ROSINA tastes the comet’s gases

Rosetta’s ROSINA instrument, the Rosetta Orbiter Sensor for Ion and Neutral Analysis, has detected its first cometary volatile molecules. The results were presented at the European Planetary Science Congress, EPSC, held in Portugal this week.

ROSINA's reflectron time of flight mass spectrometer (RTOF).

ROSINA's reflectron time of flight mass spectrometer (RTOF).

The detections were made early August when Rosetta was within 200 km of comet 67P/Churyumov-Gerasimenko, and over 500 million kilometres from the Sun – the first time that a comet’s coma has been analysed in situ this far from the Sun.

Since then, ROSINA has been almost continuously measuring the density and the composition of the comet’s coma. It has already acquired more than 40,000 high- and low-resolution spectra with its two mass spectrometers (DFMS and RTOF).

Overall, the density of the coma is relatively low at this early stage, far from the Sun, but should increase as activity picks up, as the comet moves closer to the Sun over the next year. The density is seen to vary during the comet ‘day’, as it rotates over a 12.4 hour period.

As expected, the main species in the comet’s coma are found to be water, carbon monoxide, and carbon dioxide, which are being released from below the surface layer of the nucleus, which VIRTIS has shown to be dark, porous, and probably dry.

Rosina's double focusing mass spectrometer (DFMS). Credit: ESA/Rosetta/ROSINA/UBern/BIRA/LATMOS/LMM/IRAP/MPS/SwRI/TUB/UMich

Rosina's double focusing mass spectrometer (DFMS).

However, ROSINA has made the surprising observation that the ratio between these species varies quite significantly, depending on where in the coma Rosetta is. Sometimes carbon monoxide is almost as abundant as water; sometimes it’s only around 10%. In addition, ROSINA has not only detected these main species already, but many of the expected minor ones, such as ammonia, methane, and methanol.

As Rosetta gets closer to the comet and as comet activity increases, it will soon be possible to measure the ratio of hydrogen to deuterium – an isotope of hydrogen with an added neutron – in the cometary water. This ratio is constant in Earth’s ocean water and thus can be used as a way of tracing the still unknown origin of that water: for example, was it incorporated into the Earth at the time of formation, or was it delivered from space at some later date?

In particular, 67P/C-G is a Kuiper belt comet, and the hydrogen to deuterium ratio measured for its water will help constrain how much of Earth’s water could have come from a population of impacting Kuiper belt comets, soon after the birth of the Solar System.





  • Ross says:

    "As expected, the main species in the comet’s coma are found to be water, carbon monoxide, and carbon dioxide, which are being released from below the surface layer of the nucleus, which VIRTIS has shown to be dark, porous, and probably dry."

    Has rosetta actually observed these gasses being released directly from below the nucleus surface? If not, it bothers me that this mechanism is presented as fact when ROSINA has only detected the presence of these compounds in the coma. If this were true, OSIRIS should have produced thousands of images of newly formed vents which I hope will be released before more assumptions are made.

    • Jacob Nielsen says:

      If the surface is indeed porous, vents may not be a prerequisite for material leaving the comets interior. Besides, do You have a different hypothesis regarding the origin of these volatiles?

      • Ruben says:

        I think vents must be the jets that we can see from far away due to crevices on the ground of the comet (due to small gravity theris a very low compaction and must be too easy pull out fragments of the surface -in a very "soft" way-, this process refresh the surface and must be responsible for the burst in brigness thay we can see sometimes).

        I apologice for my english.

    • cosmo says:

      According to this account, the OSIRIS team has already presented images of some kind of vents, releasing jets of gas, at the EPSC conference, but apparently they don't want to show us.

      • cosmo says:

        Now the link should work properly.

      • Adam Synergy says:

        I'm not sure this is the right place for a moan (I know that Emily can do nothing about it) but why are OSIRIS images contractually locked up for 6 months before anyone not directly working on this instrument can get to see them ? This is the 21st century for crying out loud ! NASA has successfully operated an open access policy for its planetary science mission images for many years but ESA cannot seem to understand why they should follow suit.This is an exciting groundbreaking mission, what a shame we are still shackled by antiquated notions of keeping scientific imagery soley for use by a handful of scientists.

        • logan says:

          Science is about nature, and nature is available to all, sooner or latter it will be accessible, please be patient.

        • logan says:

          I am sure scientists don't want their documents to go 'secret' for ten years. And after that to go useless because someone else got that data before...

        • logan says:

          It is more along the line of who has the right to chew first the hunted zebra.

      • THOMAS says:

        It's not just "some kind of vents". The article specifically states that the jets in the neck region originate very precisely from the brightest areas of the surface whereas darker regions "at least so far" remain inactive (in German, "Vielmehr gehen die Jets von den Bereichen des Halses aus, wo die Oberfläche zugleich am hellsten erscheint. Dunklere Halsbereiche sind dagegen - zumindestens bisher - inaktiv")

        One wonders indeed why such important information has not yet been more generally disclosed. This being very precisely one of its most obvious expectations, maybe the electric comet hypothesis is suddenly finding too much objective support from OSIRIS images for comfort.

  • Erka says:

    These gasses and more are found just about anywhere, even in distant nebulas. So far nothing new, de search goes on.

  • Prof Harvey Rutt says:

    Lighten up a bit; it's a few words in a press release, not a paper we are refereeing. If VIRTIS is giving good evidence of a porous surface, as it seems it has from thermal models, the statement is not unreasonable. Neither does it necessarily require obvious vents if it's porous.

    But we are getting very few Osiris pictures. I'm well aware of the issues of scientific priority etc, but it really is time more were released, they help hold interest from the public - who paid for it.

    • Ross says:

      I understand that this is just a press release but the falsifiability of the dirty-snowball hypothesis has become nonexistent. The comet is much warmer than anticipated, the surface is entirely dehydrated, the nucleus is black, and scientists refuse to acknowledge the mere possibility of the snowball idea being wrong. A theory is only acceptable if it can be falsified, how can you falsify the dirty snowball? The porosity issue, I believe, is due to the calculated density being much less than even ice, leaving the only current explanation being a lot of empty space inside... though the Deep Impact mission showed comet Tempel 1 was very hard and dense (production of x-rays and tiny crater). No matter what observation is made, it can always be assumed that the gasses are being produced where we can't see them; this has no scientific value.

      • Jacob nielsen says:

        Ross, I don't follow your conclusions: 1) compacted snow has a lower density than C-G has and 2) from where does your prediction of the relation between crater size and density/ porosity originate? I imagine that a bullet fired at at a pile of snow would produce... A tiny hole?

        • Don Sleeter says:

          I'm guessing that if you shot a bullet at a very large rocky snowball, you would get tiny holes at the surface AND a hollowed out spongy sub-surface where the impact energy blossomed out into super hot gasses and water vapor.

          Over time, this would result in lower density interior structures that would not compact, partly because there are hard load bearing, possibly crystalline walled bubbles inside an old small comet.

          Ross, you point is very good, we need to be careful in building upon assumptions. Or at least label them clearly as assumptions and work to find alternative explanations, which you and Jacob are doing very well, publicly.

          I am a lay person and I really appreciate the chance to follow the chatter. Thank you and enjoy the rest of the mission and science!

  • logan says:

    Thanks a lot Emily; This is the first direct report I read on ROSINA

  • Dave says:

    Surely, presence of those elements does not mean its come from under the surface. What is the surface material? and even though there is no ice at the surface is there any mechanism of erosion of the surface that will produce those elements, and at the same time, also cause the variation in relative volumes of each?
    Then we can rule out the surface or rule it in as the source of the coma.
    It seems a simple enough experiment, also it would be good to know the chemical make up of the dust that has been collected, those reports should be available by now based on last week blog info.
    Again this would give us some clues as to how the coma is produced -surface process or subsurface process

  • logan says:

    (...water, carbon monoxide, and carbon dioxide...).

    Fizzing, this duck.

  • logan says:

    What if 67P is a Kuiper-NoKuiper binary?

  • logan says:

    The periodicity of CO suggests a surface or near surface origin.

    • logan says:

      Imagine big hydrocarbons 'sweat-ed' toward porous surface and then literally being 'atomized' by the extremely ionizing solar wind. Surface acting as a porous catalyzer, too.

  • logan says:

    As this process go faster, It will loss efficiency. Comparative spectra now and then will discern the original molecules.

  • Lorand Lukacs jr. says:

    OUTGASSING from the comet is observed, but to get clear pictures, it is somtimes hidden. But on this Planetary web site illustrated and commented by emily Lakdawalla You can see some of them. God luck.

  • Dave says:

    Great pictures Lorand,
    but are the jets forcing through a generally porous comet surface (looks unlikely because its coming out of such a big area and is filomented such as you might see in a charged field), how could this happen from a generally pourus surface, it should come out in all directions.
    Or is it the surface of the comet that is being eroded by some sort of electrical discharge? If so, we would know that because there is no ice at the surface, the OH ions in the coma would not of formed from sublimating water ice. Its a big question because it has big ramifications for how the comet was formed and how old it is.
    Looking at the jets is unfortunately only a fraction of the story, we will have to wait for more pictures

    • logan says:

      Hi Dave, I like your model best than anything for surface processes. But not discarding jets below sublimation line. Sometimes evident up to surface.

    • Lorand Lukacs jr says:

      I think the surface is usually covered with dust and untherneath is frosen water, cooldioxide mathane and ammoniac keeping a temperature of minus -43 to -93 degrees celsius. When heated by sunlight and sunparticles, the surface is heated and gasspocets are formed underneath. When the gaspressure exceeds a certain value it bursts and breaks through forming a jet that also brings with it som of the dustcrust. Because of the low gravity and vacuum it explodes as there is limited amount of convection. Think of snow covered with dust on the Earth in the Spring, it takes longer time to melt than pure white snow. White snow reflects more sunlight and would build an icy crust before releasing the sublimated water wapor.
      See if you understand german language.

  • Michael5618 says:

    Will the rotation period of the comet change when the gas jets become more active?

  • Prof Harvey Rutt says:

    Re dirty snowballs, there is a well known phrase:
    "When I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck."
    Well in science we try and do a little better, and that's exactly what Rosetta is doing. Eventually the data will be fully collated and analysed, and it will, or won't, be consistent with whatever models you propose. I don't see any issue re falsifiability at all.
    But for the moment we are stuck with press releases, and something that does indeed 'look like a duck.'

  • Prof Harvey Rutt says:

    Musing on this further, if there is a 'falsifiability' ' issue this seems to be more regarding the 'contact binary' assumption, which is widespread. It's not so obvious we will get good data to distinguish a contact binary from a shape resulting from differential ablation, which still seems entirely possible to me.

    • logan says:

      Hi Prof Harvey. There is something of a wish on talking about the 'binary'. Like going to two countries in one vacation. A 'binary' is something easy to grab to us lay people, besides. Body lobe seems to be a lot more 'carbon' kind. 3D First Published Osiris Photo shows that 'neck' area has both fresh broken and old fused 'frontiers' at layering zones. Not an easy zone wherever She came from. All of this will be irrelevant going through the endeavor, as catalogs of source data are released. Is this chatting scientific? Of course not. And of course you are right on all this being asumpptions 🙂

  • Jacob Nielsen says:

    In the live transmission today I think it was mentioned that the nature of the outgassing would produce this heterogenous patterns and that the comet would likely break in two during this or the next perihelion.

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