Seasonal forecasts for 67P/C-G

Based on the press release of the Max Planck Institute for Solar System Research, Germany.

Scientists from Rosetta’s OSIRIS team have been analysing the images of Comet 67P/Churyumov-Gerasimenko and comparing them to a thermal model to estimate how much material the various parts of the comet will lose through Sun-driven sublimation during one orbit. That is, as the Sun heats the comet, ices sublimate and the resulting gases drag dust into the comet’s coma.

The results predict that the southern half of the comet will undergo dramatic changes in the coming months, losing a surface layer several metres thick, while the northern half will likely be much less affected by the Sun-driven erosion.

Followers of this blog might be familiar with the geography of Comet 67P/C-G, but it’s worth stressing that the southern “hemi-comet” does not correspond to either of the comet’s two lobes. Indeed, the rotation axis goes through the comet’s “neck” and the equator runs along both lobes.

The blue arrow indicates Comet 67P/Churyumov–Gerasimenko’s rotation axis, and the red and green arrows display its equatorial x- and y-axes, respectively. Its spin axis is tilted by 52º. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The blue arrow indicates Comet 67P/Churyumov–Gerasimenko’s rotation axis, and the red and green arrows display its equatorial x- and y-axes, respectively. Its spin axis is tilted by 52º.
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

For Earth, the rotation axis is inclined at an angle of about 23.5 degrees with respect to our planet’s orbital plane, giving rise to the seasons. The angle of inclination is much larger for Comet 67P/C-G: 52 degrees, but the comet still experiences seasons. But, together with the comet’s complex shape and highly elliptical 6.4 year orbit around the Sun, this leads to a very uneven distribution of summer and winter months across the surface of the comet. Indeed, some areas close to the poles even go through long phases of complete darkness or continuous illumination.

While the northern “hemi-comet” experiences a long summer that lasts for 5.6 years while it is far away from the Sun, the southern “hemi-comet” has a short, but intense, hot season of about 10 months. The southern “hemi-comet” is currently facing away from the Sun, but this long polar night will end soon, as sunlight will illuminate these regions again in May.

“We then expect the erosion there to pick up significantly,” says Holger Sierks, principal investigator of OSIRIS at the Max Planck Institute for Solar System Research in Germany.

The variation in illumination across the surface over the orbital period implies that the northern and southern “hemi-comets” experience very different levels of erosion driven by the Sun.

In the OSIRIS study, the scientists assumed that subsurface water-ice is covered by a very thin and extremely porous dust layer of only 50 micrometers in order to provide an estimate of the maximum loss of material for both hemispheres of the comet during one orbit.

“There is, of course, still some uncertainty in this value,” says Horst Uwe Keller, emeritus principal investigator of OSIRIS from the Institute for Planetary Research of the German Aerospace Center (DLR), who led the analysis. “It does, however, reproduce the erosion rates we see presently very well. We therefore see it as a good starting point for our model.”

The actual thickness of the dust layers is still to be confirmed – it may be several centimetres if not metres thick in places – but for the purpose of the model, a thin layer is assumed.

 

According to recent model calculations, the southern half of Comet 67P/C-G (right image)  could lose a dust layer of up to 20 metres during one orbit. Due to the seasonal cycle of the comet, the northern half (left and centre images) is much less subject to erosion.  Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

According to recent model calculations, the southern half of Comet 67P/C-G (right image) could lose a dust layer of up to 20 metres during one orbit. Due to the seasonal cycle of the comet, the northern half (left and centre images) is much less subject to erosion.
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

“Assuming that four times more dust is emitted than ice, our model leads to very different scenarios for the northern and southern hemisphere,” says OSIRIS scientist Stefano Mottola from the Institute for Planetary Research of the German Aerospace Center (DLR). “While during its short but intense summer the southern hemisphere may lose a surface layer measuring up to 20 metres in thickness, this value should be much smaller for the northern hemisphere. According to our estimations, only very few prominent peaks and cliffs may erode by more than ten metres over the course of one orbit.”

The scientists expect the southern side of the comet to change dramatically as it approaches perihelion in August. The team also notes that the insolation on the “neck” region between the comet’s two lobes is particularly weak; however, this region has displayed the strongest and earliest signs of dust activity in the past months, suggesting it might be characterised by a different composition to the rest of the comet.

“Quite possibly, 67P after perihelion will no longer be the comet we have grown used to in the past months,” says Sierks. “Witnessing these changes from up close will be an unsurpassed adventure.”

Comments

84 Comments

  • Daniel says:

    I realise that this is obviously a simplified model, but it does seem like it almost a sun (intensity) map of the comet. Worth pointing out is that the Horst says the model gives a similar value to the erosion that they’ve observed, so erosion has been directly identified. However the changes we have seen are basically concentrated in the Hapi valley, where as their model has a very low amount of loss there. This difference in the model versus observed activity is pointed out in the blog post, so I assume the measured losses that follow the model have been observed elsewhere on the comet.

  • dave says:

    Gosh, like Daniel, I am interested in the model of erosion, a 20 meter reduction in surface over the large red area is some going based on what we have seen so far, so its sure going to be exiting.

    If the unusual dust to gas ratio for this comet is caused by subsurface ice covered by ‘a Very Thin’layer (only 50 micrometers) of refractory material on the surface, does the team expect the dust to ice ratio to change radically after this thin surface layer is burnt off?

    • originalJohn says:

      This is all baseless speculation. No evidence to support the existence of ice. Any ice. Lets see some detailed surface temperature maps published and some detailed temperature and composition profiles of the jets.

      • Graham Hall says:

        why not read the science papers -they’re all on line. the escaping gases are primarily CO, CO2 and H2O. Where do you think they come from?

        • originalJohn says:

          I have read them Graham Hall. The escaping gases are CO, CO2 and H2O you confirm. A strange order you choose as I suspect CO is the least abundant. Are you suggesting they could only have an ice origin? If you are I have to disappoint you and remind you that they are renowned combustion products of hydrocarbons in the presence of oxygen, a deficit of oxygen in the case of CO. No ice required, which is good as it appears that there is indeed no ice. The hydrocarbons have been positively identified on this and other comet nuclei (and on asteroids) and the oxygen is in the rock, rock which to my knowledge has yet to be confirmed but we all know it eventually will be. So that is the reactants and the products. The energy to initiate the reaction is provided by the proton current flowing from the Sun, protons with energies at the keV level. After activation the reaction is self sustaining.

          • Graham Hall says:

            “After activation the reaction is self sustaining”

            so why then does it dramatically reduce, almost to nothing when the comet moves out to a distance equal to the orbit of Jupiter. If its self sustaining that wouldn’t happen.

            The EU theory is bunkham, you know it, I know it and YES I am suggesting that the gases come from a frozen state via sublimation, and definitely not combustion. What concentration of oxygen do you think is necessary to support combustion is space, on a comet?

          • Harvey says:

            A self sustaining reaction between a silicate rock and hydrocarbons; fascinating. Do please point us to some references, or exams les of that happening.

    • WayneC says:

      The dust layer that Horst speaks of is only 50 millionths of a meter. That’s the erosion rate for the north hemi-comet. . (According to Wikipedia, “70 to 180 µm — thickness of paper. “) That’s not very much erosion, considering the team expects up to 20 meters of erosion coming during the hemi-comet southern exposure. It should be a great show.
      Where does Philae fit into this prediction? If it is ‘bumped’ by escaping material, could it attain escape velocity? If it’s in a hole, or between cliffs, etc, it may be dislodged and find a new place to land…

      • originalJohn says:

        Graham Hall, combustion reactions typically stop if the fuel runs out, in this case at the particular reaction site. If the reaction was not fully self sustained but still required some proton input it would stop when this became insufficient.

        I don’t think I referred to anything EU. The solar proton current is mainstream fact. There is no such thing anyway as EU theory. I don.t know what “bunkham” is but bunkum is an expression used by those whose argument has dried up. The EU paradigm is drawn from several areas of knowledge including physics, plasma physics and electrical engineering. . The problem for you is that it fits observations very well in many areas and removes the need for invention of invisible entities, such as virtual ice. It does not however fit with knowledge by decree.

        A simple measurement of the temperature of the jets would establish whether they result from gas sublimation or combustion.

        • Gerald says:

          It’s not a solar proton current, but a proton flux. A possible electrical current is by far the most a matter of electrons, not of protons, since electrons have the same amount of electric charge (opposite sign), but are more than 1000-times lighter.
          The EU paradigm is drawn from a very meager understanding of actual physics, but from wishful thinking and selective perception instead.
          Combustion is at least something of the real world, although not applicable to the 67P outgassing due to lack of sufficient free oxygen. Bound oxygen in rocks needs too much energy to be able to react significantly with hydrocarbons, particularly to produce water.
          Pre-existing water could release energy when reacting with some type of rock (e.g. with olivine), but it needs to be liquid to make this option relevant.

          • originalJohn says:

            I am sorry Gerald. You have a mistaken understanding of the definition of an electric current. It is the movement of charge, positive or negative. The solar wind is indeed a current flow.
            I can see you feel threatened by the EU paradigm Gerald but rather than general vague expressions of opinion about it why not some specific instances of meager understanding etc. And when you look at some of the assertions of conventional cosmology you find not only zero understanding but complete contravention of the laws of physics. Does that not bother you too.

            We have already discussed I think that the exothermic release of energy in hydrocarbon combustion per mole is typically double that required to dissociate the single Si-O bond. However because of the tetrahedral coordination of the bond in SiO2 several bonds must be separated per mole. You have pointed out that this results in a net energy input to fully break down SiO2 in a stoichiometric reaction. Oxygen is however progressively released as the reaction proceeds and is available for the combustion reaction.
            It is a complex case. My assessment is that any energy deficit is made up by the solar protons which carry a large surplus of energy over the 4.68 eV requirement to separate the Si-O bond. Each proton could, in cascade fashion, separate hundreds of such bonds.

            The conditions therefore appear to be in place for the combustion reaction to activate and proceed and the products, including the contentious water, are already identified in the coma. By any standard it demands further investigation.

          • Gerald says:

            @originaljohn
            No need to be sorry, since electrons and protons balance their charge, hence no (macroscopic) electrical current.
            To induce electrical current you need an electric or a moving magnetic field, and then again it’s mostly the electrons in the plasma, not the protons which transport the net charge.

            Regarding EU theory I feel bored, not threatened. It’s ruled out over and over again. A waste of time to discuss it any further.

            Cosmology is too difficult to discuss possible flaws here. I can recommend to read the Planck papers; some knowledge of general relativity needed.

            Solar protons contribute to space weathering over millions of years at the very surface of an object. Their number is much too low to sustain combustion.
            Just think at the orbiter as a counterexample.

        • Harvey says:

          The ‘mainstream fact’ is that the proton current is many, many orders of magnitude too weak to provide the required hydrogen, are there are NO observations consistent with some magical concentration of that current.
          As the bow shock forms, the comet will be largely protected from solar wind protons.
          The *observed* fact is that the H/D ratio in the emitted water is totally different to that in the solar wind.

          • originalJohn says:

            The proton current in this case Harvey is not required as a source of hydrogen but as supplier of activation energy.
            Magic does not come into it with filament and pinch formations in plasma. They are acknowledged effects that occur in all plasma.
            The bow shock concept is a mistaken interpretation. The protons will continue to impact the nucleus throughout the passage around the Sun.

          • Gerald says:

            Originaljohn, you don’t get your pinch due to lack of a sufficiently strong field.
            On Earth we have several kV per meter in the atmosphere; near the comet we have just about 1V/km, if at all, in the heliosphere, and not necessarily homogenious.
            Beside this it’s the electrons which balance the voltage, almost not the protons.
            So even if we get a voltage, e.g. by tribocharging and charge separation at the jets, it’s again the electrons which balance the charge. You don’t get your protons pinched, as you wish.
            You may get higher proton flux during CMEs; still insufficient to sustain combustion.
            The idea of activation energy works only for a exothermic reactions with an energy barrier to overcome. But we’ve seen, that hydrocarbon – silicate reactions are endothermic.
            Regarding protons: How many mols of protons collide each day with the comet? What’s their energy, and how many mols of oxygen can they sputter at most within a day? Compare it with the mols of sublimating water per day. Do the calculations, then return with the results, if you are still convinced, that this can remotely work.

      • originalJohn says:

        It is a proposal Harvey and a valid one. It stands on its own. Activation requires separation of the Si-O bond with an energy of 4.68 eV. The proton energy is in the range 1-10 keV. If you don’t think it is possible say why.

        • Harvey says:

          Of course a proton can break an Si-O bond.
          But the sputter yield of O is far below unity, and most of the energy is deposited well below the surface.
          However that is extremely unlikely to lead to a continuing reaction, because hydrocarbon plus silicate reactions are strongly endothermic. Silicates are extremely stable compounds. Further more, where does the silicon go? We don’t see masses of silicon in the coma; the surface isn’t enriched in silicon; how does that work?

          The yield of oxygen by this route is completely trivial. It will occur and be the dominant mechanism at large distances from the sun. It occurs on the moon – no coma! Close to the sun, firstly the bow shock largely shields the comet from the solar wind, secondly its a minute effect many, many orders of magnitude too small to explain the coma.

  • Graham Hall says:

    The southern side is mildly active even though its not currently in sunlight. The change is going to be quite dramatic and at present we don’t even know what it looks like.

    The fates were shining on ESA and the rest when the mission was delayed and redirected to 67P. It is hard to imagine a more interesting comet than this one.

    PS when Horst say see – he means as measured, not directly visible – at least not in anything released so far!

    • masanori says:

      As for “the fate”, even though I’m sure I don’t understand its real scientific value, I would like to add Philae’s landing sites. Especially the final landing site. When I first heard Site J = Agilkia would be the landing site during that live webcast from Paris, it totally made sense to me, imagining the science team was really really wanting to do science on a comet. But to be honest, I thought such flat area can be most boring among all options, I wanted Philae to study the neck region if he had capability to do it. Now Philae is sleeping by cliff. I suspect you cannot target such place as a landing site but Philae happened to reach there. And now it seems he has a chance to study 67P near/at perihelion. I wonder how many people had expected such story!

      • Graham Hall says:

        Indeed Maaanori

        The scientists are delighted where Philae ended up as they felt the original targeted site was too safe. Of course they’re desperate for Philae to wake up fully in a couple of months time so that they get more science from it. however, 80% of the science was to come from the Rosetta only 20% from the lander so the mission is already an incredible success.

        • Harvey says:

          In addition, Philae’s primary mission was always the time it had on batteries; anything beyond that was considered a bonus. So Philae itself was also a very considerable success, if not everything we hoped for.
          To pull off a landing *at all* on a body about which we knew almost nothing at the time Philae was designed and built was a magnificent achievement; let’s not loose sight of that.

      • Kamal Lodaya says:

        Masanori: Here is an interesting but unlikely possibility: Philae may get warmed up by the heating up of the surface below it rather than directly by sunlight.

        • Harvey says:

          Unlikely. Thermal contact from the comet to the lander will be very poor, and radiative transport at these temperatures is not very effective. It needs sunlight.

      • Harvey says:

        Masanori, I’m sure everybody wanted to land in a more interesting area.
        But the landing site was subject to numerous constraints set by flight dynamics, solar illumination for power and thermal control, and the communications link.
        Then you had the balance between risk of a crash landing in rough areas ;and survival in smoother areas. Better to be ‘alive’ in a ‘boring’ area (nowhere on 67P is boring!) than dead in an interesting area.
        This was always a very, very risky operation, with only one shot at it.
        In the circumstances, the safe option made sense.

  • marcoone says:

    wow! 20m of matter in less are many for the balance between the two bodies.
    I had got the idea that the fracture, which is clearly visible in the neck area, is the residue of the union of two lobes;
    but reading now and also looking at the image of the previous post I’m thinking that the two lobes are unbalancing and fall over themselves.
    The area of the fracture would be the pivot point.
    I guess to expose 1km virgin material toward the Sun would be a sight even from Earth: 17P Holmes is still a beautiful memory.

  • Robin Sherman says:

    Thanks to Emily, Holger and the OSIRIS team for this information.

    I imagine the rate of erosion was calculated from a combination of the gas/dust ratio and the amount of Water being lost from the comet per second. This could readily be converted into a volume of material. This figure and the model are obviously using ball park figures that are an average for the whole comet, such as the thickness of the dust layer. We have seen large areas with no dust, protrusions, cliffs and mountains with no dust, which when averaged out with the dusty plains could be a fairly small value, especially if there is very little dust on the “Dark Side” as we are starting to see.

    Phillae provided visual evidence from two spots, Agilkia had a surface dust/gravel layer 10-15cm deep, but the CIVAS images from Phillae’s final landing spot showed very little dust, only at the very back of the alcove where little sunlight reached.

    What has to be remembered here is that the solid looking material we see is not in fact a solid but a highly porous mixture of dust, volatile ices and organics. While temperatures are low the only thing solid is the frozen volatiles, once they sublimate there is no longer a solid, just a pile of tiny dust grains weakly held together by complex organic molecules, Van de Waals forces and the interlocking jagged edges of the dust grains. All the time no force acts on this residue it stays put, but as was seen in the COSIMA images as soon as a force is applied this cohesion is removed.

    Sublimating gases at only very low speeds can disturb and move these micron sized dust grains. For Water to be leaving the comet at litres per second, the other volatiles at similar magnitude rates, those gases are travelling plenty fast enough to move and remove large amounts of dust from the surface. With an escape velocity of less than 1 m/s most of it will escape the comet into the coma, either as a diffuse haze slowly rising from the surface, or in more defined columns depending on the nature of the source of sublimating gases.

    The more energy available from sunlight, the more gases sublimate, the more dust is released from the comet material matrix, the more dust is removed from the comet. The complicated bit is how much does the insulating effect of the surface dust layer and it’s varying thickness, affect the rate of sublimation of the volatiles in the layers below.

    What effect does this huge disparity in mass loss between the Northern and Southern “duckiespheres” have on the rotation and gravitational forces acting within and on the comet?

    • THOMAS says:

      @ Robin Sherman

      “The more energy available from sunlight, the more gases sublimate, the more dust is released from the comet material matrix, the more dust is removed from the comet. ”

      Sorry Robin, I know this is the standard theory mantra, set in stone, but the idea has already been completely refuted by the inconvenient FACT that the overwhelming majority of the jetting activity has for months been (and still is) focused on the bottom of Hapi Valley . Now as you know, this is precisely the extended area of the comet which, for obvious topographical reasons, receives by far the LEAST “energy available from sunlight”. This FACT now needs to be addressed and accounted for.
      This obvious paradox is further reinforced by a second extremely embarrassing FACT, which emerged during Fabrizio Cappacioni’s presentation of VIRTIS data at the AGU meeting: at 4:20 into the video, he flashes up a series of images showing surface temperatures on 67P, one of which unambiguously shows an extended band of considerably higher temperatures all along the bottom of Hapi Valley. (Strangely, he makes no comment on this evident anomaly…). I freeze-framed it and reproduce it here: https://www.flickr.com/photos/130179313@N03/16464918676/. The original video can be seen at https://virtualoptions.agu.org/media/P32B-07.+Rosetta+2014+I%2C+Presented+By+Fabrizio+Capaccioni/0_eb9d69c6. The temperature data sequence starts at 4:20.

      Now in any normal scientific procedure, these correlated observations (major jetting activity from an area of considerably higher temperature despite the fact that it receives considerably less energy from sunlight) would set the alarm-bells ringing big time and be sufficient in themselves to utterly falsify the existing model of ice sublimating in the gentle sunshine…

      • dave says:

        I agree with you Thomas it seems that if 20 meters of sublimation is going to take place because the the surface will be heating up from the direct sunlight, then why is it that most of the water seems to be coming from one of the shadiest areas?
        On the Ice in the center of the core it seems to contradict both the Vitus comment that there is so much refractory material on the surface of the comet that it must be representative of the bulk pristine material. This presumably indicates that the water is somehow locked up in the refractory material (not as ice)
        Also the Consert measurements, that spoke of a homogeneous core, again presumably meaning consistent with the refractory surface.
        Plus the Consert experiment never found any spent cavities that are supposed to sublimate the gas at high pressure through a small hole to supersonic speeds. From the paper posted on the blog I think by Graham a week or so ago the model to get jets to work required a cavity 1meter deep and up to 3 meters in diameter that presumably could have been detected the Consert. The instrument was tested in the lab with several different ices and with several different Ice /dust mixes and even tested on glaciers in the arctic but it has not announced that there is ice in the core.
        Finally the dust that has been collected on Rosetta does not seem to be snow flakes or even dust coated in ice, based on the lack of evidence of water detected by the instruments.
        So it all sounds a bit strange, but anyhow, 20 meters of surface to be removed watched by Rosetta and therefore hopefully us is going to be one hell of a show, so lets sit back and enjoy.

      • logan says:

        Wanting to point to THOMAS that Hapi Valley is nothing more than a Semi-circular band above actual ‘Coraline’ gravitational center 🙂

      • Gerald says:

        @THOMAS
        The temperatures have been explained by the low thermal inertia, as mentioned on the slide you referenced.

        • THOMAS says:

          @ Gerald

          “Low thermal inertia” is not a given, since we still know nothing about the precise composition of the comet surface; it is merely *inferred* as a way of mitigating gain-saying evidence. In any case, “low thermal inertia” in no way explains *why* the most shaded part of the comet also happens to be both the most active and the warmest area of the surface.

          • Gerald says:

            Thermal inertia can be “inferred” by measuring temperature over time, particularly when the surface is cooling down after exposure to sunshine.
            The reason for higher activity is under investigation. But a straigntforward possible explanation is higher contents of volatiles. Areas of high exposure to sunshine may have already lost much of their highly volatile ices. Or else the neck region generally is of higher volatile contents, leading to faster degradation, explaining the neck topography as well as the higher outgassing rate.
            Ongoing measurements will pin this down in more detail.

          • THOMAS says:

            @Gerald

            “The temperatures have been explained by the low thermal inertia, as mentioned on the slide you referenced.”

            You still haven’t explained how “low thermal inertia” can account for the paradoxical higher temperatures recorded in an area receiving the least sunlight.

            What precisely were you trying to claim in the above statement and how does it explain the paradox? It seems to me that the VIRTIS slide annotation simply avoids the issue entirely.

        • THOMAS says:

          @ Gerald

          “Low thermal inertia” is not a given, since we still know nothing about the precise composition of the comet surface; it is merely *inferred* and in any case, it in no way explains *why* the most shaded part of the comet also happens to be both the most active and the warmest area of the surface.

          • Gerald says:

            Higher thermal inertia areas tend to cool down slower than low thermal inertia surfaces, after sunset.
            Usually dusty surfaces have lower thermal inertia than bulk ice/rock.
            So higher thermal inertia patches (hence warmer after sunset) match with an ice/rock mix covered by just a thin layer of dust and should be expected to be more active.
            More dusty, hence colder surfaces after sunset due to lower thermal inertia would be expected to be less active.
            That’s just roughly sketched. Of course activity also depends on the actual composition, so thermal inertia and activity should correlate in a random compositional settings, but not necessarily relate in a strictly functional way.

          • Marco says:

            Hi Gerald,
            The thermal hot spot cannot be explained by passive thermal material properties the way you have said. I am no fan of exothermic reactions, much less electrical effects, but there is a massive hint of a heat source other than solar radiation – given the location, it may have something to do with internal stresses at the Hathor/Hapi interface, or something that may only become clear when we see what happens on the southern perihelion summer.

          • Gerald says:

            Hi Marco,

            another relevant heat source than the (photons of the) Sun would be exciting. But I think it’s rather unlikely.
            The only remote option I could imagine is serpentinasation, if liquid water can form in pressurized pores, and gets in contact with silicates. But since it’s very unlikely, it would need lot of evidence to be considered.
            The sun as an indirect source of energy would be resublimation. That’s again unlikely, hence the usual need in such cases for clear evidence.
            Mechanical deformations can produce heat, but I don’t see a source for the needed forces. There may only be the other way round thermally induced mechanical stress due to diurnal and seasonal temperature cycling, and due to approach to the Sun.

          • Sovereign Slave says:

            @Gerald
            OK, so it seems you’ve ruled out any “normal” cause to account for the heat source at the neck, not gravitational, highly unlikely it’s heat from the sun, internal geological unlikely, friction no, chemical reactions not likely, magnetic doubtful, and apparently by your account electrical is impossible, though I still wonder what the ESA scientists were referring to by sputtering found on the surface (seems electrical sputtering would raise temperature significantly). Given that nothing seems to currently account for this anomaly, as I’ve commented before, I still find it interesting that other theories in the accepted mainstream toolbox aren’t considered, such as dark matter interactions, or dark energy, or string theory, etc etc. They’re never mentioned or given the slightest consideration by anyone, yet this stuff should be prevalent everywhere in the universe. Why are these theories not prevalent in the debate, especially as more and more anomalies are found with this comet?

          • Marco says:

            Hi Gerald,
            No combination of thermal inertia and higher percentage of volatiles makes an area both warmer and more emissive. This is because the very incidence of sublimation takes heat away from that area. The observed phenomena requires an active thermal hot spot. Being shaded it can’t be from a solar concentration, so then the suspects should be the next least improbable phenomena. Thermal expansion could minutely affect the overall angular inertia of the comet inducing stresses in the neck.

          • Gerald says:

            The Sun isn’t ruled out. It’s the by far most likely source of the heat. I don’t know for sure, but the most reasonable cause for the confusion is the time, when the measurements have been taken. It makes most sense, that the measurements have been taken after sunset. Particulary water ice has a high thermal capacity to hold warmth from the day, whereas fluffy dust cools down at the surface rapidly after sunset.
            Exposure of ice would explain the high activity in the neck region, and the higher albedo, too. So this explanation is currently my favorite. That doesn’t rule out, that someone else may find another stunningly more convincing solution.
            Regarding dark matter: The notion “dark” in this case may be a little misleading. It actually means interacting only by gravity, not noticibly by electromagnetism (e.g. light, therefore “dark”) or nuclear forces. Dark matter is so diluted, that its interaction with the comet is far below the precision of measurements.
            Dark energy may be considered as a way to circumscribe the cosmological constant of general relativity. Currently no heterogeneities of dark energy are known, although the probe EUKLID, if I remember correctly, is scheduled to check for possible heterogeneities of dark energy. The effects of heterogeneities (if they exist at all) of dark energy to the comet are even more difficult to retrieve than those of dark matter.
            That’s because those two phenomena aren’t considered when looking for causes of surprising data of the comet.
            Dark energy and dark matter play an important role to explain long-term motions of large-scale objects in the universe, starting from the motion of stars in galaxies, influenced by dark matter, up to the expansion history of spacetime influenced by dark energy.

          • Gerald says:

            Sorry Sovereign Slave, forgot to answer the sputtering question: Impacts of solar wind particles or galactic cosmic “ray” particles can sputter ions from the surface of objects. The overall power of the incoming energetic particles usually is well below 1 Watt per square meter at distances of more than 1 AU from the Sun, solar energetic particle events (SEPs) included. The total solar irradiation at 1.5 to 3 AU is several hundered Watts per square meter.
            Since the Rosetta instruments are very sensitive, they can even measure sputtered ions, like those of magnesium or sodium, which usually don’t sublimate. But the number of these sputtered ions is way below the sublimation rate of ices we are observing now.
            So there will be some sputtered oxygen ions between the gas molecules, but currently those are negligible compared to sublimation.

          • Gerald says:

            String theory is a theoretical framework which tries to find a cause for the standard model of particle physics, and beyond. So usual matter is made of molecules, atoms, ions. An atom is made of an atomic nucleus and electrons; extremely charged ions and protons may exist naked without electrons. Atomic nuclei are made of protons and neutrons. Protons and neutrons are made of quarks, kept together by gluons and other exotic particles, called bosons.
            Electrons, quarks, gluons, other bosons (and several more particles, e.g. neutrios) make the most fundamental particles we can infer by experiments and loads of statistics and theories.
            String theory tries to go even deeper and explains those fundamental particles by vibration states of an even more fundamental type of object, called string.

            So string theory isn’t the most straightforward means to deal with comets on a macrosopic scale.

          • Gerald says:

            “neutrinos”, not “neutrios”, of course.

          • Sovereign Slave says:

            Hi Gerald, very thorough answers, much appreciated. Wish I could post under each, but only one reply link available for all of course. Agreed that the sun would be the most likely explanation if it is sublimation as heat and sublimation go hand and glove. However, barring some extraordinary revelation ahead, any explanation at this point about the elevated heat at the neck, which is most shaded, still smacks of being rather conjured up. And there seems to be a habit in cosmology of rationalizing surprises and inexplicables away with things that try to sound reasonable but don’t really bear up. At this stage, I think it’s a very reasonable question to ask, “If it’s not sublimation, what’s creating the coma?” because sublimation is more and more becoming a really really big if. You’re obviously very intelligent and know science, and I’d really like to know what you think on that – just for fun, think outside the sublimation box, just take sublimation off the table, and speculate on what other forces could be causing the coma.

            Regarding dark matter, etc, I guess my main question is why this stuff never makes an appearance in our neighborhood, things we find in our solar system. It’s supposed to make up the vast majority of our universe, and perhaps I’m wrong, but I can’t think of any discovery made within our solar system by all the things we’ve put into space where the highly imaginative and exotic theories have been referenced to explain them. They only seem to apply way out there, where it’s impossible to apply scientific proofs to them. I guess so many of the theories just seem so contrived and patch worked as to be fundamentally flawed. The natural world around us doesn’t seem to behave the way mainstream interprets and explains the phenomena seen in the distant cosmos.

            But I guess one thing that strikes me about the electricity vs sublimation argument is this: I think everyone agrees that there is electrical activity taking place on the comet. Rosetta/Philae are even equipped with instruments to measure such things. So it’s not a question of IF there is electrical activity, it’s a question of that electrical activity being able to explain the coma. With sublimation, it definitely IS a question of if, for there has not been anything directly proving the existence of frozen volatiles on or in the comet. I know there’s a huge investment in frozen volatiles being there, but what if they’re not?

          • Gerald says:

            The chance that the predominant root cause of the emitted gas is something else than sublimation driven by solar heating is low. The next option would be thermic decomposition of water- and CO2-bearing minerals, more likely woud be clathrates; that’s probably considered. Next would may be highly hydrated salts, which decompose near zero centigrade, like magnesium sulfate dodecahydrate; that’s already unlikely for comets, but may occur on some moons, like Jupiter’s moon Europa.

            I think, somewhere at this line the Rosetta mission wouldn’t be able to provide sufficient evidence for any more fringe approach to be accepted by the science community. One would probably presume instrument flaws as more likely than quantitatively relevant sputtering by solar protons or other strange effects, since it’s incompatible with all other relevant data, experiments, and highly successful theories.
            Photoelectricity could explain some of the ejected dust, but would be assessed as insufficient to explain the coma. Tidal effects as heat source are negeligible, too. Micrometorite impacts are also insufficient.
            Galactic cosmic rays are present, but insufficient as an explanation for the coma. Any electric or magnetic fields are many orders of magnitude too weak to explain the coma. A high flux of neutrinos is present due to nuclear fusion ih the Sun, but neutrinos interact with matter far too rarely to be relevant here. Radioactive decay of cometary material may occur, but irrelevant for small bodies like the comet as well, although not for planets. Nuclear fusion within the comet irrelevant for the coma, nuclear fusion in the Sun is relevant instead, as heat source. All kinds of activities by aliens, nonsense. Relevant coma due to biotic or pre-biotic activity exceedingly unlikely. Heating due to galactic or cosmic microwaves irrelevant,…
            One could enumerate thousands of ideas quantitatively irrelevant for the coma, or exceedingly unlikely to occur at all.

            At the end, the discussion about quantitative relevant effects other than sublimation or decomposition of instable minerals or salts is purely hypothetical; I’d see chances for fringe explanations to become scientifically relevant well below one in a million (aka exceedingly unlikely).

            Surprises and new insights are to be expected within the established framework. That’s what the mission is designed for.

          • Gerald says:

            Dark matter is probably present in our neighbourhood (provided it exists). But it’s very few, and it doesn’t interact the way normal matter interacts; it’s like ghosts who go through walls, planets, whole stars without notice. There is just a tiny pull by gravity. You need to sum up vast regions of space filled with this rare dark matter to get any observable effect. On huge scales, however, ordinary matter seems to be much rarer even than dark matter. Therefore on these huge scales dark matter becomes dominant over ordinary matter. Think of dark matter as a very dilute gas, which penetrates everything you experience physically, without any noticible interaction in everyday’s life. Ordinary matter is more lumpy, concentrated in “lumps” like stars, planets, dust.
            This dark matter “gas” forms structures the size of galaxies or galaxy clusters.

          • THOMAS says:

            @ Gerald

            “Think of dark matter as a very dilute gas, which penetrates everything you experience physically, without any noticible interaction in everyday’s life.”

            But I thought that the distribution of dark matter (if it exists) had to be cleverly devised so that it is present in precisely the required amounts/densities to play the role which is attributed to it – not at all like a “dilute gas”.

            This is the case, most spectacularly of course, in the outer reaches of spiral galaxies, where its presence is required in increasing amounts the further out you go, to explain the otherwise incomprehensible behaviour of outlier stars (incomprehensible for the standard theory, that is). This was surely why Fritz Zwicky invented it in the first place around 80 years ago, back in the 1930s.

          • Gerald says:

            @THOMAS
            Cold dark matter isn’t needed in increasing amounts the further you go out in a galaxy; it’s more like a spherical cloud of frictionless gas embedding the galaxy. The cloud usually is densest near the center, but not as lumpy as ordinary matter (due to lack of friction).
            There are exceptions with colliding galaxies, since dark matter doesn’t collide; it may leave the visible part of the colliding galaxy due to inertia.

            Well, and some are still discussing MOND theories, therefore “*if* dark matter exists”:
            http://en.wikipedia.org/wiki/Modified_Newtonian_dynamics

            Whatever version will turn out to describe large-scale dynamics better, it’s not the cause for heating the comet.

    • JP says:

      The layer is only 50 µm, but it might well be meters thick…
      It shows how well we know the -currently- dark side of the comet 😉
      Irony set aside, building such a model must be thrilling…

      • originalJohn says:

        There is not the smallest shred of evidence, Gerald to support the ice sublimation belief as a source of comet water. It is as unlikely as some of the other possibilities you mention, the biggest problem being no ice present.
        Production of water by a chemical reaction with energy supplied by protons and transport into the coma by plasma discharge is by far the strongest option.
        In consensus community the role of electricity has been ignored for at least a hundred years so the effect of the solar wind current has to be trivialised. It is not a recognised factor.
        Do you not ever ask yourself Gerald how it is that humanity has exploited electric power to the extent that our lives are completely dominated by and dependant on it yet nature in the rest of the universe gets by without it, and favours the vanishingly weak (trillions of time weaker) force of gravity.
        You may have gone into this mission with the objective of confirming existing beliefs but I think you will find that impossibly difficult., and nothing confirmed so far.

        • Gerald says:

          Apologies for some typos. I’ve been talking about the Sahara desert. And positive and negative electric charges annihilate each other..

          • Marco says:

            Hi Gerald, in a previous comment you have said “At the end, the discussion about quantitative relevant effects other than sublimation or decomposition of instable minerals or salts is purely hypothetical; I’d see chances for fringe explanations to become scientifically relevant well below one in a million (aka exceedingly unlikely).”

            That is all well and good, but the downside to thinking that all “alternative” theories are all equally unlikely, we blind ourselves to the basic excercise of making bold, falsifiable hypotheses, in favour of fitting in dubious data such as the neck thermal profiles, and dozens of other “interesting” details such as the physical structures on the comet into “thermal sublimation” model. Cometary science becomes like the field of psychology, as described by Karl Popper, where no new data can question incumbent models.

            There is plenty of evidence for stretch theory, and stretch theory is eminently falsifiable. Stretch theory makes bold predictions that further matches will be found along particular features in particular places that are only now emerging from shadow. Also, further measurements constrain the already infinitesimal probability that the matches could have any other explanation.

            https://scute1133site.wordpress.com/2015/03/01/67pchuryumov-gerasimenko-a-single-body-thats-been-stretched-part-16/

        • Gerald says:

          Marco,
          the Sun as the only relevant heat source, and sublimation (or sublimation-like processes) as the cause for the outgassing are excessively investigated and confirmed. I’m not aware of any serious scientist who questions this.
          That’s not mainly a matter of psychology, since scientists are notoriously sceptical, particularly regarding results of their competing fellows. They are cautios with making unbased claims for the same reason. That isn’t a waterproof warranty to be always right. But in the case of the basics about comets there is few doubt.

          The neck thermal profile, as well as the electric or magnetic deviations near that regions will turn out to be due to variations in composition (including porosity and dust layer), topography, and outgassing.
          I just tell you, how things will turn out to be, to avoid to make you wrong hopes.
          You may well continue your observations, but avoid mixing them with interpretations. So your observations keep their value, as your interpretation (stretch hypothesis) will most likely turn out to be spurious.
          Working that way provides you a chance to find better interpretations for your observations.

          • Marco says:

            Hi Gerald,
            Thanks for engaging with me. Evidence of stretch and associated phenomena, far from being spurious, continues to build. Every new image gives a new chance to falsify stretch theory, but instead, gives more data that supports it. I really consider it to be a fact, and cannot understand why, firstly, you are being dismissive of it, and secondly, why it hasn’t been officially been either ruled out or classed as a possibility where evidence could be looked at. It has only been argued in depth here in the comments and in a few other blogs.
            When scientists do finally come round, they will see that the evidence was there all along, and there will be obvious explanations as to why the modelling was wrong to never show stretching.

        • Gerald says:

          Regarding electrical engineers: It’s possible to understand both, electrical engineering and other fields of physics, that’s not contradicting.
          I’m certainly not confusing electrical engineers in general with the electric universe proponents, some of whom seem to happen to be electrical engineers.
          There are a majority of very capable electrical engineers who significantly help making space missions possible, and many other applications.
          I’m not really happy with electric universe proponents hiding behind electrical engineers. Electric universe promotion actually hasn’t much to do with serious electrical engineering, as it hasn’t much to do with serious physics or other fields of science.
          A good electrical engineer knows about the applicability and limitations of electrical engineering.

        • Gerald says:

          Hi Marco,

          talking about stretch hypothesis and better interpretations: Did you consider the close encounter of 67P/C-G with Jupiter 1959?
          That might have been an event with significant tidal forces involved.

        • Gerald says:

          Marco,
          the two favoured options for explaining the shape of the nucleus are contact binary versus preferred erosion/sublimation at the neck.
          It’s uncommon to enumerate all ideas which noone in the respective science teams or in the scientific community ever has been considering as anything else than exceedingly unlikely or inconsistent with highly successful “laws” of physics.
          Just in the very rare case, that all considered options fail to explain the data, one will start to look for new alternatives. Usually there’s no lack of ideas, but lack of clear evidence.
          So if you like your ideas to be taken seriously into account, you’ll need to write a paper in the usual style, which needs to go through at least some peer reviewing process.
          My prediction is, that the stretching hypothesis at the current state of elaboration wouldn’t survive the peer review.
          Or alternatively, after adjusting the stretch hypothesis to the usually accepted laws of physics, it would approximate one of the already considered hypotheses.

          • Marco says:

            I think you may be suggesting that stretch theory is inconsistent with known physics. It is patently not. Peer reviewed papers will be written about it sooner or later. The evidence isn’t going to go away.

          • THOMAS says:

            “Peer reviewed papers will be written about it [stretch theory] sooner or later. The evidence isn’t going to go away.”

            Hi Marco,

            It’s good to be optimistic, but as you know, the problem with peer-reviewed papers is that they are reviewed for publication by like-minded peers on the basis of what has already been “established”, as Gerald puts it. Anything remotely “fringe” has no chance.

            Galileo also had a hard time with the equivalent procedure in his time.

          • Marco says:

            There are 2 reasons to believe that there will be an accelerated version of what happened with Galileo. With Galileo, anyone with a telescope could check for themselves some of the evidence. Equally here the images in the public domain enable people to check for themselves over a period of weeks rather than gradually as the technology became ubiquitous.
            Secondly, the peer pressure, funding and incumbency issues are not as strong factors as they were in the Galileo affair. There is considerable possibility of a rogue subset of the scientific peer group deciding that fame and fortune may come to the first mover in a scientific sense. Once someone in the scientific realm realises the inevitability of the new paradigm, they will be delighted to be the initial outlier.

        • Gerald says:

          Hi Marco,
          not suggesting, that you will succeed that way, just as a vague idea, you may try to check the pressure of sublimating gasses (particularly CO) inside the comet. They may expand the nucleus like a heated marshmallow.
          Be careful, this idea is fringe, as well. But I don’t see an immediate contradiction to physics.

          When looking at probabilities, a deeper understanding of the hypergeometric distribution may help:
          http://en.wikipedia.org/wiki/Hypergeometric_distribution
          Consider both, observations supporting your idea, and gaps which should have been filled with matchings.

        • Gerald says:

          Elaborated: Fringe comet theory #113: 67P as cosmic popcorn.

          The mean surface temperature of Earth is 288 K. After subtracting 33 K due to greenhouse effect, the planetary equilibrium temperature of Earth is 255 K.
          Earth’s Bond albedo is 0.306. The planetary equilibrium temperature is proportional to the 4-th root of 1-albedo, and to the inverse of the square root of the distance to the Sun. The other way round, the distance from the Sun is proportional to the square of a given planetary equilibrium temperature. The mean albedo of 67P is 0.06, hence its equilibrium temperature at 1 A.U. at ((1-0.06)/(1-0.306))^(1/4) * 255 K = (0.94/0.694)^(1/4) * 255 K = 1.35^(1/4) * 255 K = 1.0788 * 255 K = 275 K.
          The boiling point of carbon monoxide at 1013 hPa is 81.6 K.
          The temperature ratio of the equilibrium temperature at 1 A.U. for the comet to the boiling point of CO at 1013 hPa is 275 K / 81.6 K = 3.37.
          Hence 81.6 K is the planetary equilibrium temperature for 67P at 3.37² A.U. = 11.4 A.U.
          The aphelion of 67P is 5.6829 AU. It’s distance from the Sun is hence always below the distance necessary achieve a planetary equilibrium temperature high enough to boil CO at 1013 hPa.

          Carbon monoxide has been shown to be present in 67P.
          Assuming insufficient cooling by sublimation and insufficient permeability for CO, we get a pressure build-up by CO in the interiour of 67P of more than 1013 hPa, after sufficient time to establish a thermodynamic equilibrium between the surface of 67P and its interiour.
          This pressure may overcome the cohesive forces between grains and “pump up” the nucleus like “popcorn”, years after entering the zone below 10 A.U.

          http://en.wikipedia.org/wiki/Bond_albedo
          http://en.wikipedia.org/wiki/Earth
          http://en.wikipedia.org/wiki/67P/Churyumov%E2%80%93Gerasimenko
          http://en.wikipedia.org/wiki/Planetary_equilibrium_temperature
          http://en.wikipedia.org/wiki/Carbon_monoxide

          • Marco says:

            There is nothing intrinsically wrong with this theory. I am not sure that it is falsifiable, and I guess that it may go some way to explaining low density, if nothing else. Could it power jets from the inside? Could it explain observed surface features? Probably not. The advantage with going through a lot of fringe theories is that you get a better chance to match otherwise confusing observations. Keep them coming. What are the other 112?

        • Gerald says:

          Hi Marco,

          the flaw in “frnge theory #113” is hidden in the implicite assumption of the cometary material to be ductile. It’s actually brittle.
          So we get either an outburst, or a disruption of the whole comet after such a high presumed pressure build-up. The other point is the heating from outside to inside, such that the inner will be cooled by sublimation of material from outer layers.
          The expansion effect hence may occur in outer layers, but just to some small degree, until fractures open, and the pressurized gas is released, or whole comet fragments are ejected.

          I’ve fringe ideas all day long, but some basic cross-checking rapidly rules out 99%. Only a small fraction of these ideas survive more than a few seconds. And an even smaller part is worth to be elaborated or published.
          Ideas of the “electric universe” type would be ruled out before even to become conscious, just by the routine to deal with ideas, and to see severe flaws within a fraction of a second.

  • Jacob Nielsen says:

    That last quote by mr. Sierks has been my view since november 15. (Looking back I used the words: remodeled after perihelion) Let’s see! – getting closer…

  • Bill Harris says:

    The Southern Hemi-Comet will indeed become a very active location in a few months. Not only will the Southern Summer be a Perihelion Summer with a large degree of insolation, it has also been in darkness for the last 2-3 years and serves as a tremendous cold trap for the volatiles being sublimated from the current Northern and sunlit Hemi-Comet. So not only are there the primordial volatiles of the comet body there are also the redeposited volatiles of the cold trap which should sublimate quickly because they are “fluffier”.

    The Max Planck Institute Press Release:
    http://www.mps.mpg.de/3903541/PM_2015_02_09_Rosetta_Komet_Auf_der_Suedseite_wird_s_heiss

    These are interesting times.

    –Bill

  • Ian C says:

    To what extent will this material loss affect the comet’s rotational state? Is it enough to result in other parts of the comet becoming exposed to greater illumination?

  • THOMAS says:

    Great to see Sierks and his team making this sort of concrete prediction, based on their various “assumptions”. It will act as a yardstick to regularly judge the validity of the underlying “sublimating ice” theory over the coming months.

  • logan says:

    Hi Ian C. After perihelion surface and kinetics will be transmuted, Maybe even integrity 🙂

  • logan says:

    Hi Emily and Max Planck Team.

    20m erosion… Your projection sounds kind of apocalyptic. (And the day turned night).

    I’m taking it seriously.

    Starting to down-vote on the EM spectra. Solar light and heat arriving at 67P nucleus is going to slide down quite significantly.

    Tasting more like ‘Vesuvius’ now 🙂

  • Marco says:

    My seasonal forecast for the southern hemiduck is very different. There is going to be little to no “remodelling” except for the North and South polar region, which will be subject to some cryovolcanism. Temperatures will be higher of course, and outgassing will happen from the lobes as much as or more than from the neck. There will be some more reduction in rotational period due to asymmetrical outgassing.

  • THOMAS says:

    Hi Gerald,

    I’ve just read your ongoing discussion with Marco with great interest.

    For my part, I would still like you to comment on the paradoxical VIRTIS findings regarding the totally antinomic *weak sunlight/high temperature values* observations in the neck region which I have already highlighted elsewhere in my two screen-captures from the video of Fabrizio Cappacioni’s presentation at the AGU Fall meeting:
    https://www.flickr.com/photos/130179313@N03/15927644524/
    https://www.flickr.com/photos/130179313@N03/16524318826/in/photostream/

    May I remind you that this obviously crucial anomaly strangely elicited no comment from Fabrizio Cappacioni during his talk. And so far, there has apparently been no plausible explanation from anyone else in terms of the standard theory. Is there something wrong with the data, or what?

    • Gerald says:

      It took me some time to fully understand, what the data actually mean. But by now I’m rather sure that it’s quite easy, obviously too trivial to have been mentioned during the talk:
      The data have been taken at full solar illumination, since VIRTIS isn’t sufficiently sensitive to measure very low temperatures on the night side. I first considered it could have been shortly after sunset. Assuming the measurements been taken of shadowed areas is probably the basic wrong assumption leading to the somewhat strange conclusions.
      I calculated the planetary equilibrium temperature for the comet at 3 AU; it should be near 160 K. A temperature of up to 220 K is explained by the low albedo and the low thermal inertia of the surface, together with near vertical solar illumination.
      The paper calculated a thermal inertia of below 50 SI units; for the defintion, see e.g. wikipedia: http://en.wikipedia.org/wiki/Volumetric_heat_capacity#Thermal_inertia
      That low thermal inertia is most typical for a layer of fluffy dust on the surface.
      This method has also been applied to Mars to successfully predict properties of the surface layer, i.e. to distinguish exposed bulk rock from dust- or sand-covered surfaces.
      Compare also the surface temperature of the Moon; its up to 390 K, more than 120 K above its planetary equilibrium temperature.
      http://en.wikipedia.org/wiki/Moon
      So 60 K above planetary equilibrium temperature for a very fluffy dust cover on the comet in the low gravity environment, is much, but still within reasonable parameters.

      • Gerald says:

        Thermal inertia is also known as thermal effusivity e.g. in the context of cooling electronics.

      • THOMAS says:

        @ Gerald

        “A temperature of up to 220 K is explained by the low albedo and the low thermal inertia of the surface, together with near vertical solar illumination.”

        Sure, but in that case why do the same conditions not apply to the *rest* of the sunlit side of the comet which constantly receives “near vertical solar illumination” for considerably longer periods? These areas are nevertheless considerably *cooler* than the Hapi valley region!

        I’m sorry, but your contingency-based special pleading about the data highlighted in my two AGU video screen captures having probably been obtained “shortly after sunset” explains nothing. Hapi Valley is a canyon with steep walls on either side and the hypothesized low thermal inertia simply does not account for the fact that the actual *warming from sunlight* is necessarily considerably *lower* than on the fully-sunlit lobes (even at “midday”).

        This problem will not go away and it is not sufficient to simply assert that it is “too trivial to have been mentioned during the talk”. It is, on the contrary, clearly a major headache for the standard theory.

        • Gerald says:

          I’ve been wrong with my first consideration, that your two referenced AGU slides might have been taken shortly after sunset. After following the links I found out, that they’ve been taken at full solar illumination, as I’ve already said.
          I don’t see anything fundamentally unusual with these images. Nothing but temperature data, which are readily explained by reasonable surface properties and topography.

          • THOMAS says:

            @ Gerald

            “Nothing but temperature data, which are readily explained by reasonable surface properties and topography.”

            In terms of *topography*, perhaps we can make a comparison with the final resting place of Philae. The hottest region on the comet surface (the Hapi Valley neck region) happens to lie all along the bottom of a canyon, enclosed by towering cliffs. Philae is presumed to repose at the bottom of a crevice, as confirmed by the images it sent back to us of enclosing rock-walls before going into hibernation.

            The scant thermal energy received by Philae because of its unfavourable topographical situation is feared to be insufficient to power it up again, whereas if it had not rebounded from its initial landing point, it would for months past have been receiving all the solar energy it needs to operate.

            So, other things being equal, why should different laws of physics apply at the bottom of Hapi Valley which is HOT, than at the bottom of Philae’s crevice, which is COLD?

          • Gerald says:

            @THOMAS
            With Philae at Hapi he would operate right now.
            So no, the current resting place of Philae, and Hapi are rather different in terms of solar illumination.
            Besides this, the area around Philae seems to be less dust-covered than Hapi, hence it’s likely to posess higher thermal inertia.
            Towering cliffs don’t necessarily shadow the bottom. There are at least two directions free of cliffs, those along the “canyon”. There are lots of images showing Hapi in sunshine. What are the actual solar angles at the active or the warmest parts of Hapi?

            See also this LPSC2015 paper:
            http://www.hou.usra.edu/meetings/lpsc2015/pdf/2156.pdf
            “In all cases, direct
            correlation with topographic features is observed, i.e.
            largest temperature values are generally associated
            with the smallest values of illumination angles, while
            so far there is no evidence of thermal anomalies, i.e.
            places of the surface that are intrinsically warmer or
            cooler than surrounding terrains observed at the same
            local solar time and under similar solar illumination.”

            I wouldn’t rule out that the resting place of Philae starts getting active later this year, while Hapi may be going to reduce activity.
            But it depends a bit of the actual surface and material properties around Philae. Acually I hope, the solar panels won’t become covered with dust.

        • Gerald says:

          Ok THOMAS, in the meanwhile, your misinterpretation of the VIRTIS image seems to be identified in a more recent threat.
          – the VIRTIS image is not about mean temperature, but a snapshot in full solar illumination.
          A mean temperature of 220 K would have been an anomaly, not so in a snapshot at noon.

          • THOMAS says:

            @ Gerald

            “a snapshot at noon”

            What is the basis of your claim that the VIRTIS data was collected “at noon” (in *both* the images)? Are you a member of the VIRTIS team or has the full data already been released for general consultation and analysis? Even if it was, the overall absorption of solar energy at the bottom of Hapi Valley was necessarily less on that day than on the the fully exposed lobes, which were nonetheless considerably cooler. This is not a misinterpretation by any means and just calling is so doesn’t make it so.

          • THOMAS says:

            In reality, by “misinterpretation”, I suspect that you actually meant a “different” interpretation from your own.

            Even there, I beg to differ: for my part, I am “interpreting” absolutely nothing. I have simply *drawn attention to* data (the apparently anomalous VIRTIS temperature data observed at the bottom of Hapi Valley) which had thus far escaped wider publication. If, for your part, you then “interpret” the data by invoking an increasing number of required contingencies to account for it within the framework of your preferred theory, I see no problem with that. It just needs to be correctly understood that what you affirm is not actual fact but simply your own interpretation of the published data, based on prior belief.

            For my part, when it then comes to formulating a theoretical explication of the observed data, I still prefer the old-school application of the principle of Occam’s razor, without all the contingencies you invoke.

          • Gerald says:

            Quite simple, I’m reading the accompanying papers and abstracts.
            Even the VIRTIS images, you linked to, contained links to sufficient information to interprete the images in an appropriate way.
            I’ve provided direct links elsewhere, repeatedly.

          • Gerald says:

            One example, for convenience:
            “Only LST between 12 h and 14 h (i.e., those
            experiencing the maximum daily insolation) are
            shown.”
            http://www.hou.usra.edu/meetings/lpsc2015/pdf/2156.pdf

          • Gerald says:

            THOMAS: “… the apparently anomalous VIRTIS temperature data observed” is a mis-interpretation, since it’s in contrast to the version of the instrument scientists

            “there is no evidence of thermal anomalies,” of the same paper:

            http://www.hou.usra.edu/meetings/lpsc2015/pdf/2156.pdf

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