Comet ‘pouring’ more water into space

Based on the NASA-JPL press release reporting the results of Rosetta’s MIRO instrument, NASA’s Microwave Instrument on the Rosetta Orbiter and with additional inputs from the MIRO team.

OSIRIS wide-angle camera image acquired on 22 November 2014 from a distance of 30 km from Comet 67P/C-G. The image resolution is 2.8 m/pixel.  Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

OSIRIS wide-angle camera image acquired on 22 November 2014 from a distance of 30 km from Comet 67P/C-G. The image resolution is 2.8 m/pixel.

There has been a significant increase in the amount of water "pouring" out of comet 67P/Churyumov-Gerasimenko, report MIRO scientists in a paper published in the journal Science  last night. The 4 km-wide comet was releasing the equivalent of 1.2 litres of water vapour into space every second at the end of August 2014.

"In observations over a period of three months [June through August, 2014], the amount of water in vapour form that the comet was dumping into space grew about tenfold," said Sam Gulkis, principal investigator of the MIRO instrument at NASA's Jet Propulsion Laboratory, and lead author of the new paper. "To be up close and personal with a comet for an extended period of time has provided us with an unprecedented opportunity to see how comets transform from cold, icy bodies to active objects spewing out gas and dust as they get closer to the Sun."

The MIRO instrument is a small and lightweight spectrometer that can map the abundance, temperature and velocity of cometary water vapour and other molecules that the nucleus releases. It can also measure the temperature to several centimetres below the surface of the comet's nucleus.

For September, the comet subsurface temperatures were found to be in the 30 to 190 K range (approx. -243 to -83ºC), roughly 1 cm below the surface. The upper value is expected to increase significantly as the comet approaches perihelion in August this year.

The blue arrow indicates Comet 67P/Churyumov–Gerasimenko’s rotation axis, and the red and green arrows display its equatorial x- and y-axes, respectively.  Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The blue arrow indicates Comet 67P/Churyumov–Gerasimenko’s rotation axis, and the red and green arrows display its equatorial x- and y-axes, respectively.

While there are day/night variations at any one location, seasonal effects are the largest component of that range, with some latitudes being much colder than others. For example, the coldest values are found in the south polar region, which has been in winter – and not seen the Sun – for several years. Meanwhile the highest temperatures occur near the sub-solar latitude (which in September was in the comet’s northern hemisphere).

The extent of the day/night variations are also latitude dependent. Variations are near zero at the winter pole (meaning there is no sunlight day or night, so things don't change much over a rotation), while subsurface variations can be ~50 K at summer mid-latitudes.

One reason the subsurface temperature determination is so important is that the observed gases likely come from sublimating ices beneath the surface. By combining information on both the gas and the subsurface, MIRO will be able to study this process in detail.

Indeed, the MIRO team already reports that 67P/C-G spews out more gas from certain locations and at certain times during its “day,” with a substantial portion of the measured outgassing from June through September 2014 occurring from the neck region during the afternoon.

"That situation may be changing now that the comet is getting warmer," said Gulkis. "MIRO observations would need to be carefully analysed to determine which factors in addition to the Sun's warmth are responsible for the cometary outgassing."

The team is continuing to search for variability in the production rate and changes in the parts of the nucleus that release gas as the comet's distance from the Sun changes. This information will help scientists understand how comets evolve as they orbit and move toward and then away from the Sun. The gas production rate is also important to the Rosetta navigation team controlling the spacecraft, as this flowing gas can alter the trajectory of the spacecraft.

“Subsurface properties and early activity of comet 67P/Churyumov-Gerasimenko” by S. Gulkis et al. is available to read in the 23 January issue of Science.



  • Nukecad says:

    It is interesting that "a substantial portion of the outgassing" is coming from the neck region.

    Could this explain why there is a neck in the first place?
    Most of it has outgassed on previous orbits?

    And what does this imply about the structure of the comet?
    Two rocky bodies stuck together by a collar of ice?

    • Judy Hawkins says:

      I'll speculate that the neck is more recently exposed material (I'm partial to the stretch theory for the shape) and that's why it's outgassing more than other areas, which have been exposed on the surface for many more circuits of the sun.

    • Uwe says:

      a trench is "self illuminating".. i.e. where a flat surface "sees" the full overhead hemisphere as empty space at ~1..4°K in a trench the surface will see more of the surrounding surface and not the "cold sky". It will get warmer --> more gas sublimation.

    • Ross says:

      I'd presume that the magnetic field causes the jets to be produced in the neck region. Just as the image of the pit has confined separated jets in the center, imagine the jet activity necessary to produce the largest "crater" on the small lobe.

  • JustCurious says:

    Would this "fresh" water have the same Deuterium abundence as measured some months ago???
    It would be impotant to see if any Deuterium fractioning/enrichment is in place.

  • Hi--
    Any chance of releasing a current, updated 3D model of the nucleus? The previous one was a superb aid in visualizing it, and a huge help when giving talks to the general public. The current version shown in numerous released graphics would be even better, especially now that we have names for the different regions.

  • Robin Sherman says:

    This MIRO report probably had the most information to take in. Not only the outgassing rates, but all the thermal data. There are some interesting diagrams and figures about the amount of energy reaching the surface of the comet and it is interesting to see how the Hapi region actually receives less energy than the lobes of the comet. This seems counter intuitive given this is the most active area, but the activity level it seems is more dependent on the composition and nature of the region. The conclusion is that ices, and in particular water ice is a lot closer to the surface.

    We have seen quite a few NAVCAM images of the cliffs at one end of the valley and right from early on the bright exposed subsurface and cliffs suggested ice very close to or at the surface. The VIRTIS instrument has confirmed these patches of exposed ice and the detection of more water ice close to the surface along the entire valley. Unfortunately no explanation as to how or why this should be has been determined yet.

    • Marco says:

      The MIRO report suggests an upper limit of 1% ice on the surface or very near subsurface. In the areas that you talk about where ice is more probable, it is not likely to be a large percentage even in those spots, and the diurnal cycle suggests that those spots are *not* sublimating nor being replenished (close inspection reveals they were static in size and volume over a diurnal cycle), thus vapour originates below the surface, and if it is one centimetre, it could be one kilometre, for all the instruments can tell us. None of the possibilities offered answer all the questions, and it remains a puzzle, with few pieces seeming to fit.

    • THOMAS says:

      "The VIRTIS instrument has confirmed these patches of exposed ice and the detection of more water ice close to the surface along the entire valley."

      Sorry, Robin, I must have missed something. How exactly did you draw this conclusion? Could you quote your source, please? The headline for the VIRTIS report was actually "EXTREMELY DARK, DRY AND RICH IN ORGANICS: VIRTIS VIEW OF 67P/C-G". I can find no mention anywhere in the report of surface ice. On the contrary, it explicitly states: "The low albedo also indicates that there is LITTLE OR NO WATER ICE on the outermost layers of the surface of the nucleus" (my capitals for emphasis).

      • Robin Sherman says:

        It is my job to interpret IR spectra. Am I not allowed to quote my own expertise and opinion?

        • THOMAS says:

          Sure, Robin, but it just needs pointing out that your "opinion" seems to be completely contrary to the findings announced by the actual mission researchers. They presumably have not only the expertise to interpret the data but also, above all, far more images and data than we do.

  • Graham Hall says:

    Is the neck area composed of a different mix of material than that of the even more illuminated lobes? the VIRTIS data suggests so. Perhaps the inner part of the comet was built from a more volatile mix of material and once the outer shell was breached has continued to erode much faster than the rest of the comet.

    • Robin Sherman says:

      I think the insulating properties of the dusty surface layer have a lot to do with this. If, as suggested, the dust is the residue from ice sublimation, then those areas receiving more energy, the lobes, would create a thicker layer of the insulating dust. A greater energy flux would be required to induce sublimation from sub-surface ices.

      The Hapi region, receives less direct sunlight energy so its dust layer is thinner, both from lower residue and higher activity. In effect a runaway dust removal mechanism has been established in this region. There is evidence of such uneven erosion elsewhere on the comet, in large ravines and valleys. The question then would be, what was the process that initiated this runaway material loss? Impact events exposing larger areas of sub-surface would seem the most obvious, but as we are learning, the obvious is not what 67P is about.

  • Margarita says:

    Not to do with this content (great as ever) but with the date formatting on this blog. Although I'm European I have many contacts in the States where a different date format is used. When the date is between the 1st and the 12th of a month this can cause confusion.

    It would be helpful if a format which spelled out the Month were used, to make for clarity both sides of the Pond!

    I've written the same comment to US astronomy sites - we work together internationally so need to do what we can to aid comprehension.

    Many thanks

    • Ian Ridpath says:

      Actually, everyone (particularly ESA) should be using the ISO date format, which has for many years been the standard astronomical date format, namely YYYY-MM-DD. No reason to do otherwise.

  • dave says:

    Hi Thomas

    Vitis goes even further , the article says a notable feature of all the spectra is the absence of water absorption bands, this indicates no water ice rich patches are present across the nucleus surface.
    It also says no water ice down to a few hundred centimeters!
    Another paper - Sub surface properties and early activity on comet 67p-science 23 jan 2013. says to their surprise the highest water column densities are often found above shadowed neck regions where surface and subsurface temperatures are low. Inversely the low water ice column densities are above the illuminated areas, suggesting that the activity is driven by more than Solar!
    I believe this article finishes with an ironic comment, that the early calculations that support the ice sublimation theory, used the the fact that the whole surface of the comet was available to sublimate, hence sublimation could easily supply the large volumes of water.
    However this paper and the Vitis paper indicate little or no surface ice!
    From this it must show that the early model for sublimation is wrong, it may even question the subsurface theory if no water down to a few hundred centimeters is also true.

    • Robin Sherman says:

      Sorry Dave, the nature of how the VIRTIS instrument works, it measures the light reflected from the surface, means only the nature of the very top mm or so of the surface can be determined. The Water absorption bands are not absent, they are just very hard to distinguish from the multitude of other signals created by other chemicals in the surface material. Thus all they can say is there is little or no Water ice in the very top surface layer. As Gerald pointed out elsewhere it is obvious that this is the case since at the current surface temperatures in a vacuum all the surface Water would have sublimated. However if subsurface patches are exposed, see the image below, after gas activity has disturbed the surface layer of "dust", then small amounts of sublimation directly from the surface can occur. Since less than 1% of the surface area is required to account for the current activity, those patches do not need to be large or that numerous, especially if sublimation is occurring from a centimetre below the surface as the MIRO result suggests is possible.

      Could I suggest both yourself and Thomas read the explanation that goes with this image too.

      • Robin Sherman says:

        Could I also direct you to this video of one of the VIRTIS talks at the recent AGU in which it is explained quite clearly that the instrument can only measure the top 100 or so microns (micrometers) of the surface and at about 12 minutes in, there are results, spectra, showing the detection of surface Water ice at the edge of the Imhotep and Khepry regions. There is a clear association of Water ice with bright freshly exposed boulders, hundreds of which we have seen all over the comet in NAVCAM images.

        • THOMAS says:

          I've also just watched the video. Thanks for the reference, Robin. Extremely interesting!

          As regards the reference to water-ice, my comment is as above (re. the OSIRIS images): Fabrizio Cappacioni considers that the "fairly flat spectra" are "consistent with the observation of water". Being “consistent with” is a very far cry from “*showing the detection of* surface Water ice” as you claim. We await proof. You can in no way claim that “There is a clear association of Water ice with bright freshly exposed boulders, hundreds of which we have seen all over the comet in NAVCAM images”. I know that “cryorock” and “cryoboulders” are an important part of your personal, perfectly respectable, pet theory. But please don’t claim that the VIRTIS findings have proved the reality of their existence.

          What I find much more interesting and significant in the VIRTIS video are the temperature findings. As of ~4:20, we see a rapid succession of images (too rapid to be able to study them without constant freeze-framing…) showing differences in surface temperatures. What I find particularly extraordinary are the images of 1/ (at 4:21 and 4:23) a 1km+long strip of considerably higher temperature running in a near-straight line from one end to the other of the floor of the neck region and 2/ (at 4:31) a similarly extensive area of much higher temperature spreading all along the base of the towering Seth cliff.

          Even more astounding, though, is that Fabrizio Cappacioni makes no comment on these images and on the fact that the hotter areas they demonstrate manifestly correspond precisely to the area which has clearly been generating the most vigorous jetting activity since ROSETTA arrived at the comet (and which the EU proponents on this blog have consistently ascribed to electric glow discharge activity). The on-screen commentary simply states: “67P morphology induces large shadowing effects and strong thermal gradients, in particular in the neck region”. Nowhere is it pointed out that the large-scale area where surface temperatures are consistently the highest is precisely the largest area on the illuminated part of the comet which necessarily receives the least sunlight, being at the bottom of towering cliffs on either side. This is decidedly a huge embarrassment for the standard “sublimating ice” theory.

          It would be nice if these images were more widely disseminated and interpreted by the VIRTIS team.

          • THOMAS says:

            This comment was actually posted a few hours after after the one a bit further below (posted at 12:39). I don't understand why the order got inverted. This is why, in my opening lines, I refer to the content of the 12:39 post. Just for clarity...

        • Ross says:

          You cannot say that those images display clear evidence of ice at the surface. It is your bias and knowledge of prior theory that is showing you what you expect to see. A piece of charcoal on that surface could appear white, that is how much the image must be processed to expose any detail. There is NO water ice, especially make-believe "cryoboulders".

      • dave says:

        Sorry Robin,

        I must of got carried away, the depth should had been down to a few hundred micro meters,not centimeters as my blog above (just a few 0's out.)

        Even so the last paragraph of the Vitis document supposes that the refractory compounds so widespread on the surface of 67p are then representative of the bulk pristine material of the nucleus.
        This does not suggest there is going to be an icy structure underneath the surface.

      • THOMAS says:

        I’ve just followed your suggestion and read the commentary (which I had already studied a couple of days back). It states that the “spots of brighter material” seen in the image “MAY be evidence of recently exposed ice » (my capitals for emphasis). And clearly, they may NOT. This is hence mere theory-driven expectation so business as usual

        In the EU book, the brighter spots and in particular the white boulders, ridges and outcrops i.e. salient points) observed in many images over the past few months are the focus of electric glow discharge activity, which is of course also associated with the “bluer” end of the spectrum, right down to UV.

        As for the “less than 1% of the surface area […] required to account for the current activity” which you assert, you will presumably concede that the actual percentage of the comet surface currently represented by the observed “spots of brighter material” is an infinitesimal fraction of the required “1 %”.

        • THOMAS says:

          For clarity: the above 27/01/2015 at 12:39 comment was posted in reply to Robin Sherman's 26/01/2015 at 20:47 comment but somehow got shunted down the order.

      • Andi Rossini says:

        You say, "However if subsurface patches are exposed,...,after gas activity has disturbed the surface..."

        My question would be; What force caused the "gas activity". I thought "gas activity" as you put it is the result of exposed patches, not the cause. I'm sorry but your hypothesis rests on pure tautology. Do you not need energy from the sun, as the standard model dictates, to sublime gases for there to be gas activity? But you just explained how you need exposed patches for enough energy to be transferred to heat the subsurface sources. There's too much missing from your explanation to be considered valid.

  • Kamal Lodaya says:

    It might seem strange that the discussion on this blog focusses on whether Vitris found water on the surface of 67P, which is the subject of another parallel blog. Where then is the water "pouring" out found by Miro coming from? We find in the images brightly lit regions which several people see as exposures of icy material, and this would be consistent with the Miro observations. Some contributors would like to see these brightly lit regions as electrical discharges, since there is no other evidence that anything of this kind is happening on the comet. It would be more convincing to provide an explanation for the Miro data.

    • dave says:

      It has been stated on a couple of occasions by esa that the bright patches on the surface are not ice.
      Ice has not been found below the surface either, Consert data said that the comet is homogeneous.
      The Vitis results stated by Its instruments team, concluded that there is such an abundance of refractory materials on the surface of 67p that this is therefore representative of the bulk pristine core.
      I think it was graham about a week ago (apologies if it was''nt) posted a paper that modeled subsurface sublimation through a small hole. The model used a 1 meter deep cavity and said that this could grow to 3 meters in diameter. You would of expected the Consert experiment to have detected spent cavities of this size, but it has not. Again it says the comet is homogeneos.

      Also interestingly the Vitis says that volitiles and the ice that produced the surface had to be available at the birth of the comet to form the refractory compounds. The suggestion is that the organic compounds were formed by irradiation (either by UV, photons or energetic particles) of polymerization of mixed ices at low temperature.
      The Vitis instrument appears not to be sensitive to ice for areas less than about 10meters.

      So there may be some small patches, but the bulk of the evidence pesented shows there is NO ICE, confirmed by more than one instrument.

      The evidence is documented, you just have to read it

      So that does leave a problem - how is it that there is water in the coma but not on the comet? This seems to be the 6million dollor question that we should all be looking at.


      • Andi Rossini says:

        As many have suggested, the observations are consistent with what has been predicted by EU theorists; that is that hydroxyl radicals in the coma will be produced electrochemically by the combination of sputtered oxygen anions from the rock that makes up the comet and protons from the solar current (i.e. the moving charged particles which every electrical engineer knows by definition is an electrical current, yet astronomers for some reason continue to call the 'solar wind'). No need for ice in or on the comet to be the source. Just simple electrolytic reactions you can experiment with in any modest laboratory. Sounds like the most credible theory to me.

        On a side note, let me just remind those who have never studied Maxwell's electromagnetic theory; Every magnetic field is produced by an electric current, yes, even in permanent magnets. If astronomers and astrophysicists cannot bring themselves to understand this concept, they will never understand what they observe of the cosmos, but instead will write whole dissertations on 'magnetic reconnection' to explain energetic phenomena not predicted by a gravity-centered cosmology. Again to any electrical engineer the very idea of magnetic field line reconnection is utterly nonsensical and quite telling of the lack of knowledge among the astrophysical community. It's quite embarrassing actually to hear supposed professional scholars describe this fantasy explanation and then have the arrogance to dismiss and malign anyone who would suggest that the presence of magnetic fields in space, implies electric currents, and therefore electric fields.

  • Kamal Lodaya says:

    Dave: In the overview article Getting to know Rosetta's comet, we have:

    "Small patches of ice may also be present on the surface. At scales of 15–25 m, Rosetta’s Visible, InfraRed and Thermal Imaging Spectrometer, or VIRTIS, finds the surface to be compositionally very homogenous and dominated by dust and carbon-rich molecules, but largely devoid of ice. But smaller, bright areas seen in images are likely to be ice-rich."

    They are not saying it is ice for sure, but they are not saying it isn't ice either, so you can draw your own conclusions.

    • dave says:

      hi Kamal,

      yes I also read the part that the smaller , bright areas might be ice.
      I did not mention it because the smaller brighter areas mentioned could not be responsible for the gross activity on the comet.
      So even if it is ice, and therefore it would be sublimating, it is insignificant to power the activity we see.

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