CometWatch 1 March

This week, CometWatch features an image of Comet 67P/Churyumov-Gerasimenko taken by Rosetta’s NAVCAM on 1 March 2016, when the spacecraft was 26.7 km from the comet nucleus.


Enhanced NAVCAM image of Comet 67P/C-G taken on 1 March 2016, 26.7 km from the nucleus. The scale is 2.3 m/pixel and the image measures 2.3 km across. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

With Rosetta back at close distances from the comet, NAVCAM images no longer cover the whole nucleus but only parts of it, displaying a variety of interesting details on the surface.

This image shows a portion of the large comet lobe, where the Imhotep region slopes down towards Bes, on the southern hemisphere. A jet of activity is clearly seen emanating from the lower left edge, even in the original image (at the end of the post), while portions of the Khonsu region are visible towards the right.

Imhotep and Bes are also featured in a image taken with Rosetta’s OSIRIS narrow-angle camera on 10 February, and released last week via the OSIRIS image of the day website. Portions of Khepry can also be seen on the left side of this image.


OSIRIS narrow-angle camera image taken on 10 February 2016, when Rosetta was 49.2 km from the comet. The scale is 0.89 m/pixel and the image measures 1.8 km across. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Another narrow-angle OSIRIS image, taken on 27 February and released this week, shows a different portion of the large lobe, focussing on the Ash region.


OSIRIS narrow-angle camera image taken on 27 February 2016, when Rosetta was 29.7 km from the comet. The scale is 0.53 m/pixel and the image measures 1.1 km across. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

This week, a new batch of 826 new NAVCAM images was also released, spanning the weeks between 21 October and 15 December 2015. You can browse through them via the NAVCAM Image Browser tool.

The original NAVCAM image is provided below.




  • Ramcomet says:

    The Dragon still breathes!!!!!

  • Judy Hawkins says:

    I just looked over at the OSIRIS image of the day and am delighted by the thumbnail in the corner showing what part of the comet the image is from — that is an excellent tool!! Thank you!

  • THOMAS says:

    This is clearly one of the most interesting and potentially controversial images yet from the comet.

    I assume that it has escaped nobody’s attention that the jet(s) “clearly seen emanating from the lower left edge, even in the original image” are undeniably emerging from the deep shadow of the cold night-side of the comet (which, judging by the very long shadows being cast by the boulders scattered on the shelf above the jets, has clearly been deprived of the warmth of sunlight for several hours at this point). This would seem hard to square with any form of “sublimating ice” theory (for which, incidentally, not the faintest glimmer of a plausible mechanism has yet been suggested to explain the actual, observed behaviour of the jets on 67P). This is particularly true in view of the fact that the jets seen shooting out from the night-side here are the *only*ones visible in the image, in striking contrast to the apparent absence of any activity from the sunlit regions…

    Even more significant perhaps is the fact that, given the position and the angle of the jets, they are, for a good part of their length at least, necessarily in the shade themselves (again judging by the direction of the very long shadows being cast by the boulders above them). Their considerable brightness is thus necessarily *intrinsic*: no-one can invoke sunlight simply illuminating entrained dust-particles here: the geometry of the situation simply rules it out.

    The image thus constitutes a truly remarkable, unmistakable, smoking gun for all to see, which would in itself be sufficient to kill the standard ‘dirty iceball’ theory stone dead if all the other extraordinary observations and findings collected by Rosetta and Philae over the past 2 years had not already done so (shape, colour, hardness, ruggedness, temperature, “music”, oxygen content, etc, etc.).

    • Marco Parigi says:

      Hi THOMAS, welcome back. I disagree with you again in regards to the intrinsicness or otherwise of this jet’s brightness. It looks to me very likely illuminated by the sun given the relative angle of the sun.

      However the fact that it is outgassing well after local dusk and when activity in general is dropping off, should still be a red flag for theorists of all descriptions. That coupled with a lack of changes in the morphology in the small scale anywhere on the comet.

      Where is all this gas and dust coming from? Clearly not from near the surface.

      • ianw16 says:

        Sorry, but on what basis are you saying that this is ‘well after local sunset’? There appear to be higher elevation points either side of that jet that are still illuminated.
        So how long ago was sunset? Which way is the comet rotating on its axis in regard to the viewer in that image?

        And I haven’t seen any close up comparisons from the team on what morphological changes may have occurred. The gas and dust must, by definition, be coming from close to the surface. Too far below the skin and the gas wouldn’t sublimate. At the temperatures at ~2.5 AU any remaining jetting will indicate that the ice must be on or close to the surface, as already seen. The diurnal skin depth is not that great. There has been a paper on this, unfortunately it is paywalled:
        Luckily, I’ve managed to read the whole paper, and there is nothing that is particularly troubling about these jets persisting for some time after sunset, based on the thermal lag data acquired by MIRO, and a diurnal skin depth of ~6mm.
        I’m wondering what you are basing your assumptions on?

        • Marco Parigi says:

          Hi Ianw16,
          With regards to sunset and thermal lag, as well as much colder daytime surface temperatures, post sunset (or pre-sunrise) jets are not expected. Sublimation is also a highly endothermic transformation, thus if this is a continuation of a daytime jet, it should have come to a self inflicted screeching halt come nightfall or shadow. By the context of this photo it appears to be evening but it doesn’t change the argument regarding the jet as unexpected given surface, sun powered processes.

          With regards to before and after surface morphology changes in the metre scale, the few that are indicative show no changes in the texture. This should be noted as remarkable given the perihelion activity. There should be wholesale obvious texture transformations on many surfaces that showed activity. Even Imhotep’s “erosion” left surface boulders unmoved and the same texture in any of the close observations so far.

          • ianw16 says:

            Well, I’m sorry, but the scientists disagree. From the ‘Discussion’ section of the paper I linked to:
            “OSIRIS has acquired and continues to accumulate high resolution images of night-side dust activities on 67P. Our preliminary data analysis and model results substantiated that the observed sunset jets in the Ma’at region exhibit a pattern characteristic of being sustained by thermal lag in the subsurface of one to two hours, and these jets were essentially day-side jets lasting beyond sunset to become conspicuous against the shadowed nucleus.”

            And this doesn’t take account of more volatile species (CO/ CO2) that would sublimate at lower temperatures.

          • Marco Parigi says:

            Hi Ianw16,
            Unfortunately, I cannot read this particular discussion on the pay walled paper. However, I have read several scientific papers that have also suggested thermal lag explanations. They have been vague in a hand waving way saying pretty much that thermal lag is the most likely explanation, but no calculations in material and energy budgets like what happens to the sublimation latent heat. It gives me the impression that the specifics aren’t concerning as long as there is an overarching explanation.

          • Ramcomet says:

            Marco and Ian,

            A little story of something strange happening here on Earth:

            Restoring my great grandfather’s 1888 house. We replaced some 40 watt bulbs in a chandelier for more light. After a while we turned off the wall switch and walked away. One light bulb blew up within five seconds, spraying the room with glass up to 3 meters away, (glad our backs were turned)!
            This was AFTER we turned it OFF! Doesn’t make sense. Searched electricians blogs and it’s simply unheard of.

            Anyway, thought there might be some correlation or takeaway message here… 😉

            Could it be the thermal shock of sudden cooling outerglass skin contraction broke open a preexisting crack that was there all along, while hotter gas inside remained higher pressure?

        • A. Cooper says:

          Ianw16 and Marco

          I did a bit of digging on the thermal skin depth issue but just to start with, I presume the paper is referring to the same jets as those that were described in this ESA blog post?

          I remember an orangy-red heat map of the region too so I think I must have read the paper when it was free. Both blog post and abstract refer to Ma’at in April 2015.

          I sense confusion over the thermal skin depth as evidenced by the different findings and differing statements among papers, blog posts, presentations and members of the OSIRIS team, even regarding the same event, namely, these particular sunset jets. The above linked Rosetta blog post, which I should emphasise was written by OSIRIS, is seemingly at odds with your linked OSIRIS paper abstract. I don’t think there’s a problem with differing findings so long as they don’t treat any one as definitive. But seeing as a deep thermal skin depth doesn’t fit with modelled behaviour, I fear that if the actual comet says otherwise, they will be tempted to disbelieve their own eyes and attempt to fit a square into a round hole (see example near the end of this comment- it’s already happening).

          Perhaps it would be salutary to preface my little research operation with the following. “MUPUS on Philae” was tweeting today, 17th March 2016, at ESLAB50. The tweet linked below gives some indication of what’s not yet clear. It’s describing a presentation by Keller (presumably H.U. Keller from OSIRIS). The photo is of a summary of questions and statements about various aspects of 67P. It specifically lists “What is the thermal skin depth?” At number 6.

          Also, VIRTIS are quoting a different value from OSIRIS. Their value is much deeper, but for an earlier period. You might expect it to be deeper for a later period, not earlier.

          Statements in your linked OSIRIS paper abstract are at odds with the above linked Rosetta blog post written by OSIRIS. It seems the jets are hard to explain without their coming from some depth, presumably well below the 6mm that was “parameterized” in your linked abstract. That’s why the OSIRIS/Rosetta blog post said, regarding these same sunset jets:

          “The OSIRIS team think that the comet can store the incoming heat for some time beneath its surface, resulting in sustained activity from these regions even after nightfall.
          “While the dust covering the comet’s surface cools rapidly after sunset, deeper layers remain warm for a longer period of time,” says OSIRIS scientist Xian Shi from the MPS, who is studying the sunset jets.

          The scientists suspect that the comet’s supply of frozen gases that fuel the comet’s activity exists in these deeper layers.”

          ////end of quote.

          That quote can’t be referring to dust layers *and* deeper layers all within the top 6mm. Besides, could a 6mm layer really give rise to such focussed and collimated jets?

          Furthermore, Fabrizio Capaccioni (VIRTIS) talks about the water cycle in the following video, from 20:40 to 24:15 and refers to the top 10cm being where the sublimation takes place. That’s 17x deeper than the 6mm quoted above and it’s referring to the day/night thermal storage issue as well:

          Capaccioni says that low thermal inertia is needed in the top dusty layers for the top few cm (of the 10cm) to trap the post-sunset sublimation as frost on the surface. I thought the dust was inherently high thermal inertia but I suppose Capaccioni means an absolute low inertia for such a thin layer (i.e. even the top skin of a high insulator will cool quickly). Your linked paper abstract also emphasised low thermal inertia.

          Cappacioni’s initial observations were in Sept 2014 and one might infer that the 10cm thermal depth is from that period and would therefore be much deeper at perihelion (the ’10cm graphic’ comes immediately after the September obs overview). However, the frost cycle movie that follows on from the 10cm graphic takes data from August 2014 to February 2015, five months after the September obs but still six months before perihelion.

          Your sunset jets paper used photos from April 2015 and yet is modelling the thermal depth at 17 times less than Cappacioni’s from an earlier period with less solar irradiance, significantly less in September 2014.

          Meanwhile, the abstract from your linked paper also says:

          ” A general thermo-physical model was parameterized such that the thermal lag in the subsurface is consistent with the elapsed time of observation after sunset. It is found that the sublimation of water ice from a depth of 6mm and with a low thermal inertia of 50 W m-2 K-1 s1/2 could explain the spatial pattern and evolution of the apparent sources, particularly their disappearance due to the eventual cooling of the subsurface.”

          So, one perfectly sound parameter is the time from sunset to jet shut-down. That’s known, and a given. Another parameter is the stated value of 50 W m-2 K-1 s^1/2. Is that consistent with other obs? I remember reading some data on thermal inertia a long way back but I forget what they were and this specifically says it’s low. Presumably you can toggle the parameterised thermal inertia up or down and that will change the thermal depth? Would it be exponential and shoot up to Cappacioni’s values?

          So is it:

          1) 6mm (OSIRIS abstract).

          2) “deeper layers remain(ing) warm” (OSIRIS blog post).

          3)10cm (VIRTIS).

          4) Unknown (Keller summary list).

          I started with an example of the confusion and I’ll finish with another. The Rosetta/OSIRIS blog post made a statement which was pure wishful thinking:

          “One recent exception was the event captured on 12 March, which caught the onset of a dust jet at the brink of dawn, in the Imhotep region on the comet’s large lobe.”

          It was clearly nowhere near the “brink of dawn”. There was also talk of cliffs catching the first rays of the sun. But the jet was emanating from a low point, the edge of the Imhotep depression that has the famous ’roundish features’. This location isn’t near any cliffs, except the one dropping down into the depression. I said at the time that this was well before dawn and that the site of the jet was the edge of the depression in Imhotep- right on the site of the ice signature where I knew there was an exposed fracture plane. Mattias Malmer confirmed this with his sophisticated shape model and tweeted thus:

          Malmer’s tweet said:

          “The sun did not hit the “underbelly” of the duck until one hour 15 minutes later. And the area had been in shadow for five 1/2 hours or so.”

          It’s clear that OSIRIS were in denial that subsurface temps could remain high enough to cause sublimation after five-and-a-half hours of nightfall. I would infer that they knew the Imhotep outburst would have to have retained high temps at a much greater depth than any of the above thermal gradient depth values.

          None of this sunset jet discussion has a bearing on stretch theory but, if only someone would listen, stretch theory has a bearing on the sunset jets. The ones in the OSIRIS abstract and blog post are strung in a line because they fall between two clearly defined layers that tore prematurely from the body and rode up the head (Part 41 on the stretch blog). The Imhotep jet emanated from the site of the ‘orange’ crust slide (Part 42) an area of great upheaval as evidenced by the depression and the ’roundish features’. The snug fit in the roundish features’ profile is the seating from which the orange slide broke away and slid. The roundish features run in lines because they were bubbling at the bottom of 100-metre wide cracks (but not actual buoyancy-generated bubbling as I’ve been at pains to emphasise before).

          • A. Cooper says:

            That list in my last comment should have two items added to make six. So is the thermal skin depth:

            1) 6mm (OSIRIS abstract).

            2) “deeper layers remain(ing) warm” (OSIRIS blog post).

            3) 10cm (VIRTIS).

            4) Unknown (Keller summary list).

            5) In the order of metres as possibly implied by the 5.5-hour thermal storage for the Imhotep jet.

            6) In the order of tens of metres as implied by (but not essential to) stretch theory.

          • ianw16 says:

            @A. Cooper,
            I’ll only say that maybe I seem to have a bit more patience than maybe others on here. Nobody is saying that they have the models worked out to the Nth degree. As the paper I linked to said, they haven’t run the numbers for supervolatiles. Do we know that these jets were H2O?
            However, I’m sure that this mission has given people the data they need to improve the modelling beyond what it was before. We know there is ice on the surface, mixed areally and intimately. We know that there is ice below the surface. We now know that there is CO2 ice on the surface, and therefore below it at shallow depths.
            A sample from Philae of the surface material would have been nice, but in the absence of that all they can do is model the possibilities. To that end I posted a couple of links to (unfortunatelly paywalled) papers where this modelling and experiment is already underway.


            The results look very promising in terms of explaining the sintering of the H2O ice, the formation of a dark organic mantle above the ice, and the porosity of that mantle.

            Like I said, I don’t need results today. Papers were/ are still being published years after the Halley, Tempel 1 and Hartley 2 missions, based on what they found. I have no doubt this mission will be no different.
            I’ll happily await the research on this, but don’t expect to find that it is due to anything more than ices being at a temperature that is above their sublimation temperature.

          • Gerald says:

            Contraction due to cooling could have opened a fracture (thermal stress, or changes of the crystal structure/solid phase), and released supervolatiles.
            Ruling out one option doesn’t proof another option, since there are more than two alternative possibilities.
            Regarding rotation, one needs to pay attention not to confuse predicted data with measured data in SPICE. I’m not entirely sure, which of the two Mattias Malmer’s software used.

      • Thomas says:

        Thanks for the welcome back, Marco. I’ve actually been watching from a distance and waiting for truly new developments (like this image…) to comment on. There hasn’t been anything strikingly new over the past few weeks….

        I’m waiting in particular for updates on some of the crucial observations and findings of which we have so far had no news (unless I’ve missed something), namely:
        -plasma and temperature data regarding the jets, particularly the most spectacular ones such as those of the 29th July event (, the 12th August event ( and, above all, the 22nd August event (, which the blog-post famously described as being “extraordinarily bright”, before going on to state that “the teams are busy analysing the data to understand the nature of these events”. As far as I know, they are still working on it since we’ve had no news since (unless someone can point us to anything published). It looks to me like they are as much “in denial” about what they’ve found as Kathrin Altweg and her teams admitted to being for more than a year about the discovery of abundant molecular oxygen pouring off the comet.

        Regarding this new, night-time, jet, you write “It looks to me very likely illuminated by the sun given the relative angle of the sun.” I suggest you take another look, Marco. Judging by the shadows being cast by the boulders and also by the dotted-line illumination of the extremities of the vertical linear outcrop just to the right of the base of the jets (and also to the left), the rays of the sun are descending vertically. The vertical demarcation line which cuts vertically down across the jets from the overhang above is the terminator line between the sunlit part of the jets to its left and the part in night-time darkness to its right. The “problem” is that the part in darkness is almost as bright as the part in full sunshine! In other words, the brightness of the jets is necessarily intrinsic, with full sunlight simply adding slightly more brightness. This simply brings ultimate confirmation of the intrinsic brightness which was already manifest in the three spectacular events of last July and August.

        • Marco Parigi says:

          Hi Thomas,
          It looks to me like the jet is coming towards the camera, and the illuminated portion in line with the shadowed nucleus has reached sunlight. The leftward angle is fooling you. Believe me, an intrinsic brightness would excite me too, but it isn’t.

          As far as the Oxygen goes, ample liquid water inside a pressurised comet, with proportionally ample Oxygen creating bacteria explains the O2 very neatly.

          The primordial explanation is a catch-all. Whether it is O2, or CAI’s or basketballs flying out of the comet, one can always say they were in there frozen in their proportions 4.5 billion years ago. Nobody can prove otherwise.

        • originalJohn says:

          True, Thomas. What you are politely saying is that is that it is astounding how far the dogmatists will bend over backwards to shoehorn the observations into the dogma, avoiding the obvious evidence of their own eyes.

          • ianw16 says:

            Very funny. What “evidence” would that be? Yet another classic case of projection. Last time I checked, the electric comet was still an evidence free zone, whose proponents were inventing ever more impossible woo to try to keep it alive. It isn’t, by the way. All this mission has done is dig up its corpse and hammer a few more nails into the coffin lid, lest it ever show its ugly face in public again.

    • ianw16 says:

      Utter nonsense, as usual;
      And what have the shape, colour and ruggedness got to do with the price of fish? The hardness is caused by sintering, as shown in the laboratory:
      The ‘music’ has already been explained, there are no anomalous temperatures, and the oxygen just places constrains on the conditions under which it could form, i.e. at about 70 K in a dense interstellat molecular cloud.
      Not, therefore, on a planetary surface, waiting around for one of the ever so common interplanetary lightning bolts to come along and blast it into space.
      The rest of your musings are due to pareidolia, and arguments from incredulity.

      • Thomas says:

        Hi Ian,

        You are entitled to your opinions, like everyone else. But it would be nice if you occasionally addressed the problems being posed by the actual observations and data. As usual, in answer to my comment above, you carefully avoid actually responding to the substance of my comment on the clearly intrinsic nature of the brightness of this jet. Please just explain how the mainstream theory can account for the manifest brightness of the base of the jets here, to the right of the terminator line separating the sunlit and the non-sunlit parts of the jets.

        • ianw16 says:

          The jets ARE NOT intrinsically bright, as you would know if you’d bothered to read any number of papers released on the subject, or even some of the blog articles. The jet in this particular image looks about as bright as the nucleus, if that. We know the nucleus has an albedo of ~4 %. So not very bright.
          As for the temperature and composition of the brighter perihelion jets, data were released on this blog. The constituents were neutrals. And you’ve only got to look at the jets at Hartley 2 to know they aren’t hot. You do not get H20 ice grains entrained within hot jets.
          It’s total nonsense. And the nucleus temperature was measured by MIRO at the same time as it was observing H2O emissions from the nucleus. No hot spots. No anomalies. No combustio., No electric woo:

          • Solon says:

            “And you’ve only got to look at the jets at Hartley 2 to know they aren’t hot.”
            Why do they need to be hot? Never heard of cryogenic dusty plasma?
            “No electric woo:”
            Everything involves electricity, even your thoughts.

          • Thomas says:

            Ian, you write:

            “The jets ARE NOT intrinsically bright, as you would know if you’d bothered to read any number of papers released on the subject, or even some of the blog articles.”

            So if we are to understand you correctly, we should only be allowed to judge the precise nature of the brightness of the observed jets by what is asserted in the right peer-reviewed articles which, in your view has come to take absolute precedence over the prima facie evidence being provided by actual observation. What an extraordinary admission of how the scientific method which you are presumably quite happy to pay lip-service to has truly been turned completely on its head over the past half a century or more (and not only in astronomy)! I would be interested to know if any of the other regular mainstream contributors to the blog are actually prepared to go along with you in your blind faith in the absolute primacy of theory over observation.

            For the third time of asking, Ian, would you kindly at last answer my question and say how you explain the RELATIVE brightness of that part of the jets in this image which unquestionably lie in deep darkness.

          • ianw16 says:

            So still trying to rescue the evidence free zone that is the electric comet, with ever more impossible woo?
            Perhaps you could tell us what would cause these cold plasmas, what is the evidence for them, and what their composition would be?
            My understanding of plasma is that it consists of ionised material. So why not read the Hartley 2 papers and let us know how ionised these jets were?
            Hint: they weren’t.

          • ianw16 says:

            I’ve already explained it.; pareidolia. See my reply to Ramcomet and also to Harvey. If you don’t believe it, then that’s up to you.But that is all it is; a belief. No scientific evidence
            Here’s another image with part of the nucleus moved and placed against the blackness off nucleus. And remember, the nucleus has an albedo of ~4%. Think coal.

          • ianw16 says:

            Whoops, forgot to include the link to the picture:

          • Thomas says:

            @ ianw16

            “And remember, the nucleus has an albedo of ~4%. Think coal.”

            Everything is relative, Ian. Have another look at the unprocessed image of the August 22 event ( The brilliant white 1-km-wide flash happens to be identical to the second flash produced by the Deep Impact explosion on Tempel 1 ( which you’re so fond of referring to. Think white hot plasma, in both cases.

            And btw, your blind faith in the assumptions piled up on prior assumptions (“turtles all the way down”) which underpin your so-called mainstream “theory” (which is actually no more than a simple axiom…) is far more a case of your beloved, much-touted “pareidolia” than the actual evidence of multiple gainsaying observations which your further unquestioning belief in your axioms requires you to deny at all cost.

        • Ramcomet says:

          Well, I think it is both Dust-Shine and the Vee-shaped chasm in the cliff above the jet, which allows less and less sunlight illuminate the jet towards the right, creating the illusion of intrinsic glow.

          The terminator line is not a line at all but a jagged fan shape matching the jagged vee shaped iris above.

          As to Dust-Shine, for me it is easy to see the effect, having long worked with light and particulates in the form of designing, prototyping and patent work for advanced “laser” toy water gun systems. I used focused LEDs inside non turbulent coherent “glass rod” water streams, (similar to streams seen in “leaping” fountains in water parks and Las Vegas), but when the streams’ glass fiber effect broke up after just six or seven feet due to air friction roughing up the inner reflectivity, a strategically placed secondary lensed led below the stream causes the fine spray to be illuminated for another ten feet, completing enough of a “Laser Cannon” effect for an exciting night time backyard battle toy.

          Long story short, this looks like the secondary Illumination.

          • ianw16 says:

            Agreed, there is nothing intrinsic about the brightness of this jet. Just to prove it I employed the scientific principle of what I call ‘messing about in Photoshop’.
            Here is an image with part of the jet projected onto 3 differnt parts of the nucleus. I have not altered in any way the contrast/ brightness etc in any of the insets.

            Doesn’t look quite so bright after that.

          • ianw16 says:

            Exactly. The very fact that there are areas either side of the jet (apparently) that are also illuminated, should be a bit of a clue. One could use the shape model, reconstruct tha angle of the Sun from the shodowed areas (difficult from a 2D image), and prove it.
            Not worth the effort to disprove an argument based purely on pareidolia though.
            If one wanted to **prove** the argument, however, that is what one would do, rather than saying “it looks like……”

    • Booth says:


      You write, “… no-one can invoke sunlight simply illuminating entrained dust-particles here: the geometry of the situation simply rules it out.”

      I will state, without reservation, that the jets observed in this image are nothing more than sunlit dust grains lifted from the comet’s surface by sublimating volatile ices! An overly simplistic description, but very much to your point!

      I further report that none of the jets seen emanating from 67P have ever been “intrinsically illuminated” – not a one! We have, of course, observed very bright jets in the past, but that was closer to perihelion when the jets could also entrain grains of solid ices resulting in higher albedos!

      You write, “… judging by the very long shadows being cast by the boulders scattered on the shelf above the jets, (the jets have) clearly been deprived of the warmth of sunlight for several hours at this point.”

      Given a right-handed CSEQ coordinate system and rotation rate of 12.4 hours, I would estimate that sunset occurred on the jet source region approximately two to ten minutes earlier. Without knowledge of topography in the shaded region, I can’t be anymore accurate than that. Apologies!

      You write, “Even more significant perhaps is the fact that, given the position and the angle of the jets, they are, for a good part of their length at least, necessarily in the shade themselves”

      That’s odd! I see shadows being cast across and through the jet by illuminated objects perched in the sunlight above. Drop a straight-edge on the three vertical features visible within the jet and trace them back to the terminator. There is one particular outcrop that is the obvious source of one shadow. Sadly, we cannot see the base and source region of the jets as these features are actually in shadow (i.e., not illuminated by the sun).

      Back in October of 2014, Claudia published an excellent layman’s description of how NAVCAM images are processed given the low albedo exhibited by the nucleus. You may have missed that thread.

      Also, recall that the albedo reported by Capaccioni et al (2015) was 0.060 ± 0.003 at 550 nm! The obvious implication is that your “intrinsically illuminated” jets have an output that is less than that of the nucleus. Proof?

      As a test of your claim, please identify the jets in the following randomly selected single frame NAVCAM images. This is not a trick. These images are products released by ESA Rosetta.

      1) NAVCAM image : 2015/02/20 : Dist = 118.5 km / Res = 10.1 m/pix

      2) NAVCAM image : 2015/02/28 : Dist = 102.6 km / Res = 08.7 m/pix

      3) NAVCAM image : 2015/03/14 : Dist = 081.4 km / Res = 06.9 m/pix

      In these images, I see the comet’s nucleus where the brightest pixels have an albedo of 0.06. Sadly, I don’t see any “intrinsically illuminated” jets. Where are the jets? They’re obviously too dark to be seen … and they don’t appear to produce any light of their own. Again, diffuse dust grains, liberated by sublimation processes, scatter sunlight which is recorded by NAVCAM. Simple physics! Simple optics!

      Thomas! Your interpretation of this image is based on several erroneous assumptions. I hope my comments and corrections have cleared up some of the confusion.

  • Kamal says:

    Jupiter at opposition yesterday/today and 67p at opposition in another 3/4 days.

  • ianw16 says:

    For anybody interested, the first paper on the detection of a diamagnetic cavity at 67P is now freely available:
    “First detection of a diamagnetic cavity at comet 67P/Churyumov-Gerasimenko”
    Goetz, C. et al.

    The authors (including K-H Glassmeier) confirm, of course, that the “comet has no magnetic field of its own.”

    ***If Emily or Claudia are planning a blog piece on this, then this comment is superfluous, and I won’t be offended if it isn’t published :)***

  • Harvey says:

    Claudia. Is there any chance a member of the team could say definitively whether this jet shows any evidence of intrinsic emission as opposed to dust scattering sunlight?

    I don’t think it does,I think it’s just scatter as usual, but it’s hard to be absolutely certain just from the image published.
    Someone with the full data to hand would know instantly.

    It would abate quite a bit of pointless argument here.

    • ianw16 says:

      Apart from my highly scientific Photoshop efforts in a reply to Ramcomet, above, there is this: “This is the brightest jet we’ve seen so far,” comments Carsten Güttler, OSIRIS team member at the Max Planck Institute for Solar System Research in Göttingen, Germany.

      “***Usually, the jets are quite faint compared to the nucleus*** and we need to stretch the contrast of the images to make them visible – but this one is brighter than the nucleus.”

      My emphasis. From:

      Of course, if we want to see an example of something that really does look intrinsically bright, we could take something like this:×785.jpg

      Even the nucleus seems to be glowing! I wonder what the instruments found when they looked at that ‘glow’, in terms of the surface temperature and jet composition, ionisation etc?

      People should know; I’ve linked to the paper often enough 😉

      • ianw16 says:

        Here’s another Photoshop effort:
        In PS CS3 extended. Image > Adjustments > Brightness: reduce to minimum (-150).
        Then: Image > Adjustments > Levels: reduce until jet basically disappears. Nucleus still visible.
        Conclusion? Having done that, then what remains is the brightest part of the image. And it isn’t the jet.
        As I’ve said, purely pareidolia.

      • Harvey says:

        Ianw16 – I dont need convincing 🙂
        I was hoping maybe we could put this to rest – and Matt has very kindly obliged.

    • Thomas says:

      I heartily second your request Harvey. Disclosure of the full data on this event would indeed instantly settle the issue one way or the other.

      I fear though that if the collected data does not confirm the “dust scattering sunlight” scenario, then the members of the team may be as loath to go public with their findings as Kathrin Altwegg and her team were after the discovery of abundant oxygen pouring off the nucleus. They took 14 months to get over being “in denial” of their own findings. Another instance of long-awaited publication of extraordinary findings concerns the “extraordinarily bright” flash observed during the August 22 event ( As far as I know, the conclusions of the teams who were said in the blog post to be “busy analysing the data to understand the nature of these events” still haven’t seen the light of day. But it’s true that we’ve only been waiting for them for 7 months now.

      • Harvey says:

        It does confirm it; see below from Matt; end of story.

        • Thomas says:

          Not end of story Harvey, by a long chalk. See my request for long-awaited information about *particular* (not general) features in my own response to Matt, below.

    • Matt Taylor says:

      Harvey, thanks for your request – talking to the scientists from the team looking at these features in depth, they are trying to resolve the “jets” to examine if they detect sublimation from the dust grains within them, but no luck yet. The brightness profiles are telling us something about the size distribution of the dust, and this touches on the massive benefit we have with Rosetta that we are there for a number of years around perihelion, so we are looking at the way the gas and dust emissions vary (if at all). To be clear, from all observations thus far – these features, like the coma and nucleus in general, are visible because of scattering of light.

      • Thomas says:

        You speak of features in general. Does the work done by the teams “working on understanding the science data” show that the scattering of light also applies to particular features like the “extraordinarily bright”, 1-km-wide-at-its-base flash of the August 22 event I referred to in my post just above? (My inverted commas to quote from the blog post

        Thanks in advance for enlightening us on this since, to my knowledge, nothing has since been published on this specific event (or on the almost equally spectacular July 29 or August 12 events) despite these three events being the most obvious subjects for in-depth study of the nature of, and the mechanisms driving, the “jets”.

        • Harvey says:

          Matt is absolutely explicit.
          ” To be clear, from all observations thus far…”
          End of story.

          • Thomas says:

            Sorry, but I still await the conclusions of the teams who were “busy working to understand the science data” with respect to the “extraordinarily bright” August 22 flash ( which is to all intents and purposes identical to the gigantic second flash on Tempel 1 of Deep Impact fame (

            I’m not at all convinced that Matt meant to include this particular observation in his “all observations thus far” since, given the absence of news, analysis is apparently still ongoing…. You may have lost all interest in understanding how the extraordinary August 22 outburst (among others) occurred and what the driving mechanisms for it are, but I am not.

            We are very far from the end of the story.

          • Gerald says:

            the more dust, the brighter.
            The higher the albedo of the grains, the brighter.

            You might ponder, whether it’s mostly Rayleigh scattering, Mie scattering, or Thomson scattering of sunlight by dust grains.


          • originalJohn says:

            Well Harvey, it looks as though Matt has overlooked the intrinsic emissions known to occur and judged within the standard comet hypothesis to result from ionisation by both photon and electron collisions. You and I have discussed these as revealed on spectra previously.
            So not end of story from that point of view. And not from others either. There have been no published reports of any specific measurement of any sort on the jets. and by that I mean ion composition, ion/neutrals ratio, spectra, temperature distribution, current flow, magnetic field measurements, x ray emission. If ESA have this data they are being very reticent in releasing it. Or perhaps they do not have it and extrapolate their judgement from what they do have on the coma as a whole.

          • Gerald says:

            some of the ALICE data have already been published.
            Data are avaiable via HTTP at the NASA PDS:
            FTP access via ESA’s PSA.

          • Harvey says:

            “Well Harvey, it looks as though Matt has overlooked the intrinsic emissions known to occur and judged within the standard comet .”
            The discussion was about *the near comet jets*; the standard emissions of the ion tail etc are not expected, or observed there because photoionisation and solar wind interaction have not yet had time, very close in to the comet, to act.
            The standard theory expects no emission there, none is observed.
            A discharge would produce emission there.

            It’s dead, move on.

      • Harvey says:

        Matt; thank you very much for your last sentence in particular! Good of you to take the time.

        • Matt Taylor says:

          Harvey, thank you for your comments and continued efforts representing plasma science.

          • Harvey says:

            Sorry to bother you with a ‘supplementary’, but we seem to have a problem with the meaning of the word ‘all’. It would be nice to put this to rest!

            For the avoidance of doubt. ‘All’ includes the very bright event of 22nd August? It also is just a dense transient cloud of particles scattering sunlight, with no evidence of intrinsic emission?

            In fact ‘all’ means exactly that – all!?

      • Marco Parigi says:

        Hi Matt,
        Thanks for stopping by during ESLAB50! I’ve been following your various selfies, and am hoping there is a video presentation somewhere.
        I know a while back you asked if there was a paper on stretch theory. I have registered on Arxiv to post a paper However, I need an endorsement from someone in the category I would like to post, as a first time Arxiv author. The appropriate category appears to be Astrophysics – sub category planetary and earth science.
        If you or anyone you know may be happy to endorse me so I can progress your suggestion of submitting a paper, I would be very grateful.
        Is essentially the draft of the paper I am looking to co-write with A.Cooper.

        • Matt Taylor says:

          Dear Marco,
          will you be submitting the paper to a referred journal?
          I have never posted to Arxiv, but from my perspective, one should be submitting the article to a refereed journal.

          • A. Cooper says:


            OSIRIS publish regularly on arXiv. I googled four examples:





            So that should surely mean our paper wouldn’t be overlooked/repudiated because of being published on arXiv? By which I mean being overlooked based solely on publishing on arXiv and notwithstanding any issues with the science itself which may then be challenged.

          • ianw16 says:

            @A Cooper,
            In fairness, all of those papers were already in press at A & A, where they will have undergone peer review.

          • Marco Parigi says:

            Hi Matt,

            Gerald had initially suggested I post to somewhere like ArXiv, with a view and ambition to republish as a refereed or peer reviewed article in the future. The valid point being that as it stands our ideas cannot be fairly cited by other scientific papers.

            If you have read my link and have any thoughts at all, whether about strategy to publish, or about the scientific ideas themselves, I’d be honoured to hear them.

        • Jean-Baptiste Vincent says:

          Dear Marco, and Cooper,

          OSIRIS does not ¨publish¨ in Arxiv, because Arxiv is not a peer-reviewed journal. It is simply an open archive.

          What we do, like most of our colleagues from many fields, is to upload a copy of our papers to Arxiv once they have been accepted by a scientific journal like A&A, Icarus, or others. This ensures that our results are available to everybody for free.

          We never put on Arxiv a paper that has not been peer-reviewed, for the manauscript may contain a major mistake that has been overlooked. Even after many years of experience in one field, one cannot keep track of all publications and it is easy to miss some important piece of information. That’s why peer review is so important.

          • A. Cooper says:

            Jean-Baptiste Vincent

            Thank you for dropping by the Rosetta comments again. I read your papers with great interest. And thanks for explaining how you use arXiv.

  • Robin Sherman says:

    It might be pertinent to point out that the images being discussed are in fact an optical illusion created by your computer screen. To claim primacy of observation in this case is therefore at best misguided and in reality, irrelevant.

    • Thomas says:

      Hi Robin,

      Are we to understand by this that that you are quite happy to be counted among those mainstream proponents like Ian who henceforth unashamedly assert the subordination of observation to theory?

      Any more takers anywhere?

      • Tim Burns says:

        It never ceases to amaze me of just how childlike and overwhelmed with that awesome thrill of a new outer space discovery, Rosetta and Philae give me each time I revisit the blog! I still have a profound respect for everyone involved in this historical, ongoing event. I can’t wait for the moment the final decision is made to attempt to remarry Rosetta and Philae by landing Rosetta on the comet to “rejoin” the lander!

    • Sovereign Slave says:

      I don’t know, but am wondering if there have been any instruments that have actually detected the jets. Or any instruments that aren’t visually based. If not, perhaps the jets don’t actually exist, or it may be yet another example of the ever growing cases of pareidolia – they may look like jets, but they’re not. If no instruments have detected the jets, or they’re visually based, then obviously that does not constitute evidence, right? And since the sublimation model is obviously the only viable model, and since it cannot provide a detailed model of how the jets happen, and in fact the jets don’t actually seem to fit into this model when it really comes down to it, this absolutely does provide clear evidence that the jets do not in fact actually exist, right? And we all know that preserving the whole (sublimation theory) is much more important than preserving any one part (such as the jets), so we can just sort of let the whole jet thing skate. Oh, and maybe that pesky oxygen thing as well. And the comet’s shape (it’s a contact binary, really). And the shocking lack of adequate ice evident anywhere. Oh, and the…well, never mind, let’s just move along folks, nothing to see here.

      • Gerald says:

        Sovereign Slave, pay attention, that you don’t “promptly vanish[es] in a puff of logic.” 😉

        • Sovereign Slave says:

          Been on vacation, far far from internet and the ever growing forest of cell towers popping up everywhere. Happy to be back and find all the 10 to 20 faithful posters still avidly chasing their intellectual tai…,uh, I mean posting, and alas a few new names. Anyway, just for the record, my post above was quite tongue in cheek (obviously Gerald is becoming all too familiar with my antics, oh, and the poof was no doubt a close call, but I am still here (I think)). So, convoluted logic, but, I’ve noticed worse here. Did see an interesting movie while gone (that was close to a cell tower, unfortunately), The Big Short. Great illustration of perception vs reality, which is sort of the bottom line in ways for the Rosetta mission I think. I like this quote in the movie, seems pretty appropriate on several levels, and sooths my skeptics heart:
          “It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.”

          • Gerald says:

            Sovereign Slave,
            fully elaborated science results usually are double or triple cross-checked, and error propagation is applied. That way you get a good idea of how likely it is, that your results are wrong, in the sense of being worse than a reference hypothesis.
            This still doesn’t mean, that the resulting interpretation is the only valid, but just that it’s fitting better to the data than the considered alternatives.
            So, a hint to the level of appropriate scepticism applicable to a science result is usually included in the according paper.
            Since all the error analysis takes a lot of time and effort, preliminary results might treat the uncertainties more sloppy.
            On the other hand, most people are only interested in the main results, not too much in lengthy discussions about the validity of the calculations of error bounds, and the possible errors of the error bounds themselves.

          • Sovereign Slave says:

            Understood. I guess in relation to the quote and cosmology, it seems that there is a huge amount of over confidence in the large strokes theoretic structures that are adhered to. For example, no one of note seems to even question the universally accepted theory of solar system formation, so much so that you even have the latest paper, The presence of clathrates in comet 67P/Churyumov-Gerasimenko, trying to fit their findings into some aspect of it. The generally accepted solar system creation story is so widely accepted (institutionalized), this paper actually conforms itself unquestioningly to that theory. Well what if the generally accepted solar system creation story is wrong? Then this paper immediately becomes pure nonsense, and how many others with it? Also, and I’m not saying they do, but what if findings in that paper actually provided strong evidence of a totally new type of solar system creation story? Well, we’ll probably never know, because it’s unlikely that the institutional mindset and beliefs of the scientists involved with the paper leaves room to even consider it. And there’s the rub – it seems that much too often new findings are simply automatically slotted into old unquestioned theories, and opportunities of new lines of inquiries are missed.

      • ianw16 says:

        Sorry but most of that is just nonsense.
        Which instruments would you like to detect the ‘jets’? Aren’t microwave and IR good enough for you? They know where to look for the ‘jets’, due to the dust being lifted by the gas. When they look in Microwave or IR, what do they see? Gas. The gas does not follow the more collimated path of the dust.
        There have been numerous papers and blog posts on this, so I’m not going to waste my time chasing links to them all. I suggest doing a bit of researching before posting.
        As for ice, again there have been plenty of reports of its detection. Including subsurface in the southern hemisphere. Already been a paper on that, as well. And I suspect a forthcoming one on the detection of large (>1500m^2) surface patches in the SH ( ; p. 44). And now they appear to have found CO2 ice on a comet for the first time.
        And sublimation theory only requires that there be ice to sublimate, and sufficient heat to make it do so. Perhaps you could explain which part of that is missing?
        Not sure what has the oxygen got to do with anything, other than constraining the formation conditions for the comet?
        I’m not saying they’ve figured it out yet, but it points to comets having formed a long, long time ago, in a place that was very cold.
        In short, I think you have probably spent too much time around people who dream up nutty ideas over breakfast, and have them on a crank science website by lunchtime. That isn’t how science works.

      • Harvey says:

        You seem to be veering to a Bishop Berkeley like position.

        We see the ‘jets’; as a spurt of dust scattering sunlight. Rosetta cannot physically enter those jets without destroying itself. We see the dust and gas those ‘jets’ deliver to the comet environment further out with multiple instruments.

        What more do you want, within the bounds of the technically feasible? Of course the ‘jets’ exist.

        I couldn’t care less if the sublimation theory survives or not. There are huge difficulties explaining the jets. But for the moment no one has come near providing an alternative explanation other than sublimation as the prime driving force which obeys the laws of physics.

        • originalJohn says:

          Excuse my interjection Harvey but are you suggesting that the Rosetta orbiter, designed for prolonged and detailed investigation of a comet nucleus was designed with no shielding to protect it from destruction by dust impingement? Shielding was a critical part of the Giottio design 30 years ago and it was a once only fly by. The previous reason for not getting in amongst the dust was confusion of the starseeker navigation.

          Obviously the jets are a fundamental part of the comet mechanism. They are not represented in character by the coma and not in composition either as changes are known to occur in the coma and they are certainly not represented in temperature by the coma. Crucial characteristics of the jets are lost in the coma. Huge benefits would accrue from measurements made directly on the jets. You are however suggesting that this was never the intention and that it is some sort of careful stand off mission with a take what we can get policy? or at least you would be perfectly happy if that were the case? with funding in excess of a billion euros.

          • Gerald says:

            the star trackers and hence the navigation and the pointing of the antennas to Earth fails, when too much dust is present.
            And, of course lot of dust grains have been collected by COSIMA and GIADA.

            “Some of the more compact particles are thought to originate directly from active regions (as supported by GIADA measurements), while farther from the nucleus they are part of large clusters that fragment close to COSIMA.”

          • Harvey says:

            Giotto was designed for a high-speed transit using a spaced double layer impact shield, only in the direction of travel. Rosetta was not designed to operate in dense dust clouds; it has no such shield. Arguably it doesn’t need them; due to the low relative speeds, but in the dense part of the jets the physical risk of damage would be high. Spacecraft are remarkably ‘flimsy’ things – they have to be to save weight. Yes, I’ve stood next to them & designed bits of one (which never got launched 🙂 ) A very modest impact would make a mess of the solar arrays, which are huge. Also numerous instrument apertures are highly vulnerable. No one to clean the OSIRIS/NAVCAM/Star tracker lenses I’m afraid, failing little green men 🙂

            On top of which loss of navigation due to star tracker confusion would certainly trigger a ‘safe mode’ & lengthy recovery.

            I dont have access to ESAs ‘intentions’; but the craft quite clearly is not designed to or capable of safely entering the dense regions of the dust jets other than at very high risk. It was of course designed with rather poor knowledge of what the environment would be like in any detail.

            There are practical engineering limitations on any experiment. I think ESA has manifestly done a stunningly good job on this mission; but it cant do everything. And yes it was easily worth the cost.

        • Kelly Duke says:

          What about subsurface microbes?

          Why is sublimation a “better” explanation for all these observations than biological activity is?

          • ianw16 says:

            Because sublimation requires ice on and below the surface, which we have. Then it requires sufficient temperatures to sublimate it, which we have. Why invoke an extremely unlikely mechanism, when the obvious one is staring us in the face?

          • Marco Parigi says:

            Hi Kelly,

            Wickramasinghe et al have many papers supporting liquid water temperatures and pressures deep inside comets. If this were the case, active biology would be the only way to square with the O2 oxygen observations.
            Note that these papers are generally only accepted to journals such as the Journal of Cosmology, which I consider to be a “rebel” scientific peer, that nevertheless does not contradict direct observations and known physics (in the way Thunderbolts tramples over known physics and the peer review system)

            Sublimation may obviously still be happening on or near the surface regardless of whether the Oxygen and most water vapour is coming from the interior biosphere (or not)

    • Kamal says:

      Thomas: Some blogs are about how many followers they collect, this is not one of them. This blog is about science communication, what is being seen by Rosetta (and Philae) and how one makes sense of it using some basic science ideas, without getting into the calculations that research papers have to use to justify their arguments. Observation is not subordinate but the raison d’être of this blog. If you don’t like the theory someone is using to explain an observation, you are welcome to question it. I believe you are not a mainstream scientist, and from what I have seen so far you aren’t a science communicator, and you have an axe to grind. So you like to use the “scientists versus us” distinction. But the distinction is not so sharp. As far as
      astronomy is concerned I am an amateur, and I am grateful to this blog for providing quick information that is far more satisfying than press releases, as well as a forum for quick discussion.

  • ianw16 says:

    “White hot plasma”? And what is the evidence for that? Just more pareidolia, I suspect! Where was this signature in the x-ray observations from the SWIFT and Chandra spacecraft? Perhaps you would care to explain what ought to have showed up (I’m sure Harvey could help), if it had indeed been a certain cranksters claim of an electric discharge, as opposed to what was actually seen. Sorry, but evidence (or the total lack of it, in this case) trumps fairy tales based on pareidolia every time.
    Chandra paper:
    “No obvious prompt X-ray flash due to the impact was seen.”

    SWIFT paper:

    So, yet again your “evidence” is based on a hugely overexposed image, and takes no account whatever of the ACTUAL OBSERVATIONS.

    • ianw16 says:

      And I forgot to add to the above that this “white hot plasma” managed to somehow entrain solid H2O ice grains. Which rather puts something of a constraint on just how”white hot” it was.

      • Harvey says:

        Ianw16. This is not such a good argument. Solid pellets can survive in a high temperature but low density plasma surprisingly well. It’s touted as a way to refuel and control magnetically confined fusion plasmas. There is an extensive literature on that. The latent heat of evaporation of hydrogen is a lot lower than water! See
        For a popular report, lots in the literature.
        I agree entirely of course there is no evidence it’s a ‘white hot plasma’ as opposed to scattered sunlight; just that this particular argument against that is unsafe.

        • ianw16 says:

          Fair enough, I just found it hard to see how this “white hot plasma” could entrain ice particles. I am but a mere planetary science grad 🙂
          Mind you this “white hot plasma” that was entraining the H2O ice grains was imaged in both IR (in-situ) and x-ray (from the XMM-Newton telescope). Going out on a limb, but I’m guessing that would have shown something.
          Anyway, just for interests sake, this is probably the best paper describing the actual impact in-situ:

          And the impact as seen from XMM-Newton:

          And of course there were the Chandra and SWIFT papers I referenced earlier.

          Regarding the 22nd August outburst at 67P, you may wish to run your eye over this:….4741308S (may need to highlight and copy/paste this link, as adsabs links never seem to work)
          From the ALICE instrument. “We report on the two largest of these dusty outbursts observed by the Alice far-ultraviolet (700-2050Å) spectrograph, which occurred on 10 July 2015 and 22 August 2015………………….Alice observations on 22 August 2015 revealed a major dust outburst in progress, this time confined to the sunward side of the nucleus. Between 07:03 and 07:54, the brightness of dust on the sunward side faded by a factor of 7. NAVCAM images from this period also show a dramatic fan-shaped cloud of dust. Unlike the 10 July event, the 22 August event shows some evidence of increased gas emissions.”

          The rather sang-froid nature of the report suggests that they saw nothing particularly notewiorthy vis-a-vis electric discharges etc. Would they have, at those wavelengths?

          • Harvey says:

            Retry, capita problem.
            What wavelengths are emitted depends on the atomic species, ionisations states, and molecules present. It also depends on the electron temperatures (amongst other things) which will determine what electronic states get excited.

            Atoms and ions produce lines, molecules produce ro-vibrational bands.

            The only general rule I can think of is that higher temperatures will generally lead to more highly ionised states and shorter wavelength emissions because of that, into the UV, VUV etc. Which ALICE sees.

            Ultimately, at extreme temperatures, especially for light atoms, you get a situation where the species are fully ionised, and then the line emission would disappear.
            Fusion plasmas are like that, at enormous temperatures, with only H2 and D2 present.

            But in reality virtually all other discharges you get visible,, near IR and UV emission; that’s why they are often called ‘glow discharges.’

            Trying as usual to be honest, in rather special cases the visible emission can be quite faint (to the eye; obvious instrumentally.) for example in a high power CO2 laser discharge (actually a CO2/N2/He mix) the visible emission is not that bright. this is partly because it’s very ‘clean’, few species present, and it’s designed to keep electron temperatures fairly low.

            I would reiterate that my comment lends no support whatever to ‘discharge theories.’ I was purely noting that ‘snowballs can survive in hell’ rather better than one might think, so the argument is unsafe. There are a plethora of arguments against discharges which are safe, so we don’t need this one.

  • Matt Taylor says:

    A. Cooper, those papers are e-prints of papers from other journals. By putting something on arXiv, you are not publishing anything, you are simply posting a file to a server. Sorry, i am not overly familiar with arXiv as i have never used it.

    • Gerald says:

      Hi Matt Taylor,
      first, congrats on your huge success with the Rosetta mission!

      Regarding arXiv:
      I might be wrong. But it appears, that several scientists publish on arXiv, to make papers readily available, without eventually publishing in peer-reviewed magazines. See e.g. Stephen Hawking’s famous paper “Information Preservation and Weather Forecasting for Black Holes”:
      Nature cited this article two days later:
      “Stephen Hawking: ‘There are no black holes'”

      But there are counter-examples, like the flawed presumption of long-term dimming of Tabby’s star (KIC 8462852), causing quite some annoyance:
      Peer-review would have avoided the trouble.

      Despite disagreeing with Marco and A.Cooper in many aspects, I’d wish them to get a chance to make their ideas available for referencing in science papers.
      Since I doubt, that much of their ideas currently would survive a peer-review, the most likely way to get some attention would be via arXive. They may later improve their methods, and rethink their ideas, in the hope that at least some contribution remains valid, or inspires a valid idea.

      • Marco Parigi says:

        This is intended as an email, so moderators could pass it on as an email to Gerald rather than as a comment post if appropriate.

        Hi Gerald,, If you or a colleague is interested in endorsing me, the following is an email with a link that will get me an endorsement code. Any article I submit still goes through moderation before it becomes accessible on the database. (Marco Parigi should forward this e-mail to someone who’s registered as an endorser for the astro-ph.EP (Earth and Planetary Astrophysics) subject class of arXiv).

        Marco Parigi requests your endorsement to submit an article to the astro-ph.EP section of arXiv. To tell us that you would (or would not) like to endorse this person, please visit the following URL:

        If that URL does not work for you, please visit

        and enter the following six-digit alphanumeric string:

        Endorsement Code: PF9TPK

      • Matt Taylor says:

        Hi Gerald, and Marco and A. Cooper.
        I managed to loose a follow up comment, which is related to Gerald’s post and also supported J-B’s comment. i try again here – Many scientific journals require the references in their papers to be of refereed papers. So, even if a stretch theory paper got to the arxiv, it may still not be cited as it not allowed in many publications. However, as you note Gerald, having Marco et al., put the paper together may help get some interest and also scrutiny, so i believe that is the first step – getting a paper together. For that, what i miss is exactly is WHAT this stretch event is, what is the event that drove such motion. This is particularly important in this case, as all we see now is “after” the event. There has to be some clear indication of the process that drove us to where we are now.

        • Marco Parigi says:

          Hi Matt,

          Captcha in this blog has a way of eating and irretrievably losing comments in cyberspace.:-)

          As far as *what* the stretch event is and what drove the motion, the evidence is all there and fits stretch theory like a well connected puzzle, with new pieces fitting as we find them. As with real life puzzles, I can show you the picture on the box, and in detail how any one piece fits also.

          We present stretch theory as a solution to the evidence, knowing full well that there is no model solution as it stands. There is something very dynamical and non-intuitive happening as part of the stretch event, which has little hope of being modelled in advance of piecing together clear evidences.

        • A. Cooper says:

          Hi Matt

          Thanks for clarifying that. I understand the arXiv process better now.

          You said:

          “For that, what i miss is exactly is WHAT this stretch event is, what is the event that drove such motion. This is particularly important in this case, as all we see now is “after” the event. There has to be some clear indication of the process that drove us to where we are now.”

          I’m sure you won’t want to be drawn into the melee of the stretch discussion in the Rosetta blog comments. But since you ask, I have described the process in the comments before and included calculations. However I’ve been slow to post these up on the stretch blog. I was hoping for better neck dimensions to come out. But I’ve now updated the stretch blog with a ‘Spin-up Calcs’ page that’s culled from a Rosetta comment:

          From the page:

          The scenario is as follows: asymmetrical outgassing causing spin-up to the point where the comet undergoes some fragmentation, shedding slabs from its extremities due to their tangential speed being > 0.8 m/sec. This release is followed by the sub-escape-velocity core stretching into two lobes rather than releasing a lobe into orbit if it was a brittle-break release.

          All such spin-up scenarios would harbour a radius of rotation domain with tangential speeds that are conducive to throw material within the domain into orbit and not escape. There would be actual core matrix in a thick, hollow cylinder between the inner and outer radii of the domain. This matrix would be susceptible to going into orbit if shearing away in a brittle break, or stretching the comet if ductile and subject to tensile resistance (the neck) attenuating the ‘lift-off’.

          The rotation period necessary for this to happen on 67P is 2-3 hours. The models say the comet is too brittle to stretch but the multiple head-body matches and crust-sliding signatures show that it must have done. The symmetrical diamond-shaped body is a give-away for the stretching process with the head lobe undergoing an excess of stretch via herniation.


          Further context including the full comment that was used for the ‘Calcs’ page can be found in this characteristically lively Rosetta comments thread:

      • Booth says:


        With respect to the Hawking paper, it is a transcript of a talk given at The Kavli Institute for Theoretical Physics in August of 2013. Not necessarily a legit peer-reviewable paper, but it is Hawking after all, so worthy of sharing.

        Thanks for the link!

    • Marco Parigi says:

      Hi Matt,
      ArXiv is just less of a “closed shop” with regards to science. Bona Fide scientists can *publish* to ArXiv for a number of reasons – Usually to get something published in advance due to very new information or discoveries, where the delay to peer review may compromise the attribution of the discovery. Other reasons may be that there is no desire or need from the scientist to have validation from peers, or as an easy to search and access archive of actual peer reviewed papers, as it seems OSIRIS does. This does not alter the fact that ArXiv has a mixture of peer reviewed and non-peer-reviewed papers, which should not discredit the desire to publish in an easy to access scientific format.

  • Matt Taylor says:

    Harvey, sorry , i missed your comment , as im catching up after ESLAB! ok, for the record,
    indeed, it appears clarification of what ALL means is needed 🙂
    my take on the word ALL is that it means ALL, which i believe is the very same meaning that you understand.
    so, yes, i meant everything. all events that we have observed. There is NO evidence of intrinsic emission, as i said before.
    For brightness, its a function of the angle of incidence of the light on the particulates in the “jet” and the observer, the reflecting properties of the material itself, and the amount of stuff (= dust) and the size distribution of the dust also. Basically, brighter probably means more stuff or perhaps a different distribution of stuff (sizes) but that is being investigated.
    Thanks again for your continued efforts!

    • Harvey says:

      Matt, many thanks; you could hardly be more unequivocal!
      It will be interesting to see the more detailed analysis of the scatter regarding particle size & whether it changes by sublimation etc.

      Thomas et al.
      Can we actually now put this to rest?
      You might recall that ‘discharges’ are often called ‘glow disharges’; the invariably emit light, commonly in the visible, but here we have UV & IR results too. They emit light for very well understood reasons, from electronically excited states, line spectra & bands which are readily identified.
      No intrinsic emission means no discharge – as do the magnetic field results.

      We do not need to trouble with whether there is a credible physical mechanism for them (there isn’t); direct, straightforward, clear & unequivocal statements from the team rule them out.

  • Booth says:


    Re. your comment from 2016/03/24

    There you go again, jeopardizing the health and safety of the spacecraft! 😀

    You write, “Shielding was a critical part of the Giottio design 30 years ago and it was a once only fly by.”

    Giotto required shielding to protect against dust impact! For perspective, a standard 5.56 mm NATO round has a muzzle velocity of 990 m/s! During Giotto’s encounter with comet Halley, its relative velocity was approximately 68400 m/s! Since rendezvous, Rosetta’s average velocity, with respect to 67P, has been close to 0 m/s! Thus, Rosetta requires very little shielding if the velocity of the ejected dust does not exceed a few tens of meters per second. As it turns out, a well designed multilayered thermal insulating blanket also provides sufficient protection against most impacts while simultaneously reducing spacecraft weight and overall launch costs!

    Summary – Rosetta was engineered with sufficient shielding to operate safely and successfully in the escort mission it was designed for.

    You write, “The previous reason for not getting in amongst the dust was confusion of the starseeker navigation.”

    Rosetta is designed to operate within the comet’s dust environment! Instruments like GIADA and COSIMA depend on that fact! During two planned “high speed” fly-bys, it became obvious that the star tracker system was much more susceptible to navigation errors while transiting the denser dust environment near the nucleus. To ensure S/C safety and maximize science return, it was deemed necessary to cancel future high speed fly-bys, and keep Rosetta at a slightly greater distance than originally planned (on the off chance Rosetta accidentally “flew” through a randomly produced dust jet). This situation does not, of course, limit the quantity or quality of the data being gathered! Personally, I prefer two years of quality data and observations, versus any interval of badly degraded data and observations due to instrument damage and abuse brought about by poor planning and/or unnecessary risk taking! Examples of damage and abuse would include ablated optics, overexposed collector plates, and reduced solar panel power output (which would then further degrade the total volume of science being conducted by all Rosetta instruments).

    With respect to coma dust density, the scientists, engineers, and flight dynamics teams have found a compromise “altitude” that maximizes science while keeping the spacecraft safe! And yes, Rosetta is still operating within the comet’s dust environment!

    You write, “(The jets) are not represented in character by the coma and not in composition either as changes are known to occur in the coma …”

    What changes do you think take place in the coma? Do your changes violate any known laws of physics and chemistry? We know that the jets are composed of dusts lifted from the comet’s surface by sublimation processes, and we know that the coma is composed of dusts, mixed with sublimation and ionization products. The GIADA and COSIMA instruments have published numerous reports concern dust grain composition, grain size, structure, mass and density. MIRO and ROSINA have measured neutral gas compositions and volumetric outputs, as well as mapped areal sources of various neutral gas concentrations. And finally, ALICE continues to observe the ionization of neutral gases via photodissociation, electron impact dissociation, and ionization by charge exchange.

    You write, “… and they are certainly not represented in temperature by the coma.”

    Again, I would like to ask if you’ve had a chance to review my VIRTIS temperature map post? During the initial mapping phase, VIRTIS-M measured “basal” jet temperatures of 220 K in the active Hapi region. At around the same time, VIRTIS-H measured coma temperatures of 90 K at an altitude of one kilometer above the nucleus surface! What this data tells us, is that the jets are cold, and the coma is even colder! So, I feel it is safe to say, that your model’s description of the jets are certainly not represented in the coma, by any means!

    You write, “Huge benefits would accrue from measurements made directly on the jets.”

    Great idea! Let’s look at the logistics of what you are proposing!

    Rosetta was sent to 67P to do great science! Throughout the mission, all the science teams had to coordinate their individual and collective science goals to maximize the amount of data being collected. To that end, mission planners would allocate specific periods of time where one instrument would get to “drive” the spacecraft’s orientation (i.e., determine which way it was pointing). Regardless of which instrument was in control, the other teams would be “passively” gathering their own data. Of course, the final link in this planning and coordination chain is the flight dynamics team. Flight dynamics controls the attitude and altitude of the spacecraft with respect to 67P, constrained by spacecraft safety and power generation needs. So, which instrument is in control? And which way is the spacecraft pointing?

    One problem associated with measuring jetting activity is it’s random nature. Trying to scientifically capture an active jet is not a trivial matter. For example, when a NAVCAM image is recorded, it first gets sent to Earth for processing. Transmission time is a function of distance, and at 67P’s current location, one-way communication travel time is ~14 minutes. On Earth, this raw image data is massaged through a simple six step processing pipeline. These initial images rarely show jets bright enough to exceed the comet’s normal maximum albedo of 0.06, so the brightness and contrast need to be “stretched by hand” to find any active jets. If Rosetta “management” decides to reorient the spacecraft to specifically collect data from an active jet, all the affected science teams would need to be consulted. If “consensus” can be reached, flight dynamics would then assemble the requisite “move” instructions for transmission to Rosetta. Also embedded in this outgoing packet are the updated instruction sets for all the instruments involved. If this “on Earth” activity was standard operating procedure, it might be possible to get retasking instructions together in under five minutes (an overly optimistic wild guess on my part). Next, the updated instructions need to be sent to Rosetta – outbound travel time is again ~14 minutes. Assuming the reorientation operations take mere seconds, which may not be the case, the total elapsed time easily exceeds 30 minutes! In that time, what are the probabilities that the jet will still be active? Is it worth upsetting normal science operations to chase random, transient events? If my instrument is driving a specific scientific investigation, would I want to possibly miss an event my science team was waiting for?

    Of course, the science teams know that the jets are important! However, they also know that the jets are diffuse collections of dust particles liberated by sublimation processes. The suite of instruments flown on Rosetta were chosen to investigate the nucleus, the coma, the ionosphere, surface topography, and the jets! Evidence shows that jet “basal” temperatures are cold! And the jets do not produce any of the signals one would expect from electric discharges or combustion!

    Now, knowing how difficult it is to gather data from active jets, it might surprise you then, that jet measurements have been made! Unfortunately, you prefer to ignore all the Rosetta data that is being collected because it does not fit your models vague expectations.

    To that end, Sir, I would like to propose a simple thought experiment for your consideration. Your model, as it is defined, needs high temperature electric discharges and/or combustion to operate. The necessary order-of-magnitude temperatures have never been observed by any instruments onboard Rosetta! Given that VIRTIS finds 67P to be a cold body, with cold jets, and a cold coma, can you possibly modify your model to operate with maximum temperatures of ~230 K at a sun-comet distance of ~3.0 AU? Remember, your model must operate consistently at all points along 67P’s orbit.

    Now, if your model cannot operate with these cold, hard facts, perhaps your model needs to be replaced by something much more consistent with the cold, hard data being returned by this most extraordinary mission!

    Apologies! I do tend to go on, don’t I!

    PS – Do you like fishing? With respect to your model definition, what is the eccentricity cutoff value that distinguishes between comets on one side, and planets and asteroids on the other? How important is perihelion distance? How important is aphelion distance? What role does orbit inclination play? You really don’t have to answer. Comets are not electric!

    • Booth says:


      Apologies! Forgot to add something.

      Whilst composing the above post, I took a moment to calculate the ballistic kinetic energies associated with each of the three velocity examples. In the case of Giotto and Rosetta, we are concerned with potential dust grain impacts, so here, I used a 1 gram particle mass (which was the maximum estimated size of the impactor that sent Giotto tumbling during it’s fly-by of comet Halley). Given that Rosetta’s relative velocity with respect to 67P is close to zero, I also employed an overly conservative velocity estimate of 50 m/s (equivalent to 180 kph) as a worst-case engineering scenario. For comparison, I have also included a quick KE calculation for a Toyota Corolla (or any comparably smallish sized family car) traveling at 100 kph.

      Automobile traveling at 100 kph = 27.8 m/s

      Mass of Corolla = 1280 kg (curb weight)

      BALLISTIC KINETIC ENERGY = (0.5) * mass(kg) * velocity(m/s)^2

      KE(NATO) = 0.5 * 0.00402 * (990)^2 = 1970 J

      KE(Giot) = 0.5 * 0.001 * (68400)^2 = 2340000 J

      KE(Rose) = 0.5 * 0.001 * (50)^2 = 1.25 J

      KE(Auto) = 0.5 * 1280 * (27.8)^2 = 495000 J

      It is worth noting that a 1 gram dust particle traveling at a relative velocity of 68400 m/s has approximately 4.7x the kinetic energy of an automobile traveling at 100 kph. Furthermore, from an engineering perspective, it should be obvious that Rosetta requires virtually no shielding compared to what Giotto needed.

      Any questions or concerns regarding this, or the previous post?

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