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Rosetta: New Findings on Cometary Water

Where did the water in Earth’s oceans come from? It’s an open question, but new data from the Rosetta mission, in particular its ROSINA instrument (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) indicate that terrestrial water probably did not come from comets like 67P/Churyumov-Gerasimenko, around which Rosetta has been orbiting since August. There is little doubt that water reached Earth through bombardment from small bodies early in the planet’s history, but the Rosetta findings sharpen the question of where these objects came from.


Image: This composite is a mosaic comprising four individual NAVCAM images taken from 19 miles (31 kilometers) from the center of comet 67P/Churyumov-Gerasimenko on Nov. 20, 2014. The image resolution is 10 feet (3 meters) per pixel. Credit: ESA.

At work here is analysis of the ratio between hydrogen and deuterium, a heavy form of hydrogen with one proton and one neutron in the nucleus (common hydrogen lacks the neutron). This D/H ratio on 67P/Churyumov-Gerasimenko turns out to be over three times the terrestrial value, among the highest values yet measured in the Solar System, making it unlikely that comets like these supplied Earth’s oceans. Back in 1986, the European Giotto mission to comet Halley found a D/H ratio twice that of Earth’s, seeming to rule out Oort Cloud comets as the source.

67P/Churyumov-Gerasimenko and Halley are two different kinds of comet, so let’s explore this. Cometary origins are complex because of interactions in the early Solar System. Long-period comets that swing into the inner system from the distant Oort Cloud are thought to have formed originally somewhere beyond the snowline in the region where Uranus and Neptune now orbit, to be scattered by subsequent gravitational interactions with the large outer planets. 67P/Churyumov-Gerasimenko is a Jupiter-family comet, a class whose origins are believed to lie beyond Neptune in the Kuiper Belt. Comets like these sometimes have their orbits disrupted so that they fall under the gravitational influence of Jupiter, hence their designation.

In contrast to 67P/Churyumov-Gerasimenko, comet Hartley 2, which was examined by the European Space Agency’s Herschel spacecraft in 2011, turned out to have a deuterium/hydrogen ratio similar to Earth’s. The discrepancy is surprising because Hartley 2 is also a Jupiter-family comet, and models of the early Solar System produce a D/H ratio for these comets more like 67P/Churyumov-Gerasimenko, even higher than their Oort Cloud cousins.

The disparity may indicate that we know less about Jupiter-family comets and their origins than we realized. The new Rosetta data tell us that this family of comets is hardly uniform, and thus nudge us away from them and toward asteroids as the primary water delivery mechanism. Kathrin Altwegg (University of Bern) is principal investigator for the ROSINA instrument and lead author of the paper on this work, which has just appeared in Science:

“This surprising finding could indicate a diverse origin for the Jupiter-family comets – perhaps they formed over a wider range of distances in the young Solar System than we previously thought. Our finding also rules out the idea that Jupiter-family comets contain solely Earth ocean-like water, and adds weight to models that place more emphasis on asteroids as the main delivery mechanism for Earth’s oceans.”

The measurements in question were made in the first month after Rosetta’s arrival at 67P/Churyumov-Gerasimenko. With the Rosetta data, we now have D/H information about eleven comets, finding that only Hartley 2 shows a ratio matching the composition of Earth’s water. We also know that meteorites with an origin in the asteroid belt show a good fit with Earth’s D/H ratio. Although the overall water content of asteroids is lower than we find in comets, a large number of asteroid impacts could account for the primary delivery mechanism.

Meanwhile, the mission continues, and will for some time. Rosetta has now been at 67P/Churyumov-Gerasimenko for 127 days. Perihelion is 244 days away.

The paper is Altwegg et al., “67P/Churyumov-Gerasimenko, a Jupiter family comet with a high D/H ratio,” published online in Science 10 December 2014 (abstract). This ESA news release is helpful.


Comments on this entry are closed.

  • Scott December 11, 2014, 14:55

    Is there any indication that the ratio differs in proportion to distance the object was formed from the sun?

  • ljk December 11, 2014, 15:19

    Direct exploration versus lots of speculation equals often learning that the Universe does not operate the way humans think it does or want it to.

    Case in point:


    This is why I want us to ramp up SETI and interstellar exploration as opposed to endless debates about real alien life.

  • Ashley Baldwin December 11, 2014, 15:48

    The average D:H ratio of the water locked up in the chemical structure of the so called carbonaceous chondrite class of the asteroids investigated in the Asteroid belt so far is about the same as that of the water in Earths oceans. So it’s likely it was bodies like these that delivered our water during the late heavy bombardment phase supported by the Nice Theory/Jumping Jupiters.

  • Alex Tolley December 11, 2014, 18:39

    How does this finding map with the recent claim that Earth’s water must have at least some origin in interstellar space rather than de novo processing during the sun’s formation? What is the origin of asteroidal water – primordial or processed?

  • Brett Bellmore December 11, 2014, 19:23

    Given that fusion with Deuterium is hugely easier than fusion without it, I find this promising for the future of cometary colonization; It about triples the effective energy content of the hydrogen in bodies such as this.

  • James M Essig December 12, 2014, 11:55

    Awesome prospects indeed Brett. A cool idea would involve covering a comet with a reflective membrane and using the comet as a relativistic rocket fuel mass. A 10,000 metric ton crew hab could conceivably be propelled by a mass ratio of 10,000 for 100 million metric ton comets. Considering that there may be over a trillion of these suckers orbiting the Sun in the Oort Cloud, that is a whole lot of spacecraft.

    I may be the case that as these comets formed, most of the water incorporated into them was primordial. However, after the ocean started to form, perhaps the solar system passed through another comet cloud of another star picking up the hydrogen isotopic blend we currently see in our hydrosphere. An impactor event such as one proposed for the production of Earth’s moon might also be a culprit. I am not a planetary scientist but the above speculations seem tantalizing.

  • Anthony Mugan December 13, 2014, 4:35

    This is a very interesting result and one that raises more questions that it answers. It seems unlikely that there were not significant volumes of water delivered to the early earth by both comets and asteroids. It raises the question in my mind as to if models of the dynamics of the early solar system can account for a strong skew towards asteroids?
    The heterogeneity of the data for comets is also notable and I’m not clear as to why that should be so…

    Small sample size of course, and a story that may have further to go?

  • Eniac December 13, 2014, 12:30

    The notion that comets or asteroids have delivered water to the early Earth is currently popular, but it is far from proven fact. There are many other scenarios, all with various pieces of evidence for and against them. In my opinion none deserves to be called anything other than speculation.

    See this article for a balanced, not-too-deep, not-too-shallow account: http://www.huffingtonpost.com/david-j-eicher/comets-water_b_3684406.html

    Given the small percentage of the Earth’s mass that is water, I do not see how we can rule out the simplest hypothesis, that the water was baked in from the beginning, bound up in minerals, as it is wont to do.

  • NS December 13, 2014, 19:42

    Hope this isn’t too OT. Article describes this as a “new” physics-based theory of the origin of life, although IIRC similar ideas have been put forward before:


    Article contains a link to a technical paper.

  • Alex Tolley December 14, 2014, 14:49

    @NS – interesting article.

    They might find, for example, that “the reason that an organism shows characteristic X rather than Y may not be because X is more fit than Y, but because physical constraints make it easier for X to evolve than for Y to evolve.

    Niles Eldredge’ critique of Dawkins’ “selfish gene” model included this question. I always assumed that this was simply a result of what genes were available to be modified, but this may offer an alternative, or additional, explanation. I suspect however that it will be most explanatory, if at all, at the biochemistry level – e.g. what chemical processes will life use to generate energy, etc. One hypothesis that is suggested is that life will tend to have similar biochemistries, rather than disparate ones, if starting conditions are similar. That might confound ideas of panspermia.

  • ljk December 19, 2014, 14:05

    Rosetta probe’s dizzying bounce revealed: New images emerge of Philae shooting back into space – and its final, lonely resting spot

    In November, failure to launch Philae’s harpoons and a thruster caused it to bounce twice before settling

    A new blurry image by Esa captures the rapid motion in which Philae was launched back out into space

    The probe was launched to a height of 0.62 miles (1km) and then to a much lower height of 65ft (20 metres)

    Esa has also released an reconstruction of its resting place, and a view of the cliff wall looming over the probe

    By Ellie Zolfagharifard for MailOnline

    Published: 07:29 EST, 18 December 2014 | Updated: 09:34 EST, 18 December 2014

    The dramatic moment that Rosetta’s Philae comet lander bounced back into space has been captured in a remarkable image.

    Philae successfully landed on comet 67P/Churyumov-Gerasimenko in November, but not before a failure to launch its harpoons and a thruster caused it to bounce twice before settling.

    The blurry image captures the rapid motion in which Philae was bounced back. The probe was launched to a height of 0.62 miles (1km) and then to a much lower height of 65ft (20 metres) before coming to rest.

    Full article here:


  • ljk December 19, 2014, 14:27

    Rosetta Comet Science Results video from the 2014 AGU Fall Meeting:


  • ljk December 22, 2014, 12:17

    Dinosaur eggs’ spotted on Rosetta’s comet

    By Eric Hand

    18 December 2014 11:30 am

    SAN FRANCISCO, CALIFORNIA—There are places on comet 67P/Churyumov-Gerasimenko where cauliflowerlike textures appear in the dusty crust, like goose bumps under the skin. Scientists using the Rosetta spacecraft—which arrived at 67P in August and became the first mission to orbit and land on a comet—now think they may have discovered the source of these patterns on cliff faces and in deep pits: layer upon layer of rounded nodules, 1 to 3 meters across. These spherules, dubbed dinosaur eggs, could be the fundamental building blocks that clumped together to form the comet 4.5 billion years ago.

    “These could be those little cometesimals,” says Holger Sierks, principal investigator for Rosetta’s science camera and a planetary scientist at the Max Planck Institute for Solar System Research in Göttingen, Germany. Sierks presented the findings here yesterday at a meeting of the American Geophysical Union.

    Full article here:


  • ljk December 22, 2014, 17:40

    Rosetta Team Focusing on Upcoming Comet and Lander Science, Planning Ultra Close Flyby

    By Ken Kremer

    The team guiding Europe’s history-making Rosetta mission to orbit and land on a comet for the first time in human history is planning for even more remarkable science achievements at comet 67P/Churyumov–Gerasimenko in the year ahead, during its primary mission phase, including an extremely close and bold flyby.

    Rosetta and its attached Philae landing craft arrived at comet 67P on Aug. 5 after a decade-long interplanetary journey of some 500 million kilometers (300 million miles) from Earth at 41,000 mph on a mission of cutting-edge science to elucidate our origins.

    Among the objectives of the audacious Rosetta/Philae mission, developed and funded by the European Space Agency (ESA), is it seeks to determine if comets played a role in the origin of life on Earth.

    After reaching comet 67P, the Rosetta team then worked feverishly on a very compressed time schedule to find a safe and scientifically interesting landing site to deploy Philae barely three months later on Nov. 12 to touchdown on the head of the bizarre comet, shaped like a rubber ducky.

    “Rosetta’s science mission really began with the Philae landing on comet 67P,” said Matt Taylor, the Rosetta project scientist from the European Space Research and Technology Center, Noordwijk, the Netherlands, during a Dec. 17 mission press conference held at the annual meeting of the American Geophysical Union (AGU) in San Francisco, Calif.

    And Taylor reported that Rosetta’s science gathering investigation has further exciting events upcoming and may continue longer than expected.

    Full article here:


  • Dmitri December 24, 2014, 5:36

    A better video of Rosetta team presser is down below. What the D/H ratio shows:
    1) There is now a 3rd classification of comets – main belt comets to come to terms with different D/H ratios discovered.
    2) They don’t rule out possibilities Kupier belt & Oort cloud comets had interchange mechanism, especially after Pluto & Uranus switched places in early Solar system past.
    3) Can’t recall did they mentioned during press conference or I read it additionally but the D/H ratio is not clear cut. Some comets have shown different D/H ratio to Earth’s ocean but there is 1 or 2 measurements where the D/H has been on par w Earth’s ocean.
    4) 67P is über rich in hydrocarbons even as such ones that never would have expected.
    5) Early results of 67P measurements pinpoint on massive re-evaluation of knowledge we have but it does not rule out anything so far.
    6) Origin of Earth’s water is now either asteroid based or produced in-situ.

    Right now there’s nothing definite but some possibilities are less likely or soon could be regard as insignificant – some meteors contributed to Earth’s water but mainly it is asteroid origin / produced in-situ geologically.

  • Dmitri December 24, 2014, 5:39


    “Kupier belt & Oort cloud comets had interchange mechanism, especially after Pluto & Uranus switched places in early Solar system past.”

    I meant when **Uranus & Neptune switched places** as the lady from Switzerland mentioned.

  • ljk January 19, 2015, 15:13

    16 January 2015 Last updated at 16:56 ET

    Rosetta will prompt science images rethink

    By Jonathan Amos

    Science correspondent, BBC News, Paris

    The European Space Agency needs to find a new way for images and other data acquired by its science missions to come out into the public domain.

    That is the view of the organisation’s director general, Jean-Jacques Dordain.

    He was expressing his frustration at not seeing more pictures from the main camera system on Esa’s Rosetta probe, which is tracking Comet 67P.

    These images are subject to a six-month embargo to allow the mission team to make discoveries without being scooped.

    But the policy has upset the thousands of ordinary members of the public who follow Rosetta on a daily basis because they are not being shown the very best views that have been acquired.

    Nearly all of the images seen to date have come from the probe’s navigation cameras. The products of its science cameras, on the other hand, which are far superior, have been given only a very limited release because of the proprietary period.

    “Even I’ve tried to get more data,” Mr Dordain said. “I might be the DG but I’m also a fan of Rosetta and [its lander] Philae. It’s a problem; I don’t deny it’s a problem. But it’s a very difficult problem, too,” he told BBC News.

    “I understand the frustration of the public and the media, but, on the other hand, I understand the position of the principal investigators who have invented the mission.”

    Mr Dordain was speaking in Paris at his annual New Year breakfast with reporters.

    Even handed

    Esa itself has little control over the release of imagery from its science missions. This is partly due to the way these ventures are organised and funded.

    The agency procures the satellite platform, the launch rocket and runs day-to-day operations, but the instruments that gather the data are supplied – and funded – via national member states.

    Esa may drive the truck, but it does not own the merchandise in the back.

    Giving scientists on particular instruments a proprietary period has become standard practice.

    It provides the researchers with a head start, enabling them to be first to announce major discoveries and to publish the details in the top journals.

    The credit and citations that follow boost their ability to propose future programmes and win further funding. This process has become central to the way they work.

    “If these science missions exist, it’s largely because of the principal investigators who come up with these wonderful ideas and supply these instruments. And their whole life is about coming up with the discovery first. So, one can hardly blame them for that,” Mr Dordain said.

    “Maybe what we should do is distinguish better between data that would be considered absolutely key to making scientific discoveries and can be kept under wraps before publication [in journals], and the data that can be released to the public much sooner.”

    Full article here:


  • Dmitri January 22, 2015, 16:03

    Rosetta space craft team has released their OSIRIS findings of the 67/P comet.

    The punch line is dirty snowball analogy doesn’t stick anymore. It’s much much more complex. They have ID 19 different regions on the comet based on they geological features & processes.


  • Dmitri January 22, 2015, 18:24

    Better link on all related & in-depth science papers released on 67/P so far in Science including all the variations of D/H measurement.


  • ljk January 23, 2015, 12:21

    Comet 67P’s carbon blanket promises solar system birth insights

    22 January 2015

    Andy Extance

    A layer of organic material unlike anything seen on any other comet humans have studied enfolds comet 67P/Churyumov–Gerasimenko, Rosetta probe scientists have revealed. Spectrometry data shows its sunlit surface enveloped by a carbon-based coat, without significant ice cover.1

    ‘We’re looking at a comet that’s possibly more pristine, more representative of the early moments of the solar system than others,’ explains Fabrizio Capaccioni from the Italian National Institute for Astrophysics (INAF). Along with other data, the measurements provide big early steps towards Rosetta’s aim of deciphering ‘the origins of the solar system and/or life on Earth’.

    Capaccioni leads Rosetta’s Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS) team. VIRTIS can monitor sunlight reflected off comet 67P, hunting for wavelengths of light that have been absorbed by molecules on its surface. The VIRTIS team is now reporting the very first of this data, recorded from August to September 2014.

    The spectra showed no water ice absorption bands, but did contain a broad absorption band from 2.9µm to 3.6µm. This broad band is a strong sign of carbon–hydrogen bonds and oxygen–hydrogen bonds in organic molecules, in particular carboxylic acids. However, the VIRTIS team says it saw no evidence of nitrogen–hydrogen or nitrogen–carbon bonds.

    Nitrogen’s absence would stymie the hunt for life’s origins. Capaccioni admits that without it an important ingredient for forming amino acids, ‘the building blocks of life’, is missing. ‘We will keep looking,’ he adds. Work is continuing to improve the currently vague chemical analysis and Capaccioni says the VIRTIS team will soon publish further discoveries made since September. Scientists behind chemical instruments such as COSAC and PTOLEMY on the Philae lander, which also reported detecting unspecified organics, are likewise due to publish detailed analyses soon.

    Full article here:


  • Dmitri February 1, 2015, 13:22

    Two very interesting presentations made in SETI Institute in December 2014.

    1) Rosetta: Wild Bounce at comet Churyumov-Gerasimenko – Claudia Alexander

    64 min.

    Mainly discussed about the Rosetta orbiter and the luck ESA strike with Philae landing.

    2) Rosetta Lander mission: landing on comet 67P/Churyumov-Gerasimenko – Jens Biele


    90 min.

    Only about Philae lander & what they encountered on the way. Most importantly the Philae lander will wake up in April/May. Recharge batteries in June/July. Be up & running during the most interesting period July-September.

    Equinox on P67 is on May 12. Then Rosetta can start to map the souther hemisphere of the comet. At the moment it’s completely terra incognito.

    The faith & decisions of Philae are important as the Rosetta mission stakeholders have to decide will they do last attempt of locating Philae & take the pictures of the area where its whereabout is considered to be @ 6 km altitude fly-over. It means it will have impact on long term science mission. So far no decision. This, if decided in favor of the SAR mission, will be the only attempt to locate Philae. Next one will be considered only in 2016.

    Per Jens Biele presentation I got impression they have pretty good understanding based on telemetry where Philae has settled narrowing a 50m x 100m strip. He had no doubt of Philae calling back when battery is recharged enough to ping the Rosetta orbiter back letting it know about his back in business status.

  • Dmitri February 1, 2015, 14:07

    It’s now confirmed Rosetta will have on 14 Feb fly-over @ 6 m altitude to locate exactly Phliae lander location. This will be the only dedicated search mission at all. Even though the next could take place no earlier than 2016 this is the only low altitude pass Rosetta will make.
    Although Rosetta is flying to within 6 km of the comet’s surface on 14 February, the planned trajectory foresees the closest approach on the lower part of the larger comet lobe (although the trajectory also takes Rosetta over the first touchdown point). This trajectory is planned such that the Sun will be directly behind the spacecraft, allowing the acquisition of shadow-free images. The close flyby will also allow the suite of science instruments on the orbiter to take spectra of the surface with unprecedented resolution and to directly sample the very innermost regions of the cometary coma in order to learn more about how the comet’s characteristic coma and tail develop.

    “Rosetta’s busy science schedule is planned several months in advance, so a dedicated Philae search campaign was not built into the plan for the close flyby,” says ESA’s Rosetta project scientist Matt Taylor. “We’ll be focusing on “co-riding” observations from now on, that is, we won’t be changing the trajectory of Rosetta to specifically fly over the predicted landing zone in a dedicated search, but we can modify the spacecraft pointing and/or command images to be taken of the region if we’re flying close to the region and the science operations timeline allows.”

    “After the flyby we’ll be much further away from the comet again, so are unlikely to have the opportunity for another dedicated lander search until later in the mission, maybe even next year,” adds ESA’s Rosetta mission manager Fred Jansen. “But the location of Philae is not required to be able to operate it, and neither does it need to be awake for us to find it.”