This four-image mosaic comprises images taken from a distance of 28.0 km from the centre of Comet 67P/Churyumov-Gerasimenko on 31 January. The image resolution is 2.4 m/pixel and the individual 1024 x 1024 frames measure 2.4 km across. The mosaic has been slightly cropped, and it measures 4.6 x 4.3 km.
Four image mosaic comprising images taken on 31 January 2015 by Rosetta’s Navigation Camera (NAVCAM). Rotation and translation of the comet during the imaging sequence make it difficult to create an accurate mosaic, and there may be some spurious spatial and intensity features as a result of the mosaic-making process, so always refer to the individual frames before performing any detailed comparison or drawing conclusions about any strange structures or low intensity extended emission. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
The scene provides a stunning view of both the comet’s larger lobe (bottom) and smaller lobe (top right). There is an interesting contrast between the rough appearance of Anuket, the region that starts on the smaller lobe and descends along the side of the comet’s neck, and the smoother material of the Anubis region, visible on the larger lobe in this view, beneath the crags of Seth as seen on the upper edge of the lobe.
A prominent jet and other outflows are also portrayed in the image. The overall activity of 67P/C-G is evident in the way that the silhouette of the nucleus stands out against the faint glow of the comet’s coma, especially in the darkest regions (bottom left and far right).
The large number of small white blobs and streaks in the image are likely specks of dust or other small objects in the vicinity of the comet.
The four-image montage and the individual 1024 x 1024 frames are provided below:
Discussion: 101 comments
Wow, incredible jets. It would be nice to see some images of the “vents” responsible for these huge streams.
Great picture. while its clear there is material escaping from virtually all sunlit areas, the extreme nature of the jet from the neck area is stunning. Given this area actually gets less of the suns heat due to shadowing (although some heat is reradiated for the surrounding areas), the jet activity need to be explained. There is a crack in the region, and the material in the neck area is of a different composition to that on the tops of the lobes. Are the jets formed by whichever of CO, CO2 or H2O sublimes at the lowest temperature? Does this then leave a honeycomb structure of the other non sublimed gasses, or when the gases are frozen together, do they sublime only when the gas that sublimes at the highest temperature starts to sublime. in the latter case all 3 gases would sublime together. would that add to the pressure. Date from the MIRO experiment seems to indicate the speed of the material at circa 700mt per second, which is supersonic speed on Earth. Is the material in the neck are the original inner part of the comet, with the upper material now ejected into space on earlier orbits of the sun?
No It’s Electric, like everything else in the Universe.
No, it isn’t. EU cannot even explain how Rosetta flew to the comet. So it fails already at a point far before this data has been obtained.
Why does that need explaining AndreH. It is obvious. It was done by feedback control with continuous tracking and adjustments using multiple pairs of hypergolic fueled rocket thrusters.
And the tracking was done on the basis of the NAVCAM images, used to constantly monitor Rosetta’s position during the key stages of its flight (planet flybys and comet approach). IOW, largely by *visual* navigation: https://blogs.esa.int/rosetta/2014/06/25/comet-67pc-g-in-rosettas-navigation-camera/
Nothing whatever to do with our supposed knowledge of 67P’s density, if that is what you are still seeking to imply…
…except that not everything else in the universe is electric. 🙁
Mr Hall, Wikipedia says that the muzzle velocity of high velocity small arms is between 1065 and 1524 m/sec.
Are you sure the ‘outgassing’ of the jets is about 700 m/sec?
Seems quite high.
It could be that 67/P was once potato shaped and had an eccentric spin. I think the reason the neck is smaller than the rest of the comet is because it is the neck region that receives the most exposure from the sun, therefore the most radiation, and therefore the most sublimation has occurred in this location.
During its infancy, once the comet started spinning, sublimation occurred around its equator. As time passed, maybe pockets of buried ice was ejected and started an eccentric spin that continues today.
I just read the paper published in Science from the Miro instrument on Rosetta,. also look for a paper published on the jets of another comet – while there are several matters missing from the theory it suggests that the jets are supersonic, and that’s what miro has observed.
Forgot the link!!
https://www.lpl.arizona.edu/~yelle/eprints/Yelle04a.pdf
Mind you – there is no “supersonic” speed in space, as there is no sound in space.
The use of the term “supersonic” is not to give an idea of the speed of the material, but to describe the condition of the material. So, it is rightly used as a general term.
Hi Graham Hall. Would like to believe that Hapi Valley jets have a Dust/Gas ratio particularly high 🙂
I just realized I don’t understand the jets. Which force is giving these particules all this speed ? They are oriented toward the sun more or less. Initially I would have thought the trail would be oriented the other way around.
The sublimation process wouldn’t be able to transfer such speed to the gases or would it ?
There’s a couple papers on that topic, Formation of jets in Comet 19P/Borrelly by subsurface geysers, at:
https://www.lpl.arizona.edu/~yelle/eprints/Yelle04a.pdf
and another talking about comet crust formation, Primordial Comet Mantle Irradiation Production of a Stable,
Organic Crust, at:
https://people.virginia.edu/~rej/papers-old/Strazzu-icarus91.pdf
“…As long as the cavity is larger than the orifice, the pressure in the cavity will be greater than the ambient
pressure in the coma and the flow from the geyser will be supersonic. The gas flow becomes collimated as the sound speed is approached and dust entrainment in the gas flow creates the observed jets. Outside the cavity, the expanding gas loses its collimated character, but the density drops rapidly decoupling the dust and gas, allowing the dust to continue in a collimated beam. The hypothesis proposed here can explain the
jets seen in the inner coma of Comet 1P/Halley as well, and may be a primary mechanism for cometary activity”.
I owe one, Judy 🙂
Not so lost, after all.
So this Yelle, Soderblom, Jokipii model explain a lot. Biggest particles will keep on almost ballistic-ally. Molecular size particles will almost go along with the gas. A true deflective ‘screening’. ‘Dunes’ should be micrometer size ‘powder’ -or less- then. Also ‘Eaten Back ‘powder’. That’s why there is only big ‘chunks’ up there. ‘Stream terraces’ are not covered in their model. They were not known then 🙂
No extreme speed is necessary, escape velocity at the comet’s surface is less than one meter per second. All that’s necessary for these jets to look impressive is continuous transport of material.
Great picture of the main jet. It shows a couple of jet streams twisting together like a braided rope.
Surely this is an electro magnetic effect, suggesting there is some current flow in the Jets producing a magnetic field.
Dave
you couldn’t be more wrong. the jets contain co, co2 and h2o as gases having sublimed from the neck area. Surely one day this EU nonsense will go away, as its baseless in science. There are still people who don’t believe in the Moon landings – so I guess EU has to be put in the same category.
Where you see “twisting together”, others see superposition in the image of independent jets streaming into space at slightly different angles from different areas of the neck region. It’s all down to objectivity – or the lack of it – really.
Seeing what you want, and need, to see is not part of the scientific method.
Rob, perhaps you should read this article again, which is titled “Fine Structure In The Comet’s Jets.” The ESA scientists directly contradict your “slightly different angles from different areas” assertion.
https://blogs.esa.int/rosetta/2015/01/16/fine-structure-in-the-comets-jets/
But a few things do strike me as odd about the jets. One is the fact that it seems that ALL the sublimation/outgassing/dust is happening via the jets. Based on the tenants underlying the sublimation theory, I would think that the majority of sublimation would be a general sort of thing with exposed or near the surface ice gently sublimating through cracks, holes and other openings which would then gently lift the dust off the comet and create something of a haze around the comet. Seems all we see is jets of fast moving dust, and they’re SO many of them. The odds of just one jet forming through sublimation are pretty farfetched, requiring very very precise conditions to create an explosive jet through a single highly restricting nozzle. But to have them everywhere? It’s pure nonsense.
Also, if the jets are due to sublimation, the rate of dust velocity coming from the jets should vary widely based on the size of the nozzles, cracks, holes, etc, unless someone is proposing that all of these things are the exact same size, and the amount of pressure buildup and release is the exact same, the size of the cavities the exact same, the composition of the volatiles the exact same, on and on. Perhaps I’m mistaken, but seems the dust velocity of all the different jets is basically uniform. If so, it’s utterly and completely impossible for sublimation to create these jets, and to continue to hold on to this fantasy in light of such glaring gaps in logic is just more nonsense.
Read this paper.
https://www.lpl.arizona.edu/~yelle/eprints/Yelle04a.pdf
Clearly the authors didn’t know everything because in 20012/03 close up observations of a comet (such as we have now) hadn’t been possible, and they’d made a lot of assumptions – many of which seem now to be being substantiated.. e.g the jets do leave a supersonic speed. Seen from Earth comets do exhibit a cloud around them and remember too that the jets do not continue in a straight line because the comet rotates every 12.4 hours. Rosetta does not see this well because its been too close! There are many jets of different sizes but they are actually quite difficult to see at the surface because in sunlight they’re lost against the surface, its only against the backdrop of space and in shadowed areas that they become visible.
Anyone got any other papers published and peer reviewed on the topic? I’m up for a bit of reading!
Hi Graham, yes, read the paper long ago, and have commented on it already in this blog. It does present as very fanciful and again farfetched speculation trying to explain the jets through sublimation. There are a huge number of assumptions and logic flaws in the paper, but to just take one, in nature you don’t find “nozzles.” That’s a term defining man-made objects, as in “1. a projecting pipe or spout from which fluid is discharged, 2. a pipe or duct, esp in a jet engine or rocket, that directs the effluent and accelerates or diffuses the flow to generate thrust, 3. a socket, such as the part of a candlestick that holds the candle.” In nature you find terms like cracks, holes, fissures, and porous geological layers like dirt and dust, etc. The closest thing I can think of in nature to a nozzle is a geyser, but not much explanation help for the jets there either. To take a man-made TOOLED device and then to say that nature has replicated dozens or hundreds or even thousands of these in a comet is ridiculous. Again, if sublimation were happening, the gases would be escaping at different speeds through the already mentioned large-to-small cracks, holes, fissures, and porous geological layers. They would be mainly seeping away from the comet and taking whatever theoretical dust is mixed in with them at very slow speeds.
@ Rob
“Seeing what you want, and need, to see is not part of the scientific method.”
Indeed.
But when observations in the form of *several different images* consistently show the same sort of converging of “independent jets” into the same sort of “rope”, sometimes curving off to left or right, the hypothesis that the jets are being powered and organized by electromagnetic forces is considerably reinforced and the standard sublimating ice model is correspondingly challenged. This is, on the contrary, an *impeccable* example of the scientific method at work.
I suggest it is yourself who is “seeing what you want, and need, to see”.
@Graham Hall
“the jets do not continue in a straight line because the comet rotates every 12.4 hours”
If the jets are indeed supersonic, as Rosetta mission researchers have confirmed, then the curvature observed in 2-3 km jets in the “FINE STRUCTURE IN THE COMET’S JETS” image https://blogs.esa.int/rosetta/2015/01/16/fine-structure-in-the-comets-jets/ can hardly be due to 67P’s “12.4 hour rotation” since the material being blasted away was on the comet surface only seconds before! The curvature, along with the collimation, is another unmistakable sign of electromagnetic forces at work.
Superposition, eh? Lack of objectivity? Hmmmm… let’s see….
From the article, “Fine Structure in the Comet’s Jets” there is a quote, “the large-scale jets seen in previous images can now be resolved into many smaller jets emerging from the surface, which seem to merge together further away from the comet nucleus.”
So, objectively, we have large jets consisting of smaller jets streaming into space at different angles, but then they merge together. Keyword there pal, merge. A force redirected the individual streams into one farther away from the surface.
So please explain to me, objectively, how sublimation must be the only plausible mechanism.
“So, objectively, we have large jets consisting of smaller jets streaming into space at different angles, but then they merge together. Keyword there pal, merge. A force redirected the individual streams into one farther away from the surface.”
“large jets consisting of smaller jets” – you’re incorporating your conclusion in your starting conditions. Objectively, jets are jets.
Try this little experiment: fill two kettles with water, and place them side by side but slightly sparated, and nearly parallel, such that the nozzles or spouts are pointing in slightly different directions. Bring the water in the kettles to boiling point and observe the two streams of steam (OK, steam, water-vapour and water-droplets), emerging at different angles and from different points, merging together. Now name the “force” that has caused the streams to merge.
Of course, at the comet coma/solar wind interface, external forces will be at work, but that’s considerably further way from the comet than where jets are observed to merge.
@ Rob
“Seeing what you want, and need, to see is not part of the scientific method.”
Indeed.
But when observations in the form of *several different images* consistently show the same sort of converging of “independent jets” into the same sort of “rope”, sometimes curving off to left or right, the hypothesis that the jets are being powered and organized by electromagnetic forces is considerably reinforced and the standard sublimating ice model is correspondingly challenged. This is, on the contrary, an *impeccable* example of the scientific method at work.
I suggest it is yourself who is “seeing what you want, and need, to see”.
No, Dave… this is not an electromagnetic effect. And there is no suggestion anywhere that there is some current flow in the Jets producing a magnetic field. Give the electromagnetism/plasma theory stuff a rest, man. It’s gotten very old.
Give the so-called consensus view of icy comets a rest. That one has been falsified a number of times now. Comets are rocky bodies.
Define what you mean by rock. What is the density of this material on the comet and how does it correspond to earth rock?
I think the density of material on the comets has been equated to that of compressed cotton wool.
“…others see superposition in the image of independent jets streaming…”
This remind me of the answer to another former controversial case about some very peculiar quasars.
RIP, Chip.
Indeed Bancor. I make exactly the same parallel. If the electrical behaviour of 67P becomes so overwhelmingly obvious as the comet approaches the Sun that it can no longer be denied, it will in one stroke drive the final nail into the coffin of the Big Bang gravity-only model and Halton Arp’s empirical demonstration of intrinsic redshift will at last be vindicated.
Until some data from the Langmuir Probe experiment is made available, we do not know if, or what magnitude of electrical and magnetic processes are occurring. Comets such as Giacobini-Zinner exhibited strong ion acoustic activity and subsequent magneto-acoustic waves, so likely there is a good deal of similar activity at/around 67P
“The Earth is the centre of the Universe, man. Forget your telescope and what you think it’s telling you, there’s no future in it” as the church and science Establishments said to Galileo….
Steve
Esa has mentioned sputtering from the head lobe, this is electrical
So far none of the mission instruments have found ice or even ices, in fact it has been stated that there is such an abundance of refractory material on the surface that the core is probably similar.
If there is no ICE there is no sublimation! surely its as simple as that.
If there would be no ice, there would be no sublimation; this applies to an asteroid.
Since there is ice, there is sublimation; this applies to a comet.
A very simple principle, in fact!
Really? So what will you say about this fact?
https://www.nasa.gov/press/2013/november/nasas-hubble-sees-asteroid-spouting-six-comet-like-tails/#.VOo1Gi6zycE
Good find! But
“Jewitt said the spin rate could have increased enough that the asteroid’s weak gravity no longer could hold it together. If that happened, dust could slide toward the asteroid’s equator, shatter and fall off, and drift into space to make a tail.”
So it’s thought to be dust lost by centrifugal force, not sublimating ice. Hence classified as an asteroid.
But you’re right, that the boundary between asteroids and comets may be fuzzy.
“in fact it has been stated that there is such an abundance of refractory material on the surface that the core is probably similar.” Stated where, exactly? Source, please.
@ Rob
In the peer-reviewed “Science” article ““The organic-rich surface of comet 67P/Churyumov-Gerasimenko as seen by VIRTIS/Rosetta” published just a couple of weeks back, F. Capaccioni et al. make the following statements in their conclusion:
“The compositional homogeneity of the surface observed by VIRTIS, despite the rejuvenating processes acting on the nucleus (at least on the active portion of it) at every passage close to the Sun, indicates that space weathering plays only a minor role in determining the observed composition. THE REFRACTORY COMPOUNDS SO WIDESPREAD ON THE SURFACE OF 67P ARE THEN REPRESENTATIVE OF THE BULK PRISTINE MATERIAL OF THE NUCLEUS.” (My capitals for emphasis).
That should be enough, shouldn’t it? Dave’s line of argument in his above post is thus rock-solid…
BTW, I had already referred to this extract from this article in my 23 January post: https://blogs.esa.int/rosetta/2015/01/23/extremely-dark-dry-and-rich-in-organics-virtis-view-of-67pc-g/#comment-347002
I had free access to the article then but it has since apparently been pay-walled (like the other Rosetta-related articles published the same day)…
No electromagnetic/plasma data published yet Steve Kasian and no specific measurements of any sort on the jets. The ice sublimation theory is old and dead and there is no evidence of any sort to support it. It has been talked up over the years and believed by those who don’t think too much. If it was happening the jets should be loosing what heat they have by the Joule-Thompson effect, therefore should be extremely cold. They should also consist of only neutral molecules. When they are measured they will be found to be hot and consisting of both ions and neutral molecules as they are plasma discharge jets carrying away the products of a hydrocarbon combustion reaction at the surface of the nucleus.
@originaljohn
“Hydrocarbon combustion”. Although that’s still wrong, I see some progress in making your hypothesis consistent with the data, particularly the observed H2O/CO/CO2 mix.
And you provided a test. That’s appreciated.
One weak point in your approach is the oxygen source needed for the combustion, besides the plasma discharge presumption.
Actually the jets are made of a gas/dust mix. The dust should be measured by GIADA.
Well, wrong in your opinion Gerald. We will see in due course if you are right. When some detailed temperature measurements are published for the jets and the nucleus surface it should be conclusive. I am not claiming to be right or wrong. I have proposed a plausible mechanism of water production which fits the observations and invited comments. There is some more detail on the January 21 post.
No problem with the oxygen source. It is in the rock minerals as oxides, mainly silicon dioxide but probably iron, magnesium, chromium and copper oxides too, and others. The Si-O bond dissociation energy is 4.68 eV and the Fe-O bond is for example 4.23 eV. The proton energy is typically in the range 1-10 keV . Once activated the hydrocarbon combustion reaction is strongly exothermic and self sustaining.
No data has yet been published to confirm or refute the plasma nature of the jets. If they contain any ionised material it would be incompatible with gas pressure jets, regardless of temperature. The plasma discharge is what transports the neutral combustion products away from the nucleus with my proposal. It would also account for the presence of ionised material in the jets. In the energetic proton combustion the dust is a by product and formed at the combustion site. In the sublimation hypothesis the dust just happens to be there and is picked up by the escaping gas. One of these processes fits what we observe much better than the other.
The terminal weakness however for the sublimation hypothesis is the lack of observed or detected ice.
One further confirmation for the combustion mechanism would be the presence in the jets of very specific products of incomplete hydrocarbon combustion and no explanation for their presence in a sublimated vapour stream.
@ originaljohn
Give me an example of an exothermic reaction of a hydrocarbon with silicon dioxide.
I get only enothermic reactions.
Examples:
CH4 plus 2SiO2 reacting to CO2 plus 2H2O plus 2Si
is endothermic.
2C2H2 plus 3SiO2 reacting to 4CO plus 2H2O plus 3Si
is endothermic.
Maybe what we see is an emission of light filled in with local dust.
I see you don’t include the actual energy deficit Gerald. I expect in those two stoichiometric reactions, ratios of 1/2 or 2/3 moles of hydrocarbon and silicate, it is quite small. Let us surmise then that those two reactions may only be partially self sustaining and that additional energy is supplied by the continuing proton flux. This would make more sense.
The possibility of combustion reactions as a source of water, albeit a complex series, remains very strong, much stronger I might add than the possibility of ice sublimation.
A determination as to whether or not heat is being produced in the jets would be a simple measurement and a big clue in deciding whether combustion or sublimation was more likely.
originialjohn,
they made remote temperature measurement of the surface. But there haven’t been excessively hot spots, as would have been expected for subsurface combustion.
In shadowed areas ground temperatures can go down to below minus 150 centigrades. That’s about the temperature Philae tries to survive.
The type of chemical reactions you’re suggesting is one way of space weathering which could be considered.
The result of space weathering colors asteroids and unprotected planetary surfaces dark.
But these processes take millions of years to become relevant; and they are constrained to the very surface of the considered body.
In comparison to the sublimation of ices in the subsurface (or on the surface) of an active comet, space weathering is quantitatively negligible.
CH4+2SiO2->CO2+2H2O+2Si
deficite 931.4 kJ/mol
https://i.imgur.com/D7HTd3F.gif
2C2H2+3SiO2->4CO+2H2O+3Si
deficite 1265 kJ/mol
https://i.imgur.com/HQvYrzj.gif
according to WolframAlpha
Check out these views of Hyperion, a moon of Saturn. Note that it has some of the same features as 67/P. Some of the similarities are striking. Could Hyperion be a captured comet?
Is the interior of 67P similar to what we see at Hyperion? It could explain the problem of explaining 67P’s mass/density. Could the sponge-like appearance result from ‘jets?’ Sublimation?
https://wanderingspace.net/cat/saturn/hyperion/ Scroll down to find pictures of Hyperion
https://en.wikipedia.org/wiki/Hyperion_(moon)#mediaviewer/File:Hyperion_true.jpg
Click on image to enlarge
Thanks, that’s a really exciting link!
It adds some fuel to my own personal hypothesis that 67P is a mere fragment of something larger that broke up at Jupiter’s Roche limit, some time in the past (well before we started observing it.)
Initial indications are that such large voids are ruled out by CONSERT data. Porosity is indicated at a finer scale than voids 10s to hundreds of metres diameter.
@ Marco,
“Porosity is indicated at a finer scale than voids 10s to hundreds of metres diameter.”
The CONSERT data constrains the size of any supposed voids to *2-3 metres diameter maximum*, without ruling out the possibility that any voids might be much smaller: 2-3 metres diameter is simply an absolute maximum.
Yes. I was just saying that it couldn’t be anywhere near how Hyperion is on the outside for 67P on the inside, as the voids on the outside of Hyperion are at least 10 to 100 metres each. 67P’s porosity is at a much finer scale, for instance pumice, or a pebble pile, or an aerogel are candidate possibilities, while solid rock, which is a candidate for the asteroid Lutetia, is not for 67P as the calculated density is too low. If it got blasted off a rocky planet, the blasting process must have turned the rock to a pumice-like state.
Hyperion’s sponge-like appearance comes from impacts as opposed to outgassing – two completely different mechanisms. Hyperion has been riddled with impact craters over millions of years. It may well be a dirty snowball, but with the discoveries at 67P, we are learning that comets aren’t necessarily the dirty snowballs we thought they might be.
Hi WayneC
I think the Greeks who dived for sponges will not be able to hold their breath long enough to get to this one.
Very curious picture though, this is something like I would expect if lots of volatile’s were beneath a surface and some force expelled them through the surface.
On this moon the holes do actually look like they have been the cause of massive out gassing, even exposing what looks like a harder core.
If the vent holes on 67p were anything like this the conclusion would be that gases from under the core were being expelled out of those wonderful trumpet shaped vents
However they don’t look like that so I guess we still have a way to go before we understand the mechanisms.
Gerald, the remote temperature measurements do not have the resolution. They integrate the temperature. Remote is irrelevant now anyway. The craft is right there. A detailed temperature map is needed, of the nucleus surface and the jets. Would probably be conclusive.
Your concept of space weathering and millions of years is based on a hypothesis as is the ice sublimation explanation.
Thank you for the links. They express an overall reaction. The energy input of the protons is not however in the equations. I am guessing, in fact predicting, that the impact of the solar current protons at the prevailing (unknown) conditions will provide the energy to liberate oxygen in sufficient quantity. You are minimising the potential effect of the protons to space weathering. We are speculating on rate because we don’t know what the proton availability is at the surface of the nucleus.
Temperature measurements have been taken by remote sensors onboard Rosetta, and by Philae in situ. Temperature measurements are a standard for onboard instruments in order to calibrate data.
We need to distinguish of which temperature we are talking: Remote temperature measurements relate to the infrared emission from the surface, called grey body radiation. Other temperatures refer to the kinetic energy of the ions/molecules/atoms in a gas or plasma, or to the ionisation levels of the gas/plasma, or to the thermodynamic temperature of electronic chips in instruments.
I agree, that more detailed temperature measurements are desired; but they are ongoing; so I’m confident we’ll get more interesting detail.
Your guessing about integrated proton energy is not compatible with observations: The proton flux you need would destroy the Rosetta orbiter within short time, and harshly throw it out of its orbit, much more than the emitted gas from the nucleus (compare the energy deficite in your combustion approach). It’s incompatible with all radiation measurements in the heliosphere thus far, and there exist lots of measurements. It’s also incompatible with the mass loss of the Sun, considering your presumed z-pinch doesn’t occur on a scale not just to focus electron beams as known from lightnings, but also protons on an intensity level far beyond that of a nuclear reactor; remember nuclear reactors operate for years before the surfaces in the reaction chambers are destroyed by radiation.
Space weathering isn’t just a hypothesis. It can be duplicated in laboratories on Earth, and the effects are observable on the Moon, on Mars, on asteroids and meteorites.
Sublimation is a well-known phenomenon, too, easy to duplicate on Earth, easy to duplicate with a protective layer of dust or sand, in a way the ice is invisible from outside.
Sublimation is well-compatible with solar irradiation.
Water ice and carbon dioxide are found elsewhere in the solar system, e.g. on Earth,on Mars, on Jupiter moons, etc. Therefore it’s nothing exotic which would need specific evidence. All you need is the assumption, that the comet has been far enough away from the Sun most of its history not to have lost the volatiles earlier.
For so long time now these streamers are present and yet not a single clue of the cause of those events. Sad science.
Oh, there’s lots of CLUES, just no definitive answers. The scientists will be developing the definitive answers over the course of the next couple hundred years or so, I figure. But over the course of the coming year we’re going to find out a whole lot more about possible models for how the jets form.
This link will give you a sense of what we know about comets and their jets, up to 2012:
https://www.aanda.org/articles/aa/pdf/2013/01/aa19350-12.pdf
This link got posted by someone else, and it’s one of my favorites. It proposes a model for the jets; nothing proven, but it’s really interesting reading.
https://www.lpl.arizona.edu/~yelle/eprints/Yelle04a.pdf
If you haven’t dug into science papers before, they can be a bit daunting: the trick is to ignore the math that makes no sense,, just read the English around the math. And when you don’t know what a word means. search the internet, especailly Wikipedia, for definitions for the unfamiliar words. It’s rather like doing a crossword puzzle: some of the clues you get right off the bat, some you have to get some help with. I actually find it a lot fun than crossword puzzles, because I get to take home a whole lot of new knowledge.
Not true. There are, indeed, answers. The issue we face as interested members of the public is that ESA has placed a 6 month moratorium on the release of all science related to the mission, with the exception of select few images that are released via this website. The scientists most likely know pretty much everything we are wondering about this comet already; They are just not releasing it until 6 months from it’s discovery.
It seems to me that they are merely reflected light caught by the constant cloud of dust that must be accompanying the comet. They’ve already told us that the surface is actually mostly dark grey or even black where there’s no dust, and that these images are pretty highly enhanced as far as brightness is concerned. So any lighter, probably smoother and dust covered are likely to be reflecting the sunlight more intensely than the rough areas.
I think I’ll just award myself another cup of tea for being right! ;¬)
My take on this amazing view:
https://www.flickr.com/photos/105035663@N07/16271522860/
Contrast increased to make streams more visible:
https://www.flickr.com/photos/105035663@N07/16458994565/in/photostream/
Today’s mosaic is impressive.
Bravo!
–Bill
I shall leave discussion of the jets to you Bill. I have been looking at surface morphology again. Your comments on my conclusions would be appreciated, my geological knowledge is little more than basic.
I have picked out three sections of the image which contain interesting clues, debating points, misinformation, whatever. Image 1 is of the Anubis region on the body lobe and the outcrops that mark the boundary of the Seth region on the horizon.
https://www.flickr.com/photos/124013840@N06/16278376168/in/photostream/
Image 2 is mainly of the Anuket region where it meets the Hathor cliff, subtly illuminated by the comet surface and the coma, showing a possible long history of comet resurfacing.
https://www.flickr.com/photos/124013840@N06/16465372262/
Image 3 is of the boundary between Anuket and Serqet regions. This boundary is part of the protruding rim that goes pretty much all the way round the middle of the head lobe. This terrain is more jagged and angular than most of the rest of the comet, more dramatic events seem to be involved.
https://www.flickr.com/photos/124013840@N06/16279101110/in/photostream/
Explanations, amateur theories, guesses and no doubt erroneous conclusions are contained in the image descriptions.
Robin
I think the protrusions below the beak you mention actually used to be joined to the underside of the beak. They are both the same shape and orientation and are stacked below it. There are also several more protrusions below these two obvious ones which may also have been attached. If this is correct then the only conclusion that can be drawn is that all these protrusions were once layers within a larger, thicker beak and they were drawn apart in the same manner as a concertina being opened. This is very strong evidence for entire neck region we see in this photo to have been stretched. It would then follow that the heat generated in the stretch caused the cryovolcaic features for Anuket that you document in the other photos. And given the suspected loosely sintered pebble pile, what we see as possibly the result of a lot of heating, melting and resetting is in fact just a rearrangement of pebbles with former surface features and boulders being swallow up in the mix as a form of liquefaction took over. In other words, I agree it’s cryovolcanism but it needs much less energy than appears to be the case if we invoke pebbles, ‘firn’, and your phase diagram that showed sublimating gases lubricating the pebbles. Possibly very little energy was needed: just enough to break the lightly pressure-sintered pebbles. That energy would be converted to sublimated gases which would immediately lubricate the pebbles. The sum of the energy transfer to the gases would equal the sum of the energy needed to break the sintered bonds. If you imagine trying to pressure sinter cannon balls in a 80% porous matrix under 10-20 pascals (Thomson et al 2015), there were probably few sintered bonds per pebble and not very strong ones at that. This is why I think your cryovolcanism is perfectly plausible and needs very little energy to achieve what appears to be a major surface overhaul. It
I also left a reply to you on the “changes in Hapi” thread but it ended up in line at the bottom of the thread, not as a reply. It includes spin-up calcs for Imhotep slab loss.
@ A. Cooper.
Thank you for your very interesting reply. I agree that the protrusions could have been part of the same plate and the layers separated by some mechanism. This area of the head lobe is a long way from the centre of gravity. We have seen from the science team that gravity on the tops of both lobes is considerably less because of the effects of the comet’s rotation. The layers could have been forced apart by spin forces, perhaps helped by some sublimating gases within the material reducing the structural cohesion.
Many months ago I speculated that the porous nature of the comet’s core material and centripetal forces would mean the heavier dusty material would collect at the top and bottom of the comet, leaving a more volatile rich, dust depleted, band in the middle. The evidence is beginning to show this separation is real, the Hapi region having every appearance of having a different, more volatile rich, composition than the lobes.
So the question then becomes are the forces generated sufficient to separate lumps of material from the comet. Well a number of examples have been imaged, by the OSIRIS team in their paper, the one near the crater rim of Hatmehit and the two Marco pointed out in the “Amphitheatre”.
Your description of a low energy lubricating mechanism seems highly plausible and this changes the dynamics and behaviour of apparently solid material on the comet considerably. The results of a recent NASA experiment on amorphous ice contaminated with organics, that is simulating subsurface comet material, make interesting reading in this context to explain how the observed rigid crust can form. One by product of this process is crystalline ices. The polygonal shapes, linear formations, fracture planes, brittle material, all become natural consequences of this metamorphosis.
https://www.nasa.gov/jpl/rosetta/why-comets-are-like-deep-fried-ice-cream/index.html
The analogy they use is deep fried ice cream, or melted chocolate covered ice cream. This is exactly how I described the appearance of 67P back last summer, and was the seed of my ideas about fluid flow on the surface.
They have not included 70% micron sized dust particles in their mixture though. The paper you referenced above made it clear that contaminants in the ice tended to collect at the ice pebble boundaries in “Firn”, making the material even more brittle and prone to large scale fracture. The tiny spaces between the dust grains that collect at the pebble boundaries, would encourage sublimation into these spaces, lubricating the boundary between the tiny ice pebbles of the “Firn”. The extra energy required may be just the difference of a few degrees in temperature. At some point in the comet’s approach to the Sun that threshold will be crossed and things might really get exciting.
I have tried to track one of the “layers” further along, but as there is a part hidden beneath the dust it is only a speculation.
https://i.imgur.com/K8WCwti.png
Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
https://creativecommons.org/licenses/by-sa/3.0/igo/
I would love to see more images of the Aker region. It seems to be similar to Anubis and as they are on opposite sides of the body it would indicate to me that the surface features are highly dependant on how much sun (intensity) they get. I wouldn’t be surprised if the current dark side doesn’t look like Seth/Ma’At at all.
Also thank you for that NASA link, I hadn’t seen that post.
As an infrequent visitor it seems that the jets, the majority anyway, always seem to radiate from the neck area. Is it possible that this could be the reason for the double lobed shape of this comet? The two larger lobe are much more rock and dust while the center contains the icy features that depart over time leaving the characteristic shape as a result?
I’m also wondering if the jets will eventually give the comet a faster and more erratic tumble to its trajectory as they become stronger in its closest approach to the sun?
I’ve always been a believer of this explanation. There’s a lot of dust on the floor of the neck, so I’m under the impression that in the neck the sublimation process is more intensive. The dust grains ‘rain’ back to the comet and finer particles disappear in space. As more material sublimates from the neck than from other areas the neck becomes thinner and thinner and eventually disappears.
Abstracts related to Comet 67/P submitted to the Joint Assembly of the AGU Conference for Spring 2015 can be found here:
https://agu.confex.com/agu/ja2015/webprogrampreliminary/Session5978.htmlhttps://agu.confex.com/agu/ja2015/webprogrampreliminary/Session5978.html
Wayne
I’m getting 404 page not found. Could you repost the link?
Thanks a lot, Waynec 🙂
Hi Claudia, this link is double-pasted, could you help us?
now it is clear that the increased activity is in the neck,
I would keep into account the possibility that an outburst face away the two lobes and lead in different directions.
It would be good to be prepared to follow the one with Philae riding.
the fly-by on 14 February is an opportunity not to be missed and devote all looking for him.
Unless he does not care anymore.
Is anyone else seeing those newly visible cracks on Anuket? Also straddling the rotation axis.
https://scute1133site.wordpress.com/2015/01/19/67p-churyumov-gerasimenko-a-single-body-thats-been-stretched-part-10/
The fractures are certainly good candidates as sources for jets, since they provide access of the subsurface to the surface.
Monitoring the further development of these cracks is interesting. Particularly to find out, whether they come from thermal stress, mechanical (static) instability or internal gas pressure.
@ Gerald
A “fracture” can hardly be the source of km-long collimated jets of dust. In the “sublimating ice” model, a high speed jet would need a precision-machined nozzle. Any gas from any sublimating ice would just seep out of the cracks. It’s basic hydro-mechanics.
And in either case, how would any dust be entrained?
Don’t you think, CO2 would escape through a crack in a bottle of carbonated water? Did you ever open a bottle with carbonated water? What happens, when you keep the bottle horizontally when opening (to simulate low gravity)? You get your jets
Replace the water in the bottle by dust, but keep the CO2. What happens?
— The jets may be collimated in some cases, not necessarily always.
@ Marco
I can see the feature you’re referring to, marked by the yellow dots. But I don’t see it as a “crack” since it is made up of a line of closely juxtaposed “drill-holes”, some of which actually overlap to give the impression of a line made up of overlapping black dots. I went into this phenomenon in greater detail in my comment https://blogs.esa.int/rosetta/2015/01/22/getting-to-know-rosettas-comet-science-special-edition/#comment-368217 which is still awaiting moderation.
I explain there why I believe these juxtaposed “drill-holes” are the result of electric arc discharges and I reference various other examples, at wildly different scales, seen both on 67P and on Mars.
Hi THOMAS,
Having looked at the features on Anuket from a few different angles, they certainly look like cracks- much more so than the comet looks superficially like rock. I am going to trust my eyes and say they are cracks, not anything to do with electricity.
The (vertical) lines of Hathor are definitely trying to tell us something about the history of 67P. They are certainly not strata, and linear features of this length creates more questions than answers- Why just on that cliff face? Why hasn’t further activity remodelled the flat plane structure? Why is it so flat in the first place? I figure if we answer what the history of the shape was, and see what remodelling happens over a couple of years, and extrapolate a bit. We shouldn’t preempt the data, just let it speak for itself over the time of the mission.
@ Marco
” I am going to trust my eyes and say they are cracks, not anything to do with electricity.”
You make no comment on the aligned and sometimes overlapping drill-holes” I refer to. Is it because you can’t see them, because you think they are a chance occurrence or because you think they have a natural, non-electrical cause?
It’s quite obvious that the vertical lines on Hathor are dykes that are caused by escaping sublimating gases when the head lobe was pressed against the body lobe before stretch. The overlapping drill holes are side tributaries of the escaping gases. See:
https://scute1133site.wordpress.com/2015/01/07/67pchuryumov-gerasimenko-a-single-body-thats-been-stretched-part-8/
@ Marco
“The overlapping drill holes are side tributaries of the escaping gases”
‘Side tributaries’? What mechanism would that be? And is it valid for all the other images where we see drill-holes everywhere, at all scales, both on 67P and on Mars? (See the links I provided above).
Hi THOMAS, gas from the heated core is finding the weakest path to the surface. If you like, it would “drill through” the porous pebble pile until it reached the fracture plane then join the dykes making their way to the outside of the comet.
I don’t see drill holes everywhere. I see different kinds of “holes” with many different causes and contexts. Most of the ones you mention make much more sense to have physical or mechanical causes.
Cave worms dig holes too. We shouldn’t jump to conclusions until we see some as they are being formed.
Don’t you think?
@ Marco
“gas from the heated core is finding the weakest path to the surface”
Your explanation raises considerably more questions than it answers. To begin with:
-How can the core be “heated”? Logically, it should be a little colder than the surface temperatures measured on the sunlit side as the comet moves *towards* perihelion (as now) and a little warmer as the comet passes perihelion and moves back out *towards* aphelion into lower temperature zones.
-How can this cold core contain “gases”? In my understanding of the standard theory, any ice which may be present in the core is only supposed to sublimate at the “surface”, as a direct effect of the energy received from sunlight…
-What would be the “weakest path”, as if there were gas trying to force itself up to the surface?
-What has all this got to do with the “drill-holes” anyway, since they are clearly only a surface feature?
As for the different “physical or mechanical causes” you invoke, I note that the only one you actually mentioned is that of “cave worms”. No comment needed.
If you look more closely at the links I provided, you will see that the series of drill-holes, at every scale, are perfectly aligned and of exactly the same diameter. It would seem more logical to conclude that they are the product of a single process and the only one which fits the bill is electrical etching from a moving arc discharge.
Hi THOMAS, obviously you missed the first most pertinent point. These features were formed when Hathor was pressed against the body lobe. They have remained static since they became dehydrated of volatiles, retaining a record of what was happening at the shear interface which had been part of the interior of the comet. The interior was heated by the intense stretching forces caused by the original high rotation rate of the unstretched comet. Do you not wonder why there has been no “remodelling” either by mass near-surface sublimation, nor electrical ablation? The outgassing could well be coming from the deeper interior.
When the navcam took these wonderful pictures, which was the distance between the comet and the Sun? and between the comet and the Earth?
Thanks!
Hi, for 31 January it was about 508.5 million km between Rosetta/comet and Earth, and about 363 million km between Rosetta/comet and the Sun. Did you know you can use our interactive tool “Where is Rosetta?” to check distances for every day of the mission? Enjoy!
Many thanks, Emily!
@ THOMAS
“-How can this cold core contain “gases”? In my understanding of the standard theory, any ice which may be present in the core is only supposed to sublimate at the “surface”, as a direct effect of the energy received from sunlight…”
For example: the jets demonstrate that there is pressure, not only the sublimation surface.
Pressure is applied only to the outside? I Have Not! I say.
Where there is pressure there is increase in temperature, even to the core, I say.
The greater the pressure, the higher the temperature, the pressure increases ……….
It ‘just cite the theories, but I think that the purpose of the mission is to discover the truth, not only confirm the theories.
To get closer to the truth every idea is good, if not blasphemy.
@Thomas “That should be enough, shouldn’t it? Dave’s line of argument in his above post is thus rock-solid…”
Dave’s “line of argument” reads “in fact it has been stated that there is such an abundance of refractory material on the surface that the core is probably similar. If there is no ICE there is no sublimation! surely its as simple as that.”
Well, both you and Dave are mis-quoting the article “The organic-rich surface of comet 67P/Churyumov-Gersimenko as seen vby VIRTIS/Rosetta”, where the authors at no time make the claim that there is no water ice, or other ices, to be found in the comet body.
They do say “…no water-ice–rich patches are present, across the nucleus surface, at a scale larger than ~10m, with an upper limit on the water-ice abundance of ~1%. The lack of ice absorption features in our spectra, along with the relatively high surface temperature mentioned above, indicate that the top layers of the surface (estimated up to few hundred micrometers), which are probed by the reflected light, are composed mainly of dark dehydrated refractory materials.” It is a fallacy to suggest, since little or no ice has apparently been found on the surface, that no ice exists anywhere in the comet. An absence of evidence is not evidence of absence.
They go on to say “The short-wavelength shoulder of the neck band is most likely due to the addition, in this region, of a small percentage of water-ice mixed with the dark material responsible for the overall appearance of the spectrum.” So, possibly/probably some ice present on, or close to, the surface in the neck band.
Dave’s “such an abundance…” statement is a misquoting of the article’s conclusion: “The compositional homogeneity of the surface observed by VIRTIS, despite the rejuvenating processes acting on the nucleus (at least on the active portion of it) at every passage close to the Sun, indicates that space weathering plays only a minor role in determining the observed composition. The refractory compounds so widespread on the surface of 67P are then representative of the bulk pristine material of the nucleus.” – “Representative of the bulk pristine material of the nucleus” is not at all the same statement as “the core is probably similar”. The authors are simply stating that the refractory materials observed on the comet surface do not appear to have been altered significantly by space weathering.
A last quote from the article: “The VIRTIS observations indicate that high-volatility ices (CH4, CO, CO2,CH3OH, etc.), along with water, must have been readily available at the time of the formation of the solid materials that ended up forming the nucleus of 67P in the early phases of the protosolar nebula. This suggests that the larger abundance of organics on the surface of 67P, with respect to other JFCs [Jupiter family comets], could be correlated with a formation scenario in which most of the material that constitutes the nucleus of 67P is produced in a low-temperature environment consistent with large distances from the Sun, such as the Kuiper belt region.” So, ices correlated with formation of the comet, and with abundance of organics found on the surface.
Thomas, Dave: science – REAL science – is in essence about making VERY careful statements based only on observed measurements and standard methodologies, and not on supposition.
@ Rob
Your questions (“Stated where, exactly? Source, please.”) were answered precisely and pertinently. Period.
Real science is also about sourcing and accurately quoting legitimate prior research findings.
@THOMAS: …which is exactly what you have failed to do here. You misquote multiple articles throughout these pages in many of your comments, then when you are called out on it and given specific examples, word for word, of precisely what you misquoted and misrepresented, you give a blanket statement of denial of what you actually did misquote and/or misrepresent.
Then, you have the gall to say, “Real science is also about sourcing and accurately quoting legitimate prior research findings.”
@ Steve Kasian
“You misquote multiple articles throughout these pages in many of your comments”
Please give a single example.
I have ALWAYS been totally scrupulous in PRECISELY quoting from my sources, as in my reply to Rob above, when he seemed not to know of the existence of the peer-reviewed “Science” article ““The organic-rich surface of comet 67P/Churyumov-Gerasimenko as seen by VIRTIS/Rosetta” and its reference to “refractory compounds” being “representative of the bulk pristine material of the nucleus”.
How am I misrepresenting anything?
@ Steve Kasian
I suspect the problem is rather that you just don’t *agree with* the ideas I present and the supporting references I provide. You’re perfectly entitled not to like my ideas, of course, like many visitors to this blog. But please don’t accuse me of intellectual dishonesty (without any form of proof) simply to try to discredit the evidence I adduce. The discredit actually only rebounds upon yourself.
@THOMAS: All one need do is read Rob’s reply to you above to know exactly what I’m talking about. He points out examples of your misrepresentations very directly and specifically.
‘Stream terraces’ in my imagination are related to viscosity, capillarity and adherence of gases. Way out of my mundane experience.
Well, the ‘zig zag’, apparent at many photos around the formerly called ‘singularity’ neck zone [since arrival], is resolved here: A regularly spaced arc of ‘pillars’ and their corresponding shadows.
Hey very nice. Incredible images..
Hey check this link https://www.mmgmodels.com/ . It shows the interesting contrast between the rough appearance of Anuket, the region that starts on the smaller lobe and descends along the side of the comet’s neck.