CometWatch – January Part 2

In this new NAVCAM view, taken 21 January, Comet 67P/Churyumov-Gerasimenko’s small lobe and its distinctive Hatmehit depression face directly towards Rosetta.

Enhanced Rosetta NAVCAM image taken on 21 January 2016 from a distance of 78.9 km. The scale is 6.7m/pixel and the image measures 6.9 km across. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Lightly enhanced Rosetta NAVCAM image taken on 21 January 2016 from a distance of 78.9 km. The scale is 6.7m/pixel and the image measures 6.9 km across. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

The Bastet region on the small lobe faces directly up in this orientation, with Ma’at immediately to the left and Wosret to the right. In the background, on the large lobe, a swath of smoother terrain – defining Aker, with Khepry beyond – lies between the more rugged terrain of Babi (left) and Anhur (right).

Parts of these southern hemisphere regions (to the right in the NAVCAM image) were also seen in spectacularly detailed images captured by Rosetta’s OSIRIS narrow-angle camera this week. For example, the image below was taken on 27 January as part of an extensive surface mapping campaign. The complete sequence is aiming for a large coverage of the southern hemisphere to be used for 3D shape reconstruction and composition maps.

OSIRIS narrow-angle camera image captured on 27 January from a distance of 71.4 km. The image scale is 1.29 m/pixel. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

OSIRIS narrow-angle camera image captured on 27 January from a distance of 71.4 km. The image scale is 1.29 m/pixel. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The relatively flat Aker surface can be identified to the right in this image, with Khepry to the top and Anhur towards the foreground. Sobek (centre) marks the transition towards the small lobe (left) where distinctive fracture patterns are clearly seen in Wosret (far left).

As we learned in the original OSIRIS release yesterday, the image also features two regions not previously mentioned before: Neith and Bes. The details of the regions and the locations of the boundaries are still under study (and precisely why images like this are essential), but broadly speaking, Neith lies between Wosret and Sobek on the small lobe, and Bes lies to the right of Anhur and extends into the foreground of this particular image.

OSIRIS narrow-angle camera image captured on 23 January from a distance of 75.1 km. The image scale is 1.37 m/pixel. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

OSIRIS narrow-angle camera image captured on 23 January from a distance of 75.1 km. The image scale is 1.37 m/pixel. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The OSIRIS team also released a striking new view focusing on the Khonsu region this week, at the boundary with Atum and Anubis (above). A variety of fracture-like features and layers are clearly visible. For example, zooming in close to the centre of the image reveals parallel sets of fracture lines that cross perpendicular to each other. On Earth and Mars this is often an indicator of ice that has contracted below the surface (see more examples and further discussion here).

Towards the right, long and near-parallel curvilinear features are evident and can be traced for some distance from the rugged terrain in the foreground to the smoother surface beyond. Understanding how features like these relate to the internal structure of the comet, and thus to the comet’s formation and evolution, is a hot topic for Rosetta mission scientists.

Meanwhile in the background of this image, much of the Anuket region on the comet’s small lobe is seen to the centre and left, with the transition into southern hemisphere regions towards the far right.

Catch up on recent OSIRIS images via the image of the day archive.

For help navigating the regions of the comet, see our comet viewer tool.

The original NAVCAM image from today’s CometWatch is provided below:




  • Ramcomet says:

    Thanks for such beautiful pin sharp Osiris images! Wow. Hope we can get close enough to see Philae!

    Second image down: the roughly kite shaped dark gouge at center - right looks uncannily like a negative impression from the similarly kite shaped, positive feature on the left.

    Did these surfaces "kiss"?

    • A. Cooper says:


      Here's my take. The yellow line on the head is your kite v that would kiss. Your match is the pink line. Mine is the yellow due to nesting topology of slid layers. The reason yours seems to fit too is that it's part of the same nesting.

      I think the orange kiss is even better. It retains the kink at the tip (see unannotated version in Part 30 now updated with this pic plus a bit more info).

      I think we agree it's not a question of if but a question of fine tuning the how.

      • Ramcomet says:

        A. Cooper,

        Agreed... and your different lighting angle is even more revealing. The great thing about having my own 3D model, (about $70 USD for a 2" x3"- very reasonably priced at many UPS stores, as mentioned earlier), is that you can have at the same time, any lighting angle and any viewing angle you need to see together, a particular 3D question....instead of poring through hundreds of images.

        Right now the best model is Mathias's (I think) ,but also know Rosetta team is building the best soon.

        When funds allow, I will, or suggest any serious player on this Rosetta blog dig deep, spend up to $500 for a much larger 3D model of the latest and most detailed 3D model available soon, that they are willing to cut up, and prove or disprove how these puzzle pieces, do, or do not, reasonably fit together to help prove or disprove Stretch Theory.. (Allowing some slight leeway for Erosion and twisting influences)

        I also applaud Soverien Slave's eloquently stated post below, beautifully said, and want to say in addition to his words how these "tortured" terrains exist as extreme types ADJACENT to one another between head and body!

        (That is not to say I am an EU proponent, and I am not sure he is these days but at least we have open eyes and open minds)

        Shame to leave out Stretch Theory as a viable candidate.


        • Ramcomet says:

          Whoops....Except I didn't mean to agree sublimation is not likely. I should have paid more attention to all of SS's comment.

          I do believe lots of things are happening, including sublimation, erosion, stretch., ejection. I did like the description he had of the terrain in his second to last sentence below..

  • Ramcomet says:

    Third photo down, check out that incredibly revealing cutaway view of the interior and possibly jet channels at lower right!

    Also looks like the large dark boulder at center broke free of substrate and moved to the right, even deforming the cutaway jet channels to curved ones.


    • logan says:

      Hi Ram. Quite exposed 'guts', doesn't it? 😉

      Body's front-stage erosion, seen as single feature, looks like a big serif "V" subscribed by a global horizontal, parallel lattice...

  • dave says:


    The first picture looks like there are a series of cow pats slapped on to the the top (top in this view) of both large and small lobes. (sorry Harvey if I use something on earth for comparison)

    Seriously though it does not look like erosion by sublimation it looks more extrusion solidifying after a melt of indeed a splat of some softish material that has then frozen in place.

    It could be remains of a crustal material as described way back by ESA, but back then the crust was assumed to be hiding the ice and it was supposed to be relatively thin, compared to the splats shown here.

    If it is remains of a crust where bits have gradually blown off to reveal a new surface, then it looks like its a very different crust to whats been postulated.


    • Ramcomet says:

      Sticky stuff indeed Dave!

      Never mind my admittedly psychedelic teenhood, cowpatties actually grew some treasures, which I need not discuss or possibly be thrown out of here. (But I did not sip the tea!)

      Seriously though,I keep thinking of our ubiquitous marine Sea Cucumbers, which (or who?... j/k!), leave a slimy gooey tube of sand around the edges of their holes in the sandy shallows of Earth's brackish or salty rivers and oceans.

      Could the ever widening sublimating sand pits, (or even jet pits?) as Rosetta Orisis Team and Emily have so beautifully recently shown us all the evolution of, such as around Cheops on the Plains of Imhotep, due to a number of effects, have rubbery or simply hardened diameter borders that are more resistant to erosion, then filling with captured airfall dust?

      So they become raised, dust filled cups?

    • logan says:

      First than anything, at this distance everything is purely speculative. Time will say. Meanwhile, first idea is you have spotted the real comet, blanket deprived.

      Amused of your visual allegory, Dave 🙂

  • Sovereign Slave says:

    One thing I find very curious, and not favorable to the sublimation theory, is that first, it depends on the comet being composed of a more or less even distribution of dust and frozen volatiles. Second, there is only really one recognized method of "erosion," which is periodic heat from the sun. It seems that in any lab experiment where you have this basically uniform composition body and single, more or less even heat source, you'd have more or less uniformity of erosion. So what in that model accounts for the vast differences in topography of the comet? The rotation would cause uneven heating, but still, this is an often jagged, deformed, angular body with points, cuts, holes, ridges, etc etc, - very very diverse and even tortured topography. Anything besides pure guess work to account for this diversity using this theory?

    • Gerald says:

      Sovereign Slave,
      the other types of erosion processes at work are physical weathering, as also known from Earth:
      Note the exfoliation as another process creating layer-like structures::

      Significant thermal stress is to be expected on the surface of the comet due to lack of a protecting atmosphere, and as you may imagine from the high diurnal and seasonal temperature oscillations on the comet.

      Compositinal homogeneity in the interior isn't necessarily a given.
      Occasional impacts disturb any possibly presumed initially homogenious density.

      • Sovereign Slave says:

        Thanks for the response, Gerald. Your posts are always informative, and it’s much appreciated that you have the good grace to not come across as a derogatory know-it-all with pavlovian intellectual reflexes. However, your links seem to refer to erosion effects on rock for one, and on earth for another, and may be a bit of a stretch in reference to comets? (On a side note, I’d swear that at least one of those pictures are of Enchanted Rock near where I live, it’s a huge granite dome where I often went rock climbing.) Your thermal stress comment is exactly what I’m addressing in my post, and any appeal to internal variances highly speculative. So, it seems we’re still left with heat, dust, and frozen volatiles (though another poster seems to be suggesting that comets are no longer considered to be made up primarily of dust and frozen volatiles, though I have to wonder what else it could be to fit in the sublimation model…perhaps he’s referring to them being made of solid rock or something).

        • Gerald says:

          Sovereign Slave, the thermal stress near the surface of the comet probably plays a more important role as on Earth, besides maybe some dry deserts. The freeze-thaw cycling is probably less important due to lack of (relevant) liquids, but resublimation or re-crystallization may take this part.

          Solid rock is rather unlikely on the comet, with except maybe some rare meteorites, which might have hit it.
          Dust and ice may be baked together in some way due to the cyclic heating to form a crust on the comet.
          More puzzling is the lack of similarity to the known types of carbonaceous chondrites with the analysed samples.
          There seems to be no kind of material on Earth similar to most of the material the comet is made of. Although that's not too surprising, since a mix of silicate dust, water ice, clathrates, and frozen supervolatiles wouldn't survive on Earth for long, other than in some laboratory.

        • Kamal says:

          I keep saying that we know very little about comets. There is also a lot that we do know, but which I find I do not know. On the Twin tails post I came across dust trails and necklines for the first time, although they seem to be known for several decades. I was amazed to find that there are explanations, predictions (as was made by Esko Lyytinen in 2013 about the trail of 17P/Holmes, see
          and verifications of the predictions (the pictures taken in 2015 available at the same website). It appears this one observation falsifies the all-electric theory of comets in one blow: how could ions emitted at one point reconvene there after several years?

    • ianw16 says:

      "One thing I find very curious, and not favorable to the sublimation theory, is that first, it depends on the comet being composed of a more or less even distribution of dust and frozen volatiles."

      You won't find anything in recent literature on comets (from *real* science), that postulates that.
      I would suggest to anyone who is not overly au fait with comets, or believes the EU mythology based nonsense, to take a look at some of the hundreds of papers written on comets since the Halley encounter in 1986.
      It seems to me that many people have a vague idea about what Whipple wrote over 60 years ago, and the rest of their "knowledge" has come from woo merchants.

      • dave says:


        What do you mean exactly by Woo?, there is plenty of evidence of electrical activity on or near the comet, even right from the beginning sputtering was measured and reported by ESA so where is the problem?

        It seems nobody can question a feature of the comet without you thinking people are applying woo.

        Most are just trying to make sense of it, and to do that, they ask questions aloud and ponder what ifs.

        It would seem its perfectly ok to ponder the influence of sublimation, we all know its bound to be happening. However how does this 'catch all' provide the vast difference in topography all over the comet?

        What exactly is happening? Until we know, its got to be ok for observers to ponder don't you think?


        • Harvey says:


          I have no issue with speculation and questions whatever.

          It's strong assertions that it *is* this, that or the other which fly in the face of both the observations and basic physics that several of us have problems with.

          We have for example a strong assertion that 'combustion' is occurring. There is not a shred of evidence to support this, and the low partial pressure of oxygen, and low absolute pressure, essentially rule it out.

          Yes, especially at reasonably large distances from the sun before the development of the comet's magnetosphere sputtering was expected and observed.

          But aside from that, in terms of large scale, terrain-forming activity, nothing electrical is expected or observed. The comet's plasma environment is a different matter; but there is no experimental evidence, nor theoretical reason to think, that it has a role in comet terrain forming.

          I avoid using the word 'woo'; but these 'electrical' theories of what's going on in the Jets etc have no basis in rational science. The solar wind is many, many orders of magnitude too weak to do it; the proponents of these theories claim - without observational or theoretical evidence - that it is mysteriously increased in a Z pinch. This is completely ruled out by direct observation, and it would have fried Rosetta long since.

          As I said, I avoid pejorative words like 'woo', but these are simply not scientific theories; they are proposed by people whose grasp of the theory and meaning of the data is, shall we say politely, tenuous.

          Conventional theories have much to explain, are certainly partly wrong; that does not mean palpable nonsense is right.

          • dave says:

            Harvey re woo,

            Thanks for taking the time Harvey,

            I think the wilder ideas add to the blog whether they are electrical or other, much like a brainstorm it still educates and eventually helps provide a focus to find a correct description, and certainly some of the discussion acts to keep people honest whatever your persuasion.

            The blog has worked really well, I am not sure how much censoring is going on, but it has allowed a wide range of people to take part in the unravelling of the comet who normally would only see scraps of information spun by the media for impact.

            The contribution by the professionals on the blog therefore been extremely enlightening. However, thankfully, there is still much to explain, the release of the Osiris pictures give astonishing detail and no doubt there are many more theories to come, good & bad.

            As for woo, why keep on, if the electric theory does not work, its fine to say so, likewise if a std theory does not work its fine to say so, what is there to worry about?
            Its been a great voyage of discovery for all on the blog.


          • Harvey says:


            Why bother; I wonder too sometimes 🙂
            In fact I've dropped out of it for a while at times.

            Actually I miss phrased then end of my comment somewhat.

            I have no issue with someone with a limited understanding proposing any theory at all.
            But most such people understand the limits of their own understanding so to speak. So when someone says 'could it be xxxxxxxx' and you reply 'interesting idea, but for reasons X,y,z, no, that doesn't work', they maybe ask a supplementary or two, but generally accept that perhaps their understanding may indeed be limited.

            We get that, and it's absolutely fine.

            But here there are a few whose attitude is quite different.
            They are absolutely sure they are right, but have, politely, very, very limited understanding of either the data or the theory. No evidence, no argument, will ever convince them. Their explanations are often, frankly, hysterically funny if you actually know the science. But they are phrased in a highly authoritative manner, with lots of pseudoscientific nonsense, which can *sound* quite convincing to the newcomer.

            This stuff I'm sort of allergic to 🙂

          • Sovereign Slave says:

            Dave, I think you have actually sliced to the heart of all matters related to comets and summarized it quite nicely. It all to one degree or another seems to come down to woo, and re woo. All meaning to say that comets seem very reluctant to give up their secrets, and like with so many things that are mysterious, illicit a wide variety of speculation, promise, and debate.

          • logan says:

            Thanks Harvey 🙂 No doubt that at some issues, I keep flying North, on Winter coming.

            [Maybe I live South].

          • logan says:

            Just saying that the path to learning is marvelously unique for Every Soul.

          • logan says:

            I'll see All of You at the Bahamas 🙂

          • logan says:

            Maybe when I arrive The Bahamas, Harvey isn't anymore there. Maybe He had a change of mind.

            Welcome to the eternal travel of knowledge.

          • logan says:

            Teaching is not so much about what the World think of...

            But a lot about learning what the Pupil think, imagine, dream of...

        • Kamal says:

          Dave: The electric theory of comets postulates that everything can be explained using electricity, since it is much more powerful at short ranges than gravitation. i am quite prepared to believe that both gravitation and electricity play a role in comets, but I do not believe that electricity alone can explain comets. Until the electric theorists make a clear distinction between what they attribute to different forces, it is hard to avoid the feeling that the theory is incoherent.

        • sjastro says:

          You wrote,

          "It seems nobody can question a feature of the comet without you thinking people are applying woo."

          Yet when mainstreamers question electric comet ideas they are accused of being mindless dogmatists without justification.
          A mainstreamer will analyse the ideas in which case "woo" is the logical conclusion.

          Your comment in more applicable to how electric comet supporters react to scrutiny.

          You wrote,

          "Most are just trying to make sense of it, and to do that, they ask questions aloud and ponder what ifs."

          The facts are they do the very opposite.
          The electric comet idea is an ideological construct that is being preached.
          It goes beyond pseudoscience into the realm of anti science.

          For example when a piece of evidence is presented that totally contradicts the electric comet idea such as the density of the comet, the typical reaction is to dismiss the evidence and go off on a tangent by claiming the value of G, the gravitational constant must be wrong.

          This is the very antithesis to asking questions and pondering, it is prejudice driven by ideology.


          • Dave says:

            Sjastro & others
            re you wrote.

            I was not referring to electric comet or EU specifically, there have been may wild ideas over the course of the blog, also there has been many good ideas and discussion.

            My blog was what is your definition of WOO?

            I am completely lost by its constant use, Does it mean any and all electrical effects?
            It is often used where people are not even talking of electrical effects.
            It can be very frustrating with people constantly calling woo. As I said in the blog if an idea is not correct, then it will fall by the wayside so whats the problem?

            If you want to see woo in action, try a football match any incident in the penalty area will cause different ends of the ground to call into question the referees decision. Both will accuse the other of woo but only one man saw it from the refs perspective so the shouts of woo from ether end actually meant nothing both sides as bad as the other.


          • Gerald says:

            Dave, for people with at least some scientific education in planetary science or physics the Electric Universe claims about comets are about as nonsensical as the "undisputable" claim that a football "is" actually a ball lightning made of hot plasma, proven by the obvious evidence, that it flies through the air, because it is roundish, and due to its intrinsic brightness. And the opinion, that it is made of leather is just an unbased "belief" in a consensus of a prejudiced elite, which refuses to disclose the data proving, that all footballs are actually ball lightnings.

            There is a big difference between subtle uncertainties, and obvious nonsense.

          • sjastro says:


            The term woo has been directed against the couple of EU individuals here because they are clearly the main offenders.

            Here is the 10 point definition of woo. (Source RatioinalWiki)

            1. A simple idea that purports to be the one answer to many problems (often including diseases)
            2. A "scientific-sounding" reason for how it works, but little to no actual science behind it; for example, quote mines of studies that if bent enough could be described in such a way to support it, outright misapplication of studies, or words that sound scientific but make no sense in the context they are used in
            3. It involves the supernatural and paranormal (not necessarily)
            4. A claim of persecution, usually perpetrated by the government or the pharmaceutical, medical, or scientific community (see Galileo gambit)
            5. An invocation of a scientific authority
            6. Prefers to use abundant testimonials over actual scientific research
            7. A claim that scientists are blind to the discovery, despite attempts to alert them
            8. A hypothesis that remains virtually unchanged for years or decades, which is sometimes presented as a strength.
            9. A disdain for objective, randomized experimental controls, especially double-blind testing (which are kind of what makes epidemiology actually, y'know, work)
            10. And, usually, an offer to share the knowledge for a price.

            While I don't necessarily agree with all the points, the bulk of it is spot on.

            Note it is not the subject matter itself that is woo but how it is presented.

            As much as it seems reasonable to state that if the idea is wrong it will fall by the wayside, the EU individuals pushing these ideas don't play the same game.
            They will use this forum as an outlet despite the refutations and the contradictory evidence as they are in the business of gaining converts amongst those that may not have the knowledge and understanding in spotting the nonsense.


        • ianw16 says:

          First off, 'woo' is just a shorter way of writing 'pseudoscientific nonsense', and tends to stress the spellchecker a lot less. Blame Prof. Brian Cox.

          There are various ways in which the topography and morphology of the comet can be explained. For instance, the stretch/ contact/ evolution debate. I don't have a dog in that fight. All of them have strengths and weaknesses, and I'm not sold on any of them. I would never refer to any of those arguments as woo.

          The 'electric comet' idea however is pure, unadulterated woo. Unfortunately, it has led to some people having some strange ideas about comets that have continually had to be corrected. For instance:
          'We've never seen H2O at a comet, it's just OH.'
          Wrong, and that has been known for definite since 1986, and has to be explained and linked to.
          'We've never seen any ice. Where is this ice?'
          Saw it at Tempel 1 and Hartley 2. Explain and link yet again.
          'The instruments must have been wrong.'
          No, explain and link again.
          'Where are these x-rays coming from?'
          More explaining and linking to actual scientific data.
          'Look at those electron temperatures. Wow.'
          Oh dear. More explaining.
          I could go on (and on and on), but I think you get the drift.
          Now, who is responsible for these people having such a bizarre and twisted view of what comets actually are? If it were me that was getting a hard time on here for believing such woo, I'd be angry with the people who sold me this electric pup in the first place.

          As for your comment regarding electrical processes in the coma; yes, they are well known, have been observed since Halley, and predicted and modelled even before that. Nothing unusual. They are not going to affect the topography of the nucleus.
          As for electrical processes on the nucleus, I'm not aware of any. Sputtering is nothing to do with electricity, and is at such a low level (non-existent for long periods) that it won't have any effect.
          I've seen one paper on modelling electrostatic effects on dust transportation. Again, it is only active (if at all) at large distances, and cannot explain the topography.
          Any large scale electrical effects on the nucleus would be very obvious across a number of wavelengths.

          So yes, there are things that stilll need to be explained, and it may take a fair bit of time to have any sort of reasonable models for them. It may take further missions.
          But they won't be explained by looking for answers in the electric comet woo. There's no rock and no EDM, plasma discharges etc.

  • ianw16 says:

    "not favorable to the sublimation theory,......."

    You mean the theory that states;

    >Ices to be seen on the surface: check.
    >Ices to be detected subsurface to replenish the surface ice that has been sublimated: check.
    >Neutral sublimation products to be seen in the coma: check.
    >Temperatures sufficient to cause the sublimation: check.
    >Density of the body to be consistent with a porous mixture of ice and dust: check.

    Not doing very well, is it?

    • MATION says:

      Ianw16 re not favourable to sublimation

      Perhaps try playing devils advocate, There do seem to be some holes


  • Solon says:

    ">Temperatures sufficient to cause the sublimation: check"
    How are the temperatures measured?

    • Gerald says:

      "How are the temperatures measured?"

      Mostly remote by infrared spectroscopy, somewhat similar to a high-end infrared thermometer, but much more detailed:

      • Solon says:

        Thanks Gerald. Using IR spectroscopy though, doesn't this mean that only the top few microns is measured? Without drilling a hole and putting an appropriate sensor down it, how do we know if there is enough heat reaching below the surface to have any effect?

        • Harvey says:

          Yes, the mid IR measurements are very shallow.
          However the MIRO measurements do sample somewhat deeper by using far longer wavelengths which 'penetrate' (actually, it's where they are emitted from.) but even so we are talking of cm, tens of cm, that sort of depth.
          There is no direct measurement of the interior temperature beyond that, but a certain amount can be deduced about the comet's thermal conductivity from temperature fluctuations as it rotates, and internal temperatures then calculated from that, but assumptions have to be made about uniformity etc for sure.

        • Gerald says:

          They also do some microwave measurements. Those return data about the top few centimeters.

          Philae's attempt to measure temperatures directly deeper inside the comet subsurface failed. He measured only the surface.

          The exact propagation of heat deeper into the comet can only be modeled and estimated. There is certainly quite some uncertainty. But albedo and solar ilumination are very well-known. Thermal inertia, meaning the change of the temperature after sunrise, and after sunset are observed. So there are some constraints.

          Indirect evidence comes from sublimating volatiles, and the timing of this sublimation, either by observation of jets, or by measuring neutral species.

          Put things together: Temperature gradient with depth (by measuring different wavelength ranges), temperature changes with time, start/end of sublimation, measured species, sublimation temperatures of these species, and a likely model of the surface of the comet emerges.

          • Solon says:

            "But albedo and solar ilumination are very well-known."

            Is the TSI at the comet measured or assumed?

          • Gerald says:

            The so-called "solar constant" is actually almost constant. It can be obseved from Earth as well as from space probes like SOHO. The distance of Rosetta and hence to the comet is known very accurately by signal travel times.
            A simple inverse square law returns the solar power per area at the distance of the comet. The albedo of the surface of the comet is known on a wide range of wavelengths by several Rosetta instruments, e.g. Alice or Osiris.
            The surface inclinations are known at least on the meter scale for much of the comet's surface.
            So there remains very few uncertainty regarding solar illumination.
            Infrared emitted from the comt is monitired. The total energy exchange with the environment of the comet is hence known rather well.
            Time-dependent energy excess or consumption can be modeled on this basis.
            I don't see big gaps in the coverage of these kind if questions.

          • Solon says:

            "The so-called "solar constant" "

            Thanks Gerald. I have been looking for TSI data in the visible part of the spectrum, but find no information on such. The DIfferential Absolute RADiometer (DIARAD) on SOHO does not break down the spectral composition, it is just the TSI of all wavelengths. I have been able to find no figures of visible wavelength TSI from the Moon or Mars, or from their orbits, or from any orbiting spacecraft at other locations, including comets. So the figures used at 67P are assumed, you say calculated, based on the Solar Constant model. That's not really a scientific approach is it?

          • Gerald says:

            Solon, the Sun is really closely monitored on a wide range of wavelengths, including the visible light, e.g. by NOAA, which includes SOHO data:

            Detailed visible spectrum:

            Details on the applicable inverse square law, see right column of this site:

            It is of course science to apply well-tested laws of physics. Technology wouldn't work without.

            There are cameras and spectrometers elsewhere in the solar system.
            On Mars, e.g. there is ChamCam on MSL able to do remote spectroscopy from the surface of Mars.
            Those spectra are publicly available via NASA's PDS:
            But you need to select the passive spectra, and consider atmospheric dust and surface reflectance. Usually you go the other way round and determine dust absorption spectra by knowing the solar spectrum.

            Themis analyses spectra of the surface of Mars from Orbit:

            Big changes in the solar spectrum are simply not to be expected. And if it would happen, there are loads of Earth-based spectrometers which would detect these changes.
            The Sun rotates. So we see different parts of the Sun all the time. If different areas on the Sun would behave considerably different, we would see this from Earth. And indeed, there are variations. And they are observed and known, e.g. active regions or flares. But those variations don't sum up to much variability integrated over the apparent disc of the Sun in the visible spectrum.
            You would get strange unexplained color-casts in photographs taken on Earth or in space, or in telescopic observations of planets or of the Moon from Earth.

          • Kamal says:

            Solon: Rosetta reaches the comet thanks to calculations based on the gravitational constant, and people ask whether the gravitational constant measurements are accurate. Rosetta uses solar energy thanks to calculations based on the solar constant, and you ask whether the solar constant measurements are accurate. Rosetta's job is to observe the comet. It seems to me unlikely that it is designed to directly test theories about gravitation and solar energy.

          • Solon says:

            Thanks for taking the time for such a comprehensive reply Gerrald. However, I would like to hear your opinion on this post:

            Inventions and Deceptions – Total Solar Irradiance

            I have studied both SOHO and LASCO and find no spectral data such as that from SOLSPEC on the ISS, only a composite TSI from an active cavity radiometer, so no visible or IR values are available. It must therefore be considered that there is no visible or IR light from the Sun at 67P, and what little visible/IR light there is is generated by higher energy solar radiation interacting with the sparse matter of the coma. Radical proposal indeed, but based entirely on the data, or lack of, available from the instruments.

          • Solon says:

            Kamal says:
            "Solon: Rosetta reaches the comet thanks to calculations based on the gravitational constant, and people ask whether the gravitational constant measurements are accurate."

            I think Rosetta reached the comet by the use of Sun sensors and star trackers (or Navcam), and computations performed on Earth to allow for ongoing course corrections, much as did the Apollo missions to reach the Moon.

            "Rosetta uses solar energy thanks to calculations based on the solar constant, and you ask whether the solar constant measurements are accurate."

            The solar panels likely use gratings to help convert the solar radiation available out there, it can be done with little or no visible wavelength light. Without direct measurement the solar constant is an assumption.

            "Rosetta's job is to observe the comet. It seems to me unlikely that it is designed to directly test theories about gravitation and solar energy."

            Surely the addition of spectrum measuring instruments to all probes going to all destinations should be a requirement, we have no direct information otherwise, only the assumptions that the solar constant is actually a constant.

        • logan says:

          Every Soul contribution, thanks Solon 🙂

          Next Comet endeavor should include 'Spears'. with a following string of sensors... One meter? Ten?

          A stream of 'origami' solar panels and antennae at tail?

          • logan says:

            Swarms of four, speared on 'stuka' approach. Release. Brake a little. Keep taking shots of their tail mono-chromatic LEDS. See them attach or fail. Map them. Detour!

            Gravitational slope, seismic sensor, various thermal, electric, etc. Predesigned experiments among the group, and intergroup, if power allowed.

            Maybe one long spear with mini-telescope camera? Panoramas could be constructed from individual shots.
            Don't forget eyelids 😉

            Repeat at representative sampling zones.

          • logan says:

            'Origami' solar panels could self assemble on a radio reflector shape, also.

          • logan says:

            'Origami' solar panels' framing could perform as antennae, themselves.

          • logan says:

            [Feel the white, comet cold breeze on my forehead :)]

            Not knowing 'a priori' final depth string is going to be 'unreeled' from the mini-drone, which will separate at impact, and remain at surface. [Deploying anchors, not to be submerged, also].

            Spining has to be provided to the spears, and to the 'Stuka', before the release.

            Sounds fun 🙂

          • logan says:

            Extremely elliptic, asynchronous orbits, with detouring firings on rendezvous.

          • logan says:

            If wanting a low budget, low complexity mission, set aside 'Stukas' and send a train of 'Kamikazes'...With a survival orbiting transmitter.

          • Ramcomet says:

            Cool Hyper Daydreaming Logan.

            Thinking of often proposed Earth space elevator with weight out past geosyncrous orbit. But instead, anchor in a comet, send origami solar panels back out on tether reeled out to orbit from ascent module.

            Only small thrust needed for ascent module to pay out tether, just compressed gas jet.

            24/7 solar power and Osiris Cam watching changes unblinking, CONSERT, etc. etc....

          • Harvey says:

            Logan - origami ideas are indeed used in the folding of some spacecraft components.

        • Kamal says:

          Solon: Climate science is difficult, since the Earth is so very complex. To use that to divert attention from the fact that hypotheses are being made based on the first-ever close observations of a comet over a long duration, means that you are not concerned with the problem being addressed,
          but that you are convinced that scientists are motivated.

          Quite a bit of the conversation on this blog has been between people reacting to what Rosetta and Philae have been discovering and arguing about their own pet ideas. Science tends to disregard the pet ideas of a few persons, instead to go for overall consistency. Publications and refereeing also follow that model.

          Thus if you believe that there is something wrong with the gravitational constant you have to work really hard at showing why that can be correct. For example you have to show that in your model, in spite of the fact that you have different values for the gravitational constant, the Rosetta spacecraft which used the "constant" data in its calculations, correctly managed to reach Churyumov-Gerasimenko. The reason why no one takes the electric theory seriously is that its adherents do not believe in this kind of careful approach to consistency.

          I don't work on astronomy or space science or climate science. I pointed out in a post above that, based on a report I read, the all-electric universe theory is falsified, not by observing comet Churyumov-Gerasimenko but by observing the dust trail of comet Holmes. This observation
          does not require me to recalculate anything that has been hypothesized so far. My existing hypotheses regarding gravitation and the Sun are not affected. The fact that climate science is difficult does not have anything to do with this simple observation, made by a lay person with
          some amateur knowledge of astronomy.

    • Harvey says:

      VIRTIS and MIRO.

    • ianw16 says:

      "How are the temperatures measured?"

      Infrared. Using VIRTIS at this comet. Similar instruments were used at Tempel 1 and Hartley 2.

      Plenty of papers and blog posts where VIRTIS has been used at this comet.

  • logan says:

    "...If these [proto-planetary] discs are composed of mostly larger, but cooler [7ºK], grains than is currently supposed, this would mean that these compact discs can be arbitrarily massive, so could still form giant planets comparatively close to the central star."

    "...This is the first direct measurement of the temperature of large grains (with sizes of about one millimetre) in such objects."

    "... To resolve the discrepancy, the large dust grains must have different properties than those currently assumed, to allow them to cool down to such low temperatures."

    Journal from a proto-planetary disc eclipsing.

    The international team, led by Stephane Guilloteau at the Laboratoire d'Astrophysique de Bordeaux, France, with input from ALMA/IRAM [Chile/Spain] Works..

  • Robin Sherman says:

    Great post Emily. In the first Osiris image, bottom left there are hundreds of "dinosaur eggs" littering the surface. The comet's internals laid bare?. The other striking thing about these images, as others alluded to to, is the resemblance of much of the Southern hemisphere to igneous/volcanic landscapes. The resemblance to lava flows, granite and basalt formations on Earth, is striking along with the almost complete absence of "dust" over large areas.

    The surface we see now is actually the surface of the comet much earlier in its evolution, as explained by the OSIRIS team, as much as a few kilometres depth of surface has been eroded by various processes. If this is indeed the case, we are perhaps currently seeing the comet at a very early stage of it's formation. If the accretion theory of planetesimals/dinosaur eggs is correct, this accretion, if rapid enough, would create a large amount of heat from dissipated kinetic energy. Just as the Earth in it's early formation had a hot molten surface, so the comet could have had a "hot" molten surface, with lava flows of semi molten volatiles. This continual thermal mixing is likely to be the explanation for the comet's large scale homogeneity, its highly porous structure, think pumice on Earth, and its multiple layered structure.

    The second OSIRIS image has the fine layered structure mentioned by Emily which appears to be a sedimentary formation, most likely from layers of coma fallout, which occurs in a "dust" collection basin. The appearance of the Geology of the comet just shows that the universal laws of physics lead to the same types of features even though the materials are totally different. A solid/liquid/ vapour cycle plus heat leads to the same physical manifestations on the surface of a solid planetary object. See Pluto.

    Sometimes the blindingly obvious is in fact correct and perhaps we are tricked by unfamiliar conditions into thinking some new unknown science is taking place. Basically the material that makes up the comet at the temperatures and pressures it experiences, behaves very much the same as "rocks" on Earth. As speculated many moons ago, the cometary material is a form of "Pykrete" made of frozen volatiles and dust. As such it can be harder than concrete at low temperatures, <100K, but is highly volatile when temperatures are above 200K.. At temperatures in between various molten states should be possible, analogous to different lava types on Earth, each with varying amounts of "dissolved gases", leading to different appearances when they become solid.

    The big unknowns are the thermal properties of this cometary "Cryocrete" or "Cryorock", as I have called it in the past. In particular its thermal conductivity and the temperature gradients. The Rosetta team has already given broad estimates for the internal temperatures at the centre of the comet from the data from VIRTIS & MIRO, but as always the devil is in the detail of what happens in between.

    Logan's next planned cometary mission seems like a good place to start and the space elevator idea is excellent. Given the low gravity and small orbital velocity and no atmosphere to speak of, I would imagine todays carbon nanotube fibres would be adequate to make a very lightweight tether strong enough. The problem would be attaching one end to the comet. The "Cryocrete" solid surface is exceptionally hard, if extremely brittle, as Philae found out. It may require an ice drill of some sort, rather than kinetic methods, to fix the comet end of the tether. A "geostationary" orbiter would then have to deal with huge temperature and solar power fluctuations as well as the "dust" when the comet approaches the sun. I am sure the boffins at ESA could sort that all out. A solid Asteroid would be the ideal place to practice. If NASA can lower Curiosity, basically a small car, from a "Skycrane" it ought to be possible to do the same with a device to attach the tether and act as a "ground station".

  • Kamal says:

    Emily: Neith is probably the "valley" running down below one side of Wosret, it looks a little different from the surrounding regions.

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