CometWatch 30 November

This four image montage comprises images taken with Rosetta’s NAVCAM on 30 November from a distance of 30.2 km from the centre of Comet 67P/Churyumov-Gerasimenko. The image resolution is 2.6 m/pixel and each original 1024 x 1024 pixel frame measures just over 2.6 km across.

Four image NAVCAM montage comprising images taken on 30 November 2014. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Four image NAVCAM montage comprising images taken on 30 November 2014. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

In this orientation, the smaller of the two comet lobes is in the lower left of the montage, with the larger lobe occupying the upper frames as well as the lower right frame, albeit mostly cast in shadow.

The view affords a particularly nice view down onto the ‘neck’ region of the comet, where low plateaus of material with layered walls appear to rise from the smoother material that surrounds them. Similarly, some of the boulder-like features seen in the foreground of the scene have the appearance of being exposed from the underlying surface, partially covered by the finer-grained material.

In the far left of the lower left frame, this fine-grained material appears to have been shaped into a beautiful rippled pattern; perhaps as result of the underlying topography and/or due to differences in erosion by sublimation across the surface.

Due to rotation and translation of the comet during the image-taking sequence, it is again difficult to make an accurate mosaic of this set. Evidence for this can be seen in the neck region, where the shadows and fraction of the boulder field visible have clearly changed between the first (lower-left) and last (lower-right) images.

Also, stretching the contrast reveals some details in the shadowed regions, as well as some fine jet-like structures from the upper limb of the main body. But at high contrast, internal scattering in the NAVCAM optics also becomes apparent, in the form of large-scale diffuse blobs. These also make it difficult to mosaic well.
ESA_Rosetta_NAVCAM_141130_AESA_Rosetta_NAVCAM_141130_BESA_Rosetta_NAVCAM_141130_CESA_Rosetta_NAVCAM_141130_D

Comments

60 Comments

  • THOMAS says:

    The main jetting activity is again clearly focused on the boulder-field in the neck region.

  • Matthew Gray says:

    To be a Cometomorphologist - what a grand profession. I am envious. I suppose there is no chance of ramming the comet with the orbiter, or just giving it enough of a nudge to maybe bounce Philae back into the sunshine?

    • Maurice Childs says:

      The comet is about 3,000,000,000 times the mass of the Rosetta orbiter, nudging it would have no discernible effect although it would undoubtedly destroy the orbiter.

  • Bruce says:

    I'm beginning to suspect that most of the volatile material is located in the neck region of the comet. Firstly, most of the jets seem to emanate from there. Secondly, the comet has been subjected to several freeze-thaw cycles. Material that finds intself in a lquid state, due to some overpressure preventing it sublimating, will tend to migrate through the porous structure to the centre of gravity - which is in the neck region.

  • Dave says:

    The large trumpet on the upper left, with the rubble just inside it looks like it was once a source of jet of some sort.

    Could it be that there is more than one erosion mechanism on the comet?
    The jets coming from the neck on previous pictures seem to be coming from flat dust free areas.
    This trumpet however if it ever was a jet looks like something completely different. We have seen it several times before but as yet not in action.

  • lucas says:

    Hmm I wonder about this sublimation thing. How is it possible? There only rocks there, no ice, nothing to sublimate and the comet it self is, from what I've read on esa sites, is black like coal. Are there any confirment of water ice on the comet? Or are there only OH particles?

    • Ross says:

      No water ice detected anywhere on the surface. In fact, surface ice is rarely detected on comet surfaces. Both OH and water have been detected in the coma, therefore scientists assume the water must have come from the interior of the comet. Unfortunately, no other mechanism is investigated though water and hydroxyl have been formed on the moon due to hydrogen bombardment of the silicate surface via interaction with the solar wind.

    • Bruce says:

      Hi Lucas,
      Sublimation is just a phase transition.
      https://en.wikipedia.org/wiki/Phase_transition
      Sublimation is a direct solid to gas transition (deposition is the reverse). When the external pressure is too low to support a liquid state (eg. in a vacuum), solids will sublime directly into the gaseous state. In theory this happens to all substances at all temperatures above absolute zero. In practice it is incredibly slow for refractory (eg. rocky) materials. Substances that sublime at a noticeable rate are called volatiles, and include water, carbon dioxide, and ammonia.
      In the cool outer solar system, volatiles on the surface of a comet in the vacuum of space will preferentailly sublime leaving dusty material (carbon and rock) in their place.
      As the surface of the comet gets hotter near the Sun the interior ices will be heated as well and generate higher vapour pressures - through sublimation initially, but if the inetrnal pressure is great enough they may melt and boil as well. Eventually this pressure will force gaps in the overlying surface material and the volatiles will "jet" out into space.

      • THOMAS says:

        Hi Bruce.

        We are talking of temperatures which, even at perihelion, will *never* exceed -60°C (i.e the average temperature reigning in the middle of the Antarctic on Earth).

        So what sort of standard "heating" mechanism could allow "melting" (= transition from ice to liquid water) and "boiling" (= transition from liquid water to water vapour) to take place at all on 67P (and on all other comets) and, more importantly, at such extremely "hot" temperatures that the resulting internal pressure could eject those dead-straight jets of dust for over a kilometre into space, despite the rotation of the comet?

        • Bruce says:

          Hi Thomas,
          On 9 August temperatiures as high as 230K (-43 Celcius) were recorded on the surface of 67P.
          http://blogs.esa.int/rosetta/2014/09/08/virtis-maps-comet-hot-spots/
          My guess is that it was about 3 AU from the Sun at the time. perihlion is 1.25 AU. Using the inverse square law that would be nearly 6 times as much sunlight, so I'd expect surface hot spots well above 0 Celcius, although maybe not above 100 Celcius. Remember parts of 67P are pure black and constantly exposed to sunlight. They will absorb all the radiation from the Sun all day, every-day.

          As for vapour pressure. Consider water, ammonia and carbon dioxide, likely volatiles. It doesn't matter (much) if they boil or sublimate the equilibrium vapou pressure is essentially the same. CO2 has a vapour presusre of 1 atmosphere (air pressure at sea level) at -78 Celcius; ammonia at -34 Celcius and water at 100 Celcius.

          Will CO2 gas escape 67P? If we assume CO2 behaves as an ideal gas at 230K, I estimate the roort mean square velocity of the molecules is 11.4 metres/sec, well above the 1 m/s escape velocity of 67P.
          http://en.wikipedia.org/wiki/Root-mean-square_speed

          We can't use the kinetic theory of gases for water - it is highly non-ideal at this temperature, but what about water? Well 1 atmosphere pressure is actually quite substantial. A 20 kg child lying on an inflatable matress (assume body contact area of 0.2 square metres), will put the air inside under a pressure of about 1 kPa or 1% of an atmosphre (101.3 kPA). Pull the stopper and the air is coming out at that pressure. Water has a vapour pressure of 1 kPa at about 7 Celcius. At 230 K (-43 Celcius) water has a saturated vapour pressure over ice (it differs for water) of about 14 Pascals (0.014 kPa), or a bit more than 0.01% of an atmosphere. True this is low, and it is likely water pressure will become more important closer to perihelion.

        • Marco says:

          Bruce, to play devils advocate, there are several issues with your analysis. Firstly, at the point where you say the temperatures are sufficient, at the surface, is where Rosetta data is saying there is no ice of any volatile. Rosetta data also appears to show that the surface material is insulating, so that subsurface temperatures where some volatiles may lie are considerably lower - possibly too low to account for the level of out gassing. Thirdly, the "collimated jets" that we observe require a much higher surface velocity than the escape velocity. Estimated required gas velocity is supersonic.
          A solar-thermal sublimation model requires the conduction of thermal energy down to where the volatiles reside, and chambers there to account for the build up of pressure and mixing with dust, and nozzles so that the pressure can induce enough gas velocity to display the observed collimated jets.
          In which case, if we have these higher temperatures and pressures within the skin of the comet, many volatiles including water may reach their triple point and become liquid, falsifying sublimation models anyway.

          • Bruce says:

            Hi Marco,
            I don't believe it's important whether the jets are produced by sublimation or via a two-stage melting-evaporation process. The fact that the jets are strongest in the neck near the centre of gravity suggests to me that much of the volatile material has been through a liquid phase and migrated there anyway. So to me triple points are not important. I have not seen any reference to gas velocities, but I don't see why collimation requires that they be high.

            Insulation is never absolute and parts of the comet are almost continuously exposed to sunlight. Heat WILL conduct into the interior. The jets are one way it dissipates heat. We can estimate the maximum possible temperature of a perfectly black insulating surface perpendicular to the Sun using the Stefan-Boltzmann Law. At 1 AU solar radiation is 1370 Watts/metre^2. Using the inverse square law this is 1370*(1/3)^2 = 152 W/m^2 at 3 AU. A black-body insulator perpendicular to this must radiate this heat back to space. The temperature will be the fourth root of the intensity divided by the Stefan Boltzmann constant or (152/5.67E-8)^0.25 = 228 Kelvin, very close to the maximum measured by VIRTUS on 9 August which was 230K. At perihelion (1.25 AU) we would expect a maximum of (1370*(1/1.25)^2/5.67E-8)^0.25 = 353 K (about 80 Celcius).

            Now parts of the comet exposed to continuous sunlight that are not perfect insulators will not get quite this hot, but will instead conduct heat to the interior. Cavities close to the surface will reach temperatures close to these over time - the distances involved are not large and some parts are in continuous sunlight..

            I am not surprised there are no volatiles on the surface itself. They would have been rapidly lost by sublimation the first time the comet got anywhere near the Sun.

          • Marco says:

            The importance of "triple points" are that liquids will not stay near the surface of a "porous" material, and will refreeze further away from sunlight. In a previous post/comment/link, there was discussed how fast gas and micron sized dust would need to travel for jets to show straight lines into space that they do. Supersonic speeds required is the tentative scientific conclusion. Thus, small nozzles, high pressures and mixing of gas and dust subsurface. It all gets quite complex and away from direct thermal effects, as energy transfers more complex than conduction are indicated. At any rate, we cannot see anything under the surface directly, but it takes, I think, a vivid imagination to believe that it is a simple logical, thermal process.

  • Gerald says:

    Some grains look like short lines. Are exposure times available? They would tell something about the angular velocity of the dust grains relative to the camera.

  • Ian C says:

    Another stunning image from Rosetta. I'm intrigued by the profile of the "horizon" at the bottom left. It looks as though the region is populated by Butte Mesa type formations, though I guess it could just be the way the light is catching the peaks. I wonder what the creation mechanism would be?

  • WPaul63 says:

    What are the main erosive forces at work on the surface, besides the obvious ones? I'm thinking about micro-impacts with cosmic dust, for example. Would this erode the surface homogeneously or would it somehow be "path dependent"?

  • Steven says:

    The neck area between the two lobes would be the location with the most gravitational heating, which could provide the energy to drive jetting.

  • Sovereign Slave says:

    While we’re waiting on more science data, I wanted to discuss the three things that we do know as indisputable fact according to ESA findings.

    1). Perhaps the most significant indisputable fact that ESA has announced about P67 is that there is no surface ice. This was totally unexpected and something of a game changer in that all sublimation now HAS to be explained as coming from below the surface of the comet since the surface is completely dry (and actually looks just like a dusty rockball, not a dirty snowball). There has been a great deal of speculation on what the interior of the comet is composed of, but there has been no dispute that the sublimation must originate in the interior of the comet and not from its surface. So to frame the argument, for the standard model to hold true, all sublimation must now come from underneath the comet’s surface, so obviously the interior needs to be composed of frozen volatiles of some kind and not rock. According to electric universe, all removal of materials into the coma only comes from the surface through electrical processes and is not dependent on what is inside the comet. So based on what we know about the surface of the comet regarding this one point, burden of proof is on standard model since EU doesn’t need anything else but surface material to explain itself.

    2). The second fact that ESA has declared is that the color of the comet is pitch black (darker than charcoal I think was the phrase). There are only two possibilities for this. Either black is the comet’s native color, or some process has turned it black. I may be wrong, but I don’t think anyone is arguing that black is the comet’s native color, but if you are arguing this, feel free to pipe up below. Otherwise, the comet was turned completely black by some kind of process. So the question becomes, what processes turn organic materials black in a vacuum? The ones I’m familiar with that absolutely do turn things black are fire of course, and electrical discharge. There are no doubt others, perhaps oxidization and such, but whatever else is proposed needs to work in a vacuum, which eliminates fire. Again, please feel free to suggest others. Two things that I don’t believe cause organics to turn black are sublimation (unless someone has evidence to the contrary), and it doesn’t appear that radiation or heat from the sun does either. Otherwise, the moon would be black, and all other moons/bodies much nearer the sun without atmospheres that are constantly bathed in the sun’s radiation would be black also (P67 never gets as close to the sun as our earth is). So, besides electricity, not sure what is left, but again, feel free to pipe up.

    3). P67 has formed a coma (by whatever means) much of which, by the visual evidence such as this picture http://blogs.esa.int/rosetta/2014/10/23/comet-activity-is-on-the-increase/, is sublimating/removing materials in “columns” (and no, Professor Rutt, I don’t have a mathematical formula to prove this, but did the tree REALLY fall in the forest if a mathematician didn’t come up with a formula proving it, or better yet, without a mathematical formula, did the bear REALLY shi…never mind). The columns are visually self evident, and by rough calculation, I’d say are at the very least a kilometer long. So let’s first consider sublimation. We’ve all seen it happen with dry ice. The ice turns into gas, which then does what? It IMMEDIATELY dissipates. It’s a GAS. What do gases do, whether they’re in an atmosphere or a vacuum? They dissipate. And no, I’m sorry, but it’s completely farfetched to say that some pressure and a cometary vent could shoot a uniform column of gas over a kilometer long. I’ve watched videos of thrusters fire in space. The ejecta from the nozzle holds together in a column for a number of yards at best (and it’s dissipating as it does so), but not anything even approaching a fraction of a kilometer. And even if a comet could “shoot” gas in space, I can’t imagine that a comet can shoot gas at anything close to the force of a thruster, or through an opening as precise as a thruster nozzle. In a word, a comet thrusting gas in a column for over a kilometer (or even a few yards) is impossible. But even if it were possible, wouldn’t all that thrust be constantly affecting the direction of the comet, pushing it this way and that?

    According to EU theory, instead of the gases being “pushed” into space, cometary material is being lifted off the comet by electrical processes and “pulled” into space, and these same electrical processes organize the materials into long columns. These proposed electrical processes are well documented and have already been discussed in this blog. There is no question that electrical machining exits, or Birkeland currents, etc, the question is whether these and other electrical processes account for what we currently know about P67. For me at least, EU is a more realistic approach to explaining what we know right now, while on the other hand sublimation just doesn’t seem to hold water, so to speak.

    • Kamal Lodaya says:

      Sovereign slave: "...but it’s completely farfetched to say that some pressure and a cometary vent could shoot a uniform column of gas over a kilometer long...
      According to EU theory, instead of the gases being “pushed” into space, cometary material is being lifted off the comet by electrical processes and “pulled” into space, and these same electrical processes organize the materials into long columns. "

      And why would that happen? I mean, having an inscrutable Being sitting there would account for most things.

    • Jacob Nielsen says:

      "Otherwise, the moon would be black"
      And as everyone knows, the moon is yellow as cheese...Now if you care to, dig a little further.

    • Marco says:

      1) The interior could be anything that generates water gas and CO2 among other gases and dust. Could be evaporation, sublimation, or respiratiion. Sublimation and mysterious electrical processes have little direct evidence, so the source is up for grabs, as it were.

      2) Living processes create black organics - just look at crude oil or coal - very black. Doesn't necessarily have to happen on the surface of the comet.

      3) It is obvious that the lines are from dust particles being jetted out with the gases/vapours. The jets do appear to affect the rotation. Obviously a lot of mass of eject a is required to modify such a large mass rotation.

    • PTR says:

      ... who said there was no ice on the comet?
      Assuming the body was originally a more or less homogeneous mix of frozen volatiles (ice) and dust particles, wouldn't one expect that after few passages near the sun, much of the surface ice would sublimate, leaving mostly non volatile substances there? If there is enough carbon involved, radiation and heat will most likely cause some interesting chemical processes to happen, perhaps solidifying and maybe darkening the surface?
      My main problem with the idea you present is that rosetta is there. How would they orbit a much more massive "asteroid" type body successfully, without noticing a difference? How would rosetta's sensitive magnetic field sensors find no clue of 67P's eneormous electrical charge according to the EU theory? They must be extremely lucky. All the unknown effects just happen to match.
      I'm sure there is very much going on we don't understand yet (That's the whole point of the mission, isn't it?), and that the results will raise even more questions. I'm also pretty sure the EU theory isn't the answer.

      • Jon says:

        Re: albedo and passages around the sun, do we know yet what the albedo of the pristine comet Siding Spring is yet? Anyone?

        • Marco says:

          Hi Jon, they really don't know yet. First impressions are that albedo is much higher, but since the instruments are not designed for the purpose, some detailed science is required before this can be confirmed. There still is the doubt that the bright areas near the nucleus may be drowning out the light of the nucleus, rather than being a bright nucleus and that sort of thing. I suggest it will take months and years to draw together disparate bits of information into a verifiable conclusion.

      • originalJohn says:

        PTR, why assume it was originally a more or less homogeneous mix of frozen volatiles and dust particles. That is just an idea that has never been demonstrated.

        Also why assume that the nucleus exhibits no magnetic or electrical properties. No such measurements or results have yet been disclosed but I think you can certainly assume that the ESA do by now have some information about those properties which for some reason they are reticent about sharing with us.

        • PTR says:

          I was just referring to the general "dirty snowball" model, trying to say that the appearance if the comet surface is not necessarily inconsistent with a nucleus consisting of some mix of ices and dust particles/solid material. As I wrote, it's an assumption - based on what would likely be the result of material aggregating in a dust/gas cloud (also an assumption of course).
          As to electrical/magnetic properties we have the ROMAP and RPC magnetometer data that were referred to in this blog. If the findings were radically surprising, I guess someone would have mentioned it by now.
          I understand that scientists are reluctant to publish raw data before they had some time to work with it. To insinuate they'd hide something from the public, that we're not supposed to know is a bit too much "youtube science" for me.

          • originalJohn says:

            Oh good, PTR, so we can safely assume that should any results happen to contradict the often repeated ice and dust theory of comets they would be enthusiastically presented at the earliest opportunity, particularly as they would constitute a major advancement of knowledge.

          • THOMAS says:

            It happened in so-called "climate science" five years back, as the infamous Climategate "hide the decline" et al. emails attest.

            I sincerely hope we will not witness the same sort of attempted cover-up with the Rosetta/Philae data.

            The stakes are high!

  • Birgit Hofmann says:

    Wild beauty with "charisma "..
    And when we see them again osiris-images ?
    I will seek little philae !

  • Jacob Nielsen says:

    your point #3: Read this: http://www.lpl.arizona.edu/~yelle/eprints/Yelle04a.pdf

    I think one of the essences is this: what we observe is the dust. Dust is carried out at high speed by a gas. The gas soon looses it collimation. The dust particle has a higher inertia and therefore continues its path. some resemblance to firing a shotgun.

    • Dave says:

      Even a shot gun discharge spreads out, albeit its in an atmosphere.
      Would you not expect the dust to do the same, esprecially as it does not get like its been rifled down a barrel. The dust would all come off the ground at different angle and would bounce off each other in transit.

      Something has to order these columns, either rifling as it comes out of some vent or nozzle or magnetic fields.

      • Jacob nielsen says:

        Some resemblance. Wouldn't you agree that the gasses from the shotgun spread out a bit more than the shots? Did you read the article?

    • Sovereign Slave says:

      Thanks, read the article. As they state, it was previously believed by cosmetologists that the dust in the coma only came from the surface via sublimation. But then when columns were observed, they needed to then come up with some kind of explanation that fit within the dirty snowball theory, and voila, another ad hoc and farfetched explanation with an incredible amount of assumptions and unsubstantiated guess work. For me the article actually makes the idea of sublimation as being the explanation even more farfetched. According to their own best guesses in the article, to create the columns through sublimation requires a hard crust, and underneath that a chamber with gas that has to be more or less evenly mixed with dust (not sure where the dust came from, it’s just assumed to be there and that’s it has somehow evenly mixed with the gas), below that ice, then ONE opening or vent to the chamber that maintains its shape and size as the gas and dust are blown through it at literally SUPERSONIC exit speeds (768mph - that comes out to 4.5 times the speed of a sand blaster!). If that’s the case, then Rosetta may be in dire danger, because in a vacuum the velocity of all that dust would not slow down, and if it goes through one of those columns, even at 30k out, would no doubt be devastating. Same when Philae danced over the comets surface. Sorry, but I just can’t buy that sublimation could build up enough pressure to shoot dust at those speeds and then stays in such a uniform column. Instead of an article with semi-educated guess work and “modeling,” can you point us to a study demonstrating or proving that sublimating materials can build up those kind of pressures, or some natural process where frozen gas and dust can evenly mix, or that the dust can be shot through a vent at those speeds and stay in a column through sublimation? Surely these conditions could be recreated to some extent in a lab. Don’t know why these guys didn’t go to the lab and recreate similar conditions they’re proposing and measure what happens, as in pursuing some scientific leg work for their “hypothesis.” Because now that’s still all it is, a hypothesis. Anyway, according to prior blog entries, GIADA has captured dust grains, and they should know what the velocity of the dust grains were, though I’ve not found anywhere where they’re reported it. But sooner or later they would have to run across dust traveling over 700mph according to this article.

      • Jacob nielsen says:

        I am not sure, but I think the velocity requirement only goes for the gas, not the particles? I also think math goes a long way in these matters, as far as a laboratory experiment would require the axact same conditions to prove anything, as would the mathematical modeling. Of course it would be more convincing to someone like me to see things performed in materia.

      • Graham Hall says:

        I don't have any difficulty believing that there is ice sublimation taking place generally over the surface AND from cavities /jets. The former would be general and very slow, the latter more localised and dynamic. The escape velocity is quite low and a movie glimpse from the recent "sky at night" episode (UK only) showed a moving stream of particles "apparently" from the neck area moving away from the comet. Ice will sublimate from the surface but it is still very cold. We saw from Phoenix on Mars how ice identified from a scraping sublimated in the following days. The comet is still beyond the orbit of Mars so most of it is sill very cold. Closer to perihelion (next august?) the comet will be heated much more by the sun and water loss will be much greater. however its still marginal given the overall size of the comet which is thought to have been orbiting the sun at its current range for circa 1000 years. So its made circa 160 orbits, that's 160 approaches to the sun getting warmer and the colder again as it journeys out beyond the orbit of Jupiter. We see erosion on earth in rocks where water is present and as it freezes and thaws cracks the rocks due to the expansion of water as it freezes. Could not similar processes be going on the comet. We know its not made of rock, its density is too low. But the dirty snowball model would give you, after quite a few passes around the sun with perhaps a dusty surface from where the ice has sublimated underpinned by a more solid crust made primarily from ice, covering an interior of more fluffy material - but essentially the same.

        67p underwent a considerable and unexpected brightening earlier this year. when it was much further out than it is now. Perhaps part of the crust collapsed under rotational stresses. It couldn't have been due to just solar heating. We'll learn a lot more as Rosetta accompanies the comet for the next couple of years.

        So far Rosetta has identified increasing amounts of water in the tail of the comet as it approached it. As the comet gets even closer to the sun we can expect this to increase even further.

      • Marco says:

        Chambers might explain the low density....
        Yes - very hard to imagine it can be a solar/thermal energy driven subsurface sublimation process. Although your particle speed requirements are wrong, the gist of requiring vapour pressure at a nozzle point while at the same time carrying dust with it is correct. It is hard to imagine how that would happen without being designed that way. At least it doesn't break the known laws of physics....

  • Vince Williams says:

    So, if the coma material is mostly coming from the neck and this will increase as it approaches the sun, then is there a chance that the comet breaks into two separate bodies in the future ? If so, can one of those theoretically threaten us in the future?

  • ian pleasant says:

    why did they only fir the Philae with a very silly 3 inch drill, what possessed them to think that they would find anything just 3 inches down. you have got to at least have a drill bit of 12 inches for to get any kind of substantial findings.

    what a shame, but saying that what a fanbloodytastic event you have pulled off at E.S.A good on ya chaps and chappie lasses.

  • Simona says:

    Can someone see the rippled pattern announced in the caption?

    • emily says:

      Hi Simona, if you zoom into the lower left frame, and focus on the region visible on the very far left of the comet, you should see the pattern I was referring to.
      Emily

  • Tom says:

    If there are/were camera's monitoring the "legs" of the robot, in the future, one could reserve power, etc. for the last experiment to move the "robot" in say one of four direction's desired if it became necessary. Just a after thought. Any comments?

  • Steve Kasian says:

    I don't understand where all these commenters are getting the idea that ESA scientists have conclusively determined that there is no ice on the surface of the comet. In just the past few weeks, ESA has announced that when Philae bounced, it registered penetration of a dust layer x number of inches thick followed by an impact with what was described as a probable ice layer below the dust. So it is quite clear that, based on Philae's sensor data, there likely IS ice on the surface (just below the dust layer). Where is all of this rhetoric about positively no ice anywhere on the surface of the comet coming from??

    • Sovereign Slave says:

      http://blogs.esa.int/rosetta/2014/09/08/virtis-maps-comet-hot-spots/

      And ice under the dust, at this point, is still just an assumption. As far as I can tell, all that is really known is that it's apparently something relatively hard.

    • Marco says:

      The question I have asked is "where is the burden of proof that there IS ice on the surface or near subsurface?" A similar remote experiment with the Clementine mission back in the 90's was positive for ice at the poles of our Moon compared to a negative anywhere on the surface of 67P for Rosetta. Yet we haven't proven ice on the poles of the moon and we haven't proven a lack of ice on 67P supposedly. Rule appears to be that if the data doesn't fit the model, doubt the experiment. If the same experiment cannot determine ice or lack of ice, why bother with it at all?

    • Dave says:

      So far Steve,

      No ice on the surface or beneath the surface has been detected by any instrument - Its as simple as that!

      If the surface is covered in ice, rosetta could have confirmed this months ago, let alone phillae if it was working.

      The article you refer to, actually says something like hard material not inconsistant with hard ice.

      However that means he does not know, and could easily have said not inconsistant with rock.

      The drill on phillae might have solved the puzzle for us but it looks like it may not have drilled the surface and or not delivered anything to the oven for us to find out what the surface is. There may be further data to come though.

      • Steve Kasian says:

        Aah, so we find out from the latest science release and hypotheses that the solid surface structure is, indeed, made up of a frozen, icy, organic solid. That's what I've suspected. Those giant sheer walls of the "excavation zone", as I call it, between the two lobes have always looked like walls of icy material to me.

    • Kamal Lodaya says:

      Rosetta has been around the comet since August. During this period the H2O production in the coma has jumped by several factors (at the DPS meeting in Tucson the Rosetta scientists said six-fold). Where is all this H2)O coming from?

      • Allan says:

        Inside the comet presumably. Which accounts for the low density and supports the jets and hollow comet theory. The ice on the surface has long since sublimated away except perhaps in patches under thick dust.

  • Bill says:

    reCAPTCHA problems!

  • Jacob nielsen says:

    It is funny how things are upside down in this world: the lighter "snowy", "snowdrifts" are probably organics mixed with "stony" dust, while the "mountain" below is, likely, predominantly, watery ice.

  • Steven says:

    Congratulations to all the Rosetta Team on pulling off the miracle of catching up to a comet and landing a probe on 67P. Absolutely amazing. Bravo!

    What does mathematics have to say about the forces on the neck between the two lobes? There are 2 lobes of known volume rotating about a known center of mass at a known angular velocity. Gravitational force compresses the neck and acceleration draws the two lobes apart. A calculation of the net force would give some sense of the tensile/compressive forces currently acting and therefore some sense of the strength of the material that makes up the comet. At what neck dimensions do the two lobes either crush into each other, or separate?

    • Steve Kasian says:

      This is a question I posed, in a somewhat less intelligent manner, a few months ago when they first got there. Why does nobody want to answer this, or act like it's so trivial. This is a basic concept that should have been considered early on. Is anybody home? ESA??

  • Dave says:

    WHY are these frickin frackin glorious images so hard to find one one page by DATE!!!!!!!!!!!grrrrrrrrrrrrrrrrrrrrrrrrr

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