Science on the surface of a comet

Complex molecules that could be key building blocks of life, the daily rise and fall of temperature, and an assessment of the surface properties and internal structure of the comet are just some of the highlights of the first scientific analysis of the data returned by Rosetta’s lander Philae last November. This article is mirrored from the main ESA Web Portal

Images taken by Philae’s ROsetta Lander Imaging System, ROLIS, trace the lander’s descent to the first landing site, Agilkia, on Comet 67P/Churyumov–Gerasimenko on 12 November 2015. Credits: ESA/Rosetta/Philae/ROLIS/DLR

Images taken by Philae’s ROsetta Lander Imaging System, ROLIS, trace the lander’s descent to the first landing site, Agilkia, on Comet 67P/Churyumov–Gerasimenko on 12 November 2014.
Credits: ESA/Rosetta/Philae/ROLIS/DLR

Early results from Philae’s first suite of scientific observations of Comet 67P/Churyumov­-Gerasimenko were published today in a special edition of the journal Science.

Data were obtained during the lander’s seven-hour descent to its first touchdown at the Agilkia landing site, which then triggered the start of a sequence of predefined experiments. But shortly after touchdown, it became apparent that Philae had rebounded and so a number of measurements were carried out as the lander took flight for an additional two hours some 100 m above the comet, before finally landing at Abydos.

A timeline of the science operations that Rosetta’s lander Philae performed between 12 and 15 November 2015, following touchdown on the surface of Comet 67P/Churyumov–Gerasimenko.  Following Philae’s unexpected flight across the surface of the comet, the planned first science sequence had to be adapted according to the new situation. The graphic shows the approximate times (to the nearest 15 minutes) that each of Philae’s 10 instruments was activated; however, it does not indicate the success of data acquired.

A timeline of the science operations that Rosetta’s lander Philae performed between 12 and 15 November 2014, following touchdown on the surface of Comet 67P/Churyumov–Gerasimenko. Following Philae’s unexpected flight across the surface of the comet, the planned first science sequence had to be adapted according to the new situation. The graphic shows the approximate times (to the nearest 15 minutes) that each of Philae’s 10 instruments was activated; however, it does not indicate the success of data acquired.

Some 80% of the first science sequence was completed in the 64 hours following separation before Philae fell into hibernation, with the unexpected bonus that data were ultimately collected at more than one location, allowing comparisons between the touchdown sites.

Inflight science
After the first touchdown at Agilkia, the gas-sniffing instruments Ptolemy and COSAC analysed samples entering the lander and determined the chemical composition of the comet’s gas and dust, important tracers of the raw materials present in the early Solar System.

COSAC analysed samples entering tubes at the bottom of the lander kicked up during the first touchdown, dominated by the volatile ingredients of ice-poor dust grains. This revealed a suite of 16 organic compounds comprising numerous carbon and nitrogen-rich compounds, including four compounds – methyl isocyanate, acetone, propionaldehyde and acetamide – that have never before been detected in comets.

Meanwhile, Ptolemy sampled ambient gas entering tubes at the top of the lander and detected the main components of coma gases – water vapour, carbon monoxide and carbon dioxide, along with smaller amounts of carbon-bearing organic compounds, including formaldehyde.

Importantly, some of these compounds detected by Ptolemy and COSAC play a key role in the prebiotic synthesis of amino acids, sugars and nucleobases: the ingredients for life. For example, formaldehyde is implicated in the formation of ribose, which ultimately features in molecules like DNA.

The existence of such complex molecules in a comet, a relic of the early Solar System, imply that chemical processes at work during that time could have played a key role in fostering the formation of prebiotic material.

Zooming in to a portion of the fractured cliff face imaged by CIVA camera 4 reveals brightness variations in the comet’s surface properties down to centimetre and millimetre scales. The dominant constituents are very dark conglomerates, likely made of organics. The brighter spots could represent mineral grains, perhaps even pointing to ice-rich materials. The left hand image shows one of the CONSERT antennas in the foreground, which seems to be in contact with the nucleus. The dimensions of the antenna, 5 mm in diameter and 693 mm long, help to provide a scale to the image. Credits: ESA/Rosetta/Philae/CIVA

Zooming in to a portion of the fractured cliff face imaged by CIVA camera 4 reveals brightness variations in the comet’s surface properties down to centimetre and millimetre scales. The dominant constituents are very dark conglomerates, likely made of organics. The brighter spots could represent mineral grains, perhaps even pointing to ice-rich materials. The left hand image shows one of the CONSERT antennas in the foreground, which seems to be in contact with the nucleus. The dimensions of the antenna, 5 mm in diameter and 693 mm long, help to provide a scale to the image. Credits: ESA/Rosetta/Philae/CIVA

This image, created from Philae’s ROLIS descent camera, focuses on the largest boulder seen in the image captured at 67.4 m above Comet 67P/Churyumov–Gerasimenko. It is best viewed with red/blue–green glasses. The 3D view highlights the fractures in the 5 m-high boulder, along with the tapered ‘tail’ of debris and excavated ‘moat’ around it. Credits: ESA/Rosetta/Philae/ROLIS/DLR

This image, created from Philae’s ROLIS descent camera, focuses on the largest boulder seen in the image captured at 67.4 m above Comet 67P/Churyumov–Gerasimenko. It is best viewed with red/blue–green glasses. The 3D view highlights the fractures in the 5 m-high boulder, along with the tapered ‘tail’ of debris and excavated ‘moat’ around it. Credits: ESA/Rosetta/Philae/ROLIS/DLR

Comparing touchdown sites
Thanks to the images taken by ROLIS on the descent to Agilkia, and the CIVA images taken at Abydos, a visual comparison of the topography at these two locations could be made.

ROLIS images taken shortly before the first touchdown revealed a surface comprising metre-size blocks of diverse shapes, coarse regolith with grain sizes of 10–50 cm, and granules less than 10 cm across.

The regolith at Agilkia is thought to extend to a depth of 2 m in places, but seems to be free from fine-grained dust deposits at the resolution of the images.

The largest boulder in the ROLIS field-of-view measures about 5 m high, with a peculiar bumpy structure and fracture lines running through it that suggest erosional forces are working to fragment the comet’s boulders into smaller pieces.

The boulder also has a tapered ‘tail’ of debris behind it, similar to others seen in images taken by Rosetta from orbit, yielding clues as to how particles lifted up from one part of the eroding comet are deposited elsewhere.

Anaglyph view created from the stereo pair of images acquired by CIVA cameras 6  and 7 at the final landing site Abydos on 13 November 2014. The topography occupying the foreground and left hand portion of the image is estimated to be 0.8–1.2 m from the lander’s body. To the top right, the topography is likely 1.2–2 m away. In the background, towards the top left, one unit may be at least 4.5 m away, and perhaps up to 7 m away. Credits: ESA/Rosetta/Philae/CIVA

Anaglyph view created from the stereo pair of images acquired by CIVA cameras 6 and 7 at the final landing site Abydos on 13 November 2014. The topography occupying the foreground and left hand portion of the image is estimated to be 0.8–1.2 m from the lander’s body. To the top right, the topography is likely 1.2–2 m away. In the background, towards the top left, one unit may be at least 4.5 m away, and perhaps up to 7 m away.
Credits: ESA/Rosetta/Philae/CIVA

Over a kilometre away at Abydos, not only did the images taken by CIVA’s seven microcameras reveal details in the surrounding terrain down to the millimetre scale, but also helped decipher Philae’s orientation.

The lander is angled up against a cliff face that is roughly 1 m from the open ‘balcony’ side of Philae, with stereo imagery showing further topography up to 7 m away, and one camera with open sky above.

The images reveal fractures in the comet’s cliff walls that are ubiquitous at all scales. Importantly, the material surrounding Philae is dominated by dark agglomerates, perhaps comprising organic-rich grains. Brighter spots likely represent differences in mineral composition, and may even point to ice-rich materials.

From the surface to the interior
The MUPUS suite of instruments provided insight into the physical properties of Abydos. Its penetrating ‘hammer’ showed the surface and subsurface material sampled to be substantially harder than that at Agilkia, as inferred from the mechanical analysis of the first landing.

The results point to a thin layer of dust less than 3 cm thick overlying a much harder compacted mixture of dust and ice at Abydos. At Agilkia, this harder layer may well exist at a greater depth than that encountered by Philae.

Click for explanation. Credits: Spacecraft graphic: ESA/ATG medialab; data from Spohn et al (2015)

Click for explanation. Credits: Spacecraft graphic: ESA/ATG medialab; data from Spohn et al (2015)

The MUPUS thermal sensor, on Philae’s balcony, revealed a variation in the local temperature between about –180ºC and –145ºC in sync with the comet’s 12.4 hour day. The thermal inertia implied by the measured rapid rise and fall in the temperature also indicates a thin layer of dust atop a compacted dust-ice crust.

Moving below the surface, unique information concerning the global interior structure of the comet was provided by CONSERT, which passed radio waves through the nucleus between the lander and the orbiter. The results show that the small lobe of the comet is consistent with a very loosely compacted (porosity 75–85%) mixture of dust and ice (dust-to-ice ratio 0.4–2.6 by volume) that is fairly homogeneous on the scale of tens of metres.

This diagram shows the propagation of signals between Rosetta and Philae through the comet’s nucleus, between 12 and 13 November 2014. Green represents the best signal quality, decreasing in quality to red for no signal.  The signals are sent and received by the CONSERT instrument, which is on both the orbiter and the lander. The time taken for the signal to travel between the instruments, and the amplitude of the received signal offers insights into the structure of the comet’s nucleus. In particular, the travel time depends on a parameter called permittivity, which is itself linked to the nucleus porosity, composition, temperature and internal structure of the comet. The permittivity value is approximately 1.27. Credits: ESA/Rosetta/Philae/CONSERT

This diagram shows the propagation of signals between Rosetta and Philae through the comet’s nucleus, between 12 and 13 November 2014. Green represents the best signal quality, decreasing in quality to red for no signal. The signals are sent and received by the CONSERT instrument, which is on both the orbiter and the lander. The time taken for the signal to travel between the instruments, and the amplitude of the received signal offers insights into the structure of the comet’s nucleus. In particular, the travel time depends on a parameter called permittivity, which is itself linked to the nucleus porosity, composition, temperature and internal structure of the comet. The permittivity value is approximately 1.27. Credits: ESA/Rosetta/Philae/CONSERT

In addition, CONSERT was used to help triangulate Philae’s location on the surface, with the best fit solution currently pointing to a 21 x 34 m area.

“Taken together, these first pioneering measurements performed on the surface of a comet are profoundly changing our view of these worlds and continuing to shape our impression of the history of the Solar System,” says Jean-Pierre Bibring, a lead lander scientist and principal investigator of the CIVA instrument at the IAS in Orsay, France.

Based on the most recent calculations using CONSERT data and detailed comet shape models, Philae’s location has been revised to an area covering 34 x 21 m. The best fit area is marked in red, a good fit is marked in yellow, with areas on the white strip corresponding to previous estimates now discounted. One lander candidate proposed previously in the vicinity lies 62 m from the red marked area of the new CONSERT region, suggesting this is no longer a viable candidate. Credits: ESA/Rosetta/Philae/CONSERT

“The reactivation would allow us to complete the characterisation of the elemental, isotopic and molecular composition of the cometary material, in particular of its refractory phases, by APXS, CIVA-M, Ptolemy and COSAC.”

“With Philae making contact again in mid-June, we still hope that it can be reactivated to continue this exciting adventure, with the chance for more scientific measurements and new images which could show us surface changes or shifts in Philae’s position since landing over eight months ago,” says DLR’s Lander Manager Stephan Ulamec.

“These ground-truth observations at a couple of locations anchor the extensive remote measurements performed by Rosetta covering the whole comet from above over the last year,” says Nicolas Altobelli, ESA’s acting Rosetta project scientist.

“With perihelion fast approaching, we are busy monitoring the comet’s activity from a safe distance and looking for any changes in the surface features, and we hope that Philae will be able to send us complementary reports from its location on the surface.”

Notes 

The 31 July 2015 Science special issue includes the following papers:

“The nonmagnetic nucleus of comet 67P/Churyumov–Gerasimenko,” by H.-U. Auster et al.

“67P/Churyumov-Gerasimenko surface properties as derived from CIVA panoramic images,” by J-P. Bibring et al.

“The landing(s) of Philae and inferences about comet surface mechanical properties,” by J. Biele et al.

“Organic compounds on comet 67P/Churyumov-Gerasimenko revealed by COSAC mass spectrometry,” by F. Goesmann et al.

“Properties of the 67P/Churyumov–Gerasimenko interior revealed by CONSERT radar,” by W. Kofman et al.

“The structure of the regolith on 67P/ Churyumov–Gerasimenko from ROLIS descent imaging,” by S. Mottola et al.

“Thermal and mechanical properties of the near-surface layers of comet 67P/Churyumov–Gerasimenko,” by T. Spohn et al.

“CHO-bearing organic compounds at the surface of 67P/Churyumov–Gerasimenko revealed by Ptolemy,” by I.P. Wright et al.

Individual ROLIS and CIVA images are available via our “Landing on a comet” gallery.

UPDATE 10 Aug:
Note that all papers are available free-access here: http://sci.esa.int/rosetta/56291-science-special-issue-philaes-first-look/

Comments

66 Comments

  • Gabriel Gonçalves says:

    Hey, just a question. With this new studies and data gathered by Philae, are you able to understand the composition of 67P and link it with any kind of material present in our collections of meteoritical material (like, to make a guess about a specific kind of carbonaceous chondrite that resembles with 67P’s rocks)? I know it’s a tough question but this really makes me curious =)

    • emily says:

      Hi Gabriel. It’s a good question. In the CONSERT paper there is a discussion based on the ternary diagrams for ordinary chondrites and carbonaceous chondrites, and looking at how the measurements of the permittivity, the dust:ice ratio and the porosity that has been measured for comet 67P compare. The conclusion is that the CONSERT value of the permittivity excludes, as expected for primitive small bodies, the presence of ordinary chondrites in the refractory component.
      I know that’s not quite answering your question, but that’s the only related information that I have most immediately to hand!

      • Gabriel Gonçalves says:

        Hello,
        Thank you very much for answering!
        I understand that this kind of conclusion that I’m looking for is very complex to be reached and would require a lot of data and effort to be achieved.
        The Rosetta mission already led to a huge number of discoveries, things beyond what we had dreamt!
        As someone that loves astronomy, astrobiology and, specially, meteoritics, I’ll be always expecting that someday Rosetta will be able to help us to solve some mysteries about the origin of some of the most different carbonaceous chondrites that we know. But, by now, all I can do is to congratulate you guys for all the wonders that already have been discovered and everything else that is coming.
        You all are fantastic!!!

  • originalJohn says:

    A lot of results heavily condensed in this post. It is interesting that in this and other reports of results only one interpretation of results is ever considered. No other possibility is ever acknowledged. And the one that is inferred is always a reinforcement of the primordial origin and ice composition of comets hypothesis.

    For example the COSAC results found ” a suite of 16 organic compounds comprising numerous carbon and nitrogen-rich compounds ” but there was no suggestion of their likely origin, which could obviously be nothing to do with ice. It was also observed that the COSAC sample was dominated by “ice poor” dust grains, but no comment on the significance of this.

    In the Ptolemy samples, of ambient gas, water vapour, carbon dioxide, carbon monoxide and formaldehyde are reported.
    It is commented that compounds detected by both instruments could be interpreted as life forming ingredients, for example formaldehyde in the formation of ribose, a precursor of DNA. This is an enormously wild inference for the presence of formaldehyde, derived from the belief that comets brought life ingredients to Earth. No suggestion as to the origin of the formaldehyde. So I will add the suggestion that formaldehyde is a ubiquitous product of oxygen depleted combustion of hydrocarbons, as indeed is carbon monoxide. And of course water vapour and carbon dioxide are the principal products of oxygen rich hydrocarbon combustion, the presence of complex hydrocarbons confirmed by the same instruments, ie the products and the reactants.

    Jumping now to the CONSERT results it is reported as “the small lobe of the comet is consistent with a very loosely compacted (porosity 75–85%) mixture of dust and ice “. This does not rule out other explanations but simply says the preferred explanation fits ie that the nucleus is porous dust and ice. However the travel time of the CONSERT signal is stated as depending on porosity, composition, temperature and internal structure of the comet yet only porosity is inferred from this reading. Composition temperature and internal structure are ignored. What are the effects of these on permittivity. Finally why assume that the signal went through the nucleus at all with such a wide angle of no signal. From the diagram the indicated green and yellow signals look as though they could just as well have mostly skimmed across the surface, another explanation for low permittivity.

    Finally, it is stated that ” Taken together, these first pioneering measurements performed on the surface of a comet are profoundly changing our view of these worlds and continuing to shape our impression of the history of the Solar System,” says Jean-Pierre Bibring ” thus implying that the primordial origin of comets is an accepted fact when in reality it is a dubious hypothesis. Jean-Pierre’s statement is a bit of a giveaway containing positive expressions of investigation like ” profoundly changing” and ” continuing to shape” but what ? ” our impression of the history of the Solar System”, thus we anticipate the measurements reinforcing our believed hypothesis that comets predate the solar system, which we take for granted.

    • originalJohn says:

      correction : ” another explanation for high permittivity”

    • Gerald says:

      Why should they list hundreds of dead ends?
      Your combustion would be one of those, as well as the comet being split from a planet-sized body. That’s immediately ruled out.
      For natural numbers, 1 + 1 is not 97, not 98, not 99, not 100, not 101, … not 1000,000,123, …
      What should that be good for?

      • originalJohn says:

        Any temperature measurements for any of the jets yet Gerald.

        • Gerald says:

          Very likely, yes, simply by the way temperature measurements are performed. But I’m unaware of published reduced data addressing this particular question.

          You may remember H.Sierks’ wish of more intense collaboration between the instrument teams. To obtain the most reliable results about jet temperatures you need to compare OSIRIS images with VIRTIS temperature measurements.

          The latest published VIRTIS raw data are of 2012-02-08, of the Lutetia flyby, as far as I’ve seen.
          But you may login via the ftp address
          psa.esac.esa.int
          and change to the directory
          /pub/mirror/INTERNATIONAL-ROSETTA-MISSION/VIRTIS/RO-A-VIRTIS-2-AST2-V1.0/DATA/VIRTIS_H
          and transfer and read some of the QUB files (probably ISIS compatible), to be ready to dig into the 67P data yourself, as soon as they will be released.

    • ianw16 says:

      All of that would would require a sensible alternate hypothesis of the origin and composition of comets. So far we haven’t had one. Don’t forget the density is < 500kg m^3.

  • A.Cooper says:

    Using the shadows, you can swivel the 5-metre rock photo round so it’s in the same orientation as the full head shot. The shadow is pointing south so the tail is pointing west and the moat is facing east.

    This means the moat and tail are in line with the comet’s rotation plane. This is yet another example of a rock that has landed after travelling in a suborbital trajectory back down the rotation plane. It’s landed (hence the moat), tipped over and shed its dust and scree even further back down the rotation plane. Dust at its base and its scree a little further on. This gives the impression of a scree ‘shadow’, west of the rock because there’s now a pile of deposited dust around its base and a newly deposited sprinkling of scree just beyond that, further to the west. It’s the same for rocks on Imhotep. Their scree lies predominantly to the west.

    The initial detachment and lifting of these rocks would be as collateral debris from large slabs departing due to comet spin-up. They are the very few rocks that got a backwards delta v kick when the slabs were wrenched off and so didn’t escape to deep space. The only way a rock could evade escape was to get this backwards kick causing it to go suborbital (0.25 m/sec backwards kick if doing 0.8 m/sec forward rotation. 0.8 m/sec is the notional escape velocity, probably exceeded). ‘Backwards’ means in a direction opposite to that of forward rotation, which is eastward. That’s why all such rocks travelled westwards, back down the rotation plane and deposited their scree even further westwards.

    If you click on the 5-metre rock image, the Space in Images page has a description. There’s a big clue there in the words “prevailing direction”:

    “The ROLIS team thinks the tails appear as a result of the region ‘behind’ an obstacle being shielded from erosion via the impact of falling particles arriving in a prevailing direction.”

    The prevailing direction is always east to west.

    The best example of this phenomenon is the large pair of rocks on the Site A ‘amphitheatre’. Their scree is strewn westwards along the rotation plane. To the east, the flat crater is almost pristine.

    • Ramcomet says:

      A. Cooper,

      Wow, they have Philae pinned down to an area the size of my front yard now. Unfortunately for Philae, it is incredibly, absurdly rough there, Praying for at least one more transmission of images and tests as “we” approach perhileon!

      Is the current location of Philae, (called Albedos), part of, or just slightly below and left of the Hatmehit Slab Hinge, according to your theory?

      By the way, I call the missing rectangular window of material from Hatmehit’s “crater” wall “Bulldozer Pass”, because of its highly mechanical rectangular shape reminiscent of a strip mine quarry on Earth.

      Not a very Egyption name, though! .;-)

      • A.Cooper says:

        Ramcomet

        The answer to your question of whether Philae is sitting in the hinge is technically, no but in effect, yes. Sounds complicated but here’s why (according to the ramifications of stretch theory). The hinge is V-shaped like all the other V-shaped strata running across Hatmehit and down the head lobe to Serqet. If this is a surprise, check the photos in my next post, out sometime this week. The southern part of the hinge V is where Philae is. It was gouged out (~170 m x 70m x 250 m). However, due to what I call the ‘sliced facet’ (that massive slice off the south pole side of the head), half of the southern side of the V-shaped hinge went with the slice. Philae is sitting about 30 metres under the bottom of where the 70-metre-deep hinge gouge used to be before being sliced off. And it dropped down about 20 or 30 metres beyond the end of the 250-metre-long trench. If you could cgi a ghost image of the slice back onto the comet you’d be putting the full-length (500 metre?) hinge trench back and Philae would be seen to have dropped through the bottom of the hinge valley and landed on the ‘steep’ sliced facet. That position is just beyond the curved cross section of the end of the sliced hinge valley. So it’s just under the bottom of where the hinge was but only just.

        This makes no difference to the terrain Philae finds itself in. That’s because it’s sitting where material was ripped out anyway (the sliced facet) and it’s so close to the hinge valley that it’s sitting in a sort of sympathetic dip that mirrors the valley just next to it. It’s curving round from the hinge valley to the sliced facet in this 100 metres or so.

        This is why the terrain here is so rough- it’s ripped-up end-on strata. You can see the three distinct strata lines running longitudinally along the valley (see Robin Sherman’s blog for a good photo of it). And the fact they are longitudinal is why these strata were plucked out from between their neighbours so easily.

        There are well over a dozen of these strata running across ‘Bulldozer Pass’ and down past Ma’at hence the saw-toothed, strip mined appearance. They join up with their sliced facet counterparts just over the sliced rim of Hatmehit. The strata on the facet slope at 45° causing the saw-toothing at Bulldozer Pass. (That’s if I interpret Bulldozer Pass as being the sliced rim and not the cliff?).

        The fact that Philae is sitting in ripped-up terrain that was deep inside the comet at one time, will inform every data measurement it takes. The slice with all those end-on strata is sun-facing just after perihelion. That’s probably why 67P always gets more active at that point in its orbit.

        • Ramcomet says:

          Hi Andy,

          I was calling Bulldozer Pass the missing rectangular section of crater wall and somewhat below it another smaller “L” shaped rectangular gouge, but use it as you like, I like your theories.

          Check out this Mars “Flyby” , while completely different geologically, you will love that fault or rift running across that crater wall I think!

          .https://youtu.be/O_b39AHRMlw

          By the way, amidst all the excitement and new Osiris images of jets appearing, (in non stretched images now!) I was very saddened to see Holger today on the hangout not even address the possibility of Stretch Theory when Emily read your question. Hopefully he was just tired at 3-5 am in Hawaii, not just overly invested in accumulation theory.

          If so I for one would sure like to see what he means by the strata show two different objects!

          • Gerald says:

            Despite all the enthusiasm of A.Cooper and Marco about “Stretch” there is no evidence for it, and although it’s physically not completely impossible, it’s rather fringe.
            H.Sierks is a physicist and thus focuses on physically realistic options for the bilobic structure. And there are two such options: An eroded binary, and an eroded monolithic object composed of many small fragments.
            If both these generally accepted options would fail – and that’s not to be expected – one would consider other options.
            But essentially the way the scientists work usually is a little different. They don’t start with a hypothesis, and try to proof it. Instead they look at the data and try to “reduce” them, with an a-priori unknown result.
            So if H.Sierks prefers a contact binary, that’s less a result of wishful thinking, but a result of data analysis, including best-fit computer models.
            It would be hard to explain to other scientists, why to seriously consider unsubstantiated hypotheses.

          • A. Cooper says:

            Hi Ramcomet

            I saw your video link. Very nice. I have Google Mars but not in flyover mode so that was a treat.

            As for the differing strata between head and body lobe, it’s quite complicated. Holger said they show two different objects. It’s because the strata that align all the way through the body don’t align with the strata in the head (Marchi et al). Part 11 dealt with this: non-aligned strata refutes the single eroded body theory but not the fracture-then-stretch theory. But by refuting the erosion theory they jump straight to contact binary theory and forget stretch. That’s exactly what Holger did with that statement you picked up on. Part 11 deals with this and what I think are other papers presented at AAS 225 in January 2015.

            Briefly, the reason the strata don’t align is because the head tipped up before it rose from the body, taking its strata out of alignment as it did so. It’s also rather complex in that there are two sets of head ‘strata’. One set is original, undisturbed strata (but slightly tipped as mentioned). The other set were folded into slight V-shapes during head lobe stretch prior to shearing so they aren’t going to align either.

            So stretch theory is being repudiated on the basis of two signatures (tipped-up strata and stretched V’s) that are actually the hallmarks of stretch, staring right at us.

            If you’d like to see that the strata do in fact match between head and body, once head-tip is taken into consideration, then take a look at Part 6 on the stretch blog, also Part 20. Apologies for the faded dots in Part 6. I’ll be doing a post on these weird head strata soon. I’m still not convinced I’ve nailed the fine details yet. Meanwhile, Part 26 is out and it’s starting to address all these head lobe strata issues including the introduction of the V-shapes.

            If you like my ideas it means stretch theory support has just rocketed up by 50%. Welcome to the club of three, but remember also that Marco had the idea that underpins stretch theory long before I did: spin-up via asymmetrical outgassing causing stretch (as opposed to simple fragmentation). He was writing about it on his blog, for comets in general, and long before Rosetta arrived at 67P. I alighted on the idea of a Roche pass at Jupiter causing stretch as being the possible mechanism for 67P. I did so independently of Marco and much later than him, i.e. a few days after 67P’s arrival.

            I think your description of Bulldozer Pass fits what I thought.

            Incidentally, Part 11 cites 22 “flaming hoops” that the CB theorists have to jump through. I believe I said there would be “several more” to come. That was 15 Parts ago. I think there must be about 44 hoops now!

          • Ramcomet says:

            Sorry, I should have said Contact Binary theory, not accumulation theory. My amatuer status bad!

          • Marco says:

            Gerald,
            The only reason we are enthusiastic about stretch theory IS the evidence. The fact that it is routinely dismissed by professional scientists as yourself, and via appeals to the authority of experts such as H Sierks, will make it all the more special when speculation and wishful thinking is resolved later in the mission.

            Stretch theory is eminently falsifiable, so we should see incontrovertible evidence via close ups towards the end of the mission.

          • Gerald says:

            Hi Marco, you’ll need more convincing mechanisms to get considered “Stretch” somehow.
            Not intending to make unjustified hope, but just for fun:
            What about finely dispersed supervolatiles with a sublimation temperature of, say 20 to 30 K at about 1 Pa, trapped within the nucleus.
            That’s a reasonable temperature assumption for the deep interior of the nucleus.
            Assuming some of the sublimated supervolatiles can’t escape, they’ll excert an internal pressure to the nucleus and expand the surrounding matrix, provided it’s sufficiently soft.
            Take some of the observed fractures and the high porosity as some evidence for the expansion.
            This mechansim would disrupt the comet less likely than a high spin-up.
            I don’t think, that this mechnism is relevant on a global scale, but restricted to the (fringe) stretch idea, it might be an a little more plausible mechanism.

          • Gerald says:

            Marco, … think of 67P as kind of a muffin to get a remotely plausible mechanism for expansion, to play devil’s advocate.

          • Marco says:

            Hi Gerald,
            The mechanisms for stretch are completely constrained by the evidence. The “matching point” evidence both proves stretch and informs the narrative of how it works. Anything but the model with a 50meter heat conducting, pressure holding crust, with plentiful hydrocarbon liquids under the crust in some way cannot be reconciled with the data that demonstrates stretch.

          • logan says:

            Yet another scenario is combo of both:

            Still within a forming environment two big objects crushed [personal ‘pet’ model at this time].

            …………..

            Would say that Gerald knows enough of scientists’ ways of mind, as to comment something contrary. Nowadays, experience seems to bring speed to selective process of ‘pet’ models.

            As for us science fans, the speed is more related to the small formal ‘science framing’, only a few of the competing models could ‘snap’ in.

            Modeling diversity is born in the middle.

        • Marco says:

          Hi Ramcomet

          Yes. A little disappointing that Holger failed to address stretch at all, but very exciting to see Emily ask the question! I am sure that if Bibring was asked the same question, he would have addressed it.
          Great Hangout Emily!

    • A.Cooper says:

      Two of the abstracts in the newly published slew of papers mention that transport processes of dust and rock debris are evident from Philae’s photos. Rotation plane drift, as described in my last comment, is a very likely candidate mechanism, based on the photographic evidence, both from Philae and the NAVCAM.

      This concept of detritus being caught as it drifted backwards down the rotation plane is nicely illustrated in this photo of Nut and its environs.

      http://imagearchives.esac.esa.int/picture.php?/10415/category/67

      This view is looking down on the head lobe. Nut is the area of highest rock detritus concentration below the white plain and extending in a slightly wavy line towards the bottom left. This would be ‘above’ the white plain if we were looking at the upright duck.

      Most slopes here are facing notionally east or west. The rotation plane runs roughly from top left (west) to bottom right (east) and the direction of rotation is towards the bottom right. The east-facing slopes are generally slightly more shadowed and facing bottom right.

      All the detritus is on the east-facing slopes and there’s practically none on the west-facing slopes. As these slopes rotated eastwards, they acted like butterfly nets, catching the rocks coming backwards down the rotation plane. The concentration of detritus is proportional to the inclination of the slope.

      Nut has the steepest slope which is why it’s caught the most rocks. This could be verified using the gravitational slope map in conjunction with rock-counting. The thinner, wavy area of Nut caught slightly less detritus because it’s slightly less sloped, or upturned, towards the east but it has still caught far more than the west-facing slopes or the dips between east- and west-facing. Other slightly east-facing slopes that are dotted about have a modest sprinkling of rocks too. One obvious one is the gentle dip to the left (south) of the white plain and two more very small patches beyond that. There’s another small area of rocks just beyond the main strip that is Nut (towards bottom right/east of Nut). And a few more subtler ones along the cliff edge at the bottom.

      Nut is thought to be an eroded depression which is full of rocks from the erosion process. This is why it’s been given its own region name. The so-called depression is actually a signature of the head lobe stretching before being torn from the body. It then ‘filled’ with rocks via the process described above because it happened to be sticking up and travelling eastwards into the cloud of suborbital debris. That’s why the rocks are sitting on what is a predominantly dusty surface as opposed to the eroded scree slope you would expect in an eroded depression.

    • Gerald says:

      Although spin changes are physically possible, it would be interesting to get some data about actual spin changes of 67P, including changes of the rotational axis.
      This doesn’t mean, that I’m considering “stretch” as plausible. A comet would more likely disrupt at some point by spin-up.
      Rockfalls triggered either by outbursts or by simple gravitational pull on loose material (disconnected by physical weathering / thermal stress) looks much more plausible than rockfalls as side effects of (centrifugal) “stretch”.

      • Marco says:

        Hi Gerald,
        “spin changes are physically possible???” Spin changes in 67P and other comets are *well documented* to happen. Yes it would be nice to get up to date spin data that we know the mission scientists have at their fingertips, but that is another story. at this stage we can assume that 67P is speeding up again as it must have done at previous perihelion.

        As to your refusal to consider the stretch narrative in toto as implausible, all I can offer is that what the mission scientists are calling mysteries, stretch theory has the narrative and scientific consistency to explain them as expected results from the corollary to stretch. I know that sooner or later you will realise this.
        I am happy for you to look to “debunk” theories like this because theories scientifically resistant to debunking will prove to be true….

        • Gerald says:

          I’m confident, that the Rosetta mission is able to replace much of the speculation and wishfull thinking by evidence within reasonable time.
          At least the “spin” question is closely monitored, as we’ve learned (below).

          • Marco says:

            Gerald,
            Mechanisms stabilising the rotational axis all appear to be wishful thinking at first glance, since a rigid exterior appears evident. Damping vortices required are incompatible with current models. In the simplest case of torque free precession, there would be little wishful thinking required, but now that spin up due to asymmetrical outgassing torque has been established both for the past and the present, continuous, ongoing damping vortices are required because there ought to be torque induced precession as well, unless the jets are magically balanced.
            I am suggesting that internal liquids (already with several distinct arguments of mine in their favour separately) is the *least* speculative explanation for spin stabilisation.

        • Marco says:

          Hi Gerald,
          Is there any reason why the rotational axis would not be precessing/evolving? It would be very strange if the thrust forces lined up perfectly just by chance. Would internal liquids (theoretically) stabilise the rotation axis?

          • Gerald says:

            Hi Marco, yes, internal liquids would stabilize the axis (reduce torque-free precession).
            https://en.wikipedia.org/wiki/Precession#Torque-free
            Any deviation from the ridgid body model would do so.
            I agree, that rotation around just one axis for such a highly asymmetric object is a little surprising.
            For computer simulations they’ve used this simplified model. So the last word about actual axis precession is maybe not yet said.

            But on the current state of knowledge I’d accept the lack of significant precession as a vague evidence for your liquid idea, not as a proof, since there could exist other mechanisms stabilizing the axis, e.g. mobile solid objects in the interior.

          • Gerald says:

            … We’ve seen the recent outburst. I’d consider this as only possible with a cavern storing sublimated ices as a gas.
            Such caverns may also contain dust, since ice can be assumed to be mixed with non-volatiles.
            These interior (and probably some of the surface) dust deposits are likely not strictly ridgid, and would contribute to a reduction of the torque-free precession.

            The overpressure in these cavities, on the other hand, might allow some substances to get into the liquid phase. But to act as a liquid the substances need to be sufficiently clean and abundant not to adhere to surrounding solids.

          • Marco says:

            Hi Gerald,

            With stretch theory, the conclusion is that it cannot happen without billions of litres of liquid flowing under a solid surface, heated and partially pressure sealed by the conductive, low porosity crust.
            The recent outburst could also be explained by a breach exposing the pressurised liquid to the vacuum, which quickly was also sealed up by more viscous liquids hardening through evaporation.

          • Gerald says:

            Hi Marco, internal liquids under pressure would have undergone a “vapor explosion”, like a superheated liquid. This would have been hard to seal.
            Instead large amounts of liquids would have been blown out of the comet’s interior.

            If you ever superheated water in a test-tube, you know what I’m talking of. Never point the open end of a test-tube to people, including yourself.

            https://en.wikipedia.org/wiki/Boiling_liquid_expanding_vapor_explosion#BLEVEs_without_chemical_reactions

          • Ramcomet says:

            As Logan suggests on 08.08.15, movements and waves of dust and boulders ala “lakreitz”, or as retrograde post slab ejection boulder deposits ala A. Cooper, in my mind may act as a magnitudes stronger stabilization effect than internal liquids explained by larger “leverage” effects, being farther from the spinning CG, CM, CE, whatever. Just a thought, though it’s never the “One Thing” Eighties band NXS would have us all believe.

          • Marco says:

            Hi Gerald, re: internal liquids under pressure would have undergone a “vapor explosion”,

            Precisely – but I have repeatedly stated that I am talking about a complex mix of hydrocarbon mud into a cold vacuum; not very similar to pure superheated fluids into atmospheric pressure as the examples on Wikipedia are.

            However; this mechanism can explain catastrophic outbursts such as that of Comet Holmes, for example.

            Being on Anuket, the particular outburst we are talking about would have been caused by a crack opening up temporarily due to continuing stretch. Liquids in the neck have mainly migrated to the lobes, helped both by the gravity of the lobe it is closest to, and corriolis effects. Thus there was limited amounts of more volatile liquid species in the BLEVE explosion.

          • Gerald says:

            Hi Marco,
            with the complex mix of hydrocarbons you wouldn’t get the vortices you’re suggesting, since such a mix would be viscous. Vortices don’t form in viscous liquids.
            https://en.wikipedia.org/wiki/Vortex

            You need to adjust something, or consider that you’re going to run into a contradiction.

          • Marco says:

            Hi Gerald,
            You are confusing me now. In one comment you say that any deviation from a rigid body model would stabilise the axis (as it explains in the Wikipedia article you linked to).
            The same Wikipedia article states that it is the action of vortices which stabilises the axis. It is obvious by the way the article is written that “vortices” that stabilise a spin axis
            are not necessarily vortices in the strict sense of the definition you linked to In the last comment you made. Otherwise the first comment you made would be incorrect. I see a contradiction here but it isn’t me.
            Non-rigidity in the sense of a stretching body with sloshing internal hydrocarbon liquids would stabilise the axis, I think the science would show.

          • Gerald says:

            Hi Marco, I agree, that the Wikipedia article about torque-free precession should be improved at that point.
            Adding “internal stresses” instead of vortices as the only mechanism would be more appropriate.
            See
            http://www.worldcat.org/title/planetary-sciences/oclc/437299197
            Planetary sciences
            Imke De Pater; Jack Jonathan Lissauer
            New York : Cambridge University Press, 2010.
            page 393

            “The damping timescale depends upon density, radius, ridgidity of the body, a shape-dependent factor, the ratio of energy contained in the internal oscillations to that lost per cycle, and the rotational frequency.”

        • Marco says:

          Hi Gerald, you suggested:

          “What about finely dispersed supervolatiles with a sublimation temperature of, say 20 to 30 K at about 1 Pa, trapped within the nucleus.
          That’s a reasonable temperature assumption for the deep interior of the nucleus.”

          As it stands, we do not have any direct evidence of what the temperature is in the deep interior of the nucleus. A temperature of 20 to 30 K would, at this point, completely disprove stretch theory, but since an internal thermometer is not within reasonable expectations, speculation about the internal temperature is not a useful talking point, as we will not be able to agree on what a reasonable temperature assumption would be.

          There will be measurements that will be as relevant, however.

          1)Measurements of the distance between body and lobe

          2) Measurements of erosion or lack thereof, especially in zones which got a good closeup view AND are expected to show significant erosion.

          Ongoing stretch evidence via 1) should be a clear signal to start taking me and A Coopers evidence seriously.
          And an overall lack of erosion via 2) will demonstrate our points that the outgassing is originating from deep inside, and there is neither direct erosion, nor collapse due to near subsurface sublimation, and that the surface can therefore retain evidence of shear pre-stretch from matching, uneroded points.

          At the neck zone, neck stretch may at first sight also make the neck thinner (ie interpreted as erosion), but would be easily proven as stretch at that point.

          • Gerald says:

            Hi Marco, that’s clear criteria. I’m sure this will be clearly resolved within less than a year.
            My bet is on unambiguous evidence for erosion (new pits, larger old pits, outburst ejecta, rockfalls, changed regolith deposits, sublimated surface ice deposits), and only small other global shape changes, e.g. by thermal stress, by torque due to sublimation, or by spin changes, might be some “muffin” effect, i.e. local surface lifting without subsequent collapse.

          • Marco says:

            Hi Gerald, you quote :
            “The damping timescale depends upon density, radius, ridgidity of the body, a shape-dependent factor, the ratio of energy contained in the internal oscillations to that lost per cycle, and the rotational frequency.”

            I think you are trying to convince yourself that non rigidity required is covered by conventional thought on cometary processes.

            It is like seeing a spinning top that is not precessing, you tap the side of it to induce some precession, and it automatically damps the induced precession. It is just a non-rigid top, you would say.

            In what way can a non-rigid spinning top passively dampen torque free precession?

            We need to explain how the damping is absorbing energy while also obeying all the laws of physics (such as conservation of momentum) One way is stretching – As it stretches, precession energy is absorbed and the comet rotation slows down slightly. Another way is with vortices in internal liquids. Remember the spin will be given a kick by the asymmetrical outgassing. The process of damping needs to be ongoing. Random collapses or movements of dust in voids will not do that.

          • Gerald says:

            Hi Marco, the damping of 67P is likely to be high due to the non-spherical shape and the soft interior. the soft interior allows for the needed non-ridgidity and the damping of internal stress. The already estimated porosity points towards a soft interior.
            Inference of the more precise properties by observation of the damping is beyond my means, but I’d guess, that sooner or later someone will investigate this in detail and write a paper. That’s a lot of work, including theory, data analysis and best-fit computer models.
            But I don’t see a need to question the established way of thinking.

          • Marco says:

            Hi Gerald,
            I hadn’t heard any mission scientists talk about a soft interior. It had only been talked about in this blog in the context of a soft interior being a requirement for stretch.
            It doesn’t sound like the conventional way of thinking, unless you mean conventional thinking is about vague hand waving any contradictory observations away, rather than making concrete scientific suggestions in advance of the formal calculations.

          • Gerald says:

            “The crust is made of crystalline ice, while the interior is colder and more porous. The organics are like a final layer of chocolate on top.”

            “Researchers already knew that comets have soft interiors and seemingly hard crusts.”

            Source:
            http://rosetta.jpl.nasa.gov/news/why-comets-are-deep-fried-ice-cream

      • A.Cooper says:

        Gerald

        I’m looking at rotation plane change in my next post. There’s circumstantial evidence of where it used to be.

      • Booth says:

        Gerald!

        For your dining and dancing pleasure, Sir …

        Observations reported by Keller et al (2015) indicate that 67P’s rotation has slowed between the Aug 2014 rendezvous at 3.7 AU and the middle of April by ~80 seconds. They expect this situation to reverse post-perihelion. During the reported time interval there has been no observed impact on the axis of rotation.

        Post script – to avoid broken links twenty years into the future …
        Keller et al; “The Changing Rotation Period of Comet 67P/Churyumov-Gerasimenko Controlled by its Activity” Astronomy&Astrophysics 579; 2015

  • Ramcomet says:

    Maybe NASA’s Asteroid Redirect Mission (ARM), to snare an asteroid boulder and put it in orbit around the moon, can and should be “redirected” to snare both Philae and a chunk of Comet 67P when it comes back around in… 6.44 years!

    THE TIMING ON BOTH IS, QUITE FRANKLY… PERFECT!

  • masanori says:

    Excellent Job Philae!!!

    I have believed in the amount of discoveries from Philae’s FSS since I first heard that Philae’s all instruments looked survived the 10 year journey & the landings. But still so exciting to see these results!! Congratulations!! And I’m still hoping there will be chances for SD2 to do crucial works, along with other instruments.

    As by now I have come to suspect that Philae has been & is moving (even during FSS???), on or off the surface, my latest biggest wish is that Philae does not come in the sunshine for too long per comet day. 5th touchdown is OK if Philae can survive the heat, so that sooner or later there can be more contacts between Rosetta and Philae. Hope Philae can be operational until November like CNES’s Monsieur Philippe Gaudon said in https://rosetta.cnes.fr/fr/plus-dinformations-sur-les-20-minutes-de-contact-du-9-juillet

    • Peter says:

      Were there no attempts to repeat the exact conditions of july 9th (except distance), referring to the contact of july 9th described in the link.

  • ianw16 says:

    Wow. 75-85% porosity. Must be pumice. How could that be blasted off a planet and remain intact? Wonders will never cease 🙂

  • ianw16 says:

    It’s a big pity that the results from humanity’s first robotic landing on a comet has been deemed necessary to be put behind a paywall.

  • logan says:

    Speculation being that capillarity effects was very well present at landing. Coloring, shining and surface collapsing suggest this. Showing the ‘shining’ up to surface is an accident. More common is just to effect patterned depressions. Ice providing the humidity being the remnant ‘trapped on flight’ during last cooling phase. Betting Agilkia’s immediate surface is a lot drier at this moment.

  • logan says:

    That could be a very pragmatic definition of primary ‘cometary’ materials: Those ones still not subject to capillary forces. [Most of it very old and still not subject].

  • logan says:

    Would like ‘pristine’ attribute to be reserved to ‘dandelion’ order of magnitude densities. [Very few material there, at 67P].

  • logan says:

    Talking of a so dynamic process that could not believe now on bringing back samples.

    What Earth labs would be studying would be -structurally- alien to the sample originally taken.

    • Ramcomet says:

      Hi Logan,
      Always enjoy deciphering your poetic, even Haiku observations!
      New Horizons is the fastest Spacecraft ever launched, at something over 36,000 mph, but then it got a 9,000 mph boost to 45,000+ mph by slingshottimg around Jupiter to flyby Pluto and its moons in a somewhat (10 years!) reasonable timeframe. It weighed only around 153 kilos. Power to weight ration is implicit in the idea of catching 67P again on its return orbit around the sun.
      Imagine now, the new SES rocket, several magnitudes more thrust, in fact, the most powerful booster in history, surpassing the mighty Saturn V. A purpose built lightweight Philae retrieval craft, and an immense retrorocket platform capable of braking from, say, 50,000 mph to just the 30,000 that 67p is travelling, picking up Philae plus samples not so far from Earth and delivering it back home to the ISS.
      Whether the sample would be structurally alien to the original sample taken, I don’t know why not as near zero g for maintaining fluffiness, but, provided Philae carried out numerous more activities and photos stored on board, that could not be relayed to Rosetta, but could be downloaded on ISS, again, then why not?
      Maybe much better then Obama’s plan to share some asteroid boulders and put them up n orbit around the moon as some kind of circus trick to, um, prepare us to go to Mars???
      ESA’s sheer bravado and success with Rosetta/Philae begs for even more audacity from NASA. let’s build on each other’s accomplishments.

      • logan says:

        Medical science too primitive, space wise. Humans as a cosmic tribe is the ultimate aim of space exploration.

      • logan says:

        Hi RamComet: Agree in the priority of studying ‘sintered’ objects.

        On the other side, think was NASA’s Bolden who said that Over writings in Strategy cost years of diminished productivity.

        Having great hopes in the new ‘fast-track’ missions.

  • logan says:

    Waves on a particulate layer are quite feasible. All needed is a minimal viscous behavior and a change in slope.

    Changes in slope are due to many causes.

    After a year of everyone’s ideas, coming back to the original blog’s model of lakritz.

    This particular photo

    http://media.eurekalert.org/multimedia_prod/pub/web/96292_web.jpg

    With something resembling a ‘rolling’ of particulate at the top of Hatmehit hills. Following the model of the Imhotep paper, down there could be ‘draining’ flows.

    Also the big boulders at the top of the big central wave suggest a spin in the flow of the particulate. All of the flow at the central plains of Hatmehit exhibit a certain ‘swirling’. [talking of particulate derive].

  • Jordan says:

    Amazing! It’s great seeing how much modern technology is allowing us to learn about space. Thanks for sharing this!

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