Posted on 29/10/2014 by emily
CometWatch – 26 October
This four-image NAVCAM mosaic comprises images taken on 26 October from a distance of 9.8 km from the centre of comet 67P/C-G – about 7.8 km from the surface. The corresponding image scale is about 66 cm/pixel, so each 1024 x 1024 pixel frame is about 676 metres across.
Changes in perspective and shadows due to rotation and translation of the comet and spacecraft with respect to each other seem to be limited across this particular set of four images, which is why we’ve decided to present a mosaic this time. The mosaic covers roughly 1200 x 1350 metres. But as usual, we urge you to be cautious in over-interpreting the mosaic: the individual images, presented at the end of this post, provide the ‘ground truth’.
Four image NAVCAM mosaic comprising images taken on 26 October. Credits: ESA/Rosetta/NAVCAM
This scene focuses on the same part of the comet as seen in the 18 October image set, but you will notice some interesting new features, as well as some previously visited areas in a new light. (See CometWatch 8 October and the OSIRIS image of 6 August for additional context.)
Visible towards the upper left is a region of brighter material that was previously cast in shadow in the 18 October image, and that appears to lie at the base of a cliff. Some additional bright material is seen at the top of the cliff. This material may be freshly revealed and yet to be covered in dust, perhaps as the result of a recent ‘landslide’. It remains to be seen what its composition is, but no doubt the science teams will be looking out for its signature in the remote sensing data.
Remember though, that this material isn’t in fact bright white on the comet; comets are blacker than coal, and the NAVCAM images are grey-scaled according to their brightness with additional contrast adjustments to bring out the full range of features (see NAVCAM’s shades of grey for a full recap of the way in which intensities are displayed in NAVCAM images).
Also not seen previously in this much detail are the two boulders just below the centre of the mosaic, one of which takes on a heart-shaped appearance from this angle. Zooming in reveals hints of a layered structure and both objects seems to be appearing from beneath the dusty layer, just like some of the smaller ‘boulders’ around them.
Finally, over on the right hand side of the mosaic, the region cast in dramatic shadow on 18 October can now be seen in much more detail. And don’t forget the boulder Cheops and friends above the centre of the mosaic too!
Comments
47 Comments
Bonjour.
Image très impressionnantes, d'autant plus en apprenant que la surface est plus noire que le charbon!
Pourquoi n'y a-t-il pas d'image d'Osiris. Sont elles plutôt hors du champ de la comète.
Vous est-il possible d'accompagner les images d'une échelle sur l'image. La résolution ne m'aide pas à me faire une idée de la taille des structures?
Bonne continuation.
To interpret this mosaic I need a lot of faith on past photos of this site.
Too much influence from Robin's views. Seeing 'hazing' over the 'whity' areas center left of
http://blogs.esa.int/rosetta/files/2014/10/ESA_Rosetta_NAVCAM_141026_B.jpg
How do you account for these layered structures [http://i.imgur.com/Jr4OFQB.jpg] ?
Hi Ivan. Both images present layers vertical to the surface. Logan's point of interest: Go back a little. As in the 'dust' or 'sand' you can see 'drawings' here. The drawings follow a horizontal pattern. ;). I interpret as 'at least two' forces at play.
And don't forget the VanDerWaals? forces.
Are these drawings formed long back or a recent one. if it is recent is it because the comet is approaching perihelion, gets more heat which causes the layers beneath the dust/sand to move. and the sands arrange itself to take the shape of the edges of the top layer.
Hi Atom. There are slight 'clues' saying that this is ongoing phenomena.
http://blogs.esa.int/rosetta/2014/10/22/cometwatch-cheops-neighbours/?replytocom=101644#respond
The top of this mosaic brings back that 'feeling' of a big thing assembled of layers and layers of cardboard and Styrofoam nuts.
67P is 'getting rid' of his 'winter' coat.
The question is how long has that Winter been, 4 years, or 4 billion years?
'Tepui' morphology at bottom right of
http://blogs.esa.int/rosetta/files/2014/10/ESA_Rosetta_NAVCAM_141026_C.jpg
Erosion agent not being rain, but sublimation.
'Tepui' differential erosion intensified by 'Laktritz'. Other agents of differential erosion pending
diferential erotion intensified by STATIC 'Laktritz' small patches.
'tepuis' are born in 'mirrors' created by traveling 'lakritz' plaques.
Remember the 'mouths' of the 'worms' in the movie 'Dunes'?
Anyone have seen structures looking like that?
The dust area looks to me as if its been 'shaken' and the dust has slumped in parts of the area. the lines surrounding the areas show a definite pattern like rings on water that is disturbed.
I still feel that there is a vibration effect but at a very low level, perhaps like an earthquake but of low order?
Not all the time but maybe periodically and could explain how rocks and debri fall of the cliffs.
Clive
Quite interesting signaling, Clive.
"...pattern like rings on water that is disturbed." Sporadic at least, there should be 'something' flowing below there that makes displacements easier, besides the 'rumblings'.
Fantastic, thank you! I am not able to view these exotic scenes without wishing Chesley Bonestell was here to see them too.
Is there a listing of publications coming out of this project?
As the south pacific legends goes. You can add your own layer to the pearl.
Another teasing picture and the knowledge that there is a lot more to see in the Osiris pictures i will start to colorize my copies in a touch of pink. I think its about time to release a picture of this comet with a detail recognition the available ten-factor better the the navcam.
Thanks again Emily the contrast between the 8 days is nice to see.The different lighting limits comparisons, but Cheops is well lit in both images. In this later image the bright area on top of Cheops does seem to have got bigger, there is less dust.
Apologies to Logan for my "influence". That point on the cliff is the largest and brightest area we have seen and all the broken bits at the bottom of the cliff all have very shiny faces and most are producing plumes of gas. A rough estimate is the cliff edge has fallen about 15m on a world with a tiny amount of gravity. Terminal velocity is about 1m/s. A lump of "rock" falling that distance on Earth might break into a couple of smaller lumps when it hits the ground, on 67P it would barely notice the impact. Yet we see that the piece of cliff has shattered into hundreds of pieces. In fact we see this everywhere, hundreds of pieces of shattered "rocks" and "stones", scattered rubble of all shapes and sizes at the base of cliffs and slopes. The material of this comet is brittle and shatters readily, it can not be Rock!
Henceforth I shall refer to the solid surface material as ICE. Its very, very dirty ice, but ice nonetheless. It is black all the way through, so slower processes of erosion have little effect on its appearance, however a fresh fracture exposes fresh ice where radiation has not had chance to complete the blackening process.
The layering horizontally I have a theory for, but the vertical layers seen at the bottom of Image A have me temporarily stumped. Bob the Builders wall seems to have fallen over and is no longer quite so dead straight. Such is the confusion created by 2D images. The fracture to its right with the pits and holes was hidden mostly in the shadow before. It looks like a more advanced version of the fracture and dents seen on the neck plain. Lots of cliff slippage in Images C & B.
Lastly the dust waterfall at middle bottom of Image A. I have seen little skinny short dust waterfalls elsewhere, but this is the biggest one yet.
I have been banging on about this being a volcanic landscape, so I have found this picture of freshly solidified lava on a volcano in Idaho. It exhibits different types of lava and looks eerily similar to the surface of 67P, if a little less worn by the passage of time. Food for thought I think.
https://www.flickr.com/photos/124013840@N06/15040676204/
I think we need to discuss your interpretations. I see the brightened edge of the cliff, I see the bright "rubble" underneath it, but where are you getting "plumes of gas" being produced? If your mind was already biased into searching for sublimation, I don't believe there's anyway you would come to that conclusion.
If sublimation occurs at all, it's in tiny scales produced from ices of molecules formed In the coma. The nucleus appears volcanic with olivine and silicates because it's constantly being eroded by discharging, and some of the dust is attracted back to the nucleus electrostatically.
This is not my website but please visit for laboratory experiments of discharges producing all of the craters observed on 67P and planetary bodies.
http://www.setterfield.org/crater_origins/crater_origins.html
Hi Robin. Your comments an other's are of the most importance by your scientific background. I'm just a science fan, uneducated. I read all of them and do my best to understand you. I wait -sometimes days- in order to thread something that make sense. But on making my own treads the strategy at this early days is wild 'creativity'. I'll come back and laugh a lot.
Leo has tagged it as 'black ice'. Would like to know a lot of math and theoretical physics to understand his model.
"...black all the way through". Black, not blackened.
"...a fresh fracture exposes fresh ice where radiation has not had chance to complete the blackening process."
Taking it into my hat with the reserve of it being 'core' material.
Logan's def: 'core' is the material still in the original place assigned by the accretion - grow process. It's very old material. It is not the original chemistry, nor the original structure.
So my big unknown now, is those streamers. More specifically, what do the sources look like and how do they shape the appearance of the landscape? The little cups and bowls, the little mud volcanos, the jet engines, rocket launchers, huge caves or the innumerable semicircular features with one steep side and a flat bottom, that cut into any sort of sloping surface and come in all sizes from a metre to hundreds of metres across. The last would be my choice, but the mechanism and lack of any obvious associated fractures in the surface for most, still confounds me. A sublimation scenario looks more likely to explain those.
Bill, streamers/jets are your pet subject, any thoughts?
@Robin= "Bill, streamers/jets are your pet subject, any thoughts?"
We haven't seen, with our available images, actual venting vents, yet. We have seen that one line of depressions on the North Polar Plain, which is dang likely. We see odd conical depressions. We see depressions in dust on the grooved/lineated rock (best rez Site J pics). And' I'll speculate, those areas of "rubble" or scree that are dust-free and fresh looking are vent areas.
Remember, we are now looking at the aftermath of the last perihelion where the silicates and refractory organics settled down after the comet cooled and quit degassing. And we are now at just the onset of activity of this passage.
Front row seats. Yeah!
--Bill
Hi Bill. Guessing what is an old streamer vent is a fun challenge though. The rocky, rubbly areas are definitely sources of greater sublimation, as are exposed lumps of ice. Sublimation seems to create diffuse plumes and clouds of dust, as seen in front of the cliff below the Amphitheatre in the 24th October image, the kilometres long jets are made by another mechanism.
The collimated nature of those neck streamers is what needs visually explaining. We have images of large parts of the neck plain where they have been seen, but never coincidentally to link the jets to a particular type of source capable of producing this observed focusing of the jets. Round features and possibly short cracks are what I am looking for. The trouble is there are several different possibilities that might fit the bill.
Excellent commentary, and very good stitch of the images.
This is a comparison with the 26 October images with earlier images, in particular highlighting the area of the "additional bright material is seen at the top of the cliff" and boulders on the Equatorial Plain.
http://univ.smugmug.com/Rosetta-Philae-Mission/Rosetta-Comparative-Series/i-v7ghN4J/0/L/compar_26-Oct-14_images-L.png
--Bill
Robin & Bill,
I dont neccesarily think the Ice/rock has shattered on hitting the ground, in fact in Bills slope failure picture, it could be a large slab has broken off in one piece.
It could just be that the Ice/rocks are dug out of the cliffs as its eroded, this could easily be from sublimation of bits of ice holding all the rock together, or from the coarse scaring of the surfaces electrically.
@robin maybe "jets" have a very unappealing aspect when seen at very short distance. I remember having walked into Stromboli crater while it was emitting a wide panache of ashes and gazes. I had the impression of walking on a very smooth ash surface scattered with some basaltic bombs. The tons of ashes emitted were somehow percolating between the ash cover but it was completely invisible at close range.
Of course gravity was much higher than at the comet, and the air pressure may have played a role.
But I won't be too much surprised if Philae lands in the middle of a jet... and does not see anything more than a faint haze in the sky around...
I am afraid you might be right there. The dusty layer might have enough density and cohesion to largely limit sublimation, but not the higher pressure process clearly responsible for the jets. The surface dust layer is speculated to be loose and porous. The hunt for a more obvious source is more fun though until an explanation is forthcoming.
Good point Cantalloube
Bad point Philae
13 days to go...Eagerly waiting to see Philae landing safely on 67P.
Why is it taking so long (Nov 12) to drop Philae as it has entered into the comet's gravitational field on September 10 ?
why the Philae is dropped from 22.5km? Why can't rosetta go so close to the comet and drop the Philae? What are the complications involved in that?
Hi Atom. The best answer in my mind at this moment is that several programed experiments need to begin from some distance. Other arguments have been said here, relative to 'lander' design an the unusual shape of comet 67P. Precisions and corrections welcomed
@Atom Universe: Orbital mechanics. The closer you go, the faster is the orbital speed.
In order to land you have to get rid of that speed. Elliptical orbits mean fast orbital speed when close to surface, low speed when at the furthest point out.
So the position to "break" most efficiently is at the greatest distance.
If your thrusters are big enough and you would have a infinit fuel, it would not matter.
Another reason might well be "time for science" during decent.
Philiae might well get lost when it attempts to land. So the longer its instruments can do measurements before, the better.
Might be a mixture of both reasons.
There might be multiple reasons for that. One for sure was to check for the best landing site.
The other one is making sure to get as much as possible science before the next critcal step.
You never know what happens during seperation. Sometthing might go wrong, the hole probe might get lost....
So take what you can get before entering the next critical phase.
There might be other reaons, too
Pardon my ignorance if I'm wrong but isn't the Nav-Cam the wide-angle camera? And, if I am correct, why have we not seen photos lately from the narrow-angle camera?
I do not believe my eyes. I do not believe that I am seeing rocks; the physical properties of the component parts do not add up for me.
We know that P67 has a density of 0.4 g/cm^3. Consider the solid phase densities of some of the known components of P67 (all in g/cm^3): water, 0.93; CO2, 1.5; ammonia, 0.82; methane, 0.45; olivine, 3.3. I propose that the overall low density of P67 precludes the solid aggregation of these higher density components to form “rock” or solid ice.
Consider the things that we know have densities around 0.4, for example flour, 0.6; unsweetened cocoa powder 0.34; talcum powder, 0.27 - 0.4. These are dusty materials.
Comets are composed of interstellar dust, and I propose that P67 is just that, clumped dust. The striations in the cliffs represent gradations blackness of the original dust as it aggregated onto the nascent comet.
Rather than the “Dirty Snowball,” I propose that P67 is a “Dirty Dust Ball.”
It is a pity that our winter semester is running, and
I have to prepare and give courses instead of
meditating about the news of the Rosetta mission.
Good luck for the next two weeks!
Ingo.