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Re: {MPML} 2012 NJ

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  • amaury@spaceobs.com
    A bunch I wouldn t say, some, maybe. In the list of NEOs (if it turns to be a NEO), it would be the 6th largest if I am correct, quite an unexpected (and
    Message 1 of 29 , Jul 15, 2012
      A bunch I wouldn't say, some, maybe.
      In the list of NEOs (if it turns to be a NEO), it would be the 6th
      largest if I am correct, quite an unexpected (and beautiful)
      discovery. The last NEO larger than this one was discovered in 1990,
      so 2012 NJ is the largest NEO found in 22 years... I assume some
      precovery images will be found... ?
      In size it is what could be called a dinosaur killer :)
      Thumbs up for Spain...!
      Alain


      Jaime Nomen <jnomen@...> a écrit :

      > Hi:
      >
      > data source from:
      > http://www.nasa.gov/mission_pages/WISE/news/wise20110929.html
      >
      > "...The new data revise their total numbers from about 1,000
      > down to 981, of which 911 already have been found. None of them
      > represents a threat to Earth in the next few centuries.
      >
      > "...It is believed that all near-Earth asteroids approximately
      > 6 miles (10 kilometers) across, as big as the one thought to have
      > wiped out the dinosaurs, have been found... " 2011-304
      >
      > http://www.minorplanetcenter.net/mpec/K12/K12N19.html
      >
      > the today observations set this new object a little bit
      > under q < 1.30...
      >
      > Simply watching such "evasive" orbit it seems logical there
      > should still be a bunch of them out there.. right?
      >
      > Jaime
      >
      >
    • Alan W Harris
      2012 is a sort of pathological NEO, more of a comet than an asteroid. Several other quite long-period objects like it have been found over the years,
      Message 2 of 29 , Jul 15, 2012
        2012 is a sort of "pathological" NEO, more of a "comet" than an
        asteroid. Several other quite long-period objects like it have been found
        over the years, sometimes called "Damocloids". It turns out that the
        definition of "NEO" as anything with q < 1.3 AU is a bit unfortunate. Not
        only are things with q > 1.05 or so not potential PHAs (excuse the double
        terminology, but here it is correct), but also it turns out that any orbit
        that crosses or nearly-crosses Jupiter, such that it can be gravitationally
        scattered by Jupiter by a close encounter, cannot be "scattered" inward
        closer than q < 1.1 AU, unless the relative encounter velocity with Jupiter
        is great enough that a "scattering" in the opposite direction will eject it
        from the solar system. What all this means is that a "Damocloid" with
        perihelion less than 1.1 AU, and crossing the orbit of Jupiter, will be
        quickly ejected out of the solar system in a matter of thousands to tens of
        thousands of years. So it's actually not a surprise to find one or a few
        large objects of this sort, as Alain Maury suggests, but it would be
        extraordinary to find even one that truly crosses the Earth's orbit and has
        the potential for impact. With a period of around 50 years, it's not
        surprising to find a new one after so many years of surveying. And others
        may exist with even longer periods.

        All that being said, there are objects like this that are essentially
        "comets" by orbital class, but just happen not to show any coma or other
        cometary features. Looking at LP comet orbits, they have periods ranging
        all the way out to a million years or so -- the Oort Cloud. It is highly
        likely that there are thousands of objects the size of 2012 NJ out there
        with perihelia 1 AU or less, come roving in every hundred years or so, and
        show no cometary activity when they do. Are these NEAs? If so, then there
        are thousands of them, and we've only begun to catalog them. And of course
        they won't return again any time soon, so who cares? Essentially, when we
        get out past Jupiter-crossing, we are dealing with an impact hazard that
        resembles cometary, and it really is not relevant to talk about how many
        such bodies there are, but rather the flux: how many per year (decade,
        century) cross the Earth's orbit? In doing my inventories, I cut off with
        orbits that cross Jupiter or beyond (of which there are currently none
        known that also cross the Earth's orbit). Some of the numbers you'll find
        on the JPL NEO web pages are a bit mixed between "NEAs" (asteroids only)
        and "NEOs" (asteroids plus comets). Trouble is, we really can't make a
        meaningful estimate of how many comets or asteroids in comet-like orbits
        there might be, with orbit periods going all the way out to a million years
        or so.

        Coming to a bottom line, nice discovery, congratulations to La Sagra group,
        but don't make much of it in terms of impact risk or how many (if any)
        large PHAs might be lurking out there.

        Cheers,

        Alan

        At 11:38 AM 7/15/2012, Jaime Nomen wrote:
        >Hi:
        >
        >data source from:
        >http://www.nasa.gov/mission_pages/WISE/news/wise20110929.html
        >
        >"...The new data revise their total numbers from about 1,000
        >down to 981, of which 911 already have been found. None of them
        >represents a threat to Earth in the next few centuries.
        >
        >"...It is believed that all near-Earth asteroids approximately
        >6 miles (10 kilometers) across, as big as the one thought to have
        >wiped out the dinosaurs, have been found... " 2011-304
        >
        >http://www.minorplanetcenter.net/mpec/K12/K12N19.html
        >
        >the today observations set this new object a little bit
        >under q < 1.30...
        >
        >Simply watching such "evasive" orbit it seems logical there
        >should still be a bunch of them out there.. right?
        >
        >Jaime
        >
        >
        >
        >------------------------------------
        >
        >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        >
        >Posts to this list or information found within may be freely used, with
        >the stipulation that MPML and the originating author are cited as the
        >source of the information.Yahoo! Groups Links
        >
        >
        >
        *****************************************************************************
        Alan Harris Phone: 818-790-8291
        4603 Orange Knoll Ave.
        La Cañada, CA 91011-3364
        email: harrisaw@...
        *****************************************************************************
      • Dave Tholen
        ... In what way is Halley s comet disqualified? What is the Earth MOID for Halley? I recall that in 1910 there was some panic because people felt the Earth
        Message 3 of 29 , Jul 15, 2012
          > In doing my inventories, I cut off with orbits that cross Jupiter or
          > beyond (of which there are currently none known that also cross the
          > Earth's orbit).

          In what way is Halley's comet disqualified?

          What is the Earth MOID for Halley? I recall that in 1910 there was
          some panic because people felt the Earth was going to be poisoned by
          cyanogen from passing through Halley's tail. I guess that means the
          MOID for Halley's tail can be pretty small, but off the top of my
          head, I don't know what it is for Halley itself.
        • Jaime Nomen
          Being quite bright and well placed on the northern skies for many nights high resolution observations + lightcurves + spectroscopy + ?, could help to clearly
          Message 4 of 29 , Jul 15, 2012
            Being quite bright and well placed on the northern skies for many nights
            high resolution observations + lightcurves + spectroscopy + ?, could help to
            clearly classify/define this object as a dead comet or asteroid?... Any
            difference at all ?

            Jaime



            -----Mensaje original-----
            De: Alan W Harris [mailto:harrisaw@...]
            Enviado el: Sunday, July 15, 2012 23:40
            Para: Jaime Nomen; mpml@yahoogroups.com
            Asunto: Re: {MPML} 2012 NJ

            2012 is a sort of "pathological" NEO, more of a "comet" than an asteroid.
            Several other quite long-period objects like it have been found over the years,
            sometimes called "Damocloids". It turns out that the definition of "NEO" as
            anything with q < 1.3 AU is a bit unfortunate. Not only are things with q >
            1.05 or so not potential PHAs (excuse the double terminology, but here it is
            correct), but also it turns out that any orbit that crosses or nearly-crosses
            Jupiter, such that it can be gravitationally scattered by Jupiter by a close
            encounter, cannot be "scattered" inward closer than q < 1.1 AU, unless the
            relative encounter velocity with Jupiter is great enough that a "scattering" in
            the opposite direction will eject it from the solar system. What all this means
            is that a "Damocloid" with perihelion less than 1.1 AU, and crossing the orbit
            of Jupiter, will be quickly ejected out of the solar system in a matter of
            thousands to tens of thousands of years. So it's actually not a surprise to
            find one or a few large objects of this sort, as Alain Maury suggests, but it
            would be extraordinary to find even one that truly crosses the Earth's orbit and
            has the potential for impact. With a period of around 50 years, it's not
            surprising to find a new one after so many years of surveying. And others may
            exist with even longer periods.

            All that being said, there are objects like this that are essentially "comets"
            by orbital class, but just happen not to show any coma or other cometary
            features. Looking at LP comet orbits, they have periods ranging all the way out
            to a million years or so -- the Oort Cloud. It is highly likely that there are
            thousands of objects the size of 2012 NJ out there with perihelia 1 AU or less,
            come roving in every hundred years or so, and show no cometary activity when
            they do. Are these NEAs? If so, then there are thousands of them, and we've
            only begun to catalog them. And of course they won't return again any time
            soon, so who cares? Essentially, when we get out past Jupiter-crossing, we are
            dealing with an impact hazard that resembles cometary, and it really is not
            relevant to talk about how many such bodies there are, but rather the flux: how
            many per year (decade,
            century) cross the Earth's orbit? In doing my inventories, I cut off with
            orbits that cross Jupiter or beyond (of which there are currently none known
            that also cross the Earth's orbit). Some of the numbers you'll find on the JPL
            NEO web pages are a bit mixed between "NEAs" (asteroids only) and "NEOs"
            (asteroids plus comets). Trouble is, we really can't make a meaningful estimate
            of how many comets or asteroids in comet-like orbits there might be, with orbit
            periods going all the way out to a million years or so.

            Coming to a bottom line, nice discovery, congratulations to La Sagra group, but
            don't make much of it in terms of impact risk or how many (if any) large PHAs
            might be lurking out there.

            Cheers,

            Alan

            At 11:38 AM 7/15/2012, Jaime Nomen wrote:
            >Hi:
            >
            >data source from:
            >http://www.nasa.gov/mission_pages/WISE/news/wise20110929.html
            >
            >"...The new data revise their total numbers from about 1,000 down to
            >981, of which 911 already have been found. None of them represents a
            >threat to Earth in the next few centuries.
            >
            >"...It is believed that all near-Earth asteroids approximately
            >6 miles (10 kilometers) across, as big as the one thought to have wiped
            >out the dinosaurs, have been found... " 2011-304
            >
            >http://www.minorplanetcenter.net/mpec/K12/K12N19.html
            >
            >the today observations set this new object a little bit under q <
            >1.30...
            >
            >Simply watching such "evasive" orbit it seems logical there should
            >still be a bunch of them out there.. right?
            >
            >Jaime
            >
            >
            >
            >------------------------------------
            >
            >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            >
            >Posts to this list or information found within may be freely used, with
            >the stipulation that MPML and the originating author are cited as the
            >source of the information.Yahoo! Groups Links
            >
            >
            >
            *****************************************************************************
            Alan Harris Phone: 818-790-8291
            4603 Orange Knoll Ave.
            La Cañada, CA 91011-3364
            email: harrisaw@...
            *****************************************************************************
          • Alan W Harris
            ... Yes, there are any number of comets that cross both the Earth s and Jupiter s orbits, but not, as far as I recall, asteroids. Part of my little essay was
            Message 5 of 29 , Jul 15, 2012
              At 05:01 PM 7/15/2012, Dave Tholen wrote:
              > > In doing my inventories, I cut off with orbits that cross Jupiter or
              > > beyond (of which there are currently none known that also cross the
              > > Earth's orbit).
              >
              >In what way is Halley's comet disqualified?

              Yes, there are any number of comets that cross both the Earth's and
              Jupiter's orbits, but not, as far as I recall, asteroids. Part of my
              little essay was to point out that once you adopt "NEO", defined to include
              comets as well as asteroids, then the concept of "total population" becomes
              close to meaningless, and of course there are many, almost arbitrarily
              large (consider C/Hale-Bopp) objects that cross the Earths orbit. The
              sensible question becomes "how often?" not "how many?" For me, I cut off
              at Jupiter-crossing; anything that crosses the orbit of Jupiter is part of
              the "O" of NEO, not "A" of NEA. I'm not saying they don't exist, they just
              aren't part of a meaningful number inventory.

              *****************************************************************************
              Alan Harris Phone: 818-790-8291
              4603 Orange Knoll Ave.
              La Cañada, CA 91011-3364
              email: harrisaw@...
              *****************************************************************************
            • Bill J Gray
              ... I get Earth MOID = 0.0659 AU, Jupiter MOID = 0.8116, Venus = 0.0487, Mars = 0.0679. Small MOIDs, but not small enough to be interesting or terrifying.
              Message 6 of 29 , Jul 15, 2012
                Dave Tholen wrote:

                > What is the Earth MOID for Halley? I recall that in 1910 there was
                > some panic because people felt the Earth was going to be poisoned by
                > cyanogen from passing through Halley's tail. I guess that means the
                > MOID for Halley's tail can be pretty small, but off the top of my
                > head, I don't know what it is for Halley itself.

                I get Earth MOID = 0.0659 AU, Jupiter MOID = 0.8116, Venus = 0.0487,
                Mars = 0.0679. Small MOIDs, but not small enough to be interesting or
                terrifying. (Except, perhaps, to numerous people in 1910.)

                This did remind me that after 109P/Swift-Tuttle was recovered in
                1992, Brian Marsden suggested that it might hit the earth in something
                like 2126, so I checked the MOID of that object as well and got an
                Earth MOID of 0.0009 AU for the last apparition, increasing to 0.0048 for
                the 2126 apparition.

                -- Bill
              • Herbert Raab
                ... Just wanted to note that comet Halley passes the Earth in a distance of just 0.034 AU on April 10, 837, i.e., about one third of the current MOID. Unless
                Message 7 of 29 , Jul 16, 2012
                  Bill J. Gray wrote:

                  > I get Earth MOID = 0.0659 AU

                  Just wanted to note that comet Halley passes the Earth in
                  a distance of just 0.034 AU on April 10, 837, i.e., about
                  one third of the current MOID. Unless the two are actualley
                  met a the closest intersection distance of their orbits, the
                  MOID at that time might have been even smaller. (I don't have
                  the elements for that return of the comet here right now, so
                  I can't check...)

                  Cheers,
                  Herbert
                • Herbert Raab
                  ... Sorry - about half of the current MOID, actually... :) But about 1/3 of the distance of C/1996 B2 (Hyakutake) at it s closes approach. Herbert
                  Message 8 of 29 , Jul 16, 2012
                    Herbert Raab wrote:

                    > a distance of just 0.034 AU on April 10, 837, i.e., about
                    > one third of the current MOID.

                    Sorry - about half of the current MOID, actually... :)
                    But about 1/3 of the distance of C/1996 B2 (Hyakutake) at
                    it's closes approach.

                    Herbert
                  • walcom77
                    Congrats to La Sagra team for the discovery of this interesting object!! On our blog our confirmation image and an animation of 2012 NJ: http://bit.ly/Mcmfgn
                    Message 9 of 29 , Jul 16, 2012
                      Congrats to La Sagra team for the discovery of this interesting object!!

                      On our blog our confirmation image and an animation of 2012 NJ:

                      http://bit.ly/Mcmfgn

                      Ciao,
                      Ernesto Guido, Giovanni Sostero & Nick Howes
                      http://remanzacco.blogspot.com
                      http://twitter.com/comets77
                    • Bill J Gray
                      ... I can get an orbit based on observations since 1835, using astrometry available at http://www.minorplanetcenter.net/iau/ECS/MPCAT-OBS/MPCAT-OBS.html But
                      Message 10 of 29 , Jul 16, 2012
                        Herbert Raab wrote:
                        > Just wanted to note that comet Halley passes the Earth in
                        > a distance of just 0.034 AU on April 10, 837, i.e., about
                        > one third of the current MOID. Unless the two are actually
                        > met a the closest intersection distance of their orbits, the
                        > MOID at that time might have been even smaller. (I don't have
                        > the elements for that return of the comet here right now, so
                        > I can't check...)

                        I can get an orbit based on observations since 1835, using
                        astrometry available at

                        http://www.minorplanetcenter.net/iau/ECS/MPCAT-OBS/MPCAT-OBS.html

                        But with this, I get a closest approach of 0.018 AU, on 837
                        April 11. Presumably, I need astrometry from previous apparitions.
                        (And yes, non-gravs are included. Without them, residuals are
                        horrible. Elements shown below, for what they're worth. The
                        MOID is probably still about right, even if the details of the
                        approach have gotten fuzzy when extrapolated backward that far.)

                        I've hunted occasionally for "older" comet astrometry (the MPC
                        comet data mostly starts in 1870, with a few exceptions)
                        without success.

                        JPL's Small-Body Database Browser, at

                        http://ssd.jpl.nasa.gov/sbdb.cgi

                        gives various orbits. The current-epoch one is based on JPL's
                        solution, which also uses 1835-present data. Also provided is an
                        837-epoch orbit from observations made from 1607 to 1759, from
                        the 2008 SAO Comet Catalog.

                        -- Bill

                        Orbital elements:
                        P/1
                        Perihelion 837 Mar 2.470518 TT; A1=7.76e-10, A2=1.64e-10
                        Epoch 837 Apr 10.0 TT = JDT 2026871.5 Earth MOID: 0.0100 Ju: 0.9985
                        M 0.49227 (2000.0) Ve: 0.0785 Ma: 0.0203
                        n 0.01277665 Peri. 100.11344 0.54236911 -0.81565100
                        a 18.1213781 Node 44.94877 -0.83816698 -0.50890469
                        e 0.9678618 Incl. 163.43919 -0.05754866 -0.27518984
                        P 77.14 M(N) 9.1 K 10.0 q 0.58238762 Q 35.6603687
                        From 8147 observations 1835 Aug. 21-2003 Mar. 8; mean residual 1".979.
                      • Jean Meeus
                        In 1984, at the occasion of the return of Comet Halley of 1986, I calculated the least distance between the orbit of the Earth and that of the comet, for
                        Message 11 of 29 , Jul 16, 2012
                          In 1984, at the occasion of the return of Comet Halley of 1986,
                          I calculated the least distance between the orbit of the Earth
                          and that of the comet, for several apparitions of the comet. The
                          comet's orbital elements were taken from the work of Yeomans and
                          Kiang, "The long-term motion of comet Halley", Monthly Notices of
                          the Royal Astronomical Soc., Vol. 197, pages 633-646 (1981).Here
                          are some of the values I found. They were published on page 91 of
                          the "Hemelkalender 1985" that I wrote for our Belgian, Dutch-language
                          astronomical society VVS :

                          Year Least distance
                          296 0.0124 a.u.
                          374 0.0069
                          451 0.0025
                          530 0.0008
                          607 0.0023
                          684 0.0048
                          760 0.0077
                          837 0.0080
                          912 0.0126

                          Important : these are the least distances between the two orbits,
                          *not* between the Earth and the comet!
                          From these values, it appears that about the year 530 the two orbits
                          exactly crosses, so a collision with the Earth was possible!

                          Jean Meeus


                          [Non-text portions of this message have been removed]
                        • Brian Skiff
                          The persistent close MOID is why we get _two_ annual meteor showers from Comet Halley debris, yes? So this isn t such big news, que no? Brian
                          Message 12 of 29 , Jul 16, 2012
                            The persistent close MOID is why we get _two_ annual meteor showers
                            from Comet Halley debris, yes? So this isn't such big news, que no?

                            \Brian


                            On Mon, 2012-07-16 at 18:08 +0200, Jean Meeus wrote:
                            > In 1984, at the occasion of the return of Comet Halley of 1986,
                            > I calculated the least distance between the orbit of the Earth
                            > and that of the comet, for several apparitions of the comet. The
                            > comet's orbital elements were taken from the work of Yeomans and
                            > Kiang, "The long-term motion of comet Halley", Monthly Notices of
                            > the Royal Astronomical Soc., Vol. 197, pages 633-646 (1981).Here
                            > are some of the values I found. They were published on page 91 of
                            > the "Hemelkalender 1985" that I wrote for our Belgian, Dutch-language
                            > astronomical society VVS :
                            >
                            > Year Least distance
                            > 296 0.0124 a.u.
                            > 374 0.0069
                            > 451 0.0025
                            > 530 0.0008
                            > 607 0.0023
                            > 684 0.0048
                            > 760 0.0077
                            > 837 0.0080
                            > 912 0.0126
                            >
                            > Important : these are the least distances between the two orbits,
                            > *not* between the Earth and the comet!
                            > From these values, it appears that about the year 530 the two orbits
                            > exactly crosses, so a collision with the Earth was possible!
                            >
                            > Jean Meeus
                          • Bill J Gray
                            Hi Jean, Thanks both for the table and for the reference to the paper of Yeomans and Kiang. My immediate thought was that they wouldn t have data from the
                            Message 13 of 29 , Jul 16, 2012
                              Hi Jean,

                              Thanks both for the table and for the reference to the paper
                              of Yeomans and Kiang. My immediate thought was that they wouldn't
                              have data from the last (1986) apparition. However, they also
                              used historical Chinese observations to constrain the time of
                              perihelion at apparitions going back to 141... a pretty interesting
                              technique. So you should definitely trust their results (and your
                              MOIDs based on them) and ignore mine.

                              -- Bill

                              Jean Meeus wrote:
                              > In 1984, at the occasion of the return of Comet Halley of 1986,
                              > I calculated the least distance between the orbit of the Earth
                              > and that of the comet, for several apparitions of the comet. The
                              > comet's orbital elements were taken from the work of Yeomans and
                              > Kiang, "The long-term motion of comet Halley", Monthly Notices of
                              > the Royal Astronomical Soc., Vol. 197, pages 633-646 (1981).Here
                              > are some of the values I found. They were published on page 91 of
                              > the "Hemelkalender 1985" that I wrote for our Belgian, Dutch-language
                              > astronomical society VVS :
                              >
                              > Year Least distance
                              > 296 0.0124 a.u.
                              > 374 0.0069
                              > 451 0.0025
                              > 530 0.0008
                              > 607 0.0023
                              > 684 0.0048
                              > 760 0.0077
                              > 837 0.0080
                              > 912 0.0126
                              >
                              > Important : these are the least distances between the two orbits,
                              > *not* between the Earth and the comet!
                              > From these values, it appears that about the year 530 the two orbits
                              > exactly crosses, so a collision with the Earth was possible!
                              >
                              > Jean Meeus
                              >
                            • Bill J Gray
                              ... I think the reason we get two (Eta Aquarids in May, Orionids in October) has more to do with the fact that there are two places where the orbits come
                              Message 14 of 29 , Jul 16, 2012
                                Brian Skiff wrote:
                                > The persistent close MOID is why we get _two_ annual meteor showers
                                > from Comet Halley debris, yes? So this isn't such big news, que no?

                                I think the reason we get two (Eta Aquarids in May, Orionids in
                                October) has more to do with the fact that there are two places where
                                the orbits come close to each other. If you look at (*)

                                http://www.projectpluto.com/mpec.htm

                                and click on "Show Orbit in OrbitViewer", you can see this pretty
                                clearly. Pull the slider so that you're looking from above the solar
                                system, set the date to May 7, and the earth will pass very close to
                                the orbit of Halley. Set it to October 23, and it passes near another
                                point on Halley's orbit... though if you move the slider back, you'll
                                see that it's not nearly as close as the May point.

                                -- Bill

                                (*) Ignore almost everything else in the pseudo-MPEC. I chopped out
                                about 7000 lines of astrometry and residuals just to bring it down to
                                a reasonable size. Also note that the applet doesn't numerically
                                integrate, so don't use it for other apparitions.

                                -- Bill
                              • Brian Skiff
                                I wasn t being so serious, of course, but perhaps the main point, relative to the discussion about 2012 NJ, is that you can have a body with Damocloid /Comet
                                Message 15 of 29 , Jul 16, 2012
                                  I wasn't being so serious, of course, but perhaps the main point,
                                  relative to the discussion about 2012 NJ, is that you can have a body
                                  with "Damocloid"/Comet Halley-type motion that intersects Earth's orbit
                                  quite often, but odds are still extremely low that you'll get hit.
                                  Well, we plow through Comet Halley's dust twice a year (and similarly
                                  for bunches of other comets), but the big stuff (nearly) always misses.


                                  \Brian


                                  On Mon, 2012-07-16 at 14:37 -0400, Bill J Gray wrote:
                                  > Brian Skiff wrote:
                                  > > The persistent close MOID is why we get _two_ annual meteor showers
                                  > > from Comet Halley debris, yes? So this isn't such big news, que no?
                                  >
                                  > I think the reason we get two (Eta Aquarids in May, Orionids in
                                  > October) has more to do with the fact that there are two places where
                                  > the orbits come close to each other. If you look at (*)
                                  >
                                  > http://www.projectpluto.com/mpec.htm
                                  >
                                  > and click on "Show Orbit in OrbitViewer", you can see this pretty
                                  > clearly.
                                • gpobs
                                  The probability can generally be modeled by considering that a comet or a Damocloid that crosses the orbit of the earth will penetrate in two places a one AU
                                  Message 16 of 29 , Jul 16, 2012
                                    The probability can generally be modeled by considering that a comet or a Damocloid that crosses the orbit of the earth will penetrate in two places a one AU sphere centered on the sun. Each point of penetration has a circular region around it equal to the radius of the earth. The probability that the object will strike the earth is then the ratio of the areas of these two circular regions to the entire surface area of the one AU sphere or about one in 5.4 x 10^16. Admittedly, an object like a Damocloid will tend to concentrate more towards the ecliptic and the probability will be a bit higher. However, long-period comets tend to be more isotropically distributed and the probability will be similar to the above result. The total annual risk of a random impact is then the above number times the total number of earth-crossing long-period comets (many millions? many unobserved during perihelion passage) times the inverse of their period. There are statistics regarding the average periods of long-period comets but the estimates of the total population are not so well constrained.

                                    Did I do that right or did I make a mistake somewhere? Bottom line: I don't lose sleep over the threat.

                                    - Roy


                                    -----Original Message-----
                                    >From: Brian Skiff <bas@...>
                                    >Sent: Jul 16, 2012 12:08 PM
                                    >To: Bill J Gray <pluto@...>
                                    >Cc: MPML <mpml@yahoogroups.com>
                                    >Subject: Re: {MPML} Halley MOID
                                    >
                                    > I wasn't being so serious, of course, but perhaps the main point,
                                    >relative to the discussion about 2012 NJ, is that you can have a body
                                    >with "Damocloid"/Comet Halley-type motion that intersects Earth's orbit
                                    >quite often, but odds are still extremely low that you'll get hit.
                                    >Well, we plow through Comet Halley's dust twice a year (and similarly
                                    >for bunches of other comets), but the big stuff (nearly) always misses.
                                    >
                                    >
                                    >\Brian
                                    >
                                    >
                                    >On Mon, 2012-07-16 at 14:37 -0400, Bill J Gray wrote:
                                    >> Brian Skiff wrote:
                                    >> > The persistent close MOID is why we get _two_ annual meteor showers
                                    >> > from Comet Halley debris, yes? So this isn't such big news, que no?
                                    >>
                                    >> I think the reason we get two (Eta Aquarids in May, Orionids in
                                    >> October) has more to do with the fact that there are two places where
                                    >> the orbits come close to each other. If you look at (*)
                                    >>
                                    >> http://www.projectpluto.com/mpec.htm
                                    >>
                                    >> and click on "Show Orbit in OrbitViewer", you can see this pretty
                                    >> clearly.
                                    >
                                    >
                                  • Jaime Nomen
                                    Again over definitions of NEO Groups, according http://neo.jpl.nasa.gov/neo/groups.html NECs - Near Earth Comets q
                                    Message 17 of 29 , Jul 16, 2012
                                      Again over definitions of NEO Groups, according

                                      http://neo.jpl.nasa.gov/neo/groups.html

                                      NECs -> Near Earth Comets q<1.3 AU "and" P<200 years

                                      So a comet with a bit longer period than that, even crossing here beside
                                      shouldn`t be included in this group (same sort of "arbitrary" number of
                                      period of years as the minimum perihelium distance is considered)

                                      * but at least we have a maximum P for the upper limit on this group


                                      NEAs -> Near Earth Asteroids. with q<1.3 AU

                                      * no upper P, a, or Q limit stablished

                                      Therefore, it seems there isn`t a well defined NEA group on the upper end
                                      and no particular NEO group has been created for objects as 2012 NJ, apparenly
                                      asteroidal so far and Amor type orbit..¿?, better said "comet-like orbit" with
                                      longer P than most NEA

                                      Splitting them in some sort of pathological" NEO list
                                      as Alan stressed, :-) limiting when they have Q > Jupiter, could clarify all
                                      that
                                      although the reason for that iit seems only a matter of impact probability,
                                      which should be meaningless for these objects with longer periods, even though
                                      what really
                                      means short and long period?...for instance, others as the big NEO (3552) Don
                                      Quixote seems to share a similar situation but with a significant shorter
                                      period.

                                      Jaime
                                    • Bill J Gray
                                      ... It does seem like a very small threat. Can t say I ve worried about it, or seen anything here to cause worry. ...The probability that the object will
                                      Message 18 of 29 , Jul 16, 2012
                                        > Did I do that right or did I make a mistake somewhere?
                                        > Bottom line: I don't lose sleep over the threat.

                                        It does seem like a very small threat. Can't say I've worried
                                        about it, or seen anything here to cause worry.

                                        "...The probability that the object will strike the earth is
                                        then the ratio of the areas of these two circular regions to the
                                        entire surface area of the one AU sphere or about one in 5.4 x 10^16."

                                        Seems a reasonable analysis, but that end result seems off.
                                        With an earth radius of 6378 km and an AU of 150 million km, and

                                        earth cross-sectional area = pi * 6378^2 = 1.3e+8 km^2
                                        one-AU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
                                        area of _both_ earth cross-sections = 2.6e+8 km^2

                                        ...I get odds of about 1.1 billion to one. Slightly worse than
                                        this because the comet doesn't hit that sphere head-on, but at an angle.

                                        Your point remains, though: it's not much of a threat.

                                        -- Bill
                                      • gpobs
                                        Oh, I am such a twit! I got distracted and did the volume of the sphere, not the surface area. Oh, well... ... From: Bill J Gray To:
                                        Message 19 of 29 , Jul 16, 2012
                                          Oh, I am such a twit! I got distracted and did the volume of the sphere,
                                          not the surface area. Oh, well...

                                          ----- Original Message -----
                                          From: "Bill J Gray" <pluto@...>
                                          To: "gpobs" <gpobs@...>
                                          Cc: "Brian Skiff" <bas@...>; "MPML" <mpml@yahoogroups.com>
                                          Sent: Monday, July 16, 2012 4:05 PM
                                          Subject: Re: {MPML} Halley MOID


                                          >> Did I do that right or did I make a mistake somewhere? Bottom line:
                                          >> I don't lose sleep over the threat.
                                          >
                                          > It does seem like a very small threat. Can't say I've worried
                                          > about it, or seen anything here to cause worry.
                                          >
                                          > "...The probability that the object will strike the earth is
                                          > then the ratio of the areas of these two circular regions to the
                                          > entire surface area of the one AU sphere or about one in 5.4 x 10^16."
                                          >
                                          > Seems a reasonable analysis, but that end result seems off.
                                          > With an earth radius of 6378 km and an AU of 150 million km, and
                                          >
                                          > earth cross-sectional area = pi * 6378^2 = 1.3e+8 km^2
                                          > one-AU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
                                          > area of _both_ earth cross-sections = 2.6e+8 km^2
                                          >
                                          > ...I get odds of about 1.1 billion to one. Slightly worse than
                                          > this because the comet doesn't hit that sphere head-on, but at an angle.
                                          >
                                          > Your point remains, though: it's not much of a threat.
                                          >
                                          > -- Bill
                                          >
                                        • amaury@spaceobs.com
                                          Hello all, Just to clarify: Very small impact probability, the vast majority of impacts are by asteroids, but on average, much higher impact velocity therefore
                                          Message 20 of 29 , Jul 16, 2012
                                            Hello all,
                                            Just to clarify:
                                            Very small impact probability, the vast majority of impacts are by
                                            asteroids, but on average, much higher impact velocity therefore much
                                            more energy, and more destruction.
                                            Alain


                                            Bill J Gray <pluto@...> a écrit :

                                            >> Did I do that right or did I make a mistake somewhere?
                                            >> Bottom line: I don't lose sleep over the threat.
                                            >
                                            > It does seem like a very small threat. Can't say I've worried
                                            > about it, or seen anything here to cause worry.
                                            >
                                            > "...The probability that the object will strike the earth is
                                            > then the ratio of the areas of these two circular regions to the
                                            > entire surface area of the one AU sphere or about one in 5.4 x 10^16."
                                            >
                                            > Seems a reasonable analysis, but that end result seems off.
                                            > With an earth radius of 6378 km and an AU of 150 million km, and
                                            >
                                            > earth cross-sectional area = pi * 6378^2 = 1.3e+8 km^2
                                            > one-AU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
                                            > area of _both_ earth cross-sections = 2.6e+8 km^2
                                            >
                                            > ...I get odds of about 1.1 billion to one. Slightly worse than
                                            > this because the comet doesn't hit that sphere head-on, but at an angle.
                                            >
                                            > Your point remains, though: it's not much of a threat.
                                            >
                                            > -- Bill
                                            >
                                          • amaury@spaceobs.com
                                            Hello all, Just to clarify: Very small impact probability, the vast majority of impacts are by asteroids, but on average, much higher impact velocity therefore
                                            Message 21 of 29 , Jul 16, 2012
                                              Hello all,
                                              Just to clarify:
                                              Very small impact probability, the vast majority of impacts are by
                                              asteroids, but on average, much higher impact velocity therefore much
                                              more energy, and more destruction.
                                              Alain


                                              Bill J Gray <pluto@...> a écrit :

                                              >> Did I do that right or did I make a mistake somewhere?
                                              >> Bottom line: I don't lose sleep over the threat.
                                              >
                                              > It does seem like a very small threat. Can't say I've worried
                                              > about it, or seen anything here to cause worry.
                                              >
                                              > "...The probability that the object will strike the earth is
                                              > then the ratio of the areas of these two circular regions to the
                                              > entire surface area of the one AU sphere or about one in 5.4 x 10^16."
                                              >
                                              > Seems a reasonable analysis, but that end result seems off.
                                              > With an earth radius of 6378 km and an AU of 150 million km, and
                                              >
                                              > earth cross-sectional area = pi * 6378^2 = 1.3e+8 km^2
                                              > one-AU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
                                              > area of _both_ earth cross-sections = 2.6e+8 km^2
                                              >
                                              > ...I get odds of about 1.1 billion to one. Slightly worse than
                                              > this because the comet doesn't hit that sphere head-on, but at an angle.
                                              >
                                              > Your point remains, though: it's not much of a threat.
                                              >
                                              > -- Bill
                                              >
                                            • amaury@spaceobs.com
                                              Hello all, Just to clarify: Very small impact probability, the vast majority of impacts are by asteroids, but on average, much higher impact velocity therefore
                                              Message 22 of 29 , Jul 16, 2012
                                                Hello all,
                                                Just to clarify:
                                                Very small impact probability, the vast majority of impacts are by
                                                asteroids, but on average, much higher impact velocity therefore much
                                                more energy, and more destruction.
                                                Alain


                                                Bill J Gray <pluto@...> a écrit :

                                                >> Did I do that right or did I make a mistake somewhere?
                                                >> Bottom line: I don't lose sleep over the threat.
                                                >
                                                > It does seem like a very small threat. Can't say I've worried
                                                > about it, or seen anything here to cause worry.
                                                >
                                                > "...The probability that the object will strike the earth is
                                                > then the ratio of the areas of these two circular regions to the
                                                > entire surface area of the one AU sphere or about one in 5.4 x 10^16."
                                                >
                                                > Seems a reasonable analysis, but that end result seems off.
                                                > With an earth radius of 6378 km and an AU of 150 million km, and
                                                >
                                                > earth cross-sectional area = pi * 6378^2 = 1.3e+8 km^2
                                                > one-AU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
                                                > area of _both_ earth cross-sections = 2.6e+8 km^2
                                                >
                                                > ...I get odds of about 1.1 billion to one. Slightly worse than
                                                > this because the comet doesn't hit that sphere head-on, but at an angle.
                                                >
                                                > Your point remains, though: it's not much of a threat.
                                                >
                                                > -- Bill
                                                >
                                              • amaury@spaceobs.com
                                                Hello all, Just to clarify: Very small impact probability, the vast majority of impacts are by asteroids, but on average, much higher impact velocity therefore
                                                Message 23 of 29 , Jul 16, 2012
                                                  Hello all,
                                                  Just to clarify:
                                                  Very small impact probability, the vast majority of impacts are by
                                                  asteroids, but on average, much higher impact velocity therefore much
                                                  more energy, and more destruction.
                                                  Alain


                                                  Bill J Gray <pluto@...> a écrit :

                                                  >> Did I do that right or did I make a mistake somewhere?
                                                  >> Bottom line: I don't lose sleep over the threat.
                                                  >
                                                  > It does seem like a very small threat. Can't say I've worried
                                                  > about it, or seen anything here to cause worry.
                                                  >
                                                  > "...The probability that the object will strike the earth is
                                                  > then the ratio of the areas of these two circular regions to the
                                                  > entire surface area of the one AU sphere or about one in 5.4 x 10^16."
                                                  >
                                                  > Seems a reasonable analysis, but that end result seems off.
                                                  > With an earth radius of 6378 km and an AU of 150 million km, and
                                                  >
                                                  > earth cross-sectional area = pi * 6378^2 = 1.3e+8 km^2
                                                  > one-AU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
                                                  > area of _both_ earth cross-sections = 2.6e+8 km^2
                                                  >
                                                  > ...I get odds of about 1.1 billion to one. Slightly worse than
                                                  > this because the comet doesn't hit that sphere head-on, but at an angle.
                                                  >
                                                  > Your point remains, though: it's not much of a threat.
                                                  >
                                                  > -- Bill
                                                  >
                                                • amaury@spaceobs.com
                                                  Hello all, Just to clarify: Very small impact probability, the vast majority of impacts are by asteroids, but on average, much higher impact velocity therefore
                                                  Message 24 of 29 , Jul 16, 2012
                                                    Hello all,
                                                    Just to clarify:
                                                    Very small impact probability, the vast majority of impacts are by
                                                    asteroids, but on average, much higher impact velocity therefore much
                                                    more energy, and more destruction.
                                                    Alain


                                                    Bill J Gray <pluto@...> a écrit :

                                                    >> Did I do that right or did I make a mistake somewhere?
                                                    >> Bottom line: I don't lose sleep over the threat.
                                                    >
                                                    > It does seem like a very small threat. Can't say I've worried
                                                    > about it, or seen anything here to cause worry.
                                                    >
                                                    > "...The probability that the object will strike the earth is
                                                    > then the ratio of the areas of these two circular regions to the
                                                    > entire surface area of the one AU sphere or about one in 5.4 x 10^16."
                                                    >
                                                    > Seems a reasonable analysis, but that end result seems off.
                                                    > With an earth radius of 6378 km and an AU of 150 million km, and
                                                    >
                                                    > earth cross-sectional area = pi * 6378^2 = 1.3e+8 km^2
                                                    > one-AU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
                                                    > area of _both_ earth cross-sections = 2.6e+8 km^2
                                                    >
                                                    > ...I get odds of about 1.1 billion to one. Slightly worse than
                                                    > this because the comet doesn't hit that sphere head-on, but at an angle.
                                                    >
                                                    > Your point remains, though: it's not much of a threat.
                                                    >
                                                    > -- Bill
                                                    >
                                                  • amaury@spaceobs.com
                                                    Damned webmail... sorry to all. Alain
                                                    Message 25 of 29 , Jul 16, 2012
                                                      Damned webmail... sorry to all.
                                                      Alain


                                                      amaury@... a écrit :

                                                      >
                                                      > Hello all,
                                                      > Just to clarify:
                                                      > Very small impact probability, the vast majority of impacts are by
                                                      > asteroids, but on average, much higher impact velocity therefore much
                                                      > more energy, and more destruction.
                                                      > Alain
                                                      >
                                                      >
                                                      > Bill J Gray <pluto@...> a écrit :
                                                      >
                                                      >>> Did I do that right or did I make a mistake somewhere?
                                                      >>> Bottom line: I don't lose sleep over the threat.
                                                      >>
                                                      >> It does seem like a very small threat. Can't say I've worried
                                                      >> about it, or seen anything here to cause worry.
                                                      >>
                                                      >> "...The probability that the object will strike the earth is
                                                      >> then the ratio of the areas of these two circular regions to the
                                                      >> entire surface area of the one AU sphere or about one in 5.4 x 10^16."
                                                      >>
                                                      >> Seems a reasonable analysis, but that end result seems off.
                                                      >> With an earth radius of 6378 km and an AU of 150 million km, and
                                                      >>
                                                      >> earth cross-sectional area = pi * 6378^2 = 1.3e+8 km^2
                                                      >> one-AU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
                                                      >> area of _both_ earth cross-sections = 2.6e+8 km^2
                                                      >>
                                                      >> ...I get odds of about 1.1 billion to one. Slightly worse than
                                                      >> this because the comet doesn't hit that sphere head-on, but at an angle.
                                                      >>
                                                      >> Your point remains, though: it's not much of a threat.
                                                      >>
                                                      >> -- Bill
                                                      >>
                                                      >
                                                      >
                                                      >
                                                    • M.-T. Hui
                                                      Hi all, Now this object is designated as a comet -- P/2012 NJ (La Sagra). Quite an interesting object deserves all sorts of follow-up observations and studies.
                                                      Message 26 of 29 , Jul 18, 2012
                                                        Hi all,

                                                        Now this object is designated as a comet -- P/2012 NJ (La Sagra). Quite an interesting object deserves all sorts of follow-up observations and studies. Many congratulations to the team!

                                                         
                                                        Cheers, Man-To

                                                        *******************************************************
                                                        Man-To Hui (Cantonese)
                                                        ("Wentao Xu", "Wen-Tao Hsu" in Mandarin)
                                                        +23deg09m12s, +113deg18m54s
                                                        Canton, China Mainland
                                                        Undergraduate, School of Physics, WHU (2008-2012)
                                                        Astrowebsite: http://comethunter.lamost.org
                                                        Blog: http://pachacoti.wordpress.com
                                                      • walcom77
                                                        According to Cbet 3178, 2012 NJ is now COMET P/2012 NJ (LA SAGRA): http://www.cbat.eps.harvard.edu/iau/cbet/003100/CBET003178.txt a 35 tail has been reported
                                                        Message 27 of 29 , Jul 18, 2012
                                                          According to Cbet 3178, 2012 NJ is now COMET P/2012 NJ (LA SAGRA):

                                                          http://www.cbat.eps.harvard.edu/iau/cbet/003100/CBET003178.txt

                                                          a 35" tail has been reported by observers using the 1.23-m telescope
                                                          on Calar Alto on July 16, 17, and 18 UT.

                                                          Ciao,
                                                          Ernesto
                                                          http://remanzacco.blogspot.com
                                                          http://twitter.com/comets77
                                                        • Alan W Harris
                                                          Yes, all sorts , including rotational lightcurves and nucleus spectrophotometry. These marginally active barely-comets are amenable to the usual
                                                          Message 28 of 29 , Jul 18, 2012
                                                            Yes, "all sorts", including rotational lightcurves and "nucleus"
                                                            spectrophotometry. These marginally active barely-comets are amenable to
                                                            the usual asteroid-type observations (as well as "comet" type observations,
                                                            if you can see enough activity to measure).

                                                            At 10:55 AM 7/18/2012, M.-T. Hui wrote:
                                                            >Hi all,
                                                            >
                                                            >Now this object is designated as a comet -- P/2012 NJ (La Sagra). Quite an
                                                            >interesting object deserves all sorts of follow-up observations and
                                                            >studies. Many congratulations to the team!
                                                            >
                                                            >
                                                            >Cheers, Man-To
                                                            >
                                                            >*******************************************************
                                                            >Man-To Hui (Cantonese)
                                                            >("Wentao Xu", "Wen-Tao Hsu" in Mandarin)
                                                            >+23deg09m12s, +113deg18m54s
                                                            >Canton, China Mainland
                                                            >Undergraduate, School of Physics, WHU (2008-2012)
                                                            >Astrowebsite: http://comethunter.lamost.org
                                                            >Blog: http://pachacoti.wordpress.com
                                                            >
                                                            >
                                                            >
                                                            >------------------------------------
                                                            >
                                                            >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                            >
                                                            >Posts to this list or information found within may be freely used, with
                                                            >the stipulation that MPML and the originating author are cited as the
                                                            >source of the information.Yahoo! Groups Links
                                                            >
                                                            >
                                                            >
                                                            *****************************************************************************
                                                            Alan Harris Phone: 818-790-8291
                                                            4603 Orange Knoll Ave.
                                                            La Cañada, CA 91011-3364
                                                            email: harrisaw@...
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