Half Comet-Half Asteroid a Fluke? Nope

Article written: 5 Aug , 2009
Updated: 24 Dec , 2015
by

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Back in 1996, astronomers discovered a strange object in the asteroid belt. They decided it was either a “lost” comet or an icy asteroid, as it ejected dust like a comet but had an orbit like an asteroid. No one had ever seen anything like the object, called 133P. Ever since it was found, astronomers have wondered if it was just an oddity — one of a kind. We now know it is not, and the discovery of more of these half asteroids/half comets means there is a new class of objects in our solar system.

One of these new objecst, 176P/LINEAR is also emitting dust as it orbits in the asteroid belt. It was found by Henry Hsieh at Queen’s University, Belfast in Northern Ireland. Hsieh has been working to figure out the unusual behavior of 133P. He hypothesized that either one of two things could explain the existence of the comet-asteroid: “(1.) 133P is a classical comet from the outer solar system that has evolved onto a main-belt orbit, or (2.) 133P is a dynamically ordinary main-belt asteroid on which subsurface ice has recently been exposed,” Hsieh wrote in his paper. “If (1) is correct, the expected rarity of a dynamical transition onto an asteroidal orbit implies that 133P could be alone in the main belt. In contrast, if (2) is correct, other icy main-belt objects should exist and could also exhibit cometary activity.”

Hsieh thought it was unlikely a comet could have been kicked around enough to end up in orbit in the asteroid belt, so he followed the assumption that 133P was a dynamically ordinary, yet icy main-belt asteroid. He set out to prove the hypothesis that 133P-like objects should be common and could be found by an well-designed observational survey.

Hsieh made 657 observations of 599 asteroids in the asteroid belt and found 176P/LINEAR. He also determined the asteroid is partially made of ice, which is being ejected following a collision with another object, thus the comet-like attributes.

Additionally, since there is evidence for past and even present water in main-belt asteroids, Hsieh says statistically there should be around 100 currently active Main Belt Comets (MBCs) as these objects are called, among the kilometer-scale, low-inclination, outer belt asteroid population.

The Technology Review blog offered suggestions for what to name these new objects that are half comet and half asteroid: “Comsteroids? Asteromets? Hsiehroids?”

Hseih’s paper,
Hseih’s website on MBCs
Sources: Technology Review Blog, arXiv

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45 Responses

  1. Jon Hanford says

    I wonder where Comet Holmes, with its orbit in the the asteroid belt, fits into the overall scheme of things?

  2. Astrofiend says

    What about naming them ‘hemorrhoids’? That’s what trying to keep track of all of these artificial demarcations and designations f9or solar system objects is giving me! Pain in the a__!

  3. SteveZodiac says

    There’s the water for the new moonbase – go fetch!

  4. mang says

    Iceteroids!

  5. Torbjorn Larsson OM says

    How is that fitting in with that new-fangled hypothesis of comets being a relatively large part of the asteroid belt, after the initial bombardment, LHB and all?

    what to name these new objects that are half comet and half asteroid

    Depends on how the population ended up there. If it’s the above, I suggest late-cometoids.

    If it’s Hsieh’s model, I’ll think mang’s suggestion says it best.

  6. Paul Eaton-Jones says

    Didn’t I read somewhere that Chiron exhibited similar cometary features?

  7. Spoodle58 says

    I have always considered asteroids & comets the same, regardless of their chemical makeup or mass.

    I really don’t see what the point is in making a difference, unless someone can educate me otherwise.

  8. mang says

    @spoodle58 – there’s lots of reasons for them to be considered as different: composition, range of size, point of origin, visibility, orbits, and more. But broadly, yes they’re all minor bodies.

    To the man in the street visibility may be the only thing that they might notice. Orbits and the ability of a comet to surprise us (e.g. a near miss/impact) should also matter. Known comets haven’t come all that close to Earth. Asteroids on the other hand have had far more very near misses. We have a far better handle on asteroids than comets in this regard.

    To people studiying them there are already lots of subcategories based on things like composition and orbit. So this is just one more for them.

  9. ElroyJetson says

    spoodle58, that’s a good point. So far, the surfaces and compositions of all the comets examined, in sufficient detail, indicate they are basically indistinguishable from asteroids. Ice/water was not detected during the Deep Impact mission, the images were of a cratered, rocky surface, like an asteroid. The impactor, also, did not produce a significant, sustained increase in the OH, or hydroxyl, radical…the detection of which in a comets tail is assumed to come from ice sublimation. Other close encounters with comets have produced similar results.
    Other processes could be the causation for the OH detected in comet tails.
    The MESSENGER probe around Mercury has detected “magnetic tornado’s” ripping ions from the surface, as well as ongoing “chemical sputtering” as a result of constant bombardment by the solar wind plasma .

    The particles that MESSENGER can find near Mercury got there as a result of the solar wind bombarding Mercury’s surface, reacting chemically, and knocking off atoms or molecules, a process called chemical sputtering. In a way, then, when FIPS scoops up particles from Mercury’s atmosphere, it is really tasting the chemical composition of Mercury’s surface.

    What they fail to mention is that in the course of Mercury’s interaction with the solar wind plasma, is the fact that ions will recombine, or split, in the process producing new molecules and ions that were not necessarily present on the surface.
    MESSENGER also detected a cometary, stringy filamentary tail coming from Mercury. A similar tail has been detected on Venus as well.

    No spectral analyses were done on the asteroids in this paper. No mention of hydroxyl or OH. Therefore, it becomes pure conjecture to declare that these asteroids tails are from sublimating ice. Even if OH were detected, as with comets (Deep Impact) or Mercury or Venus, this does not mean it comes from sublimating ice. It could be the result of the same kind of “chemical sputtering” detected on Mercury. Perhaps these asteroids, and others like them, have a composition that causes them to occassionally “sputter” in the solar wind stream.

  10. Member
    geraldspace says

    This is not a new idea. The suggestion that many asteroids are, in fact, old, dead (or nearly dead) comets goes back at least to the early 1990s. Dr. Charles Wood wrote a paper proposing this.

  11. Member
    geraldspace says

    Should have said “early 1980s” in the previous post.

  12. ND says

    ElroyJetson,

    The Deep Impact mission did record water from the impact, it was less than expected but there most definitely was water. From the Deep Impact wiki page:

    “A total of 5 million kilograms (11 million pounds) of water[35] and between 10 and 25 million kilograms (22 and 55 million pounds) of dust were lost from the impact”

    See also: http://www.newscientist.com/article/dn7961

  13. ElroyJetson says

    According to this paper:

    http://www.iop.org/EJ/article/1538-3881/131/2/1130/205024.web.pdf

    What was detected was OH, and much less than expected. Some of the PRE-impact OH levels were as high, or higher than, post impact levels.

    Ya need to get down to the details of the actual research papers to discover the facts, which are often quite different than what’s portrayed in sensationalized media headlines and articles.

    BTW, the footnote (35), in the Wiki entry regarding water from Deep Impact is from a BBC article, not a scientific paper. LOL

  14. wiseguy says

    How about calling them “Hemorrhoids”?.Just like “Uranus.This way we would be one step closer to having the entire private anatomy of humans written in the starts.As if we do not lack sexual symbolics in our terrestrial structures.For humans every road leads to vagina and not rome”.We need more humour in these times of trouble.

  15. wiseguy says

    We all know that there are already many OHs and PRE-impact activitiy going down…down here.

    Someone is always going down on something but mostly it is all directly connected to the human obsession with copulation.

    It is all subconscious for most people of course.

  16. Jon Hanford says

    Elroy Jetson, you may want to jet over to the Wiki page on Halley’s comet, which spacecraft have visited and check out the “Structure and Composition” section of this comet. Many (but not all) comets are suspected of having rather low density, porous, weakly bound cores. Only P3200 Phaetheon (parent body of the Geminid meteor shower) comes to mind as a possible defunct comet that now serves as a repository for an annual meteor shower πŸ™‚

  17. Jon Hanford says

    That Wiki link to Halley’s Comet can be found here: http://en.wikipedia.org/wiki/Halley%27s_Comet .

  18. Jon Hanford says

    References as to the density of Halley’s comet appear as references 6 and 7 in the above linked Wiki page. Both Giotto and Russian teams came to the same conclusion that the density of the nucleus of Hally’s comets is quite low.

  19. Anaconda says

    I saw the exchange between Elroy Jetson and ND. Clearly, ND, whether intentionally or not, got caught passing on false information.

    Now, I had to hold back to see what happened because, there are those that will attack my comments, no matter what.

    No response to the paper Elroy Jetson presented on the the Deep Impact and the lack of water, which contradicts the “snowball” theory.

    Instead, Jon Hanford presents supposed data on Haley’s comet.

    Of course, that in itself is a non-answer, although, the obvious response is that all comets are alike and these other papers say Haley’s comet is consistent with a “snowball’s” density.

    But what do these Wikipedia papers really say?

    Foot note 6, Abstract:
    “What is known about the mass production, gas velocity, asymmetry factor, and angle of the nucleus of Comet Halley is examined in order to arrive at an estimate of the average density of the nucleus. An estimate of 0.6 g/cu cm + 0.9 or – 0,.4 g/cu cm is obtained. This result is compatible with ‘snowball’ models of the nucleus, although a more compact ice structure could correspond to such a density value.”

    “What is known…”

    You mean what has been ASSUMED about this. And since all “modern” astronomy ASSUMPTIONS have been that comets are “snowballs”, then no wonder, “what is known” suggests a “snowball” density.

    Consider Wikipedia footnote 7:

    Passage from abstract:
    Although some of the densities obtained by this procedure are in reasonable agreement with intuitive expectations of densities near 1 g/cm3, the uncertainties in several parameters and assumptions expand the error bars so far as to make the constraints on the density uniformative. So many of these uncertainties apply to all procedures proposed for determining the density that we conclude that secure, informative constraints on the density of any cometary nucleus must await a spacecraft rendezvous with that nucleus. In particular, the suggestion that cometary nuclei tend to by very fluffy, undersense objects should not yet be adopted as a paradigm of cometary physics.”

    I’m sorry, but the clear import of the above passage is that the data is insufficient to make conclusions about density.

    And there we have it.

    A non-response about a different comet turns out to be much less than Hanford was promoting it for.

    And why raise Haley’s comet at all?

    Because “modern” astronomy can’t stand the thought that their “dirty snowball” hypothesis is wrong and the “electric” comet theory is right.

    Why?

    Because then it becomes apparent that many other objects and processes may be consistent with an “electric” analysis & interpretation, rather than the “modern” astronomy dogma.

    But in the process of trying to refute the “electric” comet theory, they show how divorced form the Scientific Method “modern” astronomy has become.

    No wonder, when you realize how all these people believe in a whole fantasy Universe of make-believe objects.

  20. Jon Hanford says

    Anaconda, here’s some more wiki content for you to bash: http://en.wikipedia.org/wiki/Comet_nucleus πŸ™‚ . Why not write up some ‘correct’ material on comet densities and submit it to the Wiki editors. Please enlighten the entire scientific community of the ‘fantasy Universe’ they live in, Dr Anaconda.

  21. Jon Hanford says

    Anaconda, care to explain how several instrumented spacecraft in near proximity to several cometary nuclei grossly misjudged their density? These were, after all, in situ experimental observations, of the type you are so enamoured with !

  22. Jon Hanford says

    By all means, Anaconda, write up your interpretation of the ‘electric comet’ theory and submit it to Nature, Science, the Astrophysical Journal, the Monthly Notices of the RAS, or Psychology Today. Oh, and let us all know when it is to be published. Can’t wait to see that πŸ™‚ .

  23. Jon Hanford says

    And again, silence from Anaconda concerning: “A recent paper appeared at the arXiv.org site entitled “AINUR: Atlas of Images of NUclear Rings” (link to abstract & full-resolution images here: http://arxiv.org/abs/0908.0272 ) that has a great overview of nuclear rings in galaxies and a numerous examples of such, including NGC 1097. This work presents a great atlas of all known nuclear rings in galaxies that highlight the diversity of nuclear rings and the types of galaxies in which they are found. And no mention of multiple Z-pinches, plasmoids, or other EU ‘phenomena’ πŸ™‚ . And still no answer to those questions posted by myself and others (you know who you are!). Nothing from Anaconda on a number of crucial matters regarding ‘EU theory’ that have repeatedly been asked of him (primarily relevant peer-reviewed published papers in astrophysical journals or Science or Nature). Or maybe, the dog has eaten those papers, too πŸ™‚

  24. Jon Hanford says

    Anaconda, maybe you need a lesson on the history of asteroidal research. In my post above, I noted that the parent body of the Geminid meteor shower is in fact 3200 Phaethon, usually listed as an asteroid or defunct (outgassed) comet. I’ve known about 133 P/Elst-Pizzarro, P/2005 U1 and 118401 for at least a couple of years. I have followed the odd plight of Comet Holmes, which resides in the asteroid belt between Mars and Jupiter. So where do find any mention by me that all comets are ‘dirty snowballs’ or the like. Just don’t misconstrue my posts to boost your ego. One my best childhood and professional friends, Dr. Richard Binzel, is my go-to guy for all things asteroidal, as befits his title of head of the Minor Planets division of the IAU. We’ve exchanged many e-mails on this very topic over the years, and, at this point regard him as the reigning expert on small solar system bodies as opposed to a self-confessed math illiterate posting here at UT.

    Still waiting on those EU interpretations on the inner ring of NGC 1097 πŸ™‚

  25. Anaconda says

    @ Jon Hanford:

    Apparently, you don’t appreciate when somebody actually reads the footnote you directed attention to, and I say that because all your commentary ignores the actual language of the footnote you pointed to, but I quoted a passage from:

    And since you ask, here is the “poster” of the electric comet:

    http://thunderbolts.info/pdf/ElectricComet.pdf

    The evidence and reasoning is compelling (yes, Thornhill failed to give proper credit on the picutures), and self-explanatory.

  26. ElroyJetson says

    Thanks jonhanford. I was searching for info about that ‘electric comet’ thing you mentioned, found some interesting links, and noticed that one of them is the same one anaconda posted. It fits right into my thoughts on the link with the sputtering on Mercury.
    It does seem to explain a lot, and makes sense too. A highly ionized gas, like the solar wind plasma, would react like an acid so I suppose that could be another way of looking at the sputtering action.

    Apparently there isn’t much hard evidence to prove that most comets have significant quantities of water. What’s wrong with acknowledging that? Though there does seem to be quite a bit of this “sputtering” going on in different places.

    Why not look into that, and why the hostility? Sheesh, reminds me of the Inquisition or something. I was hoping for some interesting discourse, but that doesn’t seem to be happening here. More like playground bullies than anything.

    Sorry, jonhanford, if all ya got is Wiki and something akin to “my dad’s smarter than your dad”…credible? Mmmmm…Not so much. πŸ™‚

  27. ND says

    ElroyJetson,

    In the paper you posted authors are talking about water from the comet. The OH they measured is from water based on the “Haser OH production”. According to the Haser OH model, water from a cometary nucleus is expectd to dissociate into OH and H:

    books.google.com/books?id=RaJdy3_VINQC&pg=RA2-PA375&dq=haser+oh+production+model#v=onepage&q=haser oh production model&f=false

    The authors of the paper appear to be comfortable with the idea that water is the source of OH. But this is just my vague understanding of the subject after doing a quick reading here and there. Your comments about observing-OH-not-H2O sounds like red herring to me.

    Also they did detect ice on the surface of Comet Temple 1 based on direct observation.

    ncbi.nlm.nih.gov/pubmed/16456037

    From the above abstract:

    We report the direct detection of solid water ice deposits exposed on the surface of comet 9P/Tempel 1, as observed by the Deep Impact mission. Three anomalously colored areas are shown to include water ice on the basis of their near-infrared spectra, which include diagnostic water ice absorptions at wavelengths of 1.5 and 2.0 micrometers.

    A quote from the paper you linked to:

    In fact, there is no evidence of the ongoing
    release of additional dust resulting from the impact, and the data
    are consistent with no significant increase in outgassing due to a
    possible new source region at the impact crater. This, however, is
    not surprising, as the crater is presumably much smaller (<1%)
    than the $2 km2 total active area required to produce the baseline
    water production (A’Hearn et al. 1995; Cowan & A’Hearn 1979),
    and therefore below our detection threshold.

  28. Jon Hanford says

    Elroy Jetson, in wiki pages leave you unconvinced, how about this paper presented to the Lunar and Planetary Science XXXIV Symposium in 2006: http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2214.pdf . And how would you explain the densities derived from 5 spacecraft making 4 in situ measurements of Comet Nuclei (Halley, Borrelly, Temple 1 and Wild? Is NASA, the ESA and the Russian space program all lying to us concerning the measurements made by their spacecraft of the low density for these four comets? Maybe a re-read of the wiki link on ‘Comet Nucleus’ and its independent sources is in order. Please explain your reasoning for a dense comet and any ‘electric comet’ theory, preferably by citing peer-reviewed, published papers in the appropriate journals. And Pleeeaaase no links to anything by Talbot and/or Thornhill (these have already been posted ad nauseum). If these authors are correct, they deserve the Nobel Prize in Physics. I’m not holding my breath πŸ™‚

  29. Nereid says

    The bulk densities of several comets have been estimated, and they are all ~3.

    Here is one document on such estimates, a presentation at the Workshop on Spacecraft Reconnaissance of Asteroid and Comet Interiors October 5-6, 2006, “Size Distribution, Structure and Density of Cometary Nuclei”:
    http://www.lpi.usra.edu/meetings/recon2006/pdf/3025.pdf

    In my next comment I’ll provide a second link, to a paper (actually an ArXiv preprint). There are plenty more papers, but it seems that in this community (planetary sciences) the practice of putting preprints on ArXiV is not yet established, so most are only available to print journal subscribers, or for a not insignificant fee.

  30. Nereid says

    OK, that did not display as typed.

    It should read “and they are all less than approx 1 gram per cubic cm. This is completely inconsistent with the Electric Comet idea, which requires that comets’ bulk densities be greater than approx 3 gram per cubic cm (i.e. they are rocks).

    As promised, a recent preprint, accepted for publication in MNRAS, “Cometary masses derived from non-gravitational forces”:
    http://arxiv.org/abs/0811.0745

  31. Nereid says

    Anaconda introduces the infamous Thornhill poster.

    I spent some time going through it, and posted my results in a thread, started by a self-admitted proponent of EU ideas, in BAUTForum, entitled “New research results from the “Stardust” mission”^.

    From one of those posts:

    Are Thornhill and Talbott being (intellectually) dishonest? Is there something fraudulent about the “The Electric Comet” document?

    There’s a prima facie case to say they are, and that there is.

    (source: http://www.bautforum.com/1189953-post73.html)

    And no, the apparent intellectual fraud is much worse than not giving credit for some images Anaconda.

    So what about Anaconda’s “The evidence and reasoning is compelling”?

    Well, I invite him – and ElroyJetson and anyone else interested – to go through my BAUTForum posts and take Anaconda’s advice “You can delude yourself if you want, but I’ll follow the scientific evidence where it leads” (quoted from an earlier UT story comment; I bolded the bit about science). I am particularly interested in discussing scientific evidence; I am also interested in not being deluded by material that seems fraudulent (in an academic, or intellectual, sense).

    ^The main posts start at #64.

  32. Nereid says

    The link in my last comment is wrong (it includes the closing bracket).

    Here is a URL that should work:
    http://www.bautforum.com/1189953-post73.html

  33. Jon Hanford says

    Here’s a link to an abstract from the Giotto and Vega teams published in Nature in 1987 entitled “Is the nucleus of comet Halley a low density body?” In the abstract, the authors state “In this paper we estimate rho to be 0.6 +0.9-0.4g cm-3 compatible with the ‘snow-ball’ models of the nucleus, although a more compact ice structure could correspond to such a density value.” So now these authors have falsified data that conflicts with the ‘EU interpretation’ of these in situ measurements made by spacecraft from ESA and the Russian Space Agency? Sounds conspiratorial to me!

    I have no opinion on whether the majority of comets harbor any type of water. My contention is that the density of several comets have been observed in situ and found to have low densities. This doesn’t rule out all comets, of course, as I made reference to above, only that the majority of comets sampled show them as low density objects. Anaconda constantly harps on the need for in situ measurements to be made (as in his THEMIS posts), but then totally rejects those made by these 5 spacecraft of four different comets when they don’t agree with his ‘theories’. You can’t have it both ways, Anaconda. Either the THEMIS data is wrong or the 5 missions to four comets are wrong. Which is it?

    And what of Anaconda’s motto; “You can delude yourself if you want, but I’ll follow the scientific evidence where it leads”. Rings rather hollow, doesn’t it?

  34. Jon Hanford says

    The link to the 1987 Nature abstract can be found here: http://www.nature.com/nature/journal/v331/n6153/pdf/331240a0.pdf .

  35. Jon Hanford says

    Nereid, thanks for that link concerning the Thornhill and Talbot ‘Electric Comet’ nonsense. What is this ad-hoc conglomeration of sophists trying so desperately to prove? Sounds like sour grapes or uneducated guesses by some disgruntled IEEE members that ‘modern astronomers’ are close-minded and are seen as the enemy.

    Anaconda, I’m still waiting for that EU interpretation of nuclear rings in NGC 1097 being a toroidal plasma with Z-pinch mechanisms responsible for star formation in these rings. Citations, please. Did the dog really eat that paper? πŸ™‚

  36. Anaconda says

    The smothering of comments suggest they don’t want to “deal” with it.

    “Kill it before it grows.”

    So be it. read the poster, see if the presentation makes sense and know those that are “hard wired” to defend “modern” astronomy for whatever reason could be presented with the best evidence possible — but as long as the “high priests” of astronomy maintain their dogma, don’t expect the acolytes to think any different.

    In fact, the acolytes have a tendency to be even more vociferous than the “high priests” because they never want to admit to themselves that they were following a “false god”.

  37. ND says

    ElroyJetson, Anaconda,

    Any thoughts on the detection of ice on the surface of the comet?

  38. Nereid says

    There’s a post, by papageno, later in the BAUTForum thread that I referenced, that I think readers might find interesting (it’s post#91):

    Why are EU proponents getting their knickers in a twist?

    They always accuse the “mainstream” to ignore EU ideas, but when somebody does examine these ideas in detail, they complain even more!
    Nereid’s posts on the EU-comet “theory” shows the kind of examination “mainstream” scientific papers go through before and after they are published. “Mainstream” theories become such after they survived successfully such critical examinations.

    Are VanderL, Luxor or ATKINS complaining because Thornhill & Talbott’s paper has been treated just like any other scientific paper?

    Anaconda, first you say “follow the scientific evidence where it leads”, then when someone does exactly what you advise, you call it “[t]he smothering of comments”?!?

    And even declare, without evidence, “those that are “hard wired” to defend “modern” astronomy for whatever reason could be presented with the best evidence possible β€” but as long as the “high priests” of astronomy maintain their dogma, don’t expect the acolytes to think any different”?!?!?!?

  39. ND says

    “smothering of comments”. I don’t think I had heard of this rhetoric before. Must be a new tactic.

  40. ElroyJetson says

    nd, here’s a thought from NASA on the ice detected on the surface on Tempel-1:

    The comet’s surface has three small pockets of thin ice. The Tempel 1 surface area is about 116.5 square kilometers, and the ice covers 0.027 square kilometers. The rest is dust.

    Here is nd’s previous quote regarding ice on Tempel-1

    We report the direct detection of solid water ice deposits exposed on the surface of comet 9P/Tempel 1, as observed by the Deep Impact mission. Three anomalously colored areas are shown to include water ice on the basis of their near-infrared spectra, which include diagnostic water ice absorptions at wavelengths of 1.5 and 2.0 micrometers.

    Conveniently left out the little detail about the actual extent of the ice, which only covers ~ .0023% of the surface, in a thin layer, the remaining 99.9977% is dust.
    WOW. Break out the snow plows.

    As far as density goes, low density does not automatically mean ice. It could also just simply be highly porous rocky material, like pumice. The point being that density alone says nothing about composition.

    Regardless, I was talking about the possible connection with sputtering on Mercury, but nobody seems to have addressed that idea. Instead it’s been avoidance and obsfucation.

    anaconda seems to be right on with the religious dogma analogy. Even as a newbie here, I can see that anyone who doesn’t just nod and smile in agreement gets shouted down by a small group of , quite rude, “inquisitors”.

  41. ND says

    The point is that this contradicts your assertion that not ice/water was found at all and you have no evidence that there is no water on the comet while there is observational evidence for it.

  42. ND says

    ElroyJetson,

    I’m not familiar with sputtering so I’m reading up on it. It would appear that sputtering on comets has been studied. The following paper from 1977 talks about OH production from sputtering.

    http://www.springerlink.com/content/h0771w612w235113/

    At the end of the abstract is this:

    “The observed OH production rates in comets are however too large to be explained in this way and are certainly the results of sublimation and dissociation of H2O from an icy nucleus.”

    Unfortunately this is just and abstract and from 1977.

    So the question is how does the observed OH production from comets fit in with the the OH production from sputtering and water. If a nucleus is expelling water, it’s my understanding that OH will also be produced.

    Here’s another paper from 1990 talking about sputtering and comets. I have not read it, but I’m throwing out there as a point that sputtering has not been ignored:

    articles.adsabs.harvard.edu//full/1990ApJ…365L..39M/L000039.000.html

  43. Nereid says

    @ElroyJetson: I’m not sure how you came to your conclusion; would you care to explain?

    Even as a newbie here, I can see that anyone who doesn’t just nod and smile in agreement gets shouted down by a small group of , quite rude, “inquisitors”.

    For my part, the only alternative idea that has been presented is a PDF document, complete with a copyright notice, stating it is a poster at an international science conference.

    As I had spent quite a bit of time, a while ago, going through this document in great detail, I considered it appropriate to bring the results of my work to the attention of all readers.

    Further, I invited you – explicitly – to discuss any part of my findings.

    Concerning this:

    As far as density goes, low density does not automatically mean ice. It could also just simply be highly porous rocky material, like pumice. The point being that density alone says nothing about composition.

    That’s quite right.

    However, AFAIK, the distribution of the estimated bulk densities of comets and asteroids is bimodal: comets have bulk densities below approx 1 g/cc, asteroids around 3 g/cc, with none as low as 1 g/cc (caveat: I’m going from memory, and IIRC this refers to main belt asteroids and NEAs, possibly Trojans too). Would you be interested in some references?

    Further, there is a great deal of detailed material in the preprint I cited earlier, and it the papers it references, on the mass outflow from comets and its composition; may I ask if you read that material? If so, what did you learn?

    Regardless, I was talking about the possible connection with sputtering on Mercury, but nobody seems to have addressed that idea. Instead it’s been avoidance and obsfucation.

    As you know, plenty of comets exhibit ‘cometary’ behaviour well beyond 60 million km from the Sun (the approx radius of Mercury’s orbit); in particular, they are active at about 1 au, and even at Mars’ distance. Yet, AFAIK, no ‘Mercury-like’ sputtering has been observed on the Moon, Eros, Phobos, or Deimos, despite quite intensive in situ studies of the Moon (and somewhat less intensive ones of the other three).

    Comments?

  44. ND says

    To follow up on my last posting to ElroyJetson:

    Looks like Rosetta will be studying sputtering on it’s target comet “67P/Churyumov-Gerasimenko”

    rosetta.jpl.nasa.gov/dsp_structureComets.cfm?buttonSel=scienceObj&buttonSelL2=knowledge (search for sputtering).

    Also:
    – Sputtering on comets has been considered and looked into for decades.
    – lab experiments on sputtering and other processes have been done to compare with observations (Anaconda will like this I’m sure, he loves this sort of stuff πŸ™‚
    – sublimated from a comet is expected to produce OH along with sputtering.

    There are quite a few papers out there talking about sputtering on comets and sometimes at the same time with astroids and our Moon.

    And yet with all this sputtering astronomers are still talking about water on comets. Are they being dogmatic about an old idea or do they understand something you don’t?

  45. ND says

    In the course of looking into detecting ice/water via spectra, I came across the following and posting here for curiosity:

    http://www.lowell.edu/users/grundy/H2Oice.html

    The paper I linked to regarding detecting ice on the surface mentioned absorptions at 1.5 and 2.0 um. This fits in with the above absorption profile’s 2 largest peaks.

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