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Re: [comets-ml] Some Comet Lovejoy speculations

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  • jbortle@aol.com
    David - As a first approximation, I would say that your conclusions seem quite reasonable. Certainly, something quite unusual occurred with Comet Lovejoy over
    Message 1 of 14 , Jan 3, 2012
      David - As a first approximation, I would say that your conclusions seem
      quite reasonable. Certainly, something quite unusual occurred with Comet
      Lovejoy over the course of its apparition. That its post-T survival, at least
      to a degree, violates my perihelion survival "law" is most interesting,
      although I would note (as my paper on the subject indicated) that a number of
      small, periodic comets (like P/Encke, et al.) do so on a quite regular
      basis. The situation being so, this suggests to me that Comet Lovejoy must have
      experienced at least one previous perihelion passage as a totally
      independent body (i.e. it was not a fragment formed a its immediate previous
      perihelion passage) and thus had a fully formed and fairly dense overall
      insulating layer over its entire surface.Such a "baked" surface which totally shuts
      down early might well also explain why Kreutz sungrazers tend to disappear
      much sooner post-T (typical by about 1.5 AU post-T) than do other comets of
      similar intrinsic brightness.

      There is also the problem that although of a seemingly extremely faint
      intrinsic brightness both pre and post-T, Comet Lovejoy still presented a
      viable and distinct "head" post-perihelion. This while objects like the Great
      Southern Comet of 1887, assumed to be much brighter intrinsically than 2011
      W3, appeared to have survived only as huge tail apparently without any
      head. Of course, the Kreutz sungrazing group's orbital orientation so strongly
      favors visibility from the Southern Hemisphere that it has undoubtedly
      limited the opportunities to watch the development of other examples of
      seemingly faint members of this clan in the more distant past.

      I find it equally interesting how one explains the long-enduring bright
      streak extending from the position the nucleus should occupy to relatively
      far out into the tail. And the fact that this feature seems to have evolved
      surprisingly little since its sudden appearance. A few descriptions of the
      Great September Comet of 1882 do make mention of a similar "streak" in that
      comet's head, dotted with a number of brighter star-like nucleii, but that
      feature seemed fairly short lived and was on a physical scale apparently
      far smaller than that displayed by Comet Lovejoy. Are we perhaps seeing a
      very long train of tens of thousand of ONLY tiny fragments with absolutely no
      large survivers, distributed along the orbit by size/mass? But then how
      could this form so suddenly and how could a coma persist without some viable
      solid body evident at its focus? According to Rod, there is no evidence of
      any independent surviving body down to 19th magnitude in that location.

      And I'm still very curious about the nature of the faint yet distinct
      "sheath" that is seen to envelope both the dust and gas tails of numerous Kreutz
      sungrazers post-T, well seen with 2011 W3, yet does not seem evident with
      regard to other very small "q" non-Kreutz comets. What is the nature of it?
      And in the case of the Great September Comet it not only surrounded the
      tail but was described to extend well sunward of the head!

      I unquestionably foresee a long and interesting future of papers
      attempting to address the amazing sights we've seen over the course of the past
      month!

      J.Bortle




      In a message dated 1/2/2012 11:49:46 P.M. Eastern Standard Time,
      seargent@... writes:





      Hi all,
      Just a few ideas to put before the group.
      As I wrote previously, I suspect that the initial intrinsic faintness of
      this comet was not so much a function of the small size of the nucleus, but
      of the presence of a surface crust of refractory material. If the nucleus
      was about 500 metres diameter (as against the 100 - 200 as initially
      estimated) and covered by an insulating crust, this might explain how it survived
      perihelion passage intact. If the insulating layer was blown off around
      perihelion, this may even have formed a "sun umbrella" of particles that
      shielded the freshly-exposed icy surface of the nucleus, rather as is thought to
      have happened to Seki-Lines in 1962 (analysis of the dust tail suggests
      that this comet shut down for a few hours at perihelion - q = 0.03 AU - which
      also helps to explain why there were no daylight sightings of this
      intrinsically bright object). In the case of Lovejoy, a similar event may have
      been a factor in preserving its existence. Once the meteoric cloud dispersed,
      the co met burst into furious activity, however by then the worst of its
      ordeal was already over.
      The presence of an ion tail clearly indicated an active nucleus following
      perihelion. However, as this has this has now disappeared, it may be that
      ice-driven activity has ceased. This could mean that the nucleus has
      disappeared, or run out of ice or (I think the most likely explanation) has had
      the ice cooked out of the surface layers. In other words, the comet may by
      now have built up a new insulating layer that is effectively keeping heat
      from underlying ice.
      Yet, the "head" appears to be persisting as if some dust continues to be
      released. Just a speculative thought, but electrostatic repulsion caused by
      solar radiation can levitate fine dust on the surface of the Moon (causing
      the unexpected crepuscular rays seen by the Apollo astronauts) and is
      thought responsible for the small flare experienced by Phaethon in 2009. With
      respect to the latter, David Jewitt called Phaethon a "rock comet" - capable
      of low-level activity even in the absence of ice - and suggested that this
      process may even be responsible for the formation of the Geminid meteor
      stream. For what it is worth, I suggest that the present weak activity of
      Lovejoy could be due to this process lifting dust from what has again become a
      totally encrusted nucleus.
      All very speculative I know, but comments welcome.
      Cheers,
      David

      [Non-text portions of this message have been removed]






      [Non-text portions of this message have been removed]
    • RICHARD MILES
      ... I agree that a temporary surface crust of material can form, but not as you have envisaged here. One key factor here is that time near closest approach is
      Message 2 of 14 , Jan 3, 2012
        David Sargeant wrote:
        > As I wrote previously, I suspect that the initial intrinsic faintness of
        > this comet was not so much a function of the small size of the nucleus,
        > but of the presence of a surface crust of refractory material. If the
        > nucleus was about 500 metres diameter (as against the 100 - 200 as
        > initially estimated) and covered by an insulating crust, this might
        > explain how it survived perihelion passage intact. If the insulating layer
        > was blown off around perihelion, this may even have formed a "sun
        > umbrella" of particles that shielded the freshly-exposed icy surface of
        > the nucleus, rather as is thought to have happened to Seki-Lines in 1962
        > (analysis of the dust tail suggests that this comet shut down for a few
        > hours at perihelion - q = 0.03 AU - which also helps to explain why there
        > were no daylight sightings of this intrinsically bright object). In the
        > case of Lovejoy, a similar event may have been a factor in preserving its
        > existence. Once the meteoric cloud dispersed, the comet burst into furious
        > activity, however by then the worst of its ordeal was already over.

        I agree that a temporary surface crust of material can form, but not as you
        have envisaged here.

        One key factor here is that time near closest approach is relatively short -
        i.e. the nucleus remained within 5 solar radii of the barycenter for about 6
        h, and 2 solar radii for just 1.5 h. You have to consider both the solar
        electromagnetic radiation flux and also the flux of high energy baryons /
        charged particles, typically protons travelling at speeds of ~500 km/s. The
        initial effect of these is to strip away any "umbrella of dust particles"
        leaving the bare nucleus exposed to the 'onslaught' from the Sun.

        A more likely scenario may involve a Leidenfrost-type phenomenon. Here's
        how I see it:

        A large fraction of the near-surface material within the nucleus is likely
        to melt. The surface tension between the melt and any residual solids
        provides significant mechanical strength, more especially if most of the
        refractory solids are in the 1-1000 micron size range. This process
        temporarily inhibits physical break-up. Now if you assume a large fraction
        of the incident energy (electromagnetic radiation and particle kinetic
        energy) is absorbed by the surface, this will cause a proportion of the
        molten material to vaporize - but how much depends on the latent heat of
        vaporization of the material and the time-scale involved. The vapour boiled
        off from the melt is in effect a thin gaseous atmosphere, which will
        increase in pressure until a temporary bow-shock front develops. It is this
        bow-shock effect which may act as the "umbrella" - a "parapluie" could be
        more descriptive a word for this. If the gas pressure behind the bow-shock
        reaches a sufficient magnitude (Poiseuille conditions of P and T arise),
        particulates will also be entrained in the gas flow. Given this scenario,
        the surface of the nucleus can be shielded to a degree by two processes; (a)
        partial deflection of the intense oncoming solar wind by the bow-shock, and
        (b) particulates suspended in the temporary gas layer absorb some of the e-m
        radiation and re-radiate it back into space. Overall this creates a type of
        Leidenfrost effect and a temporary pseudo-steady state enabling the nucleus
        to survive perihelion passage.

        Remember, although H2O ice is an important constituent, as the thermal
        regime evolves to higher and higher temperatures, different materials which
        are normally solid will each begin to melt and play a significant role.

        What will be important now is to characterise the nature of any remaining
        particulates close to the centre of any debris field using large
        ground-based telescopes or the HST. Let's hope such observations are
        successful.

        The fate of the nucleus depends on what happened post-perihelion.
        Sufficient time has passed such that, given the very large thermal
        gradients, significant heat conduction to the central region of the nucleus
        would have occurred. You then have a complex situation in which solids melt,
        liquids vaporize and internal gas pressures develop leading to gradual
        disintegration of the nucleus. What debris remains will be to an extent an
        assay of the more refractory material from deep within the original nucleus.

        Richard Miles
        BAA
      • RICHARD MILES
        ... John - Allow me to follow through one possible interpretation based on my earlier description of the near-perihelion scenario: We talk about dust (i.e.
        Message 3 of 14 , Jan 3, 2012
          John Bortle wrote:
          > And I'm still very curious about the nature of the faint yet distinct
          > "sheath" that is seen to envelope both the dust and gas tails of numerous
          > Kreutz
          > sungrazers post-T, well seen with 2011 W3, yet does not seem evident with
          > regard to other very small "q" non-Kreutz comets. What is the nature of
          > it?
          > And in the case of the Great September Comet it not only surrounded the
          > tail but was described to extend well sunward of the head!

          John - Allow me to follow through one possible interpretation based on my
          earlier description of the near-perihelion scenario:

          We talk about dust (i.e. refractory particles ejected from the nucleus) and
          gas (low-boiling point volatiles) but there has to be a third type of
          particle created in the case of a sungrazer nucleus. This material is in
          effect the "smoke' which is created when otherwise fairly refractory
          material is vaporized and is able to recondense to an extent.

          Two mechanisms generate this "smoke". One is created in the scenario I have
          already described. The temporary gas shell / bow shock feeds molecules of
          vaporised refractories into the comet's tail. As the gas pressure and
          temperature within the tail declines from Poiseuille conditions towards
          Knudsen conditions, a dynamic situation unfolds whereby many of these
          molecules collide and stick together building up extremely fine, sub-micron
          size refractory condensates - in essence a newly-created dust or "smoke"
          forms.

          A second mechanism can also contribute, i.e. sputtering of the surface of
          the nucleus by fast, highly energetic particles in the solar wind.
          Calculations would need to be done to see whether enough "smoke" could be
          created via sputtering of the surface in the time available - I somehow
          doubt that this can be the entire explanation.

          So taking these hypotheses into account, how can we explain the absence of
          the "sheath" in other very small "q" non-Kreutz comets. My interpretation
          here is that if the nucleus is too small it cannot build up a stable melt
          zone within the near-surface, so no temporary envelope of volatilized
          refractories and no bow-shock can form. Under such conditions, refractory
          materials will still volatilze but will not experience the conditions
          required for particles to seed and grow by molecular collision. Such
          refractory molecules fail to condense along with others, hence no "smoke"
          can form. This may explain the absence of the "sheath" seen in larger Kreutz
          sungrazing comets.

          Richard Miles
          BAA
        • David Seargent
          Hi John and all, John - I agree that the comet most probably has made a previous perihelion passage as an independent body, but it may not necessarily have
          Message 4 of 14 , Jan 4, 2012
            Hi John and all,
            John - I agree that the comet most probably has made a previous perihelion passage as an independent body, but it may not necessarily have been an independent COMET. Although unlikely, it is possible that it may have broken away as a secondary nucleus while the parent was still moving toward its previous perihelion. The situation would then be a little like the Marsden sunskirters C/2004 V9 and V10. Sekanina has shown that V10 broke away from V9 about 3 months prior to its previous perihelion passage, at which the split comet was observed as C/1999 J1 (albeit not resolved into two nuclei in the SOHO images). Interestingly, the circumstances of this disruption meant that the smaller V10 (although discovered after V9) reached perihelion before V9; the opposite of what happens when comets split at or shortly after their previous perihelion passage. IF something similar has happened with W3, it is likely that the primary nucleus is still on its way and probably not very far away!
            Please, nobody read this as a prediction of another bright sungrazer in the near future. There is no real reason to think that W3 did break away from a larger object just prior to its previous perihelion, only that this remains one possibility. But it might be wise to monitor the inward path of the Kreutz group just in case...!
            Cheers,
            david





            To: comets-ml@yahoogroups.com
            From: jbortle@...
            Date: Tue, 3 Jan 2012 08:48:31 -0500
            Subject: Re: [comets-ml] Some Comet Lovejoy speculations






            David - As a first approximation, I would say that your conclusions seem
            quite reasonable. Certainly, something quite unusual occurred with Comet
            Lovejoy over the course of its apparition. That its post-T survival, at least
            to a degree, violates my perihelion survival "law" is most interesting,
            although I would note (as my paper on the subject indicated) that a number of
            small, periodic comets (like P/Encke, et al.) do so on a quite regular
            basis. The situation being so, this suggests to me that Comet Lovejoy must have
            experienced at least one previous perihelion passage as a totally
            independent body (i.e. it was not a fragment formed a its immediate previous
            perihelion passage) and thus had a fully formed and fairly dense overall
            insulating layer over its entire surface.Such a "baked" surface which totally shuts
            down early might well also explain why Kreutz sungrazers tend to disappear
            much sooner post-T (typical by about 1.5 AU post-T) than do other comets of
            similar intrinsic brightness.

            There is also the problem that although of a seemingly extremely faint
            intrinsic brightness both pre and post-T, Comet Lovejoy still presented a
            viable and distinct "head" post-perihelion. This while objects like the Great
            Southern Comet of 1887, assumed to be much brighter intrinsically than 2011
            W3, appeared to have survived only as huge tail apparently without any
            head. Of course, the Kreutz sungrazing group's orbital orientation so strongly
            favors visibility from the Southern Hemisphere that it has undoubtedly
            limited the opportunities to watch the development of other examples of
            seemingly faint members of this clan in the more distant past.

            I find it equally interesting how one explains the long-enduring bright
            streak extending from the position the nucleus should occupy to relatively
            far out into the tail. And the fact that this feature seems to have evolved
            surprisingly little since its sudden appearance. A few descriptions of the
            Great September Comet of 1882 do make mention of a similar "streak" in that
            comet's head, dotted with a number of brighter star-like nucleii, but that
            feature seemed fairly short lived and was on a physical scale apparently
            far smaller than that displayed by Comet Lovejoy. Are we perhaps seeing a
            very long train of tens of thousand of ONLY tiny fragments with absolutely no
            large survivers, distributed along the orbit by size/mass? But then how
            could this form so suddenly and how could a coma persist without some viable
            solid body evident at its focus? According to Rod, there is no evidence of
            any independent surviving body down to 19th magnitude in that location.

            And I'm still very curious about the nature of the faint yet distinct
            "sheath" that is seen to envelope both the dust and gas tails of numerous Kreutz
            sungrazers post-T, well seen with 2011 W3, yet does not seem evident with
            regard to other very small "q" non-Kreutz comets. What is the nature of it?
            And in the case of the Great September Comet it not only surrounded the
            tail but was described to extend well sunward of the head!

            I unquestionably foresee a long and interesting future of papers
            attempting to address the amazing sights we've seen over the course of the past
            month!

            J.Bortle




            In a message dated 1/2/2012 11:49:46 P.M. Eastern Standard Time,
            seargent@... writes:

            Hi all,
            Just a few ideas to put before the group.
            As I wrote previously, I suspect that the initial intrinsic faintness of
            this comet was not so much a function of the small size of the nucleus, but
            of the presence of a surface crust of refractory material. If the nucleus
            was about 500 metres diameter (as against the 100 - 200 as initially
            estimated) and covered by an insulating crust, this might explain how it survived
            perihelion passage intact. If the insulating layer was blown off around
            perihelion, this may even have formed a "sun umbrella" of particles that
            shielded the freshly-exposed icy surface of the nucleus, rather as is thought to
            have happened to Seki-Lines in 1962 (analysis of the dust tail suggests
            that this comet shut down for a few hours at perihelion - q = 0.03 AU - which
            also helps to explain why there were no daylight sightings of this
            intrinsically bright object). In the case of Lovejoy, a similar event may have
            been a factor in preserving its existence. Once the meteoric cloud dispersed,
            the co met burst into furious activity, however by then the worst of its
            ordeal was already over.
            The presence of an ion tail clearly indicated an active nucleus following
            perihelion. However, as this has this has now disappeared, it may be that
            ice-driven activity has ceased. This could mean that the nucleus has
            disappeared, or run out of ice or (I think the most likely explanation) has had
            the ice cooked out of the surface layers. In other words, the comet may by
            now have built up a new insulating layer that is effectively keeping heat
            from underlying ice.
            Yet, the "head" appears to be persisting as if some dust continues to be
            released. Just a speculative thought, but electrostatic repulsion caused by
            solar radiation can levitate fine dust on the surface of the Moon (causing
            the unexpected crepuscular rays seen by the Apollo astronauts) and is
            thought responsible for the small flare experienced by Phaethon in 2009. With
            respect to the latter, David Jewitt called Phaethon a "rock comet" - capable
            of low-level activity even in the absence of ice - and suggested that this
            process may even be responsible for the formation of the Geminid meteor
            stream. For what it is worth, I suggest that the present weak activity of
            Lovejoy could be due to this process lifting dust from what has again become a
            totally encrusted nucleus.
            All very speculative I know, but comments welcome.
            Cheers,
            David

            [Non-text portions of this message have been removed]

            [Non-text portions of this message have been removed]






            [Non-text portions of this message have been removed]
          • RICHARD MILES
            It might be helpful to the MPML group in general, and comet hunters in particular, if someone would post the apparent position of the radiant / possible
            Message 5 of 14 , Jan 5, 2012
              It might be helpful to the MPML group in general, and comet hunters in
              particular, if someone would post the apparent position of the 'radiant' /
              possible search area for the Kreutz group as seen from the Earth for each
              month of the year given the rather unusual orbit it possesses.

              Just a thought,

              Richard Miles
              BAA

              ----- Original Message -----
              From: "David Seargent" <seargent@...>
              To: <comets-ml@yahoogroups.com>
              Sent: Thursday, January 05, 2012 3:03 AM
              Subject: RE: [comets-ml] Some Comet Lovejoy speculations


              >
              > Hi John and all,
              > John - I agree that the comet most probably has made a previous perihelion
              > passage as an independent body, but it may not necessarily have been an
              > independent COMET. Although unlikely, it is possible that it may have
              > broken away as a secondary nucleus while the parent was still moving
              > toward its previous perihelion. The situation would then be a little like
              > the Marsden sunskirters C/2004 V9 and V10. Sekanina has shown that V10
              > broke away from V9 about 3 months prior to its previous perihelion
              > passage, at which the split comet was observed as C/1999 J1 (albeit not
              > resolved into two nuclei in the SOHO images). Interestingly, the
              > circumstances of this disruption meant that the smaller V10 (although
              > discovered after V9) reached perihelion before V9; the opposite of what
              > happens when comets split at or shortly after their previous perihelion
              > passage. IF something similar has happened with W3, it is likely that the
              > primary nucleus is still on its way and probably not very far away!
              > Please, nobody read this as a prediction of another bright sungrazer in
              > the near future. There is no real reason to think that W3 did break away
              > from a larger object just prior to its previous perihelion, only that this
              > remains one possibility. But it might be wise to monitor the inward path
              > of the Kreutz group just in case...!
              > Cheers,
              > david
              >
              > To: comets-ml@yahoogroups.com
              > From: jbortle@...
              > Date: Tue, 3 Jan 2012 08:48:31 -0500
              > Subject: Re: [comets-ml] Some Comet Lovejoy speculations
              >
              > David - As a first approximation, I would say that your conclusions seem
              > quite reasonable. Certainly, something quite unusual occurred with Comet
              > Lovejoy over the course of its apparition. That its post-T survival, at
              > least
              > to a degree, violates my perihelion survival "law" is most interesting,
              > although I would note (as my paper on the subject indicated) that a number
              > of
              > small, periodic comets (like P/Encke, et al.) do so on a quite regular
              > basis. The situation being so, this suggests to me that Comet Lovejoy must
              > have
              > experienced at least one previous perihelion passage as a totally
              > independent body (i.e. it was not a fragment formed a its immediate
              > previous
              > perihelion passage) and thus had a fully formed and fairly dense overall
              > insulating layer over its entire surface.Such a "baked" surface which
              > totally shuts
              > down early might well also explain why Kreutz sungrazers tend to disappear
              > much sooner post-T (typical by about 1.5 AU post-T) than do other comets
              > of
              > similar intrinsic brightness.
              >
              > There is also the problem that although of a seemingly extremely faint
              > intrinsic brightness both pre and post-T, Comet Lovejoy still presented a
              > viable and distinct "head" post-perihelion. This while objects like the
              > Great
              > Southern Comet of 1887, assumed to be much brighter intrinsically than
              > 2011
              > W3, appeared to have survived only as huge tail apparently without any
              > head. Of course, the Kreutz sungrazing group's orbital orientation so
              > strongly
              > favors visibility from the Southern Hemisphere that it has undoubtedly
              > limited the opportunities to watch the development of other examples of
              > seemingly faint members of this clan in the more distant past.
              >
              > I find it equally interesting how one explains the long-enduring bright
              > streak extending from the position the nucleus should occupy to relatively
              > far out into the tail. And the fact that this feature seems to have
              > evolved
              > surprisingly little since its sudden appearance. A few descriptions of the
              > Great September Comet of 1882 do make mention of a similar "streak" in
              > that
              > comet's head, dotted with a number of brighter star-like nucleii, but that
              > feature seemed fairly short lived and was on a physical scale apparently
              > far smaller than that displayed by Comet Lovejoy. Are we perhaps seeing a
              > very long train of tens of thousand of ONLY tiny fragments with absolutely
              > no
              > large survivers, distributed along the orbit by size/mass? But then how
              > could this form so suddenly and how could a coma persist without some
              > viable
              > solid body evident at its focus? According to Rod, there is no evidence of
              > any independent surviving body down to 19th magnitude in that location.
              >
              > And I'm still very curious about the nature of the faint yet distinct
              > "sheath" that is seen to envelope both the dust and gas tails of numerous
              > Kreutz
              > sungrazers post-T, well seen with 2011 W3, yet does not seem evident with
              > regard to other very small "q" non-Kreutz comets. What is the nature of
              > it?
              > And in the case of the Great September Comet it not only surrounded the
              > tail but was described to extend well sunward of the head!
              >
              > I unquestionably foresee a long and interesting future of papers
              > attempting to address the amazing sights we've seen over the course of the
              > past
              > month!
              >
              > J.Bortle
              >
              >
              >
              >
              > In a message dated 1/2/2012 11:49:46 P.M. Eastern Standard Time,
              > seargent@... writes:
              >
              > Hi all,
              > Just a few ideas to put before the group.
              > As I wrote previously, I suspect that the initial intrinsic faintness of
              > this comet was not so much a function of the small size of the nucleus,
              > but
              > of the presence of a surface crust of refractory material. If the nucleus
              > was about 500 metres diameter (as against the 100 - 200 as initially
              > estimated) and covered by an insulating crust, this might explain how it
              > survived
              > perihelion passage intact. If the insulating layer was blown off around
              > perihelion, this may even have formed a "sun umbrella" of particles that
              > shielded the freshly-exposed icy surface of the nucleus, rather as is
              > thought to
              > have happened to Seki-Lines in 1962 (analysis of the dust tail suggests
              > that this comet shut down for a few hours at perihelion - q = 0.03 AU -
              > which
              > also helps to explain why there were no daylight sightings of this
              > intrinsically bright object). In the case of Lovejoy, a similar event may
              > have
              > been a factor in preserving its existence. Once the meteoric cloud
              > dispersed,
              > the co met burst into furious activity, however by then the worst of its
              > ordeal was already over.
              > The presence of an ion tail clearly indicated an active nucleus following
              > perihelion. However, as this has this has now disappeared, it may be that
              > ice-driven activity has ceased. This could mean that the nucleus has
              > disappeared, or run out of ice or (I think the most likely explanation)
              > has had
              > the ice cooked out of the surface layers. In other words, the comet may by
              > now have built up a new insulating layer that is effectively keeping heat
              > from underlying ice.
              > Yet, the "head" appears to be persisting as if some dust continues to be
              > released. Just a speculative thought, but electrostatic repulsion caused
              > by
              > solar radiation can levitate fine dust on the surface of the Moon (causing
              > the unexpected crepuscular rays seen by the Apollo astronauts) and is
              > thought responsible for the small flare experienced by Phaethon in 2009.
              > With
              > respect to the latter, David Jewitt called Phaethon a "rock comet" -
              > capable
              > of low-level activity even in the absence of ice - and suggested that this
              > process may even be responsible for the formation of the Geminid meteor
              > stream. For what it is worth, I suggest that the present weak activity of
              > Lovejoy could be due to this process lifting dust from what has again
              > become a
              > totally encrusted nucleus.
              > All very speculative I know, but comments welcome.
              > Cheers,
              > David
            • RICHARD MILES
              Not to mention the comets-ml group too! ... From: RICHARD MILES To: Sent: Thursday, January 05,
              Message 6 of 14 , Jan 5, 2012
                Not to mention the 'comets-ml' group too!

                ----- Original Message -----
                From: "RICHARD MILES" <rmiles.btee@...>
                To: <comets-ml@yahoogroups.com>
                Sent: Thursday, January 05, 2012 5:27 PM
                Subject: Re: [comets-ml] Some Comet Lovejoy speculations


                > It might be helpful to the MPML group in general, and comet hunters in
                > particular, if someone would post the apparent position of the 'radiant' /
                > possible search area for the Kreutz group as seen from the Earth for each
                > month of the year given the rather unusual orbit it possesses.
                >
                > Just a thought,
                >
                > Richard Miles
                > BAA
                >
              • jbortle@aol.com
                In fact, this was done in a paper by Brian Marsden, I think, that I read many years ago...although the exact citation doesn t currently come to mind.
                Message 7 of 14 , Jan 5, 2012
                  In fact, this was done in a paper by Brian Marsden, I think, that I read
                  many years ago...although the exact citation doesn't currently come to mind.

                  J.Bortle


                  In a message dated 1/5/2012 12:27:47 P.M. Eastern Standard Time,
                  rmiles.btee@... writes:




                  It might be helpful to the MPML group in general, and comet hunters in
                  particular, if someone would post the apparent position of the 'radiant' /
                  possible search area for the Kreutz group as seen from the Earth for each
                  month of the year given the rather unusual orbit it possesses.

                  Just a thought,

                  Richard Miles
                  BAA

                  ----- Original Message -----
                  From: "David Seargent" <_seargent@..._
                  (mailto:seargent@...) >
                  To: <_comets-ml@yahoogroups.com_ (mailto:comets-ml@yahoogroups.com) >
                  Sent: Thursday, January 05, 2012 3:03 AM
                  Subject: RE: [comets-ml] Some Comet Lovejoy speculations

                  >
                  > Hi John and all,
                  > John - I agree that the comet most probably has made a previous
                  perihelion
                  > passage as an independent body, but it may not necessarily have been an
                  > independent COMET. Although unlikely, it is possible that it may have
                  > broken away as a secondary nucleus while the parent was still moving
                  > toward its previous perihelion. The situation would then be a little
                  like
                  > the Marsden sunskirters C/2004 V9 and V10. Sekanina has shown that V10
                  > broke away from V9 about 3 months prior to its previous perihelion
                  > passage, at which the split comet was observed as C/1999 J1 (albeit not
                  > resolved into two nuclei in the SOHO images). Interestingly, the
                  > circumstances of this disruption meant that the smaller V10 (although
                  > discovered after V9) reached perihelion before V9; the opposite of what
                  > happens when comets split at or shortly after their previous perihelion
                  > passage. IF something similar has happened with W3, it is likely that
                  the
                  > primary nucleus is still on its way and probably not very far away!
                  > Please, nobody read this as a prediction of another bright sungrazer in
                  > the near future. There is no real reason to think that W3 did break away
                  > from a larger object just prior to its previous perihelion, only that
                  this
                  > remains one possibility. But it might be wise to monitor the inward path
                  > of the Kreutz group just in case...!
                  > Cheers,
                  > david
                  >
                  > To: _comets-ml@yahoogroups.com_ (mailto:comets-ml@yahoogroups.com)
                  > From: _jbortle@..._ (mailto:jbortle@...)
                  > Date: Tue, 3 Jan 2012 08:48:31 -0500
                  > Subject: Re: [comets-ml] Some Comet Lovejoy speculations
                  >
                  > David - As a first approximation, I would say that your conclusions seem
                  > quite reasonable. Certainly, something quite unusual occurred with Comet
                  > Lovejoy over the course of its apparition. That its post-T survival, at
                  > least
                  > to a degree, violates my perihelion survival "law" is most interesting,
                  > although I would note (as my paper on the subject indicated) that a
                  number
                  > of
                  > small, periodic comets (like P/Encke, et al.) do so on a quite regular
                  > basis. The situation being so, this suggests to me that Comet Lovejoy
                  must
                  > have
                  > experienced at least one previous perihelion passage as a totally
                  > independent body (i.e. it was not a fragment formed a its immediate
                  > previous
                  > perihelion passage) and thus had a fully formed and fairly dense overall
                  > insulating layer over its entire surface.Such a "baked" surface which
                  > totally shuts
                  > down early might well also explain why Kreutz sungrazers tend to
                  disappear
                  > much sooner post-T (typical by about 1.5 AU post-T) than do other comets
                  > of
                  > similar intrinsic brightness.
                  >
                  > There is also the problem that although of a seemingly extremely faint
                  > intrinsic brightness both pre and post-T, Comet Lovejoy still presented
                  a
                  > viable and distinct "head" post-perihelion. This while objects like the
                  > Great
                  > Southern Comet of 1887, assumed to be much brighter intrinsically than
                  > 2011
                  > W3, appeared to have survived only as huge tail apparently without any
                  > head. Of course, the Kreutz sungrazing group's orbital orientation so
                  > strongly
                  > favors visibility from the Southern Hemisphere that it has undoubtedly
                  > limited the opportunities to watch the development of other examples of
                  > seemingly faint members of this clan in the more distant past.
                  >
                  > I find it equally interesting how one explains the long-enduring bright
                  > streak extending from the position the nucleus should occupy to
                  relatively
                  > far out into the tail. And the fact that this feature seems to have
                  > evolved
                  > surprisingly little since its sudden appearance. A few descriptions of
                  the
                  > Great September Comet of 1882 do make mention of a similar "streak" in
                  > that
                  > comet's head, dotted with a number of brighter star-like nucleii, but
                  that
                  > feature seemed fairly short lived and was on a physical scale apparently
                  > far smaller than that displayed by Comet Lovejoy. Are we perhaps seeing a
                  > very long train of tens of thousand of ONLY tiny fragments with
                  absolutely
                  > no
                  > large survivers, distributed along the orbit by size/mass? But then how
                  > could this form so suddenly and how could a coma persist without some
                  > viable
                  > solid body evident at its focus? According to Rod, there is no evidence
                  of
                  > any independent surviving body down to 19th magnitude in that location.
                  >
                  > And I'm still very curious about the nature of the faint yet distinct
                  > "sheath" that is seen to envelope both the dust and gas tails of
                  numerous
                  > Kreutz
                  > sungrazers post-T, well seen with 2011 W3, yet does not seem evident with
                  > regard to other very small "q" non-Kreutz comets. What is the nature of
                  > it?
                  > And in the case of the Great September Comet it not only surrounded the
                  > tail but was described to extend well sunward of the head!
                  >
                  > I unquestionably foresee a long and interesting future of papers
                  > attempting to address the amazing sights we've seen over the course of
                  the
                  > past
                  > month!
                  >
                  > J.Bortle
                  >
                  >
                  >
                  >
                  > In a message dated 1/2/2012 11:49:46 P.M. Eastern Standard Time,
                  > _seargent@..._ (mailto:seargent@...) writes:
                  >
                  > Hi all,
                  > Just a few ideas to put before the group.
                  > As I wrote previously, I suspect that the initial intrinsic faintness of
                  > this comet was not so much a function of the small size of the nucleus,
                  > but
                  > of the presence of a surface crust of refractory material. If the nucleus
                  > was about 500 metres diameter (as against the 100 - 200 as initially
                  > estimated) and covered by an insulating crust, this might explain how it
                  > survived
                  > perihelion passage intact. If the insulating layer was blown off around
                  > perihelion, this may even have formed a "sun umbrella" of particles that
                  > shielded the freshly-exposed icy surface of the nucleus, rather as is
                  > thought to
                  > have happened to Seki-Lines in 1962 (analysis of the dust tail suggests
                  > that this comet shut down for a few hours at perihelion - q = 0.03 AU -
                  > which
                  > also helps to explain why there were no daylight sightings of this
                  > intrinsically bright object). In the case of Lovejoy, a similar event
                  may
                  > have
                  > been a factor in preserving its existence. Once the meteoric cloud
                  > dispersed,
                  > the co met burst into furious activity, however by then the worst of its
                  > ordeal was already over.
                  > The presence of an ion tail clearly indicated an active nucleus following
                  > perihelion. However, as this has this has now disappeared, it may be that
                  > ice-driven activity has ceased. This could mean that the nucleus has
                  > disappeared, or run out of ice or (I think the most likely explanation)
                  > has had
                  > the ice cooked out of the surface layers. In other words, the comet may
                  by
                  > now have built up a new insulating layer that is effectively keeping heat
                  > from underlying ice.
                  > Yet, the "head" appears to be persisting as if some dust continues to be
                  > released. Just a speculative thought, but electrostatic repulsion caused
                  > by
                  > solar radiation can levitate fine dust on the surface of the Moon
                  (causing
                  > the unexpected crepuscular rays seen by the Apollo astronauts) and is
                  > thought responsible for the small flare experienced by Phaethon in 2009.
                  > With
                  > respect to the latter, David Jewitt called Phaethon a "rock comet" -
                  > capable
                  > of low-level activity even in the absence of ice - and suggested that
                  this
                  > process may even be responsible for the formation of the Geminid meteor
                  > stream. For what it is worth, I suggest that the present weak activity of
                  > Lovejoy could be due to this process lifting dust from what has again
                  > become a
                  > totally encrusted nucleus.
                  > All very speculative I know, but comments welcome.
                  > Cheers,
                  > David






                  [Non-text portions of this message have been removed]
                • Maik Meyer
                  Hello, ... it was the 1967 paper: http://adsabs.harvard.edu/abs/1967AJ.....72.1170M Cheers, Maik -- If they give you ruled paper, write the other way. * Juan
                  Message 8 of 14 , Jan 5, 2012
                    Hello,

                    > In fact, this was done in a paper by Brian Marsden, I think, that I read
                    > many years ago...although the exact citation doesn't currently come to mind.
                    >
                    > J.Bortle
                    >
                    > It might be helpful to the MPML group in general, and comet hunters in
                    > particular, if someone would post the apparent position of the 'radiant' /
                    > possible search area for the Kreutz group as seen from the Earth for each
                    > month of the year given the rather unusual orbit it possesses.
                    >
                    > Richard Miles

                    it was the 1967 paper:

                    http://adsabs.harvard.edu/abs/1967AJ.....72.1170M

                    Cheers, Maik
                    --
                    If they give you ruled paper, write the other way. * Juan Ramon Jimenez
                    ________________________________________________________________________
                    maik@... http://www.comethunter.de
                    International Comet Quarterly http://cfa-www.harvard.edu/icq/icq.html
                    http://groups.yahoo.com/group/comets-ml
                  • jbortle@aol.com
                    David, once again your suppositions re 2011 W3 are certainly within the realm of reasonable possibility. In fact, I recall reading a paper by Sekanina in which
                    Message 9 of 14 , Jan 5, 2012
                      David, once again your suppositions re 2011 W3 are certainly within the
                      realm of reasonable possibility. In fact, I recall reading a paper by
                      Sekanina in which he suggests just such a possible scenario for 1970 K1, W-O-B.
                      For reasons I no longer recall, Sekanina felt that a major secondary
                      component closely associated with W-O-B could possibly have been trailing it by
                      only a few months. He gave the time of potential perihelion passage as about
                      late July of 1970, when the comet would have been hopelessly hidden from
                      discovery in daylight (unless spotted in the daytime at T). Of course, as you
                      say, this does not in any way directly infer such a situation might be true
                      for 2011 W3.

                      In my mind this possibility also arises concerning the 'apparent' spate of
                      sungrazers in the late 18th century. How many additional such objects
                      might have appeared then during the annual intervals when Kreutz sungrazers
                      might only have been seen from the Southern Hemisphere and went totally
                      unreported? Lots of interesting conjecture is possible in this area with our
                      knowledge of the sungrazer family so incomplete!

                      J.Bortle



                      In a message dated 1/4/2012 10:03:31 P.M. Eastern Standard Time,
                      seargent@... writes:


                      Hi John and all,
                      John - I agree that the comet most probably has made a previous perihelion
                      passage as an independent body, but it may not necessarily have been an
                      independent COMET. Although unlikely, it is possible that it may have broken
                      away as a secondary nucleus while the parent was still moving toward its
                      previous perihelion. The situation would then be a little like the Marsden
                      sunskirters C/2004 V9 and V10. Sekanina has shown that V10 broke away from V9
                      about 3 months prior to its previous perihelion passage, at which the
                      split comet was observed as C/1999 J1 (albeit not resolved into two nuclei in
                      the SOHO images). Interestingly, the circumstances of this disruption meant
                      that the smaller V10 (although discovered after V9) reached perihelion
                      before V9; the opposite of what happens when comets split at or shortly after
                      their previous perihelion passage. IF something similar has happened with W3,
                      it is likely that the primary nucleus is still on its way and probably not
                      very far away!
                      Please, nobody read this as a prediction of another bright sungrazer in
                      the near future. There is no real reason to think that W3 did break away from
                      a larger object just prior to its previous perihelion, only that this
                      remains one possibility. But it might be wise to monitor the inward path of the
                      Kreutz group just in case...!
                      Cheers,
                      david





                      To: comets-ml@yahoogroups.com
                      From: jbortle@...
                      Date: Tue, 3 Jan 2012 08:48:31 -0500
                      Subject: Re: [comets-ml] Some Comet Lovejoy speculations






                      David - As a first approximation, I would say that your conclusions seem
                      quite reasonable. Certainly, something quite unusual occurred with Comet
                      Lovejoy over the course of its apparition. That its post-T survival, at
                      least
                      to a degree, violates my perihelion survival "law" is most interesting,
                      although I would note (as my paper on the subject indicated) that a number
                      of
                      small, periodic comets (like P/Encke, et al.) do so on a quite regular
                      basis. The situation being so, this suggests to me that Comet Lovejoy must
                      have
                      experienced at least one previous perihelion passage as a totally
                      independent body (i.e. it was not a fragment formed a its immediate
                      previous
                      perihelion passage) and thus had a fully formed and fairly dense overall
                      insulating layer over its entire surface.Such a "baked" surface which
                      totally shuts
                      down early might well also explain why Kreutz sungrazers tend to disappear
                      much sooner post-T (typical by about 1.5 AU post-T) than do other comets
                      of
                      similar intrinsic brightness.

                      There is also the problem that although of a seemingly extremely faint
                      intrinsic brightness both pre and post-T, Comet Lovejoy still presented a
                      viable and distinct "head" post-perihelion. This while objects like the
                      Great
                      Southern Comet of 1887, assumed to be much brighter intrinsically than
                      2011
                      W3, appeared to have survived only as huge tail apparently without any
                      head. Of course, the Kreutz sungrazing group's orbital orientation so
                      strongly
                      favors visibility from the Southern Hemisphere that it has undoubtedly
                      limited the opportunities to watch the development of other examples of
                      seemingly faint members of this clan in the more distant past.

                      I find it equally interesting how one explains the long-enduring bright
                      streak extending from the position the nucleus should occupy to relatively
                      far out into the tail. And the fact that this feature seems to have
                      evolved
                      surprisingly little since its sudden appearance. A few descriptions of the
                      Great September Comet of 1882 do make mention of a similar "streak" in
                      that
                      comet's head, dotted with a number of brighter star-like nucleii, but that
                      feature seemed fairly short lived and was on a physical scale apparently
                      far smaller than that displayed by Comet Lovejoy. Are we perhaps seeing a
                      very long train of tens of thousand of ONLY tiny fragments with absolutely
                      no
                      large survivers, distributed along the orbit by size/mass? But then how
                      could this form so suddenly and how could a coma persist without some
                      viable
                      solid body evident at its focus? According to Rod, there is no evidence of
                      any independent surviving body down to 19th magnitude in that location.

                      And I'm still very curious about the nature of the faint yet distinct
                      "sheath" that is seen to envelope both the dust and gas tails of numerous
                      Kreutz
                      sungrazers post-T, well seen with 2011 W3, yet does not seem evident with
                      regard to other very small "q" non-Kreutz comets. What is the nature of
                      it?
                      And in the case of the Great September Comet it not only surrounded the
                      tail but was described to extend well sunward of the head!

                      I unquestionably foresee a long and interesting future of papers
                      attempting to address the amazing sights we've seen over the course of the
                      past
                      month!

                      J.Bortle




                      In a message dated 1/2/2012 11:49:46 P.M. Eastern Standard Time,
                      seargent@... writes:

                      Hi all,
                      Just a few ideas to put before the group.
                      As I wrote previously, I suspect that the initial intrinsic faintness of
                      this comet was not so much a function of the small size of the nucleus,
                      but
                      of the presence of a surface crust of refractory material. If the nucleus
                      was about 500 metres diameter (as against the 100 - 200 as initially
                      estimated) and covered by an insulating crust, this might explain how it
                      survived
                      perihelion passage intact. If the insulating layer was blown off around
                      perihelion, this may even have formed a "sun umbrella" of particles that
                      shielded the freshly-exposed icy surface of the nucleus, rather as is
                      thought to
                      have happened to Seki-Lines in 1962 (analysis of the dust tail suggests
                      that this comet shut down for a few hours at perihelion - q = 0.03 AU -
                      which
                      also helps to explain why there were no daylight sightings of this
                      intrinsically bright object). In the case of Lovejoy, a similar event may
                      have
                      been a factor in preserving its existence. Once the meteoric cloud
                      dispersed,
                      the co met burst into furious activity, however by then the worst of its
                      ordeal was already over.
                      The presence of an ion tail clearly indicated an active nucleus following
                      perihelion. However, as this has this has now disappeared, it may be that
                      ice-driven activity has ceased. This could mean that the nucleus has
                      disappeared, or run out of ice or (I think the most likely explanation)
                      has had
                      the ice cooked out of the surface layers. In other words, the comet may by
                      now have built up a new insulating layer that is effectively keeping heat
                      from underlying ice.
                      Yet, the "head" appears to be persisting as if some dust continues to be
                      released. Just a speculative thought, but electrostatic repulsion caused
                      by
                      solar radiation can levitate fine dust on the surface of the Moon (causing
                      the unexpected crepuscular rays seen by the Apollo astronauts) and is
                      thought responsible for the small flare experienced by Phaethon in 2009.
                      With
                      respect to the latter, David Jewitt called Phaethon a "rock comet" -
                      capable
                      of low-level activity even in the absence of ice - and suggested that this
                      process may even be responsible for the formation of the Geminid meteor
                      stream. For what it is worth, I suggest that the present weak activity of
                      Lovejoy could be due to this process lifting dust from what has again
                      become a
                      totally encrusted nucleus.
                      All very speculative I know, but comments welcome.
                      Cheers,
                      David

                      [Non-text portions of this message have been removed]

                      [Non-text portions of this message have been removed]






                      [Non-text portions of this message have been removed]



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                      [Non-text portions of this message have been removed]
                    • Robert McNaught
                      ... You can create the line of variation by using mean Kreutz elements with a range of perihelion dates a few days apart for a couple of months ahead,
                      Message 10 of 14 , Jan 6, 2012
                        On Thu, 5 Jan 2012, RICHARD MILES wrote:

                        > It might be helpful to the MPML group in general, and comet hunters in
                        > particular, if someone would post the apparent position of the 'radiant' /
                        > possible search area for the Kreutz group as seen from the Earth for each
                        > month of the year given the rather unusual orbit it possesses.

                        You can create the line of variation by using mean Kreutz elements
                        with a range of perihelion dates a few days apart for a couple
                        of months ahead, predicting all these for the time of observation.
                        The locus of all these points is the projection of the orbit onto
                        the celestial sphere.

                        Cheers, Rob
                      • RICHARD MILES
                        Thanks Rob - I shall have to find the time to give it a try. In the meantime, I have followed up John Bortle and Maik Meyer s reference to (sadly missed) Brian
                        Message 11 of 14 , Jan 6, 2012
                          Thanks Rob - I shall have to find the time to give it a try.

                          In the meantime, I have followed up John Bortle and Maik Meyer's reference
                          to (sadly missed) Brian Marsden's 1967 paper at:
                          http://adsabs.harvard.edu/full/1967AJ.....72.1170M
                          in which paper Brian had indeed published a 10-day perennial search
                          ephemeris which traced the LOV of the Kreutz group from -50 days to +50 days
                          from perihelion in 10-day intervals.

                          Interestingly, Terry Lovejoy discovered C/2011 W3 just 18 days ahead of
                          perihelion at a position which lay barely 1 degree from Brian's search
                          ephemeris - if only Brian could have been around to witness Terry's great
                          discovery and the subsequent Christmas Comet of 2011 !

                          Regards,
                          Richard

                          BTW, a few weeks ago I consulted Brian's follow-up paper at:
                          http://adsabs.harvard.edu/full/1989AJ.....98.2306M
                          to learn more of the subject and consider possible search strategies.
                          I must say that both papers make fascinating reading.


                          ----- Original Message -----
                          From: "Robert McNaught" <rmn@...>
                          To: <comets-ml@yahoogroups.com>
                          Sent: Friday, January 06, 2012 9:41 AM
                          Subject: Re: [comets-ml] Some Comet Lovejoy speculations


                          > On Thu, 5 Jan 2012, RICHARD MILES wrote:
                          >
                          >> It might be helpful to the MPML group in general, and comet hunters in
                          >> particular, if someone would post the apparent position of the 'radiant'
                          >> /
                          >> possible search area for the Kreutz group as seen from the Earth for each
                          >> month of the year given the rather unusual orbit it possesses.
                          >
                          > You can create the line of variation by using mean Kreutz elements
                          > with a range of perihelion dates a few days apart for a couple
                          > of months ahead, predicting all these for the time of observation.
                          > The locus of all these points is the projection of the orbit onto
                          > the celestial sphere.
                          >
                          > Cheers, Rob
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