Today’s CometWatch entry was taken by Rosetta’s Navigation Camera (NAVCAM) on 14 March at a distance of 85.7 km from the centre of Comet 67P/Churyumov-Gerasimenko.
Cropped and processed single frame NAVCAM image of Comet 67P/C-G taken on 14 March 2014 from a distance of 85.7 km to the comet centre. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
This single frame NAVCAM image has been processed in Lightroom to bring out the comet’s activity and then slightly cropped. The scale is 7.3 m/pixel and the image measures 6.4 × 6.3 km. The original picture (uncropped) is provided at the end of the post and measures 7.5 km across.
In this orientation, the comet’s small lobe is up and the large lobe down. On the comet’s neck, the Anuket region can be seen on the right, while Hathor on the left is shielded from visibility due to a combination of shadows cast by the small lobe and of the nebulosity arising from activity near the neck region. The comet’s glowing ‘atmosphere’ is particularly pronounced around the small lobe and neck.
Some of the regions on the surface of Comet 67P/C-G are indicated in this annotated image (the approximate boundaries are marked on the regional maps here and here).
On the small lobe, the flat and smooth plain of the Serqet region, punctuated by a few boulders, is visible on the right, just above the sharp boundary that separates this region from Anuket on the neck. Two neighbours of Serqet are also visible: the smaller region, Nut, and some portions of Ma’at.
Separating the small and large lobe, some parts of the smooth, dust-covered Hapi are visible. On the large lobe, the circular features of Seth catch the eye in the central part, while the smoother plains on the sides belong to Ash (lower left) and Anubis (right).
The original 1024 x 1024 pixel frame is provided below (click on the image for full resolution):
Discussion: 30 comments
Thanks Claudia for another very interesting image. Some of the jets appear to be intersecting in this one but presumably this is because they are at different depths in the image. A feature which has not been all that obvious before but which has been commented on by THOMAS in other images is the diffuse glow not jetting but hugging parts of the surface profile of both the smaller and larger lobes. It appears exactly consistent in extent from the surface in both cases.
It also appears that there is a horizontal jet issuing to the left from behind the foreground jets from the neck (valley) region. The interesting thing is that it originates from a deeply shaded zone on the cliff wall.
Also all the jets regardless of their origin or direction seem to be glowing with a consistent intensity suggesting a consistent current density. One exception to this is what appears to be a vertical “jet” to the left of the nucleus which it seems is not originating from the nucleus at all, or perhaps two parallel jets both of lower intensity.
The sooner some direct electrical and plasma measurement are made of these jets the better. And let us not forget temperature too. That will also be very informative.
The vertical structures to the left of the nucleus are very likely due to shadows cast by the head of the comet onto the outflowing material. Look at the solar illumination angle and that’ll become obvious. We’ve seen the same kind of shadowing effects in many of the published NAVCAM and OSIRIS images.
Similarly, the rising surface “atmosphere” has been obvious in quite a few of the more recent published NAVCAMs.
Originaljohn,
I assume that “the diffuse glow not jetting but hugging parts of the surface profile of both the smaller and larger lobes” corresponds to the “sputtering” on the lobes which has already been acknowledged by the Rosetta team.
This sputtering phenomenon has since been downplayed, as no further official comment or data concerning it has published since the initial announcement some month’s ago. This seems rather surprising, since the phenomenon is clearly ongoing, ubiquitous and increasingly intense. (I had initially assumed, some months back, that the glow surrounding the nucleus might be a simple imaging artifact due to pixel bleeding but it is now clear that it was just the beginning of what we are now clearly seeing, up to increasing heights from the surface.
I also assume it is what Claudia is referring to when she speaks of “the comet’s glowing ‘atmosphere’ [which] is particularly pronounced around the small lobe and neck”. (It is also visible, albeit at slightly lower intensity, all around the larger lobe). I find use of the word “glow” particularly appropriate, evoking, as it does, a form of electrical activity.
The data acquired by various Rosetta science instruments on near-surface temperature, plasma and electrical activity, once finally released, cannot but confirm this hypothesis.
To begin, there is no electrical discharge phenomena at work here!
What we are looking at is nothing more than light reflected off dust emitted by the comet. Using the generalized concept outlined below, it will become clear that this is always the case.
If we examine the unprocessed NAVCAM image (at the bottom of this, and many CometWatch posts), we observe a low albedo (Capaccioni et al, 2015) nucleus devoid of any visible activity. This implies the filamentary features of interest exhibit a lower albedo than the nucleus (i.e., they are not reflective enough to be seen in the unprocessed image). Thus, to bring these features out, the brightness of the raw image needs to be enhanced through post-processing. Restating this —
1) with a low albedo, the nucleus reflects very little light,
2) filamentary features are not visible in unprocessed images, and
3) processing brightens the image such that filamentary features become visable.
Now, how do we know that the filamentary features are made of dust and not caused by some other process? Well …
It has been previously reported by the GIADA team (Rotundi et al, 2015) that at a distance of 3.4 AU, 67P was experiencing a dust loss rate of 7 +/- 1 kg/s. Assuming there has been no change in this rate (which is unlikely given the evolution of other cometary activity – Gulkis et al, 2015 & Nilsson et al, 2015 for example), we can calculate a conservative mass loss of over 90.7E06 kg of dust and other non-gaseous materials since September. In the four month period between Jun and Sep, GIADA captured and analyzed almost 100 unique dust grains. In the same period, OSIRIS observed and cataloged over 350 grains (some greater than a meter) in bound orbits around the nucleus.
Me thinks there is an awful lot of dust being ejected from this comet. And what mechanism might drive this dust loss? With a dust-to-gas ratio of 4 +/- 2:1 (Rotundi et al, 2015 & Gulkis et al, 2015), which includes gas contributions from H2O, CO, and CO2, I would put my money on … sublimation.
Anyone who has actually worked with glow discharges – as I did for some twenty years – will tell you that they spend a great deal of effort fighting lateral instabilities. Large area glow discharges have a very strong tendency to become strongly non uniform transversely. In fact gas laser engineering spends an awful lot of effort fighting this. It’s a particular problem in ‘dirty’ discharges containing species like oxygen, less so in pure inert gas discharges, especially He.
So to anyone who has been around glow discharges, a big uniform one is one *big* surprise needing a lot of explanation.
On the other hand, sunlight is very uniform.
What we are seeing is scattered sunlight off dust, the interesting question is why the dust is rather uniform in the jet (or appears to be; that might be an artifact of the observation.) If it were discharge light it would show the typical line spectra, unreported. It would also, depending on the conditions, be likely to show obvious structure in the current flow direction (dark spaces etc.) it doesn’t.
It’s scattered sunlight off dust.
It seems unlikely they will ever risk putting Rosetta that close in, it would be far too hazardous for the spacecraft. The signature of large scale discharges would already have been absolutely obvious from existing measurements, from magnetic fields, spectral emission, and injected ions. None reported. Aside from the fact that no physically viable mechanism exists to produce them. ESA is very unlikely to risk the mission to disprove a non-theory which is already multiply disproven.
@ Harvey
“The signature of large scale discharges would already have been absolutely obvious from existing measurements, from magnetic fields, spectral emission, and injected ions. None reported. ”
Actually, only a tiny fraction of the measurements ALREADY made and the data ALREADY collected has as yet been disclosed because of the (at least) “6-month” rule we all know about. (See ongoing discussion of this precise issue on the parallel thread).
Given the logical objective of the mission team to find supporting evidence for the standard cometary theory, it is hardly surprising to see that little of the more controversial data has yet been published and commented on. The “sputtering” pronouncement of a few months ago was a rare exception and even there I don’t know if the hard data which prompted it has been made available. Does anyone else know?
That is most certainly not ‘the logical objective’; that is to collect data, and then, of course, compare it to standard models.
The simple fact is we have ample data to discard this ludicrous ‘theory’. It’s not really a theory at all, it’s just an incoherent, unanalysed assertion. We have seen magnetic field data, plasma data, people have been taking cometary spectra from Earth since forever, we have data from other comets.
On top of which THERE IS NO VIABLE MECHANISM to run such discharges. Entangled with all this the crazy claims the mass must be wrong because it’s really solid rock, the hydrogen comes from the solar wind, claims of non existent exothermic chemical reactions between silicates and organics. It just a heap of utter nonsense to be blunt.
Harvey!
I tried to submit a rather long blog entry back on 19 March (it was a coherent summary of the eight Science articles published back in January). Apparently it has been lost in the moderator’s ether. Maybe one day it will rise ….
In the meantime, here’s a little paraphrased slice of that very blog entry as relates to density …
On 2010/07/10, Rosetta performed a flyby of the asteroid Lutetia. Using RSI and OSIRIS data, a bulk density of 3400 kg/m^3 was determined. A density of this magnitude indicates that Lutetia is made of rock (e.g., Earth’s crust is ~3000 kg/m^3). A spectral class of “M” further confirms that assertion.
On 2014/08/06, Rosetta entered an escort orbit with comet 67P. Using RSI and OSIRIS data, a bulk density of 470 kg/m^3 was established. A density of this magnitude indicates that 67P is composed of an assemblage of materials, in ratio, that sums to the reported value. If 67P were composed of rock alone (and for fun we’ll assume a density of 3400 kg/m^3), the porosity would need to be >85%, leaving 67P mechanically weak, and rather fluffy.
Funny how the same suite of instruments can generate such wildly different mass and density values.
In time, I know we will have a realistic measure of the various material ratios. Until then, MIRO (Gulkis et al, 2015) has shown that 67P is outgassing H2O, CO, and CO2, with the earliest measurements indicating a water mass loss of 0.3 kg/s, increasing by a factor of four in only two months. GIADA (Rotundi et al, 2015) also reported a dust loss rate of 7 +/- 1 kg/s. Apparently, 67P is not made of rock, but is assembled from a collection of refractory materials, combined with numerous volitile species, including H2O, CO, CO2, NH3, CH4, and CH3OH ….
More to come! Salutations!
And for those that have problems with the standard model, it is not cast in stone (did you see what I did there). All good models are subject to change when new evidence is obtained that contridicts a basic principle or property. One thing to keep clear is the fact that we have been remotely sensing comets, asteroids, planets, and stars for decades. However, in the last thirty years we have only conducted eight fast fly-bys, one sample return, one impact, and one escort mission to comets. From a scientific point of view, none of this approaches statistical significance.
Sorry I completely fail to understand your point.
The flyby of Lutetia gave a different result to the orbits round 67P. Why is that a problem? They are entirely different bodies with different densities. So what? The same technique is perfectly capable of measuring both, its hardly a huge dyamic range.
There is a multiplicity of data supporting your description of its composition; I’ve always agreed with that. ‘Solid rock’ makes no sense whatever, either for the density or the outgassing species. Neither do ‘discharges’ as the mechanism of material removal.
You seem to have confused my views with those of others here.
But of course, our detailed knowledge is increasing greatly & will increase further.
But I am an adamant *opposer* of ‘solid rock’ & ‘electric discharge’ theories, which bear no resemlance to real physics & observation.
Harvey! Re. your post 25/03/2015 at 18:31
Apologies for the confusion, Sir! The post was meant to support and extend the views we both share regarding science, the scientific method, and the specifics of this comet.
To reiterate, I have no problems with the two reported density values. The technology and techniques for determining the mass and density of celestial bodies are not complicated. Lutetia IS made of rock with a density greater than that of Earth’s crust. 67P IS NOT made of solid rock, regardless of what other people claim. If the density value for 67P is wrong, then what makes it right for Lutetia? As it turns out, at 470 kg/m^3, 67P has an average density for the six comets we have good values for (e.g., Minima: 103P/Hartley = 220 kg/m^3 and Maxima: 9P/Tempel 1 = 620 kg/m^3). While a sample size of six does not approach statistical significance, we can say that these comets have a density less than that of water, and much less than that of rock.
The line, “Funny how the same suite of instruments can generate such wildly different mass and density values” was honestly meant for members of the EU community. Apparently that concept was very poorly communicated. With my concern stated more clearly, I would really love it if any proponents of EU could explain these density differences. Why would RSI and OSIRIS yield density values for two “rocky” objects that are an order of magnitude different from each other? Perhaps the two objects have very different compositions, and one just happens to include a significant mass of volitile ices ….
Sufficient evidence has already been presented by the various Rosetta science teams (i.e, the first eight Science articles, countless Rosetta blog entries, and numeous papers dating back over a decade) to show that 67P is composed of refractory organic-rich dusts and volitile ices. In time, I know we will have a realistic measure of the various material ratios for this comet. Until then, we must be patient (though I will admit that the five year old still living inside my head wants his data NOW). Based on my readings of the EGU Conference abstracts (posted by Gerald – thank you, Sir) further details supporting the standard model of comet structure and evolution is forthcoming. Of course, I do expect a few surprises from 67P over the next several months as well.
PS – Again, apologies. And believe me, I have not confused your views with others; I share them. While English is the only language I speak, it is not the one I am necessarily most fluent in … my background is in modeling and simulation.
Sorry, previous brief comment appeared garbled.
Moderator please delete.
Booth: no problem, just so long as no one thinks I am an EU apologist! Thanks for your response.
Harvey, instead of expressing mere value judgments couched in increasingly derogatory terms (but why not if that’s how you truly feel about it – just don’t call it science), it would be nice if you actually addressed the scientific issues which 67P is raising to challenge your closed-circuit certainties.
Could you please refer us to the “ample data” from the Rosetta team concerning plasma and electromagnetic activity which would prove that 67P is electrically inert. I’m unaware of any such disclosure.
Magnetic fields (Philae descent); plasma results consistent with a photoinised plasma; visible appearance which bears no similarity to real discharges regarding axial or transverse uniformity; lack of observed spectral lines in earth based measurements of other comets; plasma results at other comets supporting standard bowshock/photoionisation theories; the absence of any reports of radio noise etc emanating from comets; the absence of any visible ‘return path connection’; the presence of high outgassing & dust ejection rates discharges are unable to explain. And so on.
You are very easily persuaded Harvey by little or no evidence if it fits your preconception. Similarly you dismiss options dogmatically, based on your assumptions and narrow laboratory bench experience. You have previously and sanctimoniously lectured on here about the need when examining a new and unique environment for an open minded objective approach. This would require not being swayed by preconceptions, particularly if they are speculative in themselves, and taking into account all possibilities regardless of how unlikely they seem in your limited experience. You should try your own recommendation. There are things to be discovered about comets here and perhaps more generally about physics too. Wait for the results and asses them objectively or make it clear that you are simply expressing an opinion. Not reported yet is not for example a result. What is and is not possible in the vicinity of a comet nucleus may be far outside your comprehension.
Ah, my ‘narrow lab bench experience’, that would entertain a few people.
Multi hundred kV/kA pulsed, multi tens of kW large transverse flow, axial high current density, low current density low pressure, corona discharge interacting with local outgassing in 500kV insulators, ……..species from pure helium via other single component, to molecular gas mixtures, halogen/rare gas mixture Cw & pulsed…. Many of the diagnostic techniques anyone every applied to a discharge, electrical, optical, some modelling work……. yup, got me, sorry, really narrow range of laboratory bench experience. I’m sure yours is far wider, wouldn’t know.
I reject *nothing* that passes simple tests of plausibility from a physics mechanism & rough quantitative view. When I first heard of the EU theory, I though ‘interesting; I wonder if there is anything in it?’ So I went & looked; thats an open mind; the answer was, very clearly, there isn’t. The web sites presenting it & presentations on it are littered with errors & contain no quantitative predictions. It breaks numerous laws of physics, contradicts many observations, & the ONLY supporting data is a percieved (largely incorrectly) visual similarity to a discharge.
Could the jetting process be the cause of neck formation?
Hi Robert Meijer. Yes, it could. And what could had caused a strong jetting just there?
This new image also shows a new example of a curving jet (the furthermost left one, curving outwards at 10 o’clock). What is striking here again, as in several other images showing the same phenomenon, is that the bend in the jet is most pronounced near its base, with relative straightening further out. Now this is remarkably similar to what happens to electrostatic field lines, as shown by the Wiki diagram: https://upload.wikimedia.org/wikipedia/commons/d/d9/Electrostatic_induction.svg. (h/t Harvey, who directed me to this diagram in his post of yesterday on the https://blogs.esa.int/rosetta/2015/03/06/cometwatch-28-february/ thread). All of the field lines are initially perpendicular to the surface of the charged object, then some of them bend sharply to conform to the more general, self-organizing electrical environment.
Other images showing the same pronounced bend in the lower parts of jets are:
https://blogs.esa.int/rosetta/2015/02/13/last-stop-before-close-flyby-cometwatch-9-february/ (the jet on the far left, which seems to be coming towards us, over our left shoulder),
https://blogs.esa.int/rosetta/2015/02/09/last-waltz-at-28-km-cometwatch-3-february/ (the jet at 9 o’clock on the left, apparently emanating from the cliff-face of Hathor),
spectacularly in https://blogs.esa.int/rosetta/2015/01/16/fine-structure-in-the-comets-jets/
It is hard to see how “outgassing”, on the other hand, with its hypothesized high-pressure jets shooting out of subsurface chambers could behave in this way: logically, we should expect the opposite, with an initial dead-straight section at the base being followed higher up by a possible curving due to the comet’s rotation as momentum is lost. This is the exact opposite of what we are seeing in the images.
Electric field lines are normal to the surface of CONDUCTING bodies.
NO such constraint applies to insulating bodies.
But *is* 67P an insulating body? That is the question!
In the extreme conditions you so often invoke to pour scorn (if not worse) on the down-to-Earth comparisons made by anyone who doe not share your standard certainties, perhaps it’s actually a *conducting* body.
Try to think outside the standard tool-box, Harvey.
Yes Thomas, I do indeed ‘live in a box’, the box called real physics.
Its floor, which applies roughly from solar system to nucleon scale, is the so called ‘laws of physics’. Actually we don’t have ‘laws’, we have ‘our current best approximation’, which is tested & rechecked endlessly, & when we find a better one out goes the old. But the ‘laws of physics’ relevant to this discussion have passed those checks & rechecks innumerable times. I guess the last really *big* revision was the neutrino oscillation. *Outside* the solar system to nucleon scale, everything is much more questionable; dark matter, dark energy, WIMPS, sterile neutrinos, SUSY, how to include gravity, the bets are off; but inside it, it’s a pretty solid floor. You want to make a hole in it GREAT – but your evidence had better be good, and consistent with everything to date.
Its walls are numerical estimates & ultimately detailed calculation. To start, make everything as favourable as you can, plug in the numbers. If you are one, two orders out, look again, maybe, or maybe it’s a minor effect but significant. If you are ten, fifteen, twenty orders out, look elsewhere. If it looks right, build a model. You can check your assumptions, check the effect of error, compare with measurement, and predict what new measurements are good tests to distinguish mechanisms.
Its roof is comparison to data. Think about the accuracy, precision, resolution (not synonyms) of your data, its limitations. Use ALL the data, don’t cherry pick. Look for consistency, if we saw A, and our mechanism is right, we should have seen B. Sometimes there are ‘holes in the roof’, data you don’t have; spend a couple of billion Euros, wait ten years, & Rosetta gets (some of) it for you.
I am absolutely happy to examine any hypothesis that fits in that box, however outrageous, anti-establishment, counter intuitive etc. If it’s outside it, it belongs in the superb novels of Iain Banks and the like. That is where the EU theory resides.
And yes, my exasperation shows at times; there are only so many Bowdlerised synonyms for ‘nonsense’.
BTW, theoretical considerations apart, can you attempt an explanation for the objective *OBSERVATION* I am drawing attention to, i.e. the anomalous curvature profile of the jets (“anomalous ” in my understanding of standard-theory mechanisms)? Or does the standard tool-box contain no tool to fix this sort of problem?
I can’t see an easy explanation for ‘jets turning through right angles’ in *any* model. I think the possibility of it being an illumination/imaging artefact needs to be carefully considered first. We are looking at a projection of light scattered off the dust; it could be an effect of the sun angles, shadows, compression etc. If it’s real, perhaps the pressure is high enough there for viscous flow effect? – surprising, needs gas dynamic modelling to see if that works.
But could we please have an explanation of how this ‘discharge’ is supposed to work at the most basic, primitive, level.
We are told the comet is ‘negatively charged’ and the jets are ‘discharges’; electrons move away from the comet, ions *to* it. That means there is a current flow in the discharge; nobody gives a value. Well, to move just *one mol/sec* as ions – 18g/sec for water – needs a current of just under 10kA. Comets are known to degas *FAR* more than that, factors of thousands, hundreds of thousands more. Discharges are very inefficient at accelerating neutrals (electron/molecule mass difference) so that doesn’t work well. At the very least we need to provide the sublimation energy, around 40-50kW needed for 1 mol/sec of water depending on whether its ice or liquid – so 10kA at a few volts. Just relying on ‘intuition’ (dangerous) these are huge scale ‘discharges’, they move tons of material, the current is going to be pretty big. We routinely run 100’s of kA pulsed discharges, 100A CW discharges, in labs, in welding workshops.
So, maybe the comet is a charged capacitor. Let’s not worry yet about how it got charged, gets recharged for the next orbit. It has a capacitance, if we make it a 5km sphere (overestimate) of 0.28uF. Let’s charge it to a MV – yes, a megavolt; I think we’d have noticed that by now, but whatever. The charge is 0.28C. Just ONE AMP will discharge that in 0.28 *seconds*. Desperation, how about a GV, a gigavolt; you get 280 seconds; five minutes, then the lights go out.
Oops. So, something is *supplying* the charge, just like a real CW discharge. The electron leaves the surface of the conducting electrode and its replaced by the wire connected to the power supply whose other end goes to the anode; a circuit. So, somewhere else on 67P, where is the supply of electrons arriving? Why don’t I see some distinctively different region, certainly dissipating power? Where do they come from, what provides the power & the charge? (No, just saying ‘the sun’ will NOT do.) Why do they flow *to* 67P here by some mechanism, when very nearby they flow *away* from 67P? It needs to be a conducting body to get the charge from the ‘arrival point’ to the ‘departure point’, so how can the electric field apparently point in opposite directions onto the same conducting body with no nearby ‘electrode’? (Oh, & rock, ice & polymeric organics don’t conduct too well.)
And of course for these huge currents, why don’t we see the magnetic field, why did Rosetta specifically report a plasma consistent with photionisation of degassing H2O (as other spacecraft have) & not this huge plasma injection, why are there no reports of appropriate optical emission, why does it stay transversely uniform unlike most discharges, why are the no ‘cathode dark spaces’ etc visible axially. In other words, why doesn’t it actually look like & behave like a real discharge if it is one? The supposed visual comparison is simplistic in the extreme.
At the most basic, simple, physics 101 level, it does not begin to make sense.
The wiki example is missleading for our purposes (though totally correct) for two reasons. Firstly everything is conducting. Secondly the rather symmetrical placing of the metallic objects around the central + exaggerates the extent to which field lines remain normal.
In the *supposed* case here we are talking about the comet and the sun, several AU away. Very different.
This site might help understand fields a little better.
https://www.physicsclassroom.com/class/estatics/Lesson-4/Electric-Field-Lines
But as you do, you will realise that for a conducting body the ‘valley’ will tend to be a low field, ‘partially screened’ region.
Looks so near to splitting in two.
Where is Philleigh located?
Here’s an interesting article…Since we know the comet is made up of dust particles proabably created during the formation of the solar system, if we look at similar samples, we find that this “cosmic dust” likely contains organics, ‘amorphous’ water ice and other frozen gases. Sublimation in the presence of vacuum, solar wind (high energy protons) and heating will obviously release these gases and leave behind the organic dust. The speed of these jets indicate the high energy that is being unlocked by this process.
https://www.space.com/13401-cosmic-star-dust-complex-organic-compounds.html
Curious aromatics on that illustration. Really there is an internal fight not to chat of biochemistry 🙂
Given the prediction that upto 20 metres of surface might be eroded during the perihelion passage, is Anubis one of the candidates for heavy erosion, given its heavy mud buildup? (See also the picture on 6 March.)
As for accepting a purely aerodynamic model for all of neck phenomena, having trouble accepting such ‘simple’ drawings of those slow dust paths.
This particular angle exhibits weakness of neck.