not larger than one meter in the sqare.

      Far more interesting for me are the layers of rock as shown on one pricture on the left edge, which show, that Tschuri might be a big bolder of a erstwhile planet . Those layers are to be found in the Himalayas and Alps as witness of a plate tectonic activity.

  • Ivo Westerlaken says:

    Where is the ice?

    • Steve Kasian says:

      Everywhere. You're looking at it!

      • THOMAS says:

        You can apparently see things that nobody else can. The Rosetta mission scientists themselves have admitted they haven't yet seen a single tiny scrap of ice anywhere....

        • The snowman says:

          There is no ice visible on the surface because tha thas already sublimated. The ice is beneath the surface - its that stuff that's being detected as H2O, and CO and it streams away from the surface.

          And I should know what happens to melting ice in a vacuum!

  • JOHAN says:

    What a great navigator has ESA, pinpoint and at a distance o f 491 million kilometers. Thanks for the stunning pictures and that all for us on sunday. Great.

  • Elias says:

    Great to see this close flyby was a success. What was the speed of Rossetta relative to 67P during this flyby and was there any danger of striking particles released by 67P that could damage the craft or it's equipment?

  • Aga says:

    Hello! I find those photos really beautiful and I would love to use them for an art/fashion project. What is the licensing terms/copyright permissions for those?

    Thank you!

  • Rod says:

    According to Nasa site article "Deep fried icecream" referring to Comets. Amorphous ice turns to crystaline ice as it warms to 150 kelvin and expels PAHs.
    I presume , according to this that crystaline ice must be sublimating.
    If as has been suggested by ESA and others that some bright spots may be surface ice, and that the dust samples collected didnt have ice (implying that ice might be a possibility)then I assume from that information that it is considered reasonable that ice is not going to be sublimating on the surface. Then I just dont get it!
    Where is the energy for these jets coming from?
    Is it from the expelled PAHs maybe?

    • Gerald says:

      The energy for the jets is coming from the Sun, by heating subsurface ices of volatiles like water and carbon dioxide.
      Volatiles (e.g. water ice) contained in small dust grains are rapidly sublimating with exposure to vacuum, leaving dry dust. But with higher cometary activity grains containing ices might reach the Rosetta instruments before all ices will be sublimated.

    • Harvey says:

      Quite simply from the sun; the comet is very dark, it absorbs sunlight very strongly.
      PAH's cannot supply any energy; they are probably formed via UV induced photochemistry, and then just evaporate off.
      The visible surface seems to be a mix of rocky dust and organic 'muck'. The ice is (almost?) entirely hidden from view under this. Obviously the surface layer will become enriched in material that sublimes less easily. It is quite surprising just how well 'hidden' the ice is - but remember it only needs a very thin layer on top to do that.

      • dave says:

        Hi Harvey,
        It is surprising just how well the ice is hidden.
        To be honest I am astonished that at least some of it has not been exposed on the surface as a significantly sized patch considering the length of time we have been watching.
        Based on the model that we have for the formation of the comet we surely should have eroded the surface to expose an icy core somewhere, if its there of course.
        If the surface layer is as thin as a sheet of paper, how can it resist erosion for so long?
        Is it time to begin to look for a different method for the production of water in the Coma? After all the sublimation equation seems to have no left hand side to it.

        • Gerald says:

          To find out the exact way, how ices, rocks and dust are mixed, is certainly one of the interesting research objectives of this mission.
          Are there grains of pure ice? If yes, of which size? Or are the ices constraint to pores in the rock? What are the mixing ratios? How heterogenious is the nucleus? How is the distribution of organics? ...

        • Robin Sherman says:

          Hi Dave. There are likely to be virtually no large areas or volumes of "just" ices at any level in the comet. Around three quarters of the comet is actually silicate dust and the ices are mixed in with it. This particular comet is best described as an "icy dustball". The OSIRIS team have already stated the comet material is remarkably homogeneous, that is, extremely well mixed.

          The ices are trapped between all the tiny dust grains and dark organics. Bits of the surface where the dust has been recently removed will still be only slightly less dark, the more consolidated material underneath, although it may contain some volatile ices, is essentially dust coloured as well. It has been pointed out previously that even the areas we see as being "white" in the images are in actuality still very dark. In short ice at or near the surface can only be seen spectroscopically. One such determination, spoken about at the AGU meeting in December, examined some very "bright" newly exposed material and a figure of about 3.5% water ice was given. Examine the same area now there would probably be none, it should all have sublimated into the vacuum by now.

          Longer exposure of dust free sub-surface material, allows the UV and cosmic radiation to in essence "cook" the surface and increase the organics content through photochemical reactions at the surface, hence long exposed areas actually appear darker, because of the surface film of burnt organics.

          • Fabio says:

            3/4 silicates, "icy dustball"? Wasn't it 3/4 of water and "dirty snowball"?

          • dave says:

            Hi Robin,

            I can follow the logic Robin, but if the small sparsely distributed bright patches have 3% ice, Then there is not much to drive the sublimation especially if this ice is mixed with silicate dust so of that 3% only 25% of it may be available to sublimate to water, so this does not look a good bet for the volume of water being recorded. Of course any surface ice that is exposed through the organic surface layer would sublimate so it may be elusive, but the if the core is ice or even even dirty ice, it should just continue to sublimate, so ice should be visible on the surface as it sublimates exposing more ice as it goes as it goes
            The ice under the surface is supposed to accelerate gas to supersonic speed through a hole from a cavity of ice, but the diameter of the jets seem to be too big for the required small hole in the ground to be able produce a jet of the required size.
            However, I am still mindful of the Consert measurements, this instrument was calibrated in the lab on different mixes of dirty ice, but it did not find any on the comet as far as we know, nor did it find any of the cavities that are supposed to be present to form the high speed jets of gas and dust.
            All you need is an unambiguous source, how hard can that be on such an active comet?

        • Harvey says:

          The absence of visible ice has been a surprise certainly. Perhaps in hind sight it's not so surprising. It only takes microns of material to hide the ice, and refractory material will be selectively be concentrated on the surface.

          Sure, the ablation model has all sorts of problems, as I've often said.

          But there quite simply *is no other credible source of the water*. Suggestions it comes from the solar wind do not bear the most cursory examination. It just doesn't work. Aside from the quantitative problems, the D/H ratio in the solar wind and the degassing water are now known to be totally different.
          So, faute de mieux, it's sublimation, unless someone has a *credible* alternative.

          • THOMAS says:

            @ Harvey

            “It only takes microns of material to hide the ice, and refractory material will be selectively be concentrated on the surface.”

            Apparently not, according to the peer-reviewed "Science" article "“The organic-rich surface of comet 67P/Churyumov-Gerasimenko as seen by VIRTIS/Rosetta” published just a couple or three weeks back, in the conclusion of which F. Capaccioni et al. make the following unambiguous statements:

            “The compositional homogeneity of the surface observed by VIRTIS, despite the rejuvenating processes acting on the nucleus (at least on the active portion of it) at every passage close to the Sun, indicates that space weathering plays only a minor role in determining the observed composition. THE REFRACTORY COMPOUNDS SO WIDESPREAD ON THE SURFACE OF 67P ARE THEN REPRESENTATIVE OF THE BULK PRISTINE MATERIAL OF THE NUCLEUS.” (My capitals for emphasis).

          • originalJohn says:

            As I have pointed out before Harvey the D/H ratio varies throughout the solar system. It is not a constant. Yet the Sun and the solar system are held to have formed together.
            The solar wind proton/ oxygen from rock reaction is a recognised means of water formation in the solar system and should be considered. As for production quantity the model you cite fails to acknowledge natural current density increases that occur locally in plasma and is therefore not conclusive in any way. It is an attempt to minimalise the possibilities.

            I have also proposed an additional viable method of water production which does not involve the solar protons as a water constituent. The reactants and the products exist for a combustion process at the surface of the nucleus and require a small contribution from the proton energy for activation. In such a case the reaction sites and the jets would be hotspots and easily distinguishable from hypothesised cold jets of expanding sublimated gas.

            So the ice sublimation process is not the only option and it is not a viable option in the absence of ice. Very much a quantitative problem there. This has always been the case and is no different with this comet. There has never been any evidence to confirm either the presence of ice or that sublimation is taking place.

        • originalJohn says:

          Correct Dave and the nucleus is undergoing regular thermal cycling stresses. It is totally inconceivable that ice hidden beneath a thin crust all over the surface would have failed to break through at many points. Probability zero. Just wishful thinking among the faithful. The sort of thinking that has led to statements like no evidence of ice doesn't mean evidence of no ice. The same as saying no news is good news. In science no evidence is no evidence. So no ice until there is evidence. And no validity in talking about ice and sublimation with the presumption that they are proven facts until disproved. In the twenty five or more years history of comet flybys and now during the accompaniment of this one on its journey the only detection of ice has been on one nucleus, a few small patches of frost on the surface. That's
          it nothing else. Zero. No justification whatsoever for continuing the obsolete ice/sublimation story that was dreamed up when comets were just a light in the sky. So zero evidence that the comet nucleus is ice or contains ice and zero evidence that the jets are sublimated gas issuing at high pressure from vents. Just wishful presumptions. The only
          valid scientific statement that can be made about the jets from what is published so far is that they are of unknown composition and unknown origin. The shared story about ice and gas does not qualify as reality.

          You ask if it is time Dave to start looking for a different source of the water in the coma but surely with such a flimsy ice story to rely on we should have been considering alternative sources of water all along. There has never been any
          justification to do anything else. Unless we would care to admit that scientific deductions are based on belief and hope.

          When comets were distant and mysterious perhaps any explanation of them might have been acceptable but now we are fortunate to be there, alongside one with a craft bristling with measuring instruments. There is therefore an
          opportunity for a brief investigation to resolve the ice issue once and for all. Detailed measurement at high resolution is required of the temperature distribution in one of the jets or a group of jets, from the surface at the
          point of initiation to a distance of 1 or 2 kilometres. If the jets are the result of sublimated gas issuing at high velocity and high pressure from vents they will be refrigerated. If they are not refrigerated they are not vented high pressure gas jets. Problem solved and on to the next question.

        • Harvey says:

          There really is nothing surprising here. The surface layer is the more refractory, lower vapour pressure materials, so it doesn't ablate. It will be constantly renewed from the underlying material.
          What is surprising perhaps is that areas don't seem to 'flake off', leave temporarily exposed surfaces with more ice; but it only needs microns of material to hide the spectroscopic signature of ice. I've spent an awful lot of time on glaciers on earth where you see virtually no ice, despite standing on a huge thickness of it.

          Sure, as I've said many, many times, the ablation/sublimation model has all sorts of problems.

          But the other 'models' are utterly at variance with established physics and observed facts. They do not, pun intended, hold even a drop of water.
          Most recently of course we have an observed H/D ratio wildly different to the solar wind; yet further proof, not that any is needed, that a solar wind source is wrong.

          • Robin Sherman says:

            In a number of replies here it is stated that there is no evidence of Ice. This image is from the paper published by the OSIRIS team.


            A second image is included.


            I would also suggest rereading these two blog posts too.



            In short, there is evidence from the Rosetta science measurements, for Ice on the comet's surface, further added to in the AGU lecture mentioned above. The development of a measurable Ionosphere and its associated Magnetosphere, eliminates almost all interaction of the Solar Wind with the surface of the comet. In addition one crucial comment made during the AGU presentations was that the current activity from the comet can be accounted for by sublimation from around 1% of the surface area of the comet. Small patches dotted here and there, the large number of bright, exposed boulder surfaces all over the comet can quite easily account for this area. They may only contain small percentages of Ice, but the subsurface ice they are clear evidence of, can also be added to that, given the porous nature of the surface layers.

            As to the idea that sublimation has not been experimentally proven, this is just wrong. The triple point and phase diagrams of the volatiles detected in the comet's coma have been known for well over 100 hundred years and the topic of the sublimation of such volatiles in the presence of a vacuum can be found in any appropriate text book, there are several excellent pages on Wiki if you prefer. Ices and a vacuum are present at or near to the surface of the comet, therefore sublimation of these volatile ices to gas occurs. We can speculate as to how this process would manifest itself in the environment found at the surface of 67P, but the laws of Physics dictate that sublimation will occur.

            We now know this particular comet is not made of dirty ice. It is largely made of dust, or "dirt" if you like. The ice, organics and dirt are thoroughly mixed throughout the comet as the capitalised quote in Thomas's post emphasises. Those of us who have experienced snow and ice to any degree know that only a small amount of dirt can readily change the appearance of a pile of snow and ice.

            I can not argue that a material that contains probably 90% dust at least, at the surface of the comet is going to look much the same as "rock". If that material contains and is coated in a very dark mixture of carbon and organic material, it is likely to look even more "rocklike".

            Every rock we are familiar with on Earth has undergone erosion by wind, rain and chemical activity. On 67P there is no atmosphere to enable such erosion to shape the surface material, so how can it have the same appearance as Earth rock? The answer is simple, it is not the same material as Earth rock.

            The erosion is due to sublimation of the volatiles trapped within the material. Once the volatiles have all gone you are left with a pile of dust weakly held together by the organic "glue" making up about 5 to 7% of the comet material. Where there are more organics, the darker areas, the material is slightly more solid and resists erosion to a greater extent.


            In lighter areas, the material is broken down more readily, to smaller and smaller pieces. In the most active areas, the constant agitation by the moving gases, creates an even finer dust. The finer dust is able to settle to a less porous, more compact layer and as a result more able to restrict the diffusion of gases, thus building up a higher gas pressure below the dust layer. Higher pressure, smaller dust particles, means, faster, longer, denser, brighter and more collimated, dust columns.

            This is not special cometary physics, or interplanetary mega forces at work here. Those that insist that there is no ice anywhere on the comet do so because that is the only way to argue the requirement for these other postulated scenarios. In addition, for some reason, they feel obliged to continue to argue against a "standard model" that has already been proven, and accepted as being, erroneous. 67P has been shown not to be a "dirty snowball", a likelihood that was fully expected and admitted by the Rosetta science team long before Rosetta took a single piece of data.

            The Rosetta mission was sent to 67P to obtain the data necessary to construct a new, more accurate model for comets in general. That means all the data must fit that model, not just the bits that suit some pre ordained theory and then ignore or rubbish the rest that inconveniently disprove or falsify that theory. Which theory has been adapted, changed, reappraised in light of the data and which one has remained without evidence and its proponents ignoring, or refusing to accept, results and conclusions that don't fit?

            Isn't it time, as we have come to the end of the initial mapping phase, that we all accept that all pre arrival theories and scenarios were incorrect and base our speculation and interpretations on the hard data, what we know now, not prejudiced assumptions, opinions and dogma. The comet is not made of Ice and it is not made of Rock. For anybody to to continue to argue either case is pointless and irrelevant.

            It is a big pile of interplanetary dust stuck together with volatile ices in a ratio of about 3 or 4 to 1 and infused with some interesting organic compounds. In six months of close observation of the comet, no electrical discharges have been reported. Electromagnetic phenomena that have been measured and reported, have taken the form of ionisation by radiation and interaction of the Solar Wind/Solar Magnetic field with the comet's coma.

  • Rod says:

    Is the Rosetta craft capable of a soft landing on 67PChuryumov-Gerasimenko ? Maybe on one of the poles. Or at least risk getting up real close up for some almost macro photos.

    • space mud says:

      Well, That was the purpose of Philae.

    • AJ says:

      They've already said that Rosetta is not capable of making a soft landing, but that they might purposely crash land on the comet when Rosetta comes to the end of her mission/life cycle.

    • Gerald says:

      May be they'll do that near the end of the mission. It's discussed.

    • Harvey says:

      it would probably be possible to land Rosetta on 67P with a low impact speed; but pointless.
      It has no landing 'gear' and would certainly be damaged. It could no longer orientate it's solar cells to the sun or its communication antennas to earth, so would loose power and Comms link.
      Going close in is increasingly dangerous to the craft. There is also a great deal to learn about the corona around the comet, which needs Rosetta further out, and we want the craft alive as we approach perihelion to watch what happens.
      So concentrating on 'macro shots', close in - it's not certain they would show anything especially interesting - has to be balanced against keeping the craft safe and getting lots of data from further out. The balance is being struck with these occasional close fly byes.

      • logan says:

        What about saving some fuel from now on and stationing at L1 Lagrangian point when the party ends? Essentially extending mission until sun power allows?

        • Marco says:

          I'm with you Logan. Much better for the long term to find a stable parking orbit that tracks the comet. I wander if there is a dynamically stable area between the lobes of the comet at a duck-stationary orbit? If Rosetta could stay in touch, and Philae survives to a second perihelion that would be a great long term mission.

          • JP says:

            well, there are plenty of orbits available to be stable and safe for the comet.
            I guess a lagrangian point is kind of literally an utopia for a strongly elongated, irregular, mass-loosing body...
            Once running out of fuel, I guess the main challenge is maintaining contact with the ground, especially after going into hibernation for several years.
            And ESA staff do have other thrilling missions to monitor, even though they might seem more mundane in comparison.
            GAIA is for instance a quite boring one navigationally speaking, orbiting an Earth Lagrangian point 😉 to map the Galaxy...

          • Marco says:

            The L1 Lagrangian point has the advantage that 67P will always show it's lit surface. The L2 is problematic done to the unlit side facing. The L3, L4 and L5 points are irrelevant in this case. However, taking the two lobes as separate gravitational entities opens up the possibility of a dynamically stable area about 60' in front or behind the smaller lobe, but a few kilometres further away. This would be a difficult and dangerous position to get into, but once there, would stay there with perturbations feeding back in a tiny relative gravitational well. At least through Aphelion, where activity would not threaten.

  • J.H. says:

    I can't get any idea of the scale that I'm looking at....There needs to be a terrestrial image at the same distance and scale of a town or some iconic landscape area, so that you can form a mental image of what you are looking at.... Amazing pictures though.

    • Harvey says:

      All the images have the scale given in the caption. The detailed shot here is approximately 1.35km square.
      Adding some terrestrial object would be aesthetically appalling!

  • Thanks a lot, Emily, for these wonderfull NAVCAM pictures! The layer with dep verttical wall at the center is
    very interesting: what material could produce this kind
    of strucure without liquid water? Surely some Osiris picture should be usefull on this subject. But, AGAIN, no Osiris pictures have been released. It is clear that Osiris camera has some big problem, because it is absurd that, during the past 8 months, only few pictures cropped and of low resolution were released.

    • Robin Sherman says:

      The position of the Sun between Earth and Rosetta means that data transmission rates are currently very low. The higher data content of the OSIRIS images mean that they will take longer to download. Hopefully Holger will be able to pick a nice one out for everybody in a couple of weeks.

  • Kamal Lodaya says:

    J.H.: Here is a picture at roughly the same scale:

    An Airbus 321 is about the same size as the boulder Cheops.

    • J.H. says:

      Thanks Kamal.... Now that brings a bit of perspective back in......

    • Robin Sherman says:

      Excellent work there Thomas, thank you. Images 2 & 4 are the most interesting as they show large bits of the "Dark Side" we have only had glimpses of up until now. The difference in surface appearance of the Southern Duckiesphere is very stark. The pits and craters are not filled with dust, just lots of rubble and don't have steep, raised rims. Most surprising is the rapid change in the appearance, dusty and rounded to the left, bare and angular to the right. Both on the head and body lobe the surface is generally flat, as if erosion has removed most of the variability in the terrain. The back of the neck is similar, dark rugged and virtually dust free. The suggested 20m per orbit of lost surface does not seem to be unreasonable in light of these images.

    • logan says:

      Thanks Thomas. Your levels adjusted take shows 67P as a very angular astronomical object 🙂

    • emily says:

      Nice, thanks for sharing your links, Thomas!

  • seema says:

    Did you see Philae during this close flyby of Rosetta? Waiting to hear the news....

  • Michael Feuerbacher says:

    Thank god the weather was good and there were no clouds hanging in the way during the flyby!

  • Lucas says:

    I've just seen rosetta closest encounter. At 1:34 there is a diagram showing CO2/H20 on the surface. Is there really H2O found on the surface of 67p?
    movie link:

  • Chris says:

    Does anyone know what the approximate scale is on this picture?
    Eg. 1cm = ?? Or 1 pixel= ?

  • Iván García says:

    There's any chance of getting images of this affair from an earth based telescope? As a photographer looks pretty difficult to me, but seeing where have you send that gear, makes me think that maybe, is possible?

  • duckdiver says:

    I also don't understand the rock vs ice arguments. Understand a "Rock" to to be a piece of matter that has been seperated from a larger parent body.
    A chunk off of a lava flow would be a lava rock, off a glacer would be a water rock.

    • THOMAS says:

      @ duckdiver

      I think you'll find that in the discussions on this blog, "rock" is invariably used in its geological sense, as defined by Wikipedia:
      "rock is a naturally occurring solid aggregate of one or more minerals or mineraloids" (

      "Ice" or "water rock" is thus something entirely different.

    • Gerald says:

      The discussion is mainly about the volatile / non-volatile ratio in the subsurface.
      Rock / dust is mostly used in the sense of non-volatiles; ices for volatiles.
      Some organics are somewhere in-between.
      Rock in this sense is mostly composed of silicates, but there may be more exotic or "pre-solar" stuff like diamonds, silicon carbide, or complex organics from interstellar dust.
      Typical ices are those of water, carbon dioxide, carbon monoxide, ammonia, methanole.

  • Rod says:

    Great job on the mosaics Thomas

  • THOMAS says:

    I note with interest that during the official ESA video release on the flyby
    the commentator says of Philae’s unknown whereabouts (at 2:37):
    "We know from this image that Philae is in the shadow of what resembles a cliff or rocky overhang."

    “Rocky”, eh? She’s right, of course, but it’s not a term we’ve often seen or heard coming from ESA itself…

  • Luna says:

    I made a game based on the rosetta.

    Hope your guys like it

  • Robin Sherman says:

    Rod mentioned this article on the NASA website and I posted it earlier.

    Any amorphous ice making up the inside of 67P, the 70-80% porosity strongly suggests that is the case, would be buried some way below the surface, how far is not know, though I am sure the Rosetta science team aim to find out. Each orbit of the comet some thickness of surface is lost, the point at which the temperature is -150K therefore moves lower into the comet. A new layer of "chocolate covered ice cream" forms. That is a harder shell of crystalline ice is produced, with the organics and no doubt plenty of dust, expelled to the top creating a definite boundary.

    Large amounts of energy are released by the phase change, sub-surface gas and possibly liquids are created on top of the new crystalline ice layer. All sorts of scenarios could then ensue.

    To illustrate this speculative idea I have marked the layers we can see in the Imhotep image.

    Well defined layers are also visible in this image.

    Of course in 67P's previous more distant orbit the amount of surface loss was far less, so the layers would be thinner. The thickness of the layers would depend also on local surface composition, insolation and the thermal conductivity of the material below the surface and above the amorphous ice. Are these layers we see like tree rings recording the shrinkage of 67P?

    Not at all sure how viable this idea is, I am not even rating it as a theory, just a "maybe" put out there for discussion.

    • Kamal Lodaya says:

      Robin: Two possible ideas re layering: evacuation on the right hand side of the image leading to subsidence, or flow of (fluidized?) material from the left hand side. That CO and CO2 emission ratio against H2O is highest close to Imhotep region (noted by Bill) also may have to be factored in.

    • dave says:

      Hi Robin,
      Its nice to see some ideas I wish there were more original thought going on.

    • marcoone says:

      ok Robin, I add another "maybe" 🙂
      I'm not surprised to see areas stratified on an object that has behaved like a vacuum cleaner for 4G years.
      I guess I've gone through clouds of dust and gas, absorbing large bodies or nanoscale, of different nature and consistency; rather surprise me if it were uniform.

      The circular shape and concave great platform, and its edges stratified make me think of the not dramatic impact with another object (perhaps the same one that has moved the comet from its cloud and pushed her toward the inner solar system).
      An impact would have compressed and hardened the area, making it more resistant to erosion / subsidence / morphological transformation ... or whatever it is.

      • Robin Sherman says:

        I like that "maybe". You might expect such a bowl shape and stratification due to the pressure wave travelling through the comet. The fly in the ointment would be the large raised circular area bottom left. Such differential erosion to leave such a feature might be difficult to explain without a later smaller impact.

  • THOMAS says:

    I too am intrigued by the “long, layered and fractured exposed surface at the lower left” of the image showing Cheops which several posters have commented on. This is the clearest example of “layering” we have seen yet, since the layers extend in dead-straight “horizontal” lines for several hundred metres. When viewed in close-up (zoom x 5, for example), it becomes increasingly difficult to believe that these layers are made of anything other than solid rock, since they look identical to types of undisputed rock formations imaged on Mars, for example:

    What is also striking about the 67P formation are the series of aligned, juxtaposed drill-holes visible in many places in the cracks separating the layers (just as in the image from Mars, in fact, if you blow it up…).

    I’ve indicated some of these series of drill holes in this image, circled in red:

    It only shows a part of the layered feature: many more are to be seen in the other extended part of the layered formation.

    • Robin Sherman says:

      Hi Thomas. We have both commented on these black holes before. They must be the result of some sort of erosion process, most likely an internal one, but not necessarily. They appear all over the comet in all sorts of places, usually on exposed, non dust covered material, but not always.

      What I find striking is how they often appear in dead straight lines of half a dozen or more, each pit/hole of almost equal size and amazingly regularly spaced. It makes me think it is the nature of the more solid looking material that leads to them being formed in this pattern, but as to explaining what the mechanism is for making them, at this point, is open to conjecture.

      I would like to think they are the sources of smaller sublimating gas vents, but I have no evidence for that idea. Maybe tiny craters from impacting debris, we are lead to believe that near Perihelion pieces of ejecta might be metres in size, that might explain the linear pattern I suppose, the regular size and spacing so frequently, maybe not.

      Maybe aliens used 67P for laser target practice, given their similarity to the pits made by Curiosity's laser. 😉

      • Harvey says:

        The holes are indeed intriguing; though I'd like to see a statistical analysis, some lines look pretty convincing. However we'd need better image quality to be sure all the things in the line are the same phenomena.
        But let's assume they are real for the moment.
        Lines of craters have a name, catena, and are well known on a much larger scale.
        I wonder if some sort of slow motion, small scale version of the Roche limit breakup followed by impact mechanism could occur?
        Some sort of ejection, break up, re impact, on a small, slow scale onto a fragile surface?
        (Not Roche, some other fragmenting mechanism)
        No, I don't have any details, musing for once. One would need to find a systematic mechanism to give the thought any flesh.

        • THOMAS says:

          @ Harvey

          I’m also intrigued by a row of four circular depressions neatly aligned along the edge of a plateau just above Hapi Valley which were visible in the image on ESA's 22 January Cometwatch page entitled "More Change in Hapi?” I have highlighted them in this screen capture (Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0):

          It seems hard to believe that this neat arrangement could be the result of outgassing from subsurface ice. The arrangement bears more resemblance to the innumerable series of 3 to 5 perfectly aligned and juxtaposed "drill-holes" which can be seen in every image of the comet, at every scale, with diameters ranging from millimetres up to tens of metres. The circular depressions in this photo are clearly in the latter category and strongly resemble the rows of aligned, often overlapping "craters" seen in many places on Mars, as here:

          I also find it hard to believe this is a catena, since there is not the slightest trace of ejecta anywhere. The shallow sides of these Martian depressions are intriguingly scalloped, a bit like a cupcake mould. I suggest that both these features on Mars and the line of shallow depressions above Hapi Valley may be the result of electrical discharge machining (particularly given that the line of depressions on 67P are located in the most active area of the surface).

        • A.Cooper says:

          Harvey and THOMAS 

          I'm not too sure what these four craters are but since you mention some other fragmentation process I should cite these two 'rocks' as a precendent for such a process. They too are on the Site A amphitheatre and one has, without any doubt, drifted 170 metres across the crater floor.

          The other one probably did too.

          These two rocks drifted in a line parallel to the rotation plane. The line of four craters you refer to is also in line with the rotation plane. The only problem is that if a fragmentation process of this nature or any other nature took place, the rocks have since disappeared or sunk for some reason. 

          Also there are three less noticeable craters in the chain that dog-leg slightly and follow the rim. So I think it's more likely they have something to do with the nearby cliff. However, it is true that the four you cite aren't right on the edge like the others, are uniquely straight and are in line with the rotation plane. 

      • marcoone says:

        It would explain the presence of the monolith that is emerging at the center of the picture, perhaps the brother of TMA-1 (2001: A Space Odissey) 🙂

    • Jacob Nielsen says:

      I have a task for you THOMAS: Assuming you are advocating for the a it's-a-fragment-of-an-exploded-planet - or something the like theory, I have one question: Why would the layering or stratification follow the curvature of the nucleus? - as it does in your highlighted examples. If 67p inherited its layering from a significantly larger object, would the layering not only briefly be level with nucleus surface? Did you investigate the mutual orientations of the different "layered" sections - are they parallel? do they otherwise fit a "bigger object origin"?

    • Harvey says:

      It looks pretty much like Dobos Torte too; I reckon the similarity is just as relevant.

  • Robin Sherman says:

    We have in fact seen this layering close up in the CIVAS image of Perihelion Cliff.

  • Harvey says:

    This, of course, is not solid rock......

    It has no more relevance to what goes on on 67P than any musing about earthly features things look like; they are irrelevant.

  • Sol88 says:

    Pitted Terrain, Scalloped Edged, Terraced Crater

    Sublimation at it's best!

    Original image rotated 90 Degrees

  • Tim Burns says:

    We are still watching on the edge of our seats! The excitement has not dwindled in the least! Thanks for the stunning up close pics of our comet; as we await phileas's awakening and a whole nother, exciting chapter of the world's greatest space mission!

  • Harvey says:

    The 'reply' sequence seems a mess.

    Re D/H

    Whether the primordial D/H ratio was, or was not, uniform is of no importance. More than any other isotope pair D and H are subject to fractionation processes ; this is true a fortiori in the sun, where large amounts of D are both created and destroyed. What would matter is how much D,H escape.

    The important point is quite simply the observation.

    The solar wind contains virtually no Deuterium, as directly observed; I posted links to that a while back.

    The Rosetta coma is heavily enriched in Deuterium.

    These are simple, straightforward, observations.
    Therefore, one cannot be the source of the other.
    How that situation arose is irrelevant to that deduction.

  • Dave says:

    Thanks Harvey, I did see the article where you were asking for information, you were going to do some investigstion, if you did investigate, I must of missed it.
    As original john has posted a couple of times on d/h ratio, I guess it was a reply to one of your blogs.
    Anyway I can see your scrupulous logic but you still have nothing but a theory. It is so easy for me to say " no ice, no sublimation'
    Maybe we are both wrong, but neither of us can claim a proof until we get direct corroborating evidence of what we are looking for. All the maths in the world won't help ether of us until then.

    • Harvey says:

      I have an observation.
      Solar wind, almost no D.
      Comet coma, high D.
      Just how can one result in the other?

      • Kamal Lodaya says:

        Harvey: Some see this as validation for the Nice model:

        • Harvey says:

          That's really a separate issue; I think the models of the early solar system still have a long way to go, much to learn.

          My point is much simpler.
          There are those here who 'believe' (I choose the word deliberately) that the hydrogen in the coma comes from the solar wind, not from subliming ice.
          But the solar wind contains virtually no deuterium, and the coma contains a lot. This is very strong evidence one is not the source of the other.

        • dave says:

          Hi Kamal

          Re NICE model for comet formation.

          Its nice to see yet another model for the cataclysmic formation of comets - This seems rarely to be taken into account (even when the comets we see are so different to dirty snowball)
          However I posted a similar model about a week ago ref the theory that a planet exploded scattering debris to become comets and asteroids.
          Of course the EU model is also a cataclysmic model for the birth of comets..
          If only we had landed a human on the Comet we would know already.

  • THOMAS says:

    In an attempt to summarize the current state of play in the ongoing discussion about the respective merits of the competing ‘standard’ and ‘EU’ models, and reasoning “ab initio” (from first principles), I take the dynamic process at work for each of these models to be the following (but please correct me if I’m wrong):

    ‘STANDARD’ MODEL: Thermal energy from sunlight  heating of surface  outgassing (sublimation of sub-surface ices, liberating neutral gas molecules and entraining dust with them). The observed 700 metre/second jet velocity and the apparent merging and collimation of the jets are the simple results of heat and sub-surface pressure propelling the gas and dust into a vacuum. The effect of any putative electromagnetic fields is presumed to be null.

    ‘EU’ MODEL: Charge difference between comet nucleus and ‘solar wind’  electric discharge activity at surface (machining of silicates & production of both neutral and ionized gas molecules), with concomitant heating of surface. The observed 700 metre/second jet velocity is imparted by electric currents which, along with the ionized molecules, incidentally entrain neutral gas and dust. The jets are collimated and merge under the effect of the attendant spiraling magnetic fields. Thermal energy from sunlight plays no role.

    The striking simplicity of the standard model and its expectations are confirmed in advance in the mission-preparing 2013 Astronomy & Astrophysics article “Spin and activity of comet 67P/Churyumov-Gerasimenko” (, signed by Rosetta mission researchers J.-B. Vincent, L. M. Lara, G. P. Tozzi, Z.-Y. Lin, and *H. Sierks*. (Many thanks to Judy Hawkins for the pointer, in another thread, BTW!) Their aim was to use observations and data acquired by ground-based facilities during the previous perihelion passages of 67P in 2003 and 2009 to further constrain the “critical parameters” of “the spin orientation and the distribution of active regions on the surface” in preparation for Rosetta’s arrival at the comet. The presumed direct correlation between these two “critical” parameters is confirmed in the body of the article:

    “The spin axis orientation of the nucleus is a critical parameter for simulating the activity, and on a general scale for the whole Rosetta mission. It controls the illumination of the surface at different latitudes and whether areas *can be active or not*.” (my emphasis)

    In the light of these expectations, the VIRTIS temperature data shown during Fabrizio Cappacioni's presentation at the AGU Fall meeting thus seems to be now severely constraining this simple standard solar-energy-correlated-with-outgassing model, since it demonstrates (with ‘hard’ data) that by far the hottest and most active region of the comet nucleus, the neck region “Hapi Valley”, is precisely the area on the sunlit side of the nucleus which receives the *LEAST* thermal input from the Sun. See and

    The ‘EU’ model which, for its part, takes no account of the *thermal* input from the Sun, has no problem with this particular observation. In the ‘EU’ model, the reason why most of the discharge activity (jetting) occurs on the ‘sunlit’ side of the nucleus has nothing to do with the *thermal* effects of *sunlight*; it is simply the side of the comet which is exposed head-on to the *electric* input supplied by the so-called ‘solar wind’: it is facing directly towards the most active part of the electrically charged plasma sheath bounding the coma (aka the “bow shock” in standard theory parlance) which carries the greatest difference in electric potential (and exponentially increasing difference, as the comet approaches the Sun) between the net negative charge of the comet nucleus and the net positive charge of the Sun. If the EU model is valid, discharge activity may well also be observed on the “night-side” of 67P in the coming weeks and months (as it has already been observed in close-up images of the nucleus of Comet Hartley 2 acquired by “Deep Impact”s extended mission: If it occurs, it will be a sure sign of exponentially increasing electrical stress on the comet which can only be alleviated by increasingly extensive discharge activity from ever wider areas of the surface.

    It follows logically from all this that there is a perfectly simple acid test to determine which of the two competing models corresponds to the reality of the jetting phenomena being observed at the surface of 67P (a little like the ADN which, in a murder case, unfailingly identifies which of the two main suspects is the true culprit…): as Originaljohn has pointed out elsewhere, the simple detection of ionized molecules in the jets together with detectably higher temperatures, will conclusively prove the validity of the EU model and will, a contrario, falsify the standard model which, ab initio, entails *no ionization* and *cooler temperatures* in the jets.

    For my part, I would be delighted to accept that the EU model has been falsified if the data shows absence of ionization and of detectable higher temperatures in the jets. This data has necessarily already been collected. Are there any takers from the standard theory side to accept that the averred *presence* of these phenomena in the jets would falsify the standard subliming-ice model?

    • THOMAS says:

      In the two alternative processes described above, the symbol "" should be read as meaning "leads to". (My original symbol "-->", was somehow transformed in the publishing process).

    • Harvey says:

      The standard model does *not* predict no ionisation; it predicts a weakly photionionised plasma, already seen further out by Rosetta.
      The extent of Joule Thomson cooling will be limited as the gas rapidly becomes virtually collision less. Translation, vibration, and rotation may well not be equilibrated owing to the very different collision numbers for those to exchange energy. Which temperature are we talking about? R, V or T? MIRO has already demonstrated low translational temperatures from Doppler
      Night side activity is not inconsistent, it simply results from thermal inertia.

      Lots of interesting problems and puzzles, I'm pleased to say.

      A bow shock is NOT the same thing as a 'sheath' or double layer. It is NOT 'aka', they are totally different animals.

      EU would need to demonstrate:/explain
      Far higher ionisation levels
      Why is there no obvious spectroscopic signature (GLOW discharges mainly GLOW)
      Consistent magnetic fields
      Why the D/H ratio in the solar wind and coma differ drastically
      How the discharge accelerates neutral gas and dust in a very low density environment
      How you can generate enough O, what happens to the residual Si
      How you can conceivably sustain the enormous currents required to supply enough H
      How you manage the power issue if all the H is coming from the solar wind (far too much power deposited to provide enough H)
      How you deal with the very low sputter yield
      And about fifty other things.

      • THOMAS says:

        @ Harvey

        "Night side activity is not inconsistent, it simply results from thermal inertia."

        But it would be inexplicable on 67P in terms of simple thermodynamics since theA VIRTIS team has inferred the thermal inertia to be LOW. (See the first written comment on the VIRTIS temperature slides:

        • Gerald says:

          As yu can see in the image on the slide, thermal inertia is not that low in the active area.

          • THOMAS says:

            @ Gerald

            "As yu can see in the image on the slide, thermal inertia is not that low in the active area."

            This was precisely my impression too, Gerald, (particularly since I believe the comet nucleus is made of solid rock...), yet the caption "Thermophysical modelling shows that a low thermal inertia (<50 SI) is required to maintain these temperatures" seems to claim exactly the opposite. (

            So how do standard theory proponents explain these discrepancies/contradictions both in the crucial VIRTIS data itself and in the way it is being presented?

          • Lucas says:

            So why is it so high if it's mostly in shadow? Only this part of interia has warmed up? This make no sense...

        • THOMAS says:

          @ Harvey

          "Night side activity is not inconsistent, it simply results from thermal inertia."

          And if night-side jetting should indeed occur, I assume the inference will then logically be that the thermal inertia must, on the contrary, be very high (as if it were solid rock, in fact, rather than being supposedly 80% porous...).

      • originalJohn says:

        Replies to your listed points Harvey.
        -Nobody said a bow shock was a double layer. So as they are different concepts then a double layer can exist at the boundary between the coma and the heliosphere as it does and you can imagine your bow shock somewhere else.
        -how do you propose the "EU" demonstrate higher ionisation levels. The ESA have control of the investigation. Wait for the results and the explanation will follow.
        - who knows whether there is a spectroscopic signature or not. Do you.
        -It is a simple fact that plasma accelerates neutral material. Look it up.
        -Enough oxygen can be generated if there is enough proton energy, intensified by natural plasma processes, such as the double layer. A huge surplus of oxygen is available. The residual silicon ends up as dust, either on the surface or in the coma.
        -enormous currents are available in the heliosphere.
        - all the H need not come from the solar wind. All the H could be supplied by the surface hydrocarbons, therefore intrinsic.
        - you have transferred the concept of sputter yield from the lab bench to the unknown environment of the comet nucleus, where it probably has no relevance.

        And the rest Harvey?

      • Kamal Lodaya says:

        Harvey: Many (most?) comets have ion tails. They are said to be formed by interaction with solar plasma. Do they form later, after the dust tail, as the comet comes closer to the Sun? This has been observed, for example, for comet McNaught in 2007. Could it be that our instruments are better at detecting dust tails and poorer at detecting ion tails?

        • Harvey says:

          Kamal, in a sense Rosetta can't see either tail, because in is inside both of them. We see the source of dust tail as sunlight scattered from the particles being ejected. We see the source of the ion tail as the neutral gas which then becomes photoionised but the sun's UV, and the early part of its formation via Rosetta's plasma instruments. The shape of the ion tail is determined by the interaction of that plasma with the weak interplanetary field.

          Nothing I have been saying precludes an ion tail.

          The argument is over whether there are far more intense 'discharges' close in to the comet eroding its surface, and whether the solar wind is the source of the hydrogen in the coma. Despite many assertions here, there is not a shred of evidence either of these is true, and a great deal that they are not.

        • Kamal Lodaya says:

          Harvey: For 67P, the VLT saw the beginnings of a dust tail last August when the comet was more than 3.5 AU from the Sun. No ion tail seen. I do not know if this was because of poorer visibility of ion tails with an instrument like the VLT, or one can conclude that there was no prominent ion tail around that time.

      • Kamal Lodaya says:

        Harvey: Apparently ion tails are seen only when the comet is about 2 AU from the Sun, dust tails are seen from much further out. But this is only what I found in web search, not really authentic data.

        • Harvey says:

          The 'classical' ion tail is intimately linked to the formation of the bow shock. That can only form when there is 'enough' out gassing, so I guess somewhere between one and two AU might be about right typically.
          The dust tail doesn't have that 'threshold' process of bow shock formation, so provided enough dust gets ejected yes, it can be seen further out.
          (I'm not clear if *any* ion tail can exist before bow shock formation. Maybe.)
          But both tails are commonly seen together 'towards perihelion.
          What reference were you using BTW?

    • dave says:

      Thomas like you if the data shows a absence of ionization and of detectable higher temperatures in the jets I would accept that the EU model has been falsified.

      Roll on the data!

      • THOMAS says:

        @ Dave

        Glad to hear it, Dave! And particularly from someone who for months past has been objectively weighing the data as it has been trickling in. (I particularly appreciated your “balance-sheet” post).

        I'm now waiting for someone clearly committed to the *"standard theory" side of the argument* to make the same sort of statement with regard to the detected presence of significant ionization and higher temperatures in the jets which should logically falsify the standard model. (No takers for the moment…)

        Above all, I'm waiting for the pertinent data in the relevant fields to be finally released and commented on. In the meantime, the evident high surface temperature/low solar thermal input/high jetting activity anomaly revealed by the VIRTIS data in the crucial neck region (see and which I have attempted to draw attention to over the past few weeks has still strangely received no comment whatever, either from mission scientists or from the standard theory proponents on the blog.

        It's a waiting game...

    • Gerald says:

      Neither combustion nor exceedingly high proton flux to explain outgassing can occur.
      We have shown that patiently and repeatedly.

    • Gerald says:

      The standard model predicts ionization of the sublimated gas after some time by uv radiation. In terms of temperature this corresponds to several 1000 K. So a vague increment of temperature isn't very useful in testing the standard model.

      Near perihelion the solar irradiation is a little above 500 W/m². Take the insolated area of the nucleus as about 3km x 4 km = 12 km². Say 10 km² for simplicity. So we get about 500 W/m² x 10,000,000 m² = 5,000,000,000 W = 5,000 MW solar power for the comet, corresponding to about 5 large nuclear power plants.

      Mean sublimation rates needing above this power might challenge the standard model.

      • Gerald says:

        If icy fragments are ejected, add the area of their shadows on a plane perpendicular to the direction to the Sun.

      • originalJohn says:

        Well you big it up Gerald by considering a surface area of ten million square metres but if you are right about the 500 watts per square metre that is the heat of a very small domestic electric resistance heater spread over each square metre of surface and then there is all the depth of rock underneath, Billions of cubic metres to heat and very poor thermal conductivity. So at watts per cubic metre not so much heat getting to the interior after all..

      • Harvey says:

        Just a word of warning about the use of 'temperature'
        As commonly used, this is an equilibrium concept, in which all degrees of freedom have the same temperature. We assume a Maxwell-Boltzmann energy distribution. This requires lots of collisions to get everything into equilibrium.

        But in an environment like a comet coma, that simple, obvious 'how hot is it' question does not have a simple answer always. In the coma, at very low pressures, collisions become much less common.

        Take a coma molecule, water, carbon dioxide.
        It has a translational temperature, T;, a rotational temperature, R; and a vibrational temperature, V.
        But, if we take CO2, it has three different vibrational modes, one of them doubly degenerate (the bend) and actually these three can have quite different temperatures! So actually for we need T, R, V1,V2, V3 to describe it properly. Only if all five are the same is the simple commonplace idea of temperature valid.

        It only takes a very few collisions for molecules to exchange R, T energy; but it can take thousands of collisions, tens of thousands, for vibrational modes to exchange energy, and it depends on the mode. These temperatures can differ dramatically. To take an admittedly extreme example, in a CO2 laser discharge, T,R might be ~~400K, V3 a few thousand K (don't recal v1,2 - lower.)

        So one needs to take care with that obvious, commonplace idea 'temperature'. If, say, MIRO a measures the Doppler width of a line, it measures translational temperature; only. If we can measure the relative strengths of ro/vibrational lines, we can extract the other temperatures.

      • Harvey says:

        Gerald, you dropped a ten.
        10km squared is 100,000,000, not 10,000,000m^2
        So the final answer is 50GW, not 5GW.
        You can sublime an awful lot of ice with 50GW 🙂

  • A.Cooper says:

    The large, circular formation that THOMAS and Robin are discussing is the same size and near-perfect circularity as the half-dozen or so largest craters on 67P. It would therefore be reasonable to suggest that it used to be such a crater and that for some reason it had its rim removed along with the dust at its centre. In other words that it's been scalped. Certainly, from a distance it does look as though it might have been scalped. This scenario would have provided the mechanism:

  • dave says:

    'Kamal Lodaya

    Re 'Dave why cant there be sublimation and other mechanisms?'
    Sorry I missed your post to me.
    Of course there can be more than one mechanism for water to come from the comet, I have suggested this more than once.
    If there was some ice exposed to the surface why wouldn't it sublimate?
    The difficulty for both the most debated theories is;

    For sublimation, there seems to be virtually no evidence of ice on any of the comets we have seen nor have the instruments detected any, save for some very small patches.

    For the EU, very little data from the instruments on rosetta that could show evidence of plasma, current flows, temperatures etc have not yet been published. So There is nothing to give support to the EU theory either, save that we have evidence from the moon missions and lab experiments that there can be some sputtering to produce water (assumed to be the mechanism for water ice on the moon). However Both Nasa and Prof Harvey confirm that the rate of conversion is orders of magnitude to low to account for the water we see expressing itself from the comet.
    So seemingly at the moment both theories suffer the same problem.
    No where near enough ice visible to account for the sublimation and nowhere near enough sputtering to satisfy EU theory.
    There have been several other ideas on the source of the water besides these two theories posted on the blog, including a modified EU type theory from original john.
    So I agree with you it would be a surprise if just one method was responsible, the key question is what method will be the source of the bulk of the volume.

    Roll on some Data so that it can become clear.

  • dave says:

    @ Kamal Lodaya

    'Is the dirty snowball theory ruled out?'

    Yes it is! It has been stated by ESA in public that this is not what we have.

    apparently we now have a snowy dirtball - make of that what you will.

    I can see a dirty ball, but can't see snow.

    However sublimation has not been ruled out.


  • Daniel says:

    Probably just an illusion, but it looks like a spot is darker now than it was before. Seen in the 10:15 GMT NAVCAM image.
    Comparison with other views:

    ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

  • emily says:

    Just a friendly reminder to all commenters to please keep comments relevant to the original post. With the exception of a few comments here, we are getting a little off topic! This post is for comments and discussion relating to the close flyby. Any further comments submitted on an unrelated topic will not be approved here – please find an alternative post instead.
    Thanks for your co-operation!

  • Harvey says:

    Sorry, absolutely right. So sticking to the flyby.
    Do we know which other instruments were operating?
    OSIRIS and NAVCAM produce the pretty pictures, but what other data can we ultimately expect?
    Some instruments may not have been operable for 'safety' reasons ' close in?

    More generally, which instruments are 'mutually exclusive', not simultaneously operable? Can't find that on the web anywhere. Power availability, required spacecraft orientation, electromagnetic compatibility ((especially perhaps for the plasma and magnetic field instruments) etc must all constrain what can operate simultaneously.
    Is there any information on that?

    • Gerald says:

      Of what I've seen of this kind of operative information it's just too much to post in a blog. You've a complex schedule of overlapping instrument operation periods each day.
      You may assume, that observation and measurement intervals are defined in a fair way between the instrument PIs, as far as possible within the technical and mid-term mission constraints.

      • Harvey says:

        Gerald yes, I wasn't asking for the operational data; probably too dynamic. I'm sure there are some fun discussions on instrument prioritisation. Having sat on a good many program advisory committees (PAC) for instruments (on earth) with limited availability, I know all too well how difficult the assignment of limited time can be!
        My question related purely to the technical aspect of which are mutually excluded by, say, power availability or EMC issues

  • logan says:

    Such is the geological diversity that doesn't seem to be a lot of any exemplar feature. As Robin said before, what is regular on this comet?

  • logan says:

    Given all the textures and 'temperatures' of Imhotep, could bet the shot was with a near infrared filter 🙂

    • Harvey says:

      Logan. For NAVCAM and OSIRIS a images, there is no connection between temperature and choice of filter.
      Those cameras can only respond to wavelengths shorter than~ 1um because they are silicon based.
      At 300K, the black body radiation peak is at 10um and there is virtually no emission at all at 1um (or the world arround us would glow in the dark on CCD cameras with no IR block filter!)
      The pictures are from reflected incident light, not infrared emitted by the surface.
      VIRTIS a uses a HgCdTe array and *can* see the emitted infrared between roughly 1 and 5um. It is imaging emission on the short wavelength side of the black body peak, which falls very rapidly towards shorter wavelength. But it's resolution is much more limited, 341*550 pixels, by the technology of this type of detector mainly.

      • logan says:

        Thanks Harvey. Info you provide solves a painful doubt I had since following this mission.

  • logan says:

    Daniel the menace [comic strip] said that poetry is rap, without music. How can I put my mind ab initio?

    On relating to

    Would like to chat about the amazing geology of the beak.

    Seems that 'stream terraces' -when reactivated- are not 'terraceous' at all. Remember those old table games where a plastic circle floated over a pressurized layer of air? Dust/Sand travels stream down of this beak's structures, keeping core's material pores open by 'sanding', [exposing more 'waxy' material] and cascading at edge.

    Just bringing back fluidization to forefront.

    Logan's definition: 'Wax' is just smoothed, clean 'core' material surfaces. [To remain dust/sand free, the material has to be sublimating, actually].

  • logan says:

    Scales, on global comet shrinking those surfaces behave like scales.

    • logan says:

      That makes plausible big 'cathedral' inner spaces. First chatted by Alembe and Robin, if remembering well.

    • logan says:

      Those supposed 'cathedrals' then slowly refilled with depositions, ices, flows and crystals.

Comments are closed.