Exposed ice on Rosetta’s comet confirmed as water

This article is mirrored from the main ESA Web Portal.

Click for high-res version.

Click for high-res version.

Observations made shortly after Rosetta’s arrival at its target comet in 2014 have provided definitive confirmation of the presence of water ice.

Although water vapour is the main gas seen flowing from comet 67P/Churyumov–Gerasimenko, the great majority of ice is believed to come from under the comet’s crust, and very few examples of exposed water ice have been found on the surface.

However, a detailed analysis by Rosetta’s VIRTIS infrared instrument reveals the composition of the comet’s topmost layer: it is primarily coated in a dark, dry and organic-rich material but with a small amount of water ice mixed in.

In the latest study, which focuses on scans between September and November 2014, the team confirms that two areas several tens of metres across in the Imhotep region that appear as bright patches in visible light, do indeed include a significant amount of water ice.

NAVCAM images showing the locations of the icy exposures in Imhotep. Credits: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

NAVCAM images showing the locations of the icy exposures in Imhotep. Credits: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

The ice is associated with cliff walls and debris falls, and was at an average temperature of about –120ºC at the time.

In those regions, pure water ice was found to occupy around 5% of each pixel sampling area, with the rest made up of the dark, dry material. The abundance of ice was calculated by comparing Rosetta’s VIRTIS infrared measurements to models that consider how ice grains of different sizes might be mixed together in one pixel.

The data reveal two different populations of grains: one is several tens of micrometres in diameter, while the other is larger, around 2 mm.

These sizes contrast with the very small grains, just a few micrometres in diameter, found in the Hapi region on the ‘neck’ of the comet, as observed by VIRTIS in a different study.

“The various populations of icy grains on the surface of the comet imply different formation mechanisms, and different time scales for their formation,” says Gianrico Filacchione, lead author of the new study, published in the journal Nature.

At Hapi, the very small grains are associated with a thin layer of ‘frost’ that forms as part of the daily ice cycle, a result of fast condensation in this region over each comet rotation of just over 12 hours.

“By contrast, we think that layers of the larger millimetre-sized grains we see in Imhotep have a more complex history. They likely formed slowly over time, and are only occasionally exposed through erosion,” says Gianrico.

Assuming a typical grain size of tens of micrometres for ice grains on the surface, as inferred on other comets as well as Rosetta’s comet, then observations of millimetre-sized grains can be explained by the growth of secondary ice crystals.

One way this can occur is via ‘sintering’, whereby ice grains are compacted together. Another method is ‘sublimation’, in which heat from the Sun penetrates the surface, triggering the evaporation of buried ice. While some of the resulting water vapour may escape from the nucleus, a significant fraction of it recondenses in layers beneath the surface.

This idea is supported by laboratory experiments that simulate the sublimation behaviour of ice buried under dust, heated from above by sunlight.

These tests show that more than 80% of the released water vapour does not make it up through the dust mantle, but rather is redeposited below the surface.

Additional energy for sublimation could also be provided by a transformation in structure of the ice at a molecular level. At the low temperatures observed on comets, amorphous ice can change into crystalline ice, releasing energy as it does so.

“Ice grain growth can lead to ice-rich subsurface layers several metres thick, that can then affect the large-scale structure, porosity and thermal properties of the nucleus,” says Fabrizio Capaccioni, VIRTIS principal investigator.

“The thin ice-rich layers that we see exposed close to the surface may be a consequence of cometary activity and evolution, implying that global layering did not necessarily occur early in the comet’s formation history.”

“Understanding which features on the comet are left over from its formation and which have been created during its evolution is somewhat challenging, but this is why we are studying a comet up close: to try to discover what processes are important at different stages of a comet’s lifetime,” adds Matt Taylor, ESA’s Rosetta project scientist.

The Rosetta scientists are now analysing data captured later in the mission, as the comet moved closer to the Sun in mid-2015, to see how the amount of ice exposed on the surface evolved as the heating increased.

“Exposed water ice on the nucleus of comet 67P/Churyumov–Gerasimenko,” by G. Filacchione et al is published in the journal Nature



  • Marco Parigi says:

    This is rather interesting: “The thin ice-rich layers that we see exposed close to the surface may be a consequence of cometary activity and evolution, implying that global layering did not necessarily occur early in the comet’s formation history.”

    The argument that Gerald had made in the blog comments regarding Steno's law not requiring a "fluid" layer to be actually liquid for it to cause layers seems quite a lot harder using "cometary activity and evolution" than it does with arbitrarily modellable accretion formation scenarios.

    • ianw16 says:

      From the paper:

      "Although micrometre sized water-ice grains are the usual result of vapour recondensation in ice-free layers, the occurrence of millimetre-sized grains of pure ice as observed in the Imhotep debris falls is best explained by grain growth by vapour diffusion in ice-rich layers, or by sintering. As a consequence of these processes, the nucleus can develop an extended and complex coating in which the outer dehydrated crust is superimposed on layers enriched in water ice. The stratigraphy observed on 67P/Churyumov–Gerasimenko, is therefore the result of evolutionary processes affecting the uppermost metres
      of the nucleus and does not necessarily require a global layering to have occurred at the time of the comet’s formation."

      • logan says:

        "... and does not necessarily require a global layering to have occurred at the time of the comet’s formation."

        This is really about 'modularization' of models. Which is a very inclusive form of doing science 🙂

      • Harvey says:

        Yup. Next mission needs to take a big saw and slice the comet in half 🙂
        Which in a sense was what the CONSERT experiment was trying to do. Of everything lost with Philae's unfortunate premature demise, I think the lack of CONSERT data is in many ways the most unfortunate. It was the only way to 'look inside'.

        • ianw16 says:

          I believe there will be more to come from CONSERT. However, as you say, only based on the limited operation time it had available. I'm assuming this will become a paper at some time:

          • Harvey says:

            I'm sure they will mine what data they got for every grain of understanding. But it was very limited sadly.

        • logan says:

          Maybe knowing now landing approximation and crystallization axis. Reintegration could be made optimized to the new knowledge.

    • Gerald says:

      Take one of the smooth dust deposits. Let part of it sink in due to local loss of subsurface supervolatiles, and you get terraces looking like layering.
      Uneven sinking may be due to compositional variations or by different solar illumination, e.g. by shadows of cliffs.

      Some of the evidence for the contact binary hypothesis is going to get ambiguous, and can be used as evidence for a mainly erosional model, as well.

      The captcha showed waterfalls with similar terracing.

      • Marco Parigi says:

        Hi Gerald,
        If you model this "sinking" on a supercomputer or a suitable experiment, the flatness of the bottom just reflects the incumbent flatness of interface between volatiles of contrasting volatility. How that interface became flat, or layered is what is interesting, and can be reasonably explained by Steno's law, and on Earth, layers can be by Steno's law or by living processes, such as growth rings in trees, or onion rings.

        Explaining terraces ie. Flatness to gravitational vector by the proximal processes that can be observed, to me, is similar to explaining growth rings in petrified wood as due to the process of petrification rather than the growth of the wood.

        The layers on 67P are pervasive, and what could explain a single flat area, say with a dust covering that could make a filled in hole look flat, cannot explain the sheer number and variety of flat areas and their seeming interrelatedness when following the lines the way a field geologist would.

        • Gerald says:

          Hi Marco,
          the sinking doesn't need to be flat. The settling debris and dust will fill in part of the depression, and form a smooth and almost flat surface.
          Although once the deepest part of the depression is filled with dust, it will slow down sublimation there due to thermal isolation. Small hills stay more exposed to the Sun, and degrade faster, with an almost flat surface as a result.

        • Marco Parigi says:

          Hi Gerald,
          I'm not sure why, after promoting Steno's law in previous posts, you have essentially dismissed it in this more recent post, as an explanation for layers and flatness.

          What we need as a reality check for you is to see if the ongoing observable "erosion" on the large flat expanse of Imhotep follows your narrative. It clearly does not.
          Also, visible strata that follow on from flat areas, that can be seen parallel when viewed from side on really points to layers being exposed rather than being formed by erosion. They look fractured or delaminated.

          Also How is it that the amphitheatre is so flat, yet nearby Hapi, with even more of a dust coating is not. The dust filling, and differential small hill erosion is an ad hoc explanation that superficially works for some instances of flatness, but just cannot explain the layering. Steno's law still needs to be invoked in some way or another.

          • Gerald says:

            Hi Marco,
            I'm trying not to be prejudiced to one singular scenario, but instead to look at the physically reasonable possibilities within the observational evidence.
            Flat areas can form by sedimentation as well as by some kinds of erosion, as well as by some mix of the two.

            Dust settlement can easily be made consistent with Steno's laws. But erosion/weathering/sublimation is evident, too. So both can act intertwinned together, and needs to be kept in mind.

            Those missions are interesting, because we can learn something. Just selectively looking for confirmations of whoever's presumptions would underappreciate the richness of the experience and risk loss of science return. So I try to understand the possible options, and as long as they don't run into too many nested ad-hoc assumptions they stay options.

          • Marco Parigi says:

            Hi Gerald,
            I have no problem with not being prejudiced to one singular scenario. In fact, I find the dichotomy between erosion and sedimentation (of dust grains in a microgravity vacuum) to be quite limiting.
            Steno's Law, at least, has a very broad base of application and verified examples.

            In the larger scale, the nucleus is supposed to be eroding from the outside in. A lot of dust and boulders reaches escape velocity and is lost forever. That leaves very little scope for the redeposition of layers, and erosion should be smoothing in the large scale (ie. Making the nucleus closer to a sphere) rather than flattening this or that area with a very un-spherical total body., defying a description of a rubble pile. In fact, early predictions of nuclei were of bright spheroids rather than dark peanuts.

            Possible options are all well and good, but many, such as stretch, and relatedly, a warm core or thicker crust are routinely dismissed. There would be no harm to adding other, physics consistent options, even if they are inconsistent with the pristine, cold soak narrative of comets.

          • Gerald says:

            Hi Marco,
            comets made of material of e.g. Saturn's rings or ejections of Io's volcanoes would be interesting. But it needs convincing evidence to be more than purely hypothetical.

          • logan says:

            Hi Marco. "In the larger scale, the nucleus is supposed to be eroding from the outside in..."

            Why do you think that, if according to lab testing 80% of sublimation doesn't reach surface?

            I'm not sure if surface is changing more than inside.

          • logan says:

            On chat have heard my engineer brother talk of vapor 'trailing' of citric oils. So, that 80% subsurface sublimate's kinetics are also 'trailing' organics, ceramics and salts. [domestic trade ;)]

          • Marco Parigi says:

            Hi Logan,
            In the standard cometary model, there is no alternative to erosion happening from the outside in, in the large scale.
            This is because in the standard model, heat only reaches effectively to the top few metres. For the heat to reach further down, the top layer has to erode or collapse down. Sure, there would be some thermal exchange and diffusion due to various thermodynamic cyclical effects, but the average thermal profile would have material in the nucleus hotter the closer the point is to the surface. Thus the "80 % of sublimation doesn't reach the surface" is necessarily a temporary diurnal feature, as resublimation again can only happen from the outside in, at the heating side of the cycle and overall.

            As far as the shape goes, yes, plastic deformation implies the fizzing goes wild, but whether that means disintegration is inevitable is another story. There is actually evidence for fizzing (or bubbling mud pools) that have since hardened, at least from my interpretation of the surface morphology in areas around Imhotep. The fizzing appears to be self limiting.

          • logan says:

            Hi Marco. On Teams acknowledging a porous object the concept of erosion is no longer surface only. Layering, fracturing, differential sublimation and later polyhedral clues has scaled up this acknowledging. There are paths speculatively reaching even half the radius of ducky. [Some outbursts at body have show clues of traversing all of the body -both sides-, etc.]

            On OSIRIS publications, believed this issue consented.

          • logan says:

            Supporting the general visual allegory of a crumbling down, abandoned vessel. But sooner or later -at an active comet- some chamber is going to pressure cede, or simply collapse. And Erosion will go suddenly well below the decameter envelope. Some well thermally isolated layer is going to have the time window to fill with fluid, and start a sliding, etc.

            Maybe this is just my fiction, Marco 🙂

        • logan says:

          Hi Marco. Remember the selfie of ROSETTA shadow on that extreme close-up? proto-mantle material?

          I have no doubt 67P could be subject to plastic deformation. But occurring on a global scale, fizzing would go mad, and at this micro-gravity would mean disintegration.

          Fizzing is a very important deterrent of plastic flow, on micro-gravity.

          • logan says:

            As for myself, could see those proto-mantle deposits as re-sintered, almost [but not quite] dry dense foams. Happy selfie, Ducky 🙂

          • Marco Parigi says:

            Hi Logan,
            To be clearer, I will use the analogy of the Grand Canyon. One can say that erosion from the Colorado River does not just happen on the surface. One can also say that not all flat areas on the Grand Canyon are caused by the primeval layering subject to Steno's law. However, the formation of the canyon from erosion is necessarily from the top down (from the outside in), and that the layering *Must* predate the erosion process considerably. To even contemplate internal erosion, the primordial cold soak paradigm must be changed.

          • logan says:

            Hi Marco. How erosion is happening at Yucatan white plains? Please be careful while you walk around..

          • logan says:

            "...and that the layering *Must* predate the erosion process considerably."

            I err a lot on this also, Marco. The complexity is enormous. Space in the modeling should be allowed, for a continuing deposition, as strongly suggested at Imhotep basin an other sites, as well as the undisputed erosion happening right now.

      • logan says:

        Likely scenario. Sinking should happen before sintering repeat itself.

  • ianw16 says:

    Interesting paper. Not all that surprising about the cliff locations, given the link Jean-Baptiste Vincent posted in another thread a few days back, about the activity in those regions. As well as the bright exposures on many of the boulders which was published some time ago.

    For anybody interested in the plasma environment at 67P, there was a paper released recently which gives some recent observations (free access):
    Contains the first (other than conference abstracts) confirmation that a diamagnetic cavity was observed, although that isn't what this paper is primarily reporting on.

    • Harvey says:

      Thanks for the link; it takes a bit of working through!

      • ianw16 says:

        " takes a bit of working through!"
        Glad I'm not the only one! The lead author offered to take me through it, but I fear I won't live that long!
        Thankfully, the submitted paper on the diamagnetic cavity (which I do understand!) is submitted to the same journal, so will be open access (Götz, C., Glassmeier, K.-H., and More: First Detection of a Diamagnetic Cavity at Comet 67P/Churyumov-Gerasimenko, Ann. Geophys., submitted, 2015.)

        • originalJohn says:

          Ah that plasma stuff, so difficult eh, hardly worth bothering with compared to the photon induced warming of a lump ice in a vacuum story. But yes this sort of stuff does more to obscure the significance of the plasma environment than clarify it. Some straightforward ion identification and concentration analysis would be more useful along with a magnetometer plot of the magnetic field of the nucleus so that its extent, shape and origin could be seen.

          • ianw16 says:

            Have you read any of the papers that have been published from this mission? Or any other? THERE IS NO MAGNETIC FIELD. End of story. The only magnetic fields are those in the coma, induced by the SW interaction with the sublimating neutrals/ ions. There is plenty of data from this mission, and from Halley in particular, about such things. Philae landed on the comet. NO MAGNETIC FIELD. RPC have been studying it for nearly 18 months. Nothing. Zero. Zip. Read up on the diamagnetic cavity. NO MAGNETIC FIELD. Read the literature.
            As for ions, there is plenty, and more to come. Neutrals massively outnumber ions for a start. None of this helps this silly, evidence free electric comet nonsense.
            As for the paper we were talking about; I'm sure you can find the lead author's contact details; email him and tell him how wrong he is, and how EU know far more about plasma than he does. And how all the time he spent in Alven's lab was a waste of time, because EU knows better.
            Just be sure to lay out your qualifications first. And your sources.

          • martin says:

            Of course you could have a look at this paper, it's full of plasma yummieness and it is freely available

        • Sovereign Slave says:

          In the paper (thanks for linking, martin), it says this:

          "The solar wind transports magnetic fields from the Sun towards the comet."

          I'd never heard this before, though it may easily be common knowledge. But I'm trying to wrap my head around a magnetic field (whatever that is) holding together and being "transported" as some independent, self-sustained phenomena. How are these fields formed, sustained, and transported; are they continuous and everywhere, and if not, how big are they, what is their shape, what keeps them unified magnetically as a "field" and what keeps them magnetized; at what speed do they travel, do they diminish with distance from the sun?

          • Harvey says:

            Sovereign Slave.
            I sympathize with the question.But unfortunately any comprehensive answer is book thick!
            I always feel like saying 'its too complicated to explain here........' sounds like a get-out, but sometimes its just true. Plasma physics is one of the most complex & difficult subjects I know.

            The easy bits:
            Yes, it is continuous in the mathematical sense.
            The fields are very small, typically nT, tens of nT (compare the earths field, order 50uT or 1000 to 10000 times stronger.That itself is a small field - you only notice it if you have a compass. In the lab I've used 10T field.) However because they operate over huge distances they still have an effect.
            The fields are basically due to current flows; but because the conductor, plasma, can move, that gets complicated.
            A magnetic field stores energy; energy cannot be created or destroyed; the field will persist until something acts on it to change it; add or remove energy; its spatial distribution, local intensity could evolve; but overall it can't decay.
            A perturbation in a magnetic field *in vacuum* travels at the speed of light; ; but in *a plasma* a whole collection of wave phenomena exist with differing propagation speeds, see

            The underlying problem is the vocabulary, inherent unspoken assumptions & analogies that are second nature to plasma physicists.
            I'm not one & I struggle at times.
            No one thinks field lines 'exist' as some here imagine; they are simply a way to visualize the continuous field.
            So how can 'field be transported'?
            In a way, this is a shorthand.
            We have the system in some given state, and the field contains some recognizable structure.
            We compute, or measure it, at some later time; That structure, maybe distorted a bit, still exists but has moved; it moves & evolves continuously with time. So to the eye that structure has been 'transported' by whatever is going on in the system. Nothing 'picked it up & moved it' which is the commonplace meaning of 'transported'. That's just how this system behaves - so the shorthand is that the phenomenon 'transported' the field.

            There are many (over) simplifications here, & my understanding of this is relatively superficial, but I think that gives you an *idea*. Corrections or improvements by those with better knowledge to the explanation welcome.

          • Gerald says:

            The SOHO movies may add a mosaic piece in understanding how the plasma and the magnetic fields behave:
            Things are complicated by the rotation of the Sun. It twists the magnetic field, which would be more or less symmetric without this rotation.

          • Sovereign Slave says:

            @Harvey, does seem like semantics often plays a large role in trying to understand what's being explained. Seems much of cosmology could use your advice about not using earth based corollaries when naming stuff in space, like "winds," "waves," "fields," etc. Having said that, I'll proceed to use one, however. As I read you, plasma creates the magnetic fields. My understanding is that plasma is a form of energy, and one of the results of that energy is the magnetic fields. If this is a dependency relationship in which the magnetic fields in this instance cannot exist independently of the plasma, and plasma is the energy source, how is it that a magnetic field could "store" energy? Seems that would imply that the magnetic field could then exist independently of the plasma within its own energy source. So, as to my earthbound analogy, seems similar to saying that an electric magnet could store energy once the electricity is cut off. Heady stuff, but very interesting.

          • Gerald says:

            Sovereign Slave,
            indeed, a magnetic field stores energy. You'll get a spark when suddenly cutting direct current from an electromagnet.

            Plasma is a very hot gas, a forth phase after solid, liquid, gas.
            It stores energy, as well. But due to the high temperature it is ionized, and can thus conduct current. So the plasma can form kind of an electromagnet.
            An attempt to reduce the magnetic field will again induce a current into the plasma.

            Magnetic energy on Wikipedia:

            Ignition coil used in cars:

          • Harvey says:

            Sovereign Slave.

            One problem with semantics, is that it depends who is listening.

            If you say 'wave' to me in this context, I have no image of a water wave say; what comes to mind is the wave equation, and extremely general equation that turns up all over the place. What pops into my head it d^2 u/dt^2=c^2 Del^2 u, not crashing breakers on a shore.

            Similarly 'field' has a very specific meaning, with defined mathematical properties. ('Wind' however is a bit less precise..)

            Saying 'plasma is a form of energy' is not a phrase I would use. Certainly it stores energy in a whole clutch of different ways, and to call it 'a form of energy' is an oversimplification that obscures more than it illuminates.

            It's perfectly possible to have a plasma with no magnetic field, and it's perfectly possible to have a field with no plasma. A magnetic field stores energy in the absence of a plasma, and it consumes some energy to establish it, but not to maintain it. For example a coil of wire of inductance L carrying a current I stores an energy E=(L I^2)/2.
            If the wire is superconducting, the field will just sit there indefinitely - indeed it's been proposed for energy storage, but it's rather impractical. However in the lab it is commonplace to use superconducting coils in 'persistent mode' to generate high magnetic fields.

            In many cases, especially in astrophysics, magnetic fields and plasmas are intrinsically and intimately interlinked. The conductor generates fields, but the fields can move the conductors, in a very, very crude summary of the problem.

            Unfortunately, whilst some people wish to deny it, there are things that really only are describable in more than the most basic terms - and sometimes barely that - if you don't have the math. Here the basic tool is vector calculus, which is well into degree level math, and one many students find difficult :-(.
            That 'Del^2' in the wave equation is the Laplacian from vector calculus. Without these tools, any detailed up understanding is.......difficult.

            Math is the language of physics. If you want to really study French literature, you need to speak French. Physics and math have pretty much the same relationship, crudely put. Putting it into words is (worse than) translating the French into English; much is lost in that translation.

    • logan says:

      Thanks ianw16 🙂 Way out of my league... Seems to preliminarily suggest that 2015jun outburst was caused by purely thermodynamic phenomena.

      • ianw16 says:

        ".......was caused by purely thermodynamic phenomena."

        Oh, I don't think there's much room for doubt there. The lead author of the plasma paper frequents a forum I use. To paraphrase him, 'the solar wind has been missing for months. We're only just starting to see it again now." That was written within the last week or two.
        Any 'hypotheses' for various process on the surface that invoke the solar wind, will have to explain them in terms of the density (when it does reach the surface), and the continuation of those processes when the solar wind is no longer reaching the surface.

      • martin says:

        Okay, I guess I did something wrong posting the last time, so try once more.

        In the beginning I thought that the processes observed in the RPC data were linked to the outburst, but then that did not seem to fit, and I got the solar wind data, which made more sense.
        So, yes, the outburst is still a thermodynamic phenomenon. And as the picture is so pretty and it shows how active the comet is, I left it in our paper.

        • logan says:

          Thanks Martin. Hope your Team eventually ponder Out-Reach products, on the extremely definitory issue of 67P plasma evolution 🙂

    • Dave says:

      Interesting link to Diamagnetic cavity.

      I will need to read it a few more times yet though.

      This may be repeated (captcha issues)


  • logan says:

    "...Although water vapour is the main gas seen flowing from [67P]...", surface ice is a lesser actor at surface, suggesting of a very active inside.

  • logan says:

    "These tests show that more than 80% of the released water vapour does not make it up through the dust mantle, but rather is redeposited below the surface."

    This makes for a lot of mass transit!

    • logan says:

      Wander is this 80% reference is an average. It should be high 9X% at aphelion...

  • originalJohn says:

    Well, where to begin on this presentation of the quest for the longed for ice. You say emily

    "a detailed analysis by Rosetta’s VIRTIS infrared instrument reveals the composition of the comet’s topmost layer: it is primarily coated in a dark, dry and organic-rich material"

    This hugely dominant organic layer and its possible role in comet activity appears however to be of little or no interest to the investigators in their supposedly objective examination of the nucleus.

    In any event let's start this criticism with the upper central image showing the abstractions of the areas of analysis. Two circular regions a few hundred metres across progressing to two rectangular areas a few more hundred metres across and finally to a rectangular analysis area with no length scale but perhaps suggested to be about 400 m across. Now I am normally quite good at shape recognition in images but I do not see any shape match from one image to the next in these. What are these abstractions supposed to depict?

    Nevertheless it is apparent that in both cases the extent of the water ice region is 50 metres or less. About the size of a large boulder and not at all representative of the nucleus surface. And let us be clear that the water ice maximum abundance shown of 0.5% is not the abundance over the nucleus as a whole or even within the selected area. It is the abundance within one pixel, as the text explains. So what?

    Areal ( a nice helpful word that nobody has ever heard of) or intimate the abundance of ice is so minute as to be of questionable significance at all, and on a body held to be composed mainly of ice. And once again I would say that white cannot be used as a definitive band on a colour scale when there is no colour possible beyond white.

    Clearly the left hand side colour image and the image from the VIRTIS camera are of matching areas, with the white areas in the colour image matching the deepest red of the VIRTIS image. The red in these areas does however appear deeper than the maximum shown on the colour scale and corresponds to the maximum intensity of white. These areas are therefore indicating higher temperatures than the scale maximum, and there is no comment on this. In fact the most striking thing on the VIRTIS image is the extent and distribution of the "hot" zones and that even in the position corresponding to the ice there is a hot ring around it. And the fact that a large hotspot occurs in the lower right corner of the frame or what happens further to the right is of no interest. Hardly an objective depiction of the VIRTIS data,

    I hope to continue this in a further comment but finally for now I would say that both VIRTIS images show a surprisingly fragmented temperature distribution over a comparatively small area of nucleus surface for a massive body hypothesised to be heated only by uniform photon radiation from the Sun. A span of 38 deg C. the difference between a sweltering hot day and a freezing cold day here on Earth, multiply leaping up and down over an area a few hundred metres across. No comment on this by the investigators. More the sort of thing to be expected from local surface reactions producing heat.

    • emily says:

      Hi OriginalJohn

      Sorry that you found the images unclear. The circles in the main NAVCAM image are there to guide the eye to the locations of the exposures and clearly do not directly translate to the rectangles, which are excerpts from different images (and chosen with the intention to find the best examples of the icy exposures). You can find links to the full size originals in the caption information, in case that is helpful:
      Scales are given on all three images to give you an idea of the size.

      Re: the day-night temperature difference; while not a focus of this particular story, note that this has been reported before – the reference that immediately springs to mind is not however at Imhotep, but reported in situ by Philae at Abydos; for example:

    • ianw16 says:

      "VIRTIS images show a surprisingly fragmented temperature distribution.............More the sort of thing to be expected from local surface reactions producing heat.''
      No. Try reading some of the relevant papers from this mission. Including this one. The ice rich areas are generally cooler, for a start. Secondly, this is chaotic terrain, so it is not a flat plain where every area is at the same angle with respect to the Sun. Big difference in a vacuum.

      As for the temps, they are clearly labelled in the paper:
      Fig. 2d 150-188.4 K. Fig. 2f 155-205 K. Those will be the maxima and minima. If you don't believe that, try emailing the author. His address is on the paper, and "Readers are welcome to comment on the online version of the paper."

      As for the areal (a word I most definitely have heard of) extent of the ice, it is merely an indication of what the rest of the area may be like. These are debris falls. Ergo, this material is indicative of the terrain from which it fell. They probably don't have time to sample the entire surface.
      However, it would be freakishly coincidental if the exact area they smashed an impactor into at Tempel 1 happened to be the only area on the comet with similar sized ice grains. Ditto that they just got lucky at Hartley 2, when the CO2 jets just happened, of all the places, to occur where there was surface/ subsurface ice.
      As it stands, we now have subsurface ice, as seen by MIRO in the first few 10s of cms below the surface. Also borne out by the Tempel 1 and Hartley 2 data. We have transient ice observed in shadowed areas before it sublimes as part of the water ice cycle. We also now have ice mixed areally and intimately on and near the surface.
      And we have the sublimation product of this ice in the coma.
      Nowhere have we seen any massive increases in flux of the solar wind. And nowhere have we seen any temperature anomalies of note.
      Have I missed anything?

  • Jon says:

    It's unfortunate that Philae was lost. I haven't followed much detail since. I do recall that Bibring mentioned that they had samples in Philae that could be analyzed when it came back up briefly (last spring?). Were those samples analyzed??

    • Gerald says:

      Besides the initial analysis after landing, there haven't been received according data, as far as I know.

  • originalJohn says:

    In this second part of my criticism I would like to refer to Gianrico Filacchione's inferences about the relationship of ice particle size to ice origin, These are entirely speculative. It is impossible to deduce the origin of ice particles from their size. There are dozens of factors that can affect this. So once again the preferred inferences are chosen and highlighted, If water were produced at the surface by some other means than the chosen hypothesis and the comet origin was other than the preferred explanation exactly the same ice particle range could form for numerous reasons, At the very least it would be expected that two or three possibilities would be discussed.

    Returning now to the optical and VIRTIS images, in the right hand pair of images (2) there is no length scale but assuming a similar size of area to region 1 the lowest temperature blue zones ( around -100 deg C) are again a few tens of metres in extent. There are however far fewer of these blue areas than in image 1, hardly any at all, with the image dominated by temperatures above (more positive than) -93 deg C with temperatures in the region of -68 deg C being most obvious. For some reason too a different scale temperature range, with a hotter maximum, by 17 deg C, has been selected for this image gathering. Interesting too that despite Booth's lengthy and spirited defence of white as a valid scale maximum it has been abandoned for these VIRTIS images ( though not for the ice abundance image) and an intense blue to intense red scale used. Harder to see in this no 2 image but once again the greatest intensity of red in the image appears to exceed the scale maximum ie depict hotter regions than the scale maximum.
    Once again I would like to ask the VIRTIS personnel: if this VIRTIS camera in this configuration were pointed at the Sun what colour, in their expectation, would it display.

    A curious aspect of this pair of images is that the top centre (blue) elliptical shaped cold region (approx -100 deg C) ie coldest, is approximately matched in the optical image by the brightest white zone surrounded by lets call it medium grey corresponding to a very pale orange or about -85 deg C on the VIRTIS scale. It would be expected therefore that a lighter grey in the optical image would correspond to a colder temperature than -85 deg C. However these light grey areas in fact correspond to the hottest areas of the VIRTIS image. Hotter than -68 deg C. This is inconsistent, Why ?

    Finally with regard to the spectrum we do of course respect the investigators interpretation of it as an ice spectrum and that it reasonably matches their model and allow them that they have mistakenly labelled the observed spectrum as a darker blue or perhaps black when it is in fact depicted as red, Once again however it should be emphasised that this is a spectrum for one pixel. So representative of what. And it is stated that the remaining 98.8% of the pixel is composed of material containing 3.4 % of ice with a different particle size mixed with the remaining amount ( the 96.6 % amount) being " dark material" Why refer to it as dark material when they know exactly what it is. A layer of hydrocarbons which covers the surface of the nucleus but judging by the interest of the investigators is considered completely irrelevant in the activity of the comet.

    • emily says:

      While details on the specific details of the analysis can only be answered by the team themselves, what I can point out at least is that the labels on the spectrum are correct: the red indicate error bars, as stated in the caption:, and are overlayed on the black line that indicates observations.

      • originalJohn says:

        OK emily, accepted. Difficult to separate black and dark blue at that compressed scale. Difficult to see the error bars too. I had assumed that the red represented a band of multiple observations.

    • logan says:

      Hi OriginalJohn: Also find difficult to understand this dust/ice genealogy. Maybe my mind is confusing this proposal with previous one. VIRTIS was argument -ed before and believe it Out-Reach clarified by now. Hydrocarbons/ceramics/salts skin of great interest, but maybe not highly relevant to perihelion thermodynamics.

      I have no access to the document.

      Finally, these are the sayings of Filacchione, De Sanctis, Capaccioni and allies. Not Emily's.

    • ianw16 says:

      ".......the longed for ice"
      Sorry? You missed the bit about the solid ice excavated from Tempel 1, yes? Or the solid ice in the jets of CO2 at Hartley? And 17P Holmes, etc. How much ice would you like them to find? And where would you like them to find it? How long until EU come up with a scientifically literate excuse for it being there?
      Don't forget MIRO has already detected it subsurface.
      So, what is the 'new' EU Official position on ice?
      Or should I quote Thornhill's nonsense from as recently as 2010, that denies there even being water vapour?
      More proton implantation nonsense, due to an invisible 10 magnitude increase in the solar wind flux? Silly stuff about combustion? 'Electrochemistry' from the same solar wind that is 10 orders of magnitude (minimum) too diffuse?
      Lay out the 'hypothesis'. Give us some numbers. Give us some observations. What would confirm it (nothing so far)? What would falsify it?
      Just more fairy tales, by the sound of it, all to back up a non-existent unscientific belief.

      • originalJohn says:

        Yes ian solid ice was not excavated from Temple !. It was an assumption because it was found in the ejecta. As I have said repeatedly to you the presence of ice particles or water vapour in a comet coma is not evidence of a nucleus composed of or even containing ice. Water or CO2 can legitimately be formed at the surface as combustion products or plasma discharge products and can be transformed to ice. Awkward for you I know but true.

        You see yourself as a scientist and perhaps you would agree that the scientific process is observation, hypothesis, experiment (measurement), conclusion (theory). Yet you began this mission clearly with an inherited old hypothesis and throughout the year or so of the Rosetta craft accompanying the comet neither you nor anybody else has proposed a single measurement that could be made to categorically test the ice sublimation idea. You have simply interpreted all observations as indicative of the presence of ice and its sublimation. So your pseudoscientific process is hypothesis, observation, confirmation of hypothesis. This is not science ian. The experiment stage is completely missing, as is any proposal for it.

        On the other hand myself and THOMAS have repeatedly in the last year proposed measurements to test the hypotheses we support. So here I will do your work for you and propose an experiment to test your ice sublimation hypothesis. Measure the temperature of the visible jets within a few kilometres of the surface. Your hypothesis would require the jet temperature to be not much above 200 deg K, but I would allow you some leeway right up to just above the freezing point at Earth's atmospheric pressure say 280 deg K. Any hotter and it is not ice sublimation, particularly in view of the expected Joule Thompson effect. And then just to confirm it one way or the other I suggest that the ion content of the jets be measured. According to ESA published figures the neutral sublimed vapour would be expected to consist of no more than 1 ppm of ions from photoionisation. But lets allow you ten times that and say 10 ppm. Any more and it is not sublimed water vapour. So go ahead and stick in the proposal. Test your hypothesis. If you could measure a temperature of no more than 280 K and a a jet ion proportion of no more than 10ppm it would demonstrate to everyone including me that the most likely source of the jets and the water content of the coma was sublimation of nucleus ice to neutral water vapour with the heat energy supplied by solar photons.

        Funnily enough the tests that both THOMAS and I have scientifically proposed many times are also measurement of both the jet temperature and the jet ion content, Not necessarily with the same instruments however. To prove our hypotheses we would be looking for a jet temperature in the region of anywhere between 1000 and 5000 deg K and an ion content of between say 1 and 30 %. Vastly different from the expectations of your hypothesis.
        So lets get those definitive measurements done eh ian.

        In fact Thomas and I have repeatedly demonstrated on this blog that we are true scientists. And I would add to the team Sovereign Slave, who has legitimately and scientifically remained on the fence throughout, in the absence of evidence, and also Dave for similar reasons. Not forgetting of course Logan who has been a scientific example to us all, with his complete openmindedness and willingness to examine new ideas. We are the scientists.

        You and the rest of the profferers of the ice hypothesis in the blog comments, having failed to come up with a single scientific proposal in a year, I would class as dogmatists. You have your inherited hypothesis and everything is interpreted on that basis.

        • ianw16 says:

          Sorry, but the whole of that is just pure pseudoscience.
          "Combustion"? That is pure woo, with not an iota of evidence to back it up, nor even a mechanism. Got a link?
          "Plasma discharge processes"? Utter nonsense. Got any links to scientific works that show how that actually works? That is, how does this invisible discharge turn dust into solid ice? How does it get below the surface to 10s of centimeters? How come the water vapour produced is neutral and cold?

          The increased species in the coma were shown on this blog, following one of the outbursts. They were neutrals.
          Not enough time for much ionisation. Jets have been observed on comets at various wavelengths. As they were at Hartley 2. Just neutrals (CO2). Cold CO2. What do you think extremely high temperatures would show up like in an IR spectrum? How do you get solid ice surviving in 5000 C jets? Tip: you don't.

          As usual, EU proponents propose a lot of impossible, unobserved mechanisms for their denialism about what comets are, and have been seen to be. And despite claiming to be 'true scientists', having a seemingly scant knowledge of how to interpret scientific data, such as temperature maps and electron temperatures, and an inability to grasp such simple concepts as Keplerian orbital mechanics. And also seemingly haven't even bothered to read any of the current or previous papers on cometary exploration.
          Neutral to ion densities have been measured and reported in a number of papers at this and other comets. Generally, you are looking at 4-6 orders of magnitude fewer ions than neutrals. Including at Halley, which was a far more active comet than this one. And, as mentioned, solid ice grains DO NOT exist in 'hot' jets. Their thermal signature would be easily seen. As the Hartley 2 data showed from the most active area, no thermal anomalies.

          It is pure evidence-free pseudoscience, that doesn't stand up to even a moments scrutiny.
          The only people burying their heads in the sand due to this mission not providing a single jot of evidence for their preconceived ideas, are those still clinging to this pseudoscientific silliness.

          • originalJohn says:

            Once again I refer you ian to the the investigation that is taking place, the Rosetta mission. No comparison with the Halley, Hartley 2 or Tempel I observations, which were fleeting approximations by comparison. It is obvious though why you persist in looking back to them. There is so little relevant information so far from the current mission. The answers needed will come from Rosetta. So far there has been little to no temperature data and even less plasma and magnetic data. And as far as I am aware no measurement at all of the visible jets near the point of emission, the region that would provide most information. This is where the maximum temperature and ion density would be expected, not out in the rarefied coma. It would be perfectly feasible too for ice particles to form in these jets, once they had cooled rapidly as they dispersed into the coma. How far out? Let Rosetta find out. I would guess at 50 km plus. Nothing much in the overall size of the coma.

            Even with your sublimation hypothesis it would of course be surprising to find ice particles close to the comet nucleus as the mechanism is supposed to be sublimation of ice to vapour that forms the jets. But the closer to the nucleus ice formed the better chance your hypothesis would have. I would guess again that within 5 km of the nucleus and perhaps you are onto a good thing. There you go. Another test for your hypothesis.

            May I remind you ian that you are not looking to identify the presence of ice to justify your hypothesis. You are looking to demonstrate that the comet nucleus consists mainly of ice and that it is the sublimation of that ice that causes the characteristic comet jet emissions. I note that you have claimed previously that MIRO readings had shown that ice exists a few tens of centimetres below the surface of this comet nucleus. I think this is wishful interpretation on your part. As I understand it the MIRO instrument can measure temperature below the surface and to a depth of a few centimetres. You appear, perhaps unwittingly, to have increased this by a factor of ten.
            Admittedly it is a difficult thing to do, to prove not only that ice exists below the surface but all the way through and out the other side. But you have latched on to the hypothesis so it's up to you to come up with something. Otherwise it remains dogma.

          • Gerald says:

            Originaljohn, the thus far published measurements say one part ices vs. four parts dust. Ices are a mix of water ice, ices of carbon dioxide, carbon monoxide, nitrogen, oxygen, and several organic volatiles, and possibly clathrates.

            At lower temperatures, dust jets are mainly driven by supervolatiles. Above about 200K sublimation of water becomes important.
            So you might see grains of water ice at temperatures below 200K due to sublimation of supervolatiles.
            At temperature leading to non-negligible partial pressure.for water, finding free floating grains of water ice is less likely, since they would sublimate rapidly.

        • Harvey says:

          You state
          "Water or CO2 can legitimately be formed at the surface as combustion products or plasma discharge products and can be transformed to ice. Awkward for you I know but true."
          No, neither awkward nor true.
          You have *never* produced the slightest credible evidence, nor a numerically credible mechanism, this.
          It remains, as its always been, pure pseudoscience.
          As I often remark, there is much to explain, much that may be wrong in our current ideas, about what goes on at comets. But including utter nonsense won't move that forward..

          • originalJohn says:

            Harvey, evidence is not a requirement of a plausible hypothesis. Plausibility is and combustion at the surface of a comet nucleus is fully plausible. What don't you understand. The fuel is there in abundance, in the form of the hydrocarbon coating. It has been shown now that the oxygen is there in abundance too, a possibility that you repeatedly denied. All that is needed in addition is a small input of activation energy. We know that the comet is moving at high velocity through a stream of higher velocity solar wind protons. Do you think they do nothing. And once the reaction starts it is exothermic and self sustaining until the fuel or the oxygen is exhausted. If you can't accept this you can't accept simple basic chemistry. It is indeed a hypothesis but fully plausible. No hint of pseudo about it at all. The mainstream consensus has never addressed it, that's all. No point arguing whether it occurs or not as we are not in a position to collect evidence. Only the Rosetta team can do that. You have no argument though regarding plausibility.

            As for the plasma discharge aspect, a dense electron cloud has recently been identified close to the nucleus. The nucleus has in the past been found to be emitting low frequency electromagnetic radiation and Dr Glassmeier has announced that it exhibits a magnetic field. These are all clues Harvey that it is an electrical body, yet you would still prefer to believe it is a neutral lump of ice moving in a vacuum ? A great deal more evidence is required to confirm the electrical properties and once again that is in the hands of the Rosetta team.

          • Gerald says:

            Originaljohn: "...combustion at the surface of a comet nucleus is fully plausible...".
            That's incredible nonsense.
            Paper, wood, trees, tomatos, cheeseburger, the asphalt of the streets, animals, human beings, clothes, soil rich in organics, all this would sponaneously burn, even in the deepest winter, ignited natural radioactivity, by cosmic rays, or by
            On Earth the oxygen partial pressure and most of the time the temperature are considerably higher than in the comet subsurface.

          • Harvey says:

            If you take a mixture of hydrogen and oxygen, one of the most readily ignited mixtures there is, at atmospheric pressure it will ignite over a very wide range of compositions.
            As you reduce the pressure that range gets narrower and narrower.
            By pressures *FAR* higher than those at 67P, there is *NO* mixture that will ignite.
            I posted links to this previously.
            Combustion is a collisional process; collisions become rare at these pressures. Furthermore the oxygen concentration is very low.

            Conditions on the comet are completely antithetical to combustion. Neither is there the slightest evidence it's happening.

        • sjastro says:

          My goodness originaljohn you must have been looking in the mirror accusing various individuals here of being closed minded dogmatists.
          A classic case of the psychology of projection at work.

          Pointing out that you have a limited comprehension of the theoretical and experimental nature of science is only stating the obvious and not an exercise in dogmatism.
          The putting of labels on individuals who make these points is a cop out as you don't have to consider the possibility you might be wrong or open yourself to the possibilities of actually learning the science.

          You wrote,

          "Funnily enough the tests that both THOMAS and I have scientifically proposed many times are also measurement of both the jet temperature and the jet ion content, Not necessarily with the same instruments however. To prove our hypotheses we would be looking for a jet temperature in the region of anywhere between 1000 and 5000 deg K and an ion content of between say 1 and 30 %. Vastly different from the expectations of your hypothesis.
          So lets get those definitive measurements done eh ian."

          One of the criticisms of EU supporters I have read in various forums is that they constantly whinge and expect mainstream to do their job.
          Here is a wonderful example for you to be the true scientist instead of a self proclaimed one, or as Thomas puts it a citizen scientist.

          You don't need to directly measure the temperature. If Rosetta or an observatory such as ESO has measured the albedo of a jet, the albedo, the luminosity of the Sun and the comet Sun distance are used to calculate the effective temperature by modelling the jet as a blackbody and using the Stefan-Bolzmann law.

          Why don't you try it. You will be doing some real science and learning in the process.
          Unfortunately what it will show you the temperature will be no where near your minimum requirement of 1000K.

          • ianw16 says:

            "Why don't you try it. You will be doing some real science and learning in the process."

            I think you may have written that more in hope than expectation.
            Let's just take some of the recent nonsense.

            To paraphrase OJ "ice can be formed within the jets, maybe at 50 km" ?????
            How, exactly? The temperature of the jets is supposed to be too high, according to EU woo. The temperature outside of the jets is too high in July and August. Simple equation to work out the temperature at 1.3 AU. Not going to happen. How did the CO2 jets at Hartley 2 form H2O ice? But not CO2 ice? That encounter took place at 1.06 AU. Complete unscientific nonsense. A desperate attempt to salvage an unscientific , mythology based pseudoscientific 'idea'

            As for ice beneath the surface, one could simply read the published literature: Dark side of comet 67P/Churyumov-Gerasimenko in Aug-Oct 2014
            Which was followed by:, which was presumably written after they had used their data on the improved shape model.

            As for temperatures of the gas? Well, they are known, and I haven't seen any banner headlines reading "SHOCK; Rosetta scientists find 1000 K gas on 67P!"
            Again, from:

            Surface and subsurface temperatures have been taken simultaneously as H2O outgassing has been observed: As indeed they were at Hartley 2:

            Again, there is no magnetic field intrinsic to the nucleus, and K-H Glassmeier did NOT say there was. One could email him, if one was really interested. I think he said it was "induced". And then that has been misinterpreted to mean "induced by the nucleus." No, it is induced by the coma, due to the interaction between the SW and the outgassing neutrals. Besides, how do we observe a diamagnetic cavity if the nucleus is magnetic????

            Then there is the sputtering data; where is all this Si?
            Trivial, compared to the amount of H2O measured.
            And how is all this non-existent, scientifically impossible combustion and sputtering happening when the SW isn't even reaching the surface for long periods

            So I think, Sjastro, that you may be being somewhat optimistic. Thankfully, real scientists will be writing the papers on this mission, as well as the text books for future generations of scientists.
            As Harvey has said, this is merely an exercise in preventing the less scientifically literate from being taken in by pseudoscientific woo.

          • sjastro says:

            Thanks for the links ianw16.

            I realise my attempts to get originaljohn to use albedo data to calculate the effective temperature to test his "hypothesis", is clearly futile, as are your links illustrating why he is so emphatically wrong, given this gem of a comment.

            "Harvey, evidence is not a requirement of a plausible hypothesis. Plausibility is and combustion at the surface of a comet nucleus is fully plausible."

            Strange given that evidence gathered through observation or experiment is how a hypothesis is assessed as being "plausible" or otherwise in the first place.
            This also assumes the hypothesis is theoretically sound to start with, which it clearly isn't.

            A wonderful example of dogmatism at work which he accuses others of.

            Another way of refuting this "hot comet" nonsense is to simply point out that in the visible wavelength range photons are reflected but in the sub-millimetre and millimetre wavelength range photons are radiated by the comet which indicates it is cold.

            It was my hope that originaljohn looking at the jet as blackbody problem would have seen the light:)

          • originalJohn says:

            Gerald, you are claiming that the organics, the hydrocarbons, you hopefully list do not ignite in the Earth's atmosphere? Many of them of course do, every day all over the Earth. An input of activation energy is required then off they go, combusting merrily for hours or days. The forest fire, the house fire, the bonfire, the crop fire. Even the struck match or the gas cooker flame or the petrol engine. The hydrocarbons are there and the oxygen present supports their combustion. Fortunately for us all the activation input is required otherwise life would be a constant fire. But it is a comparatively small energy input and often accidentally applied. So Earth fires are common.
            We know from recently published data that the coma in the vicinity of the comet nucleus is rich in oxygen, free oxygen, and we know of course that the nucleus is covered in a layer of hydrocarbons. So as with the Earth situation a small input of activation energy is required to set off the combustion. And it is extremely plausible to suppose that it is provided by the extremely high energy solar wind protons impacting the nucleus surface. This is plausibility personified, Gerald. Fuel +oxygen +activation energy = combustion. And I reiterate that the products of this combustion, of hydrocarbons in oxygen are typically, H2O, CO2, CO, CH2O, carbon, atomic hydrogen, oxygen (surplus), unburnt hydrocarbons, and in the acknowledged presence of nitrogen, cyanide and ammonia in different proportions depending on the conditions. All of these have been identified in the coma of this comet. Sulphur compounds too.
            Incredible Gerald? I don't think so. Credible in the extreme. Nonsense Gerald? i don't think so. Makes perfect sense.

          • originalJohn says:

            And Harvey the pressure of oxygen at the surface of the nucleus of this comet is? The hydrogen is present as solid and liquid hydrocarbons to a depth of several metres. The hydrogen pressure during the reaction of these hydrocarbons would be extreme.

          • originalJohn says:

            Ah, up springs the jack in the box. No sjastro I was not looking in the mirror. And neither am I a citizen scientist. THOMAS may like to think of himself as that but he is firmly in the scientist group along with the others listed and myself.
            You are not selected sjastro because your arguments are a constant stream of dogma, beliefs without support. You are firmly in the group with the dogmatists. A popular, consensus dogma but nevertheless dogma.

            Your absurd suggestion that it would be preferable to model the temperature of the comet coma from its albedo than measure it directly is a typical dogmatists suggestion. The resolution of the albedo from Earth would be such that it could only separate the coma and the tail as averages. The proposal I have made is to measure the temperature of individual jets adjacent to the nucleus surface. Only that would prove what surface reactions are occurring. The Rosetta orbiter is there and capable of doing it. You believe a scientist would prefer to sit at home and try and model it from the albedo? Laughable.

            The fact that you think modelling is real science categorises you beyond dispute. And the fact that you call reiterated proposals whingeing is simply indicative that you would prefer not to hear them because they might destroy the dogma.
            I have proposed that the temperature of the jets be specifically measured to test either the ice sublimation hypothesis (dogma) or the plasma discharge/ combustion hypotheses. It would provide definitive evidence and be an irresistible measurement to a scientist. But I can see a dogmatist would prefer not to do it.

            Finally I would remind you that the Rosetta mission is at the comet to collect the evidence. That is their job, a job only they can do. The job of objective scientists is to analyse and criticise the evidence and the conclusions the Rosetta team come up with.

          • Gerald says:

            Originaljohn, there is neither sufficient oxygen nor the necessary activation energy to maintain or trigger combustion on the comet.
            Near-vacuum is a highly efficient way to stop combustion.
            Nor do the temperature measurememts remotestly indicate combustion.
            Sporadic protons cannot trigger combustion. The solar wind proton flux is orders of magnitude too low to increment temperature even a few Kelvins, but you need several hundreds of Kelvins to trigger combustion in settings which would allow combustion.
            Not even solar illumination is able to provide the activation energy, despite being orders of magnitude more energetic per area than your protons.
            So both preconditions to allow combustion are absent at the comet: Activation energy, and oxygen partial pressure of roughly 100 mbar, at least.
            Why are there no indications at all at the night side of the comet for temperatures anything above 150K?
            There is neither any theoretical nor any observational evidence for combustion.
            Your claims are highly implausible, to say it in the most diplomatic way.
            The combustion is restricted to your imagination, unrelated to reality.
            All you get is space-weathering over longer timescales.

          • ianw16 says:

            All this impossible combustion woo (any links? To observation? Experiment? Modellling? We been asking long enough) is a totally moot point anyway. The solar wind was missing from late April until ~ January. And given the robust detection of a diamagnetic cavity on nearly 500 separate occasions, it totally rules out the SW as being involved in anything going on at the surface during that period.
            And it still can't explain the entrained ice at Hartley 2. H2O will not condense at the temperatures around 1.06 AU. If it could, then this should be a regular feature of all comets which are outgassing H2O. In which case, every comet we observe should be surrounded by a halo of ice grains, as the sublimated H2O condenses to form ice.

            It's all just mythology inspired sci-fi.

          • sjastro says:

            Third attempt to post due to captcha issues.

            You wrote,
            "Ah, up springs the jack in the box. No sjastro I was not looking in the mirror. And neither am I a citizen scientist. THOMAS may like to think of himself as that but he is firmly in the scientist group along with the others listed and myself.
            You are not selected sjastro because your arguments are a constant stream of dogma, beliefs without support. You are firmly in the group with the dogmatists. A popular, consensus dogma but nevertheless dogma."

            You just don't get it.
            An individual who claims that ice can form in conditions approaching 5000K, combustion can occur in near vacuum conditions or a plausible theory does not require evidence, to name a few is in need of some serious education.
            This has nothing to do with defending dogma let alone relate to comets but to address your profound ignorance of science at a fundamental level.
            Your obsession with turning this into a dogma issue is a simply a reflection of your own dogmatic beliefs that are bereft of science as per your examples.
            A classic case of the psychology of projection.

            You wrote,
            "Your absurd suggestion that it would be preferable to model the temperature of the comet coma from its albedo than measure it directly is a typical dogmatists suggestion. The resolution of the albedo from Earth would be such that it could only separate the coma and the tail as averages. The proposal I have made is to measure the temperature of individual jets adjacent to the nucleus surface. Only that would prove what surface reactions are occurring. The Rosetta orbiter is there and capable of doing it. You believe a scientist would prefer to sit at home and try and model it from the albedo? Laughable.
            The fact that you think modelling is real science categorises you beyond dispute. And the fact that you call reiterated proposals whingeing is simply indicative that you would prefer not to hear them because they might destroy the dogma."

            Your response clearly shows you haven't even bothered to study the subject you are criticizing. This is pure ignorance and dishonesty in making comments where you have no knowledge or comprehension.
            You see the word model and base your entire argument over a single word.
            Now that is laughable.
            Perhaps if I used the less inflammatory term blackbody spectrum instead of blackbody model would that improve matters?
            Irrespective of the terminology, by studying the subject matter instead of engaging in this mindless diatribe over a single word, you would find it is based on MEASUREMENTS using photometry.

            The problem as usual is since your knowledge of science is rudimentary at best, you have this naive notion the only way to measure temperature is to stick a thermometer into a comet. Not so.

            Detectors act as photon counters and a spectrum of photon count versus frequency can be constructed. Since one is only interested in radiated photons it is important to know the geometric or Bond albedo.

            Measurements indicate the dominant wavelength is in the microwave/IR range which leads to the calculation of a comet's effective temperature based on the photon count vs frequency data as being a blackbody spectrum. Technically a comet (or planet or star) is not an ideal blackbody but is close enough to be approximated as one.

            One of the earliest activities of Rosetta was to measure the surface temperature of the nucleus and compare it to the calculated blackbody temperature with a measured 4-5% albedo. The results as expected were consistent.

            Your excuse that albedo is going to be averaged out between the tail and coma is complete utter nonsense.
            An albedo map can be constructed showing variations between the coma and tail since they are spatially resolved in the image and photometry, used to calculate the albedo, is performed on select areas that can be as small as a few pixels.

            It is only when an albedo map is required of a cometary nucleus that up close imaging is necessary to provide the spatial resolution such as of comet 9P/Tempel 1.

            Ironic isn't it the albedo map showing blackbody temperature variations indicates cryo-volcanic activity that pours yet another bucket of water (excuse the pun ) over your electric/combustion/solar irradiation/and what ever else comet nonsense.

            You wrote,
            "I have proposed that the temperature of the jets be specifically measured to test either the ice sublimation hypothesis (dogma) or the plasma discharge/ combustion hypotheses. It would provide definitive evidence and be an irresistible measurement to a scientist. . But I can see a dogmatist would prefer not to do it."

            You don't have to measure the temperature at all.
            A consequence of your 1000K-5000K nonsense is that the dominant wavelength is pushed out into the VIS/UV range and the blackbody spectrum extends out into the FUV.

            Apart from the significant increase in brightness of the jets in the visual range, ALICE should have detected an FUV background radiation during the investigation that led to the finding that electrons were responsible for the disassociation of water and carbon dioxide molecules?
            The Sun's contribution to the background is minor by comparison as the FUV albedo is small.

            The absence of very bright jets relative to the coma and a significant FUV background is yet another piece of "evidence" of the implausibility of your theory.
            You don't comprehend the scientists that you call dogmatists have already done your work!!!!

    • ianw16 says:

      First off, it is ice. End of story.
      Secondly, pareidolia when looking at temperature maps is neither science, nor evidence.
      As the paper notes in the methods section: "On the Imhotep plain, the MIRO experiment has measured a maximum diurnal subsurface temperature of about 120 K with both millimetre and submillimetre channels." And: "while modelling VIRTIS-M data a diurnal surface temperature of 180-190± 15 K has been inferred."
      The "inferrred" refers to a previous paper. Followed by: "In the thermal image of BAP1, VIRTIS-M has measured a temperature lower than 160± 30 K on pixels where water-ice features are more prominent."
      Thirdly, yes they can determine the grain sizes from the spectra. Or at least constrain them.
      I'd suggest reading the paper again, including the 'methods' section, and the references therein (I assume you've read the paper, and the supporting references; it would be a bit presumptuous to be criticising the work if you haven't)
      This is the same sort of spectral work the was done at Tempel 1, with similar results. The difference being that on that occasion, they also saw the ice grains in the coma (and later, also, at Hartley 2).
      As the Tempel 1 author wrote to me in response to another claim made on here: "....we did indeed detect water ice. It is unambiguous................Our instruments are good enough to not only identify the water ice, but constrain the sizes and they are both consistent with laboratory data at the appropriate temperature."
      That was ice in the impact ejecta.
      So your arguments are purely from incredulity, and an apparent lack of understanding of the subject area.

      • originalJohn says:

        Well Gerald, you claim that there is neither sufficient activation energy to trigger hydrocarbon combustion at the nucleus surface nor sufficient oxygen partial pressure to sustain it and you imply that the atmospheric pressure at the surface of the nucleus is "near vacuum" . A scientific argument would go on to say : We have measured the proton flux density at the nucleus surface and it is ?? and we have measured the oxygen partial pressure at the surface and it is ?? But we do not get that from you do we Gerald. We just get the assertion. In other words the statement of a hopeful belief.

        And as far as the near vacuum claim goes, even your ice sublimation dogma would establish a gas pressure at the jet outlets which could not by any stretch of the imagination be described as near vacuum. You haven't measured the atmospheric pressure at the nucleus surface have you, and certainly not within the boundary of a jet.

        You go on to describe the protons as sporadic. Based on what ? Sporadic measurements presumably and none near the nucleus surface. You have no idea what the proton flux density or energy is at the nucleus surface therefore no way of knowing if it is orders of magnitude or a tiny amount insufficient for anything. You even state that not even solar illumination is able to provide the activation energy when you know that photon energy is many orders of magnitude less than the solar proton energy, and remember no figure for proton flux density.

        As far as temperature goes, or let us call it potential surface reaction temperature, you are seemingly satisfied to rely on accidental temperature measurements to decide whether or not combustion is occurring. A scientific option would be to make specific measurements at the possible sites of combustion (or sublimation), particularly in view of the recognised fact that combustion temperatures can be extremely localised. To use one of your favoured types of analogy you would find that you can touch the burner body of a methane burning appliance with no discomfort but you risk serious injury if you place your finger in the flame a couple of centimetres away above the burner.

        To summarise then Gerald you have neither theoretical nor evidence based argument to dismiss the possibility of combustion at the comet nucleus surface. You have simply a number beliefs, extrapolations and assumptions which you use to defend your dogma, your unsubstantiated belief that the jet emission from the comet is neutral water vapour from ice sublimation. The mission went all that way over ten years and not only do you not want to test reasonable new hypotheses for the comet mechanism but you don't even want to test your own old, preferred hypothesis. Is that science Gerald ?

  • M. Reda says:

    Heavy water or deuterium oxide is a form of water that contains a larger than normal amount of the hydrogen isotope deuterium rather than the common hydrogen-1, that makes up most of the hydrogen in regular water.I wonder if any effort was made to detect heavy water. This would make the European tax payer feels that it was worth his money.

    • emily says:

      Determining the D/H ratio was indeed a highly anticipated result of the mission:

    • Harvey says:

      M Reda
      Just for clarity.
      'Heavy water', a readily available commercial product, is often over 99.9% deuterium, You can readily buy 99.96%. In fact 100mL of 99.9% deuterated heavy water would cost you about £203 plus tax. So most of the molecules are D2O, di-deuterium oxide, very little hydrogen in it.
      But in the water from the comet the percentage of deuterium remains very low, and the great majority of the deuterium is present as HDO, that is water with one normal hydrogen and one deuterium atom. Its really H-O-D bent through roughly 120 degrees, water is H-O-H and heavy water D-O-D
      This actually changes its properties (especially spectroscopy) a lot.
      So yes, D has been measured, Emily gave you the links - but no 'heavy water' in the normal meaning of those words.

  • logan says:

    Have finished reading the document. See it as a first class Scientific paper and also an Out-Reaching achievement. Of good taste all of its conclusions, also 🙂

    • logan says:

      "During that time [3.6-1.6 AU] the sub-solar latitude migrated from +42.4º to -5.7º, therefore the results we present here apply only to the Northern Summer on 67P."

      "It is important to keep in mind that other types of activity may arise, and our classification of active sources is still a work in progress." 🙂

    • logan says:

      Found it in my download folder, at home. Was it open the day of publication?

  • logan says:

    Find your article very easy to grab. Thanks! Emily 🙂

  • logan says:

    All of what We have seen at 67P make elongated comets' a lot more intriguing. Shouldn't exist, neither 😉

    Moving them also to the interstellar formative environment...

    A photonic shape. This is fiction.

  • ianw16 says:

    @Anyone interested in the "induced magnetic field", it is described here:

    "The sounds ‘emitted’ by 67P/C-G are oscillations in the magnetic field around the comet. Its space environment is permeated by the solar wind – a continuous stream of electrically charged gas (called plasma) and magnetic field lines strung along from the Sun – *which interacts with the comet’s gas-dust atmosphere.* A consequence of this interaction is an *induced* cometary magnetosphere. In other words, even though *the nucleus of 67P/C-G has no magnetic field of its own* (as announced at this year’s EGU General Assembly), the comet’s atmosphere or coma is magnetised."

    My emphases. Report by Claudia on a paper by K-H Glassmeier:

    tl;dr? The nucleus isn't magnetised.

    • ianw16 says:

      Sorry, the above should read 'paper by I. Richter.'
      K-H Glassmeier was a contributing author.

    • originalJohn says:

      Yes ian, what that post says or reiterates is that the comet nucleus is not magnetised, ie it is not made from magnetic material. This is not the same thing as not having a magnetic field.
      The authors then go on to explain the magnetic effect associated with the comet as a modification of the solar magnetic field. This is an erroneous interpretation. It is either the solar field or the comet's field.
      It is also separately specifically stated that the coma has a magnetic field. This is the comet's magnetic field. It is caused by current flow ( ion movement) within the coma plasma which is distinct from the solar wind current flow and the Sun's magnetic field and is focused on the comet nucleus. If the nucleus was not there the field would not be there.

      With reference too to past assertions of yours the presence of a diamagnetic cavity does not indicate no magnetic field. The Earth's field has a diamagnetic cavity associated with it

      • ianw16 says:

        Pointless arguing. Email K-H G if you're so sure. Or link to a paper that says it is magnetised, or has an intrinsic magnetic field.
        And last time I looked, 0nT = no magnetic field.
        I'll just go with what the experts say in the published scientific literature, if it's all the same to you.

        • ianw16 says:

          And, further to the above: "Based on magnetic field measurements during the *descent* and subsequent multiple touchdown of the Rosetta lander Philae on the comet 67P/Churyumov-Gerasimenko, we show that no global magnetic field was detected within the limitations of analysis."

          Seems pretty specific to me. "No global magnetic field" is kind of the clue.

          "This is an erroneous interpretation......" According to whom? Link please, otherwise I'll just assume it has been conjured out of thin air.

          • ianw16 says:

            And further to the further, Originaljohn said, "If the nucleus was not there the field would not be there."
            Well, that much is true, as we need the nucleus to provide the sublimation products that slow the solar wind and cause the magnetic field to pile up, which in turn causes the diamagnetic cavity.
            However, leave the gas in place and subtract the comet, and the same process would happen. In case anybody has forgotten, there were the AMPTE experiments in 1984/85:
            A couple of canisters of barium or lithium were exploded around a km in front of a probe. The gas expanded into a shell, through which the probe flew. There was nothing inside the shell that could cause a magnetic field. However, they found an induced magnetic field pile-up region, and within that a diamagnetic cavity. Just as they found a little later at Halley, and have now seen at 67P. Proof positive that it is not necessary for a cometary nucleus to have an intrinsic magnetic field for a magnetic pile-up region to form ahead of the comet, and within that a diamagnetic cavity with, by definition, no detected magnetic field therein.

            And as far as Halley was concerned, ""Inside a region of enhanced magnetic field magnitude, i.e., the magnetic pile up region, an inner volume of space with a magnetic field magnitude of essentially zero was found."
            Which means Halley's nucleus also had no measurable magnetic field (at ~ 600km), same as 67P down to 0km.

  • ianw16 says:

    @Anybody interested in whether solid ice can exist in jets close to the nucleus:

    See this paper:
    "Water Ice and Dust in the Innermost Coma of Comet
    103P/Hartley 2."

    In particular, have a look at Fig. 2a (at the end of the article; this is the Arxiv version, which isn't paywalled. All other versions seem to be).
    Take particular note of Box B in that figure.
    Now, Hartley 2 is roughly 1.2 - 1.6 km at its longest (
    So what would be an estimate for the distance of Box B from the nucleus? I'd say ~200-300m.
    Box B is where unambiguous detections of solid H2O ice were made within the neutral CO2 jets.
    Not very hot then.

    • logan says:

      Thanks for the link Ianw16:

      Will chew this one on ices at HartleyII.

      ...Humbly had to accept the paper on magnetism. At those times proposed scattered magnetism for the 'music of the spheres'. Harvey put good argumentation against it.

      Logan is placing again scattering magnetism over the bar, now that polyhedral clues are more consented.

      • logan says:

        If being shock 'screaming' related should vary, relative to Mach speed. If being core related should stay constant, relative to spin.

    • logan says:

      Please. Environmental [background plus impact bow] magnetism being the source. Core the sample. Traversing [Yea, a traversing curve is happening on arrival] ROSETTA the sensor...

      • logan says:

        Not asking for the string notes, I'm asking for the percussion tempos...




  • ianw16 says:

    Further to these findings, it would appear that further similar identifications of surface ice have been made in the Khepry and Anhur regions by the same instrument:

    Page 50.

  • Booth says:


    In this post, I would like to take a few minutes to address an excellent question you raised back in October of 2015, and again, on 2016/01/21. To get things started, I am going to take the liberty to paraphrase so as to capture what I believe is the essence of both questions -

    "If the VIRTIS camera, as configured for the Rosetta mission, were pointed at the Sun, what colour or image would it display?"

    Honestly, a really good question! And if you ask a good question, you deserve a good answer ...

    First, VIRTIS is an imaging spectrometer that provides two channels dedicated to spectral mapping (i.e., VIRTIS-M) and one channel to high resolution point spectroscopy (VIRTIS-H). Because the thermal maps published by the VIRTIS team are generated using the -M optical subsystem, that will be the focus of this post.

    As noted, VIRTIS-M consists of two channels, a visible channel, using a silicon CCD to detect wavelengths from 250 nm to 1000 nm, and a HgCdTe infrared focal plane array (IRFPA) to record wavelengths from 950 nm to 5000 nm. But I'm getting ahead of myself ....

    Before we can continue discussing VIRTIS, we need to address several scientific and engineering facts that are critical to the question asked.

    1) Recall that the Sun can be modeled as a black body with a temperature of ~5800 K. Using Wien's Displacement Law, we find that the peak spectral energy density occurs at around 500 nm (i.e., within the green region of the "visible" spectrum). As it turns out, this wavelength is also near the peak sensitivity of the human eye. We also know that the human eye evolved unique photoreceptor cells that are sensitive to three different colours of light - red, green, and blue! It should be obvious then, that the visible spectrum is so called because that is all of the electromagnetic spectrum that our primitive eye can see! On average, a human eye perceives light in the range of ~380 nm to ~710 nm - a very narrow range compared to the full extent of the EM spectrum (i.e., picometers to kilometers).

    2) Digital colour cameras that employ CCD technology normally use a "Bayer mask" to gather EM data. A Bayer mask is a colour filter that allows specific wavelengths of light to pass through to the pixels beneath. For every 2x2 matrix of four pixels, there is one red filter, two green filters (because the human eye is much more sensitive to green light), and one blue filter. This RGGB Bayer mask allows the human eye to recreate visual images from digital data using only these three basic additive colours. Of course, better colour separation may be achieved by using three CCDs, where each individual unit is dedicated to one of the three colours ... but then the "cost" of the camera goes up proportionally.

    3) Remote Sensing involves collecting data from an object at a distance, typically by using reflected or emitted electromagnetic radiation. Now, on its own, this data is meaningless without comparable, physically correlated reference (or "ground-truthed") data. For example, the LandSat program (which is just one of thousands of RS programs) has been gathering data for over 40 years, with LandSat 8 being the latest in the family. At present, LandSat 8 records data from the following eleven electromagnetic "BANDS" ...

    Band 01 : 430 - 450 nm - Coastal Aerosols
    Band 02 : 450 - 510 nm - Blue
    Band 03 : 530 - 590 nm - Green
    Band 04 : 640 - 670 nm - Red
    Band 05 : 850 - 880 nm - Near IR
    Band 06 : 1570 - 1650 nm - Shortwave IR 1
    Band 07 : 2110 - 2290 nm - Shortwave IR 2
    Band 08 : 500 - 680 nm - Panchromatic
    Band 09 : 1360 - 1380 nm - Cirrus
    Band 10 : 10600 - 11190 nm - Thermal IR 1
    Band 11 : 11500 - 12510 nm - Thermal IR 2

    So, why is this important? Remember, the human eye can only "see" three colours - RGB. Digital cameras only need to gather RGB electromagnetic radiation to reproduce pretty pictures! LandSat 8 records eleven bands of EMR data ... which bring us to the next step - the eleven LandSat bands can be combined in a number of ways to map specific land use processes and features found on the surface of the Earth. The following table lists only six of the more common combinations found in geography, geology, and land use management applications. Note, the band numbers, as written, are assigned sequentially to the RGB colours that the human eye can see.

    Landsat 8 - Short List of EM Band Combinations (RGB)
    4-3-2 = Natural Colour - As if viewed from altitude
    5-4-3 = Colour Infrared - Vegetation displays as red
    5-6-2 = Vegetation Health - Vegetation displays as red **
    6-5-2 = Agriculture (Farming) - Vegetation is bright green
    7-5-4 = Shortwave IR - Applicable to geological mapping
    7-6-4 = False Colour - Vegetation is green, Water is bright blue

    ** The LandSat 8 equivalent of the NDVI

    As you can see, there are many ways in which to measure, and display, the areal coverage of different types of vegetation and it's associated health. The NDVI, or Normalized Difference Vegetation Index, which is used by NASA's ERTS and NOAA's AVHRR missions, is another way in which data can be displayed and managed. And this is where remote sensing gets exciting. The NDVI is actually a calculated value that uses data from two different bands to generate a completely new "band" of information! The equation is,

    NDVI = ((NIR - VIS) / (NIR + VIS))

    While there are literally thousands of internet pages that display and discuss the science behind LandSat data reduction and manipulation, you should check out these sites for a brief taste of what is happening with just this ONE remote sensing mission!

    The Many Band Combinations of LandSat 8 - Pay particular attention to the last two images on the page, and their associated descriptions

    Effects of 40+ Years of Water Mining in Kansas using Colour Infrared

    Global Maps Using NASA Satellite Data - More than just LandSat! And check out the various temperature maps.

    Now, back to VIRTIS! And here's the first kicker ... VIRTIS-M is NOT a camera!

    VIRTIS-M is a HYPERSPECTRAL SENSOR! While the human eye senses three bands of EMR, and LandSat 8 records eleven bands, VIRTIS-M records an astounding *860 BANDS* of EM data in hyperspectral cubes!!!

    Now, given all that, good Sir, I ask you ... What colour would you like the Sun to be today? If we assign a red hyperspectral band to the red gun, green to green, and blue to blue, our image of the Sun will come out ... white!

    And here's the second kicker ... The human eye cannot "see" infrared electromagnetic radiation! The human eye cannot "see" heat! The human eye cannot "see" temperature! In other words, there is absolutely no colour associated with any temperatures!

    So, what is a VIRTIS temperature map? It is a product derived (i.e., calculated) from specific bands within the IR portion of the hyperspectral cube! Remember the NDVI for vegetation health here on Earth? A similar concept, but with radically different data and, of course, radically different code, results, and meaning. The following bullets are also important ...

    *1 - A minimum temperature "value" will be contained within a hyperspectral cube
    *2 - A maximum temperature "value" will be contained within the same "data" cube
    *3 - Minimum and maximum temperature "values" will vary from one cube to another
    *4 - No hyperspectral cube will ever be the same, or contain the exact same data

    In the end, the derived temperature map is an areal matrix with each individual pixel containing an actual temperature value. It should also be obvious, that this data set will contain a minimum and maximum temperature. As there are no colours associated with temperature, we can arbitrarily assign any colour we like to represent a given temperature. Because of our physical experience with heat, we will set the minimum temperature for the data set under investigation to black, the maximum data set temperature to white, and fill in the middle with shades of orange to complete the scale! Of course, we could flip the scale around making white the minimum and black the maximum, but that would be counter-intuitive and unnecessarily confusing (so we won't go there). Other scales include the rainbow (as was used for some data visualization by VIRTIS on Venus Express), or we could replace the orange with shades of blue, or green, or purple! There is no colour associated with temperature, so it's up to the scientists to pick a scale that best represents the data.

    As an aside, the "blue-white-orange" temperature scale found in this presentation is *typically* used to display data that deviates from an average. When used thusly, white is the average for the data set, blue represents data values below the mean, and orange (or red) represents values above the mean. Check out the NOAA NCDC website for climate change examples. Note - This aside is a passing comment. It is not an indication that the temperature data is being presented as deviations about a mean. It is offered as another example of how coloured scales may be used to visualize data!

    Restating - Because there are no colours associated with temperature, we can assign any colour to any temperature we like. White may represent the minimum, the maximum, or something in the middle. We may chose to not use white at all. Red could be used instead of white. Green could be used instead of red. All we need do is make the appropriate assignment and inform the reader so that they can make sense of the presented data. As noted, the VIRTIS team has in past preferred the "black-orange-white" scale to display temperature data!

    So, where does that leave us? VIRTIS temperature maps are derived from hyperspectral data and the instrument's associated calibration (i.e., ground-truthed) data. Dozens of maps have been released by Rosetta over several years of operations. For example, the following short list of unique maximum temperature values have been reported ...

    245 K at 21 Lutetia (Coradini et al 2011)
    230 K at 2867 Steins (Tosi et al 2014)
    230 K at 67P (ESA Blog 2014/10/03 - measuring comet 67pc-g at rendezvous)
    210 K at 67P (ESA Blog 2015/09/23 - rosetta reveals comets water ice cycle)
    188 K at 67P (ESA Blog 2016/01/13 - exposed ice confirmed as water - BAP 1)
    205 K at 67P (ESA Blog 2016/01/13 - exposed ice confirmed as water - BAP 2)

    At this point, I would like to draw your attention to bullets *3 and *4! Each hyperspectral cube contains different data, with unique minimum and maximum temperatures. Because there are no colours associated with temperature, each maximum can be assigned the colour white, or in the case of this thread, dark red! There is nothing wrong with the temperature data, and there is nothing wrong with the temperature scales chosen. No anomalous temperature data! No confusion with the scales being used! Look at the data! It is accurate and represents the actual surface temperatures at 67P!

    There is one more maximum temperature of note that I left off the list. At the Dec 2014 AGU, Mr. Capaccioni presented several slides of maximum temperatures in the vicinity of Hapi. Members of the EU/EC community labelled these temperatures as anomalous, and claimed (without evidence) that the VIRTIS instrument was saturated. In light of what has been presented here, it should now be obvious that the maximum temperatures measured at Hapi, the most active region on the comet at that time, were no more than 220K! This maximum temperature was recorded at the base of the jets seen emanating from Hapi! Conclusion - the maximum temperature measured at the base of the Hapi jets was 220 K! This very low temperature is inconsistent with electrical discharge or combustion. It is, however, consistent with the sublimation of water ice! The evidence provided by 67P and VIRTIS is sufficient to dismiss EU/EC nonsense. I hope you now see the light, so to speak, and will reexamine the merits of following a deadend model.

    And of course there's more. As we can see from the short list of maximum temperatures, VIRTIS finds that comets (and asteroids) are cold celestial bodies. Furthermore, there has never been any anomalously high temperatures, of any description, reported in the literature. There has never been any recorded evidence of electrical discharges occurring around comets (the periodic loss of EM-based RF communication between Rosetta and Earth would be sufficient evidence to validate that EU claim - yet nothing)! I knew I had read something about VIRTIS temperature measurements being made off limb well over a year ago, but could not for the life of me come up with the right keywords to relocate the article ... until recently!

    I quote, "These measurements of the gas in the coma (the subject of the particular weblog thread) now allow the science team to say something also about the temperature at some distance from the surface.

    The current measurements correspond to a height of one kilometre above the surface, where the temperature falls by more than 100°C to around -183°C. This large drop is expected, and is due to gases accelerating away from the surface and expanding in the coma, leading to cooling by so-called ‘adiabatic expansion’."

    Again, this data is consistent with comets being made of ices and dust. It also shows that adiabatic cooling dominates in the coma, further destroying the notion of high temperature electric discharges or combustion. Tis nothing more than simple thermodynamics!

    Now, back to task. As I've said many times before, the coloured temperature scales used by the VIRTIS scientists are "arbitrarily" chosen. There have never been any temperature anomalies! There have never been any temperature discrepancies! There have never been any unmeasureable temperatures! There have never been any temperatures recorded by VIRTIS at 67P exceeding 350 K! Comets are cold celestial objects made of ices and dust! There are no electric discharges or combustion reactions occurring on this, or any other comet! Science is about evidence and observations! Science is an iterative process that builds knowledge based on past evidence and observations.

    From the beginning, VIRTIS-M has given us accurate temperature maps of planets, asteroids, and comet 67P! Instead of dwelling on the scale colours, look at the actual temperature data being presented. That's where you will start to see the science - again, comets are cold bodies made of ices and dust! ALL the evidence and observations support this!

    Finally, here are three more data visualization treats to close this out ...

    1) Referring back to VIRTIS-M's view of the Sun (and I'm just eyeballing this), if we do something silly like assign a UV band of ~300 nm to red, and IR bands of ~3200 nm to green, and ~1200 nm to blue, the Sun will come out looking purple! Your challenge (if you wish to accept) is to figure out why.

    2) From the specification and calibration document for VIRTIS on Venus Express, please refer to Figure 19. It is an RGB image acquired from the VIRTIS-M Vis channel, and it brings a smile to me face every time ... enjoy!

    3) The Solar Dynamics Observatory website provides near realtime, remotely sensed images of the Sun. I would like you to look at one Atmospheric Imaging Assembly (AIA) image in particular. It is the one labeled AIA 304, 211, 171. Unlike the majority of images that have arbitrary colours assigned to a single EM band, this image is an RGB representation of three different UV bands.

    AIA (Atmospheric Imaging Assembly)
    30.4 nm = R (EUV, chromosphere temperature of 50000 K),
    21.1 nm = G (EUV, corona temperature of 2000000 K), and
    17.1 nm = B (EUV, corona temperature of 1000000 K)

    originaljohn! I hope I've addressed some of your concerns regarding VIRTIS-M temperature maps! There are no anomalous temperatures. All the temperature data presented by the VIRTIS team is accurate! The reported scale minimums and maximums represent the minimums and maximums for all the pixels in a displayed data set! You have mistakenly misinterpreted the temperature data from the beginning! Comets are made of ices and dust! VIRTIS, MIRO, ALICE, GIADA, RSI, etc. all confirm this! Science!

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