[meteorite-list] Three New 'Trojan' Asteroids Found Sharing Neptune's Orbit

From: Larry Lebofsky <lebofsky_at_meteoritecentral.com>
Date: Sat Jun 17 17:24:24 2006
Message-ID: <1150579460.4494730487552_at_hindmost.LPL.Arizona.EDU>

Hi again Sterling:

I have to keep this short since I have a journal article to review and a
magazine to edit.

Even an asteroid scientist can learn something once in a while:

The Lagrange points (the stable ones) are gravity lows (they can get in but
they can't get out). I knew that.

1. To be in a Jupiter Trojan orbit, you have to be between 5.05 and 5.40 AU
from the Sun (Earth is 1 AU from the Sun, if there is anyone here not familiar
with that term and Jupiter 5.20 AU). I just learned that.

2. If you go to the Minor Planets Center site,

http://cfa-www.harvard.edu/iau/lists/JupiterTrojans.html


there is a list of all the Trojan asteroids and their orbital elements. Some
of the Jupiter Trojans have orbital inclination over 40 degerees (I didn't
know that).

So, with even higher velocities at the distance of Jupiter, and that high of
an inclination, you would again think that they would be running into one
another. But, space is big and space is dark to quote a t-shirt.


Oh, Sterling, going back to Planet V (remember that?) One of the models for
the formation of the Solar System (and for the late heavy bombardment) is the
moving of the planets: Jupiter moves in, Satuen moves out (when Saturn's
orbital period is twice that of Jupiter, asteroids get flung all over the
place), and Uranus and Neptune also move out. In some models, Neptune starts
out being closer to the Sun than Uranus!
Quoting "Sterling K. Webb" <sterling_k_webb_at_sbcglobal.net>:

> Hi, Larry, List,
>
> It is a little puzzling, but I assume that what
> they're describing is the discovery of an asteroid
> in an orbit identical to Neptune's but tilted 25 deg
> to Neptune's and having an asteroid in the Trojan
> position to where Neptune would be if Neptune
> were in that orbit instead of the orbit that Neptune
> actually is in, if a woodchuck could chuck wood....
>
> What's unclear to me is why an asteroid would
> settle down in the Trojan position of an asteroid
> in an orbit identical to Neptune's but tilted 25 deg
> to Neptune's and having that asteroid in the Trojan
> position to where Neptune would be if Neptune
> were in that orbit instead of the orbit that Neptune
> actually is in, if Neptune isn't actually IN that orbit,
> providing the gravitational situation which makes
> the Trojan position stable?
>
> I spoze that Neptune's gravitational influence
> out there in them thar wide open spaces is great enough
> to provide stability even to an inclined co-orbit. My
> first thought was that maybe Neptune's influence on
> an inclined orbit was only strong enough to sustain
> Trojans in a zone near to Neptune's orbit, but then
> I realized that all these inclined orbits would have
> nodes with the orbit of Neptune, so that the Neptune
> Trojans in inclined orbits would pass through Neptune's
> orbit at two points, the nodes.
>
> Since, as Larry pointed out, the Trojans of a major
> planet like Jupiter are actually a "cloud" of asteroids.
> He says, "...they can be inclined to the orbit of Jupiter
> slightly closer or further from the Sun, or slightly in front
> of or behind the 60 degree point." To indulge is Science's
> favorite sport, the Quibblefest, only the ones slightly
> "above" and "below" the major planet's orbit have a
> different inclination; the examples cited vary in axis
> and time of perihelion passage, but of course the vast
> majority of those Trojans vary in all three parameters.
> Such a "cloud" should be roughly ellipsoidal stretched
> to banana shaped and lying within the boundary wherein
> the major planet's gravitational influence greatly exceeds
> that of all other bodies, which in the case of major
> planets in the wide open spaces of the outer system is
> probably a pretty big ranch.
>
> An object in ANY inclined orbit that was in the
> "Neptune" position would smack right into Neptune,
> so we can expect this point and all the orbital territory
> even near to it to be completely empty by now! And,
> unless the pictures in my head are all wrong (it could
> happen), the "Neptune" Trojan point should also pass
> through Neptune's "Neptune" Trojan point!
>
> This raises the prospect of what I can only call an
> example of really heavy cross-town traffic as the asteroids
> of the inclined Trojans slice through the "regular" Neptune
> Trojans at the inclined angle. This is not as exciting and
> video-game-like as it sounds, since the orbital speed out
> in them thar wide open spaces is only 5.43 km/sec mph.
> Still, it must get interesting at times... Particularly since
> all the differently inclined orbits' Trojan points should
> be making that passage at pretty much the same time!
> Every 165 years...
>
> This raises some interesting considerations. How could
> such a population of inclined Trojans arise?. Method One:
> start with asteroids everywhere and stir and churn for 4 billion
> years until only the stable ones are left. Fly in Ointment: four
> billion years isn't long enough. Method Two is more intriguing...
> Suppose that there are largish objects (500 to 2000 km) in
> inclined Neptune-like orbits (as well as in the Neptune orbit).
> Repeated low-speed collisions would create Trojan "clouds"
> of smaller objects.
>
> Method Two B is for a still larger object 1000 to 3000
> km) to be lurking in an high-inclination Neptune co-orbit
> which would periodically deflect Neptune Trojans into inclined
> orbits (not the same as the intruder). I hear the astronomers
> grimacing; it would eventually hit Neptune. Nah! Every
> close pass would alter its orbit, making eventual collision
> very improbable. Or, maybe it's impossible. Hard to tell
> about dynamic arguments without working it out, but odd
> synchronizations abound...
>
> But... But... Surely we would have found it! Hey! Not
> of you don't ever point the telescope out-of-plane... Galileo
> found Neptune with the World's Largest Astronomical
> Telescope -- 30 mm objective with quality we would
> consider suitable for a child's toy, or maybe not even that.
> *Galileo first observed Neptune on December 28, 1612
> It was stationary because it had just turned retrograde
> that very day; he thought it was a star and charted it as
> such.
>
> As the "more asteroids than in the Main Belt," they are
> apparently talking about asteroids 60 km diameter and
> larger when they say, "Neptune Trojans may outnumber
> the tens of thousands of asteroids in the main asteroid belt."
> The Main Belt, of course has far more asteroids than tens
> of thousands! Although it is not clear to me why there
> would not be numerous small asteroids in this Neptune
> Trojan crowd also.
>
> Ron's newer post of
> http://www.newscientistspace.com/article/dn9340-new-trojan-asteroid-hints-at-
huge-neptunian-cloud.html
> contains more details. The "freeze-in" theory they propose
> would require there to be a minimum of 100,000,000
> big asteroids to be Neptune co-orbits prior to the freeze,
> so they are nothing if not very generous with their asteroids!
> (Actually it might require a billion or more, but I don't
> want to quibble...) ALL the theories require a big bag
> of asteroids for the Outer Outer System. And you know
> that whatever the mechanism that starts with big numbers
> and then wastes them, many if not most of them would
> have been scattered outward.
>
>
> Sterling K. Webb
Received on Sat 17 Jun 2006 05:24:20 PM PDT