Three new 'Trojan' asteroids found sharing Neptune's orbit Options

[Jyril]

Hmm....Chiron is truly anomalous, then.

Hardly. It is one of the many Centaur asteroids (comets?) thought to originate from the Kuiper Belt. As is the case with near-Earth asteroids, orbits of Centaurs are not stable.

[nprev]

New Horizons is going to be flying through-- I believe-- the L5 Lagrange point of Neptune in 2014, so I'm hoping that there are some discovered there within the next 8 years for NH to take a peek at.

http://pluto.jhuapl.edu/overview/piPerspec..._5_1_2006_2.php

Interesting. Actually, I'm almost alarmed by this...I hope the dust density in Neptune's L5 is reasonably low, given NH's relative velocity. There certainly can't be as much solar radiational "clearing" of that stuff way out there...

Wasn't there some offhand reference in a Larry Niven story to a manned flight that had to abort because they accidentally launched from Lunar orbit through one of the Earth-Moon Lagrange points & sustained damage from dust erosion?... (not precisely experimental evidence, I know! )

[nprev]

Hardly. It is one of the many Centaur asteroids (comets?) thought to originate from the Kuiper Belt. As is the case with near-Earth asteroids, orbits of Centaurs are not stable.

"Anomalous" was a bad word to use...I think that "ephemeral" is a better choice.

What I'm wondering is what the mean survival time of Centaurs at or inside the orbit of Uranus but no closer than Saturn might be given the fact that bodies like Chiron are sublimating at a fairly rapid rate, and what the implications might be for the apparent absence of Uranian & Saturnian Trojans....shooting from the hip here, I'd guess 10-15 million years of coherent existence for a whopper like Chiron, barring catastrophic collision/destruction or ejection to a more distant orbit.

Of course, all this would depend considerably on the gross composition of a given body, and I know that there are both a lot of unknowns and already a variety of identified types of outer-system minor planets. Still, I think that there are some valid research questions here.

[Guest_AlexBlackwell_*]

Note that the final versions of the Sheppard and Trujillo paper, as well as an accompanying Perspectives piece by Marzari, were published online today in the July 28, 2006, issue of Science. See the summary: Companion group for Neptune.

And I believe that Sheppard is offering access to his paper via his publications page.

[nprev]

Been a slow thread...time to reinvigorate it (hopefully! )

One thing that seems apparent is that Trojan bodies are artifacts of a capture process...there don't seem to be any primordial Trojan asteroids, unless Jupiter's gravity gradient was sufficient to produce most of the observed population, and even then that seems anomalous (that word again!), given the paucity of Trojan asteroids for any other outer system planet save Neptune. Therefore, why do Saturn and Uranus seem to lack them?

My theory: One or more catastrophic events disrupted the process for Saturn and Uranus. Saturn's rings and Uranus' odd axial tilt are the sole remaining artifacts of this (or these?) event(s). Did a large planetary body, perhaps even a brown dwarf, pass through the outer solar system at an oblique angle with respect to the ecliptic? If so, why are the orbits of Saturn & Uranus relatively regular and stable? If not, why are there no currently observable Trojan asteroids associated with either planet?

Lots of holes in this, I know...but I look forward to the comments of people far more knowledgeable!

[ljk4-1]

Is the theory that giant planets begin existence close to their star and then
migrate outward still viable?

If this theory still holds, that act alone could certainly create enough
disruption along the way for the Jovian worlds and any objects unfortunate
enough to be in their outward paths.

[tty]

Is the theory that giant planets begin existence close to their star and then
migrate outward still viable?

I should think that the resonance sweeping of Jupiter and Saturn migrating outwards would have completely eliminated the asteroid belt and perhaps the Kuiper belt too.

There is another theory that Uranus and Neptune migrated inwards about 4 x 10^9 years ago and that this caused the "late heavy bombardment".

tty

[infocat13]

[quote name='ljk4-1' date='Aug 15 2006, 10:44 AM' post='64369']
Is the theory that giant planets begin existence close to their star and then
migrate outward still viable?[quote]

If this theory still holds, that act alone could certainly create enough
disruption along the way for the Jovian worlds and any objects unfortunate
enough to be in their outward paths.
[/quote]




I believe if you consult the many websites that deal in exoplanet discoveries that many of the jupiter class planets discoverd in extreme close orbits to there stars start out in life in orbits further out and then as they eject objects OUT of there solar systems the jupiter mass objects spiral INWARDS.
this topic in astrodynamics is a most fascenating one as any earth size object in a inner orbit to a gas giant that once was in the goldilocks zone would find itself ejected into the intersteller void

[ljk4-1]

I guess the next question is, why aren't our Jovians circling the Sun in
orbits way tighter than Mercury?

[Jyril]

Maybe because the protoplanetary disk evaporated before Jupiter had time to plummet, or there were giant Jovians that traveled all the way into the Sun. In that case the familiar giant planets would be "second generation" planets.

[tasp]

Would a possible criteria for a close flyby of a Neptunian Trojan be as follows:

If statistical surveys of the numbers of KBOs external to Pluto indicates a smaller deflection of the New Horizons will still assure 2 KBO encounters post Pluto, then any Neptunian Trojan reachable within the revised propellant excess should be visited?



{it's my best shot, me wants to see a Neptunian Trojan without hampering the main mission of New Horizons}

[nprev]

Would a possible criteria for a close flyby of a Neptunian Trojan be as follows:

If statistical surveys of the numbers of KBOs external to Pluto indicates a smaller deflection of the New Horizons will still assure 2 KBO encounters post Pluto, then any Neptunian Trojan reachable within the revised propellant excess should be visited?
{it's my best shot, me wants to see a Neptunian Trojan without hampering the main mission of New Horizons}

Sounds like a good heuristic, Tasp, and I'd love to see a Neptune Trojan up close & personal as well. However, I'm still worried about the dust density in Neptune's Trojan points wrt NH's survival during transit...do you suppose that the Spitzer people might be persuaded to give this region a quick look?

Alan, if you're there, what do you think? Are my concerns overblown? AFAIK, no spacecraft has ever flown through an outer-planet Trojan point before, much less one with a known population of objects (which would seem to imply at least some increase in dust density above the background level...question is, how much?)

[alan]

I'm not the Alan your asking, but a Neptune Trojan flyby would require two deflections, one to get to the trojan and one to bring New Horizons back on a path to Pluto. The deflection to bring New Horizon's back to Pluto wouldn't have as long to take effect, few AU's travel to Pluto instead of up to 15 AU for a Kuiper Belet Object.

the other alan

[nprev]

Hmm. Okay, so if i read you right, Alan, this is quite technically feasible. However, I still would like to see some solid data on the dust density of Neptune's Trojan points...having NH blast through there at 20 km/sec or more solar relative still sounds damn risky until we understand this property of that region...

[ugordan]

However, I still would like to see some solid data on the dust density of Neptune's Trojan points...

Even if the dust concentration there were say 100 times greater than interplanetary space, I don't think that would pose any hazard to the spacecraft. We're talking really sparse dust population here. Note that Cassini successfully flew through one of the ring "gaps" (granted, with the HGA in ram direction) and had hundreds of thousands of dust particle hits within minutes -- yet it survived. I'm sure any dust clouds (if any) aren't going to be anything near that of a Saturnian ring "gap". IMHO, there's nothing to fear of passage through Neptune's L4 point.