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Re: {MPML} P100Oms Uranus Trojan?

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  • Bill J Gray
    Hi Tomas, My apologies; Find_Orb has misled you here. With this short an arc and this great a distance, the orbit is almost completely indeterminate.
    Message 1 of 4 , Jul 27, 2011
      Hi Tomas,

      My apologies; Find_Orb has misled you here.

      With this short an arc and this great a distance, the
      orbit is almost completely indeterminate. (Except to say
      that it's probably pretty darn far off.) In such cases,
      Find_Orb just tries some Vaisala orbits and looks for one
      that has the closest to "reasonable" results. In this
      case, it's putting the object near aphelion (note the
      M=180) at about 21.5 AU.

      This should serve well for finding the object on another
      night, but it's probably not close to the real orbit.

      The current "in development" version of Find_Orb shows
      the U parameter for better-determined orbits. In this case,
      it should probably show "U V", or "U (huge)", just to
      warn you that Find_Orb is guessing.

      -- Bill
    • andrew_j_walker
      A strange coincidence, here http://www.minorplanetcenter.net/mpec/K11/K11O47.html and here http://www.minorplanetcenter.net/iau/lists/NeptuneTrojans.html 2004
      Message 2 of 4 , Jul 28, 2011
        A strange coincidence, here http://www.minorplanetcenter.net/mpec/K11/K11O47.html

        and here

        http://www.minorplanetcenter.net/iau/lists/NeptuneTrojans.html

        2004 KV18 is the second known Neptune Trojan at L5. There have been
        a number of new TNOs announced by this group over the last few weeks
        based on old observations, maybe they been using better detection
        software?

        Andrew

        --- In mpml@yahoogroups.com, Alan Harris <awharris@...> wrote:
        >
        > Thoughts: As a rule of thumb, not strict, trojan orbits are more stable
        > with a planet that does not have massive neighbors both inside and outside
        > of it. Thus, Jupiter, with nothing all the way in to Mars and being the
        > most massive planet in the solar system, has a very stable trojan
        > zone. Neptune, with no significant mass on the outside, likewise has a
        > pretty stable trojan zone (and even a stable 3:2 resonance zone where Pluto
        > lives). Uranus is more problematic, with Saturn on the inside and Neptune
        > outside, and Saturn likewise, with Jupiter inside and Uranus outside. Mars
        > and Earth are marginal. Mars has nothing outside, but is not very massive;
        > the Earth has Mars to the outside, but again, it outweighs Mars by a lot so
        > it sort of doesn't have much on the outside, all the way to Jupiter.
        >
        > Thinking specifically about the claimed Earth trojan, if you have a look at
        > the Nature paper, the libration amplitude is almost 180 degrees, that is,
        > it librates about the 60-deg L4 point all the way from zero to 180 degrees,
        > with a period of about 400 years. In fact, about 1600 years ago, if you
        > believe the integrations back that far (you probably shouldn't) it
        > "horseshoed", and before that was librating about the L5 point. Now here's
        > the problem: the current argument of perihelion is 45 degrees, and the
        > eccentricity is substantial. So currently (hundreds to a thousand or so
        > years), when the object librates to be almost at the Earth's longitude, it
        > doesn't get very close to the Earth because it is far inside or outside of
        > the Earth when it is at node, and far above or below the Earth when it is
        > at 1 AU. But that doesn't last forever. The period of the trojan
        > libration (~400 years) is not commensurate with the period of circulation
        > of the argument of perihelion. sooner or later, the libration will carry
        > it to the Earth's longitude at a time when the argument of perihelion is
        > near 90 (or 270) degrees, and it will make a series of very close passes by
        > the Earth, very likely resulting in ejecting it from "trojan"
        > configuration. Typically the period of perihelion circulation is some tens
        > of thousands of years, so my guess is that this object probably got parked
        > in its present configuration some thousands of years ago, and will get
        > ejected back out some thousands of years in the future. But as properly
        > noted in the Nature paper, the motion is chaotic over only hundreds to a
        > thousand years, so one really can't track it 10,000 years and say what will
        > actually happen or when. But certainly, this object is not in a stable
        > configuration like the current Jupiter Trojan population.
        >
        > At 04:32 PM 7/27/2011, Tomas wrote:
        > >Could we have a uranus trojan on our hands? The first four sets of
        > >observations available on NEOCP currently give the following elements:
        > >
        > >P100Oms
        > > Perihelion 2053 May 26.294451 TT = 7:04:00 (JD 2471048.794451)
        > >Epoch 2011 Jul 27.0 TT = JDT 2455769.5 Ur: 0.7678 Find_Orb
        > >M 180.00780 (2000.0) P Q
        > >n 0.01178013 Peri. 333.53195 -0.73404352 -0.67826697
        > >a 19.1294492 Node 163.61868 0.64231709 -0.70952696
        > >e 0.1244084 Incl. 6.85767 0.22047418 -0.19111616
        > >P 83.67 H 8.5 G 0.15 q 16.7495849 Q 21.5093135
        > > From 12 observations 2011 July 25-27; RMS error 0.391 arcseconds
        > >
        > >Which would place the object into a zone of stability as described by
        > >Dvorak, R.; Bazsó, Á.; Zhou, L.-Y. in Where are the Uranus Trojans?
        > >
        > >http://adsabs.harvard.edu/abs/2010CeMDA.107...51D
        > >
        > >any thoughts
        > >
        > >
        > >
        > >------------------------------------
        > >
        > >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        > >
        > >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
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        > >
        > >
        > *******************************************************************
        > Alan W. Harris
        > Senior Research Scientist
        > Space Science Institute
        > 4603 Orange Knoll Ave. Phone: 818-790-8291
        > La Canada, CA 91011-3364 email: awharris@...
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        >
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