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

[Guest_AlexBlackwell_*]

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

See also the related Space.com story.

[Guest_AlexBlackwell_*]

See also Scott Sheppard's page for more details.

[Guest_AlexBlackwell_*]

See also Scott Sheppard's page for more details.

Sorry for the drip, drip of posts but, since the press releases and Space.com story don't really make clear, the new discovery is being published in Science Express, which is the early version of articles that are later assigned to the regular journal.

For the abstract of Sheppard and Trujillo, click here. Also, there will be an accompanying Perspectives piece by Marzari.

[jsheff]

Thanks, Alex. I don't have access to the entire paper, but how can they deduce the following?

"Evidence suggests that the Neptune Trojans are more numerous than either the main asteroid belt or the Jupiter Trojans,"

That's a pretty significant statement. There are tens of thousands of asteroids in the main belt. Does this imply there are at least that many Neptune Trojans?

- John Sheff
Cambridge, MA

[Guest_AlexBlackwell_*]

Thanks, Alex. I don't have access to the entire paper, but how can they deduce the following?

"Evidence suggests that the Neptune Trojans are more numerous than either the main asteroid belt or the Jupiter Trojans,"

Mainly due to the high inclination of 2005 TN53, which implies a thicker population disk.

EDIT: Here's an excerpt from the paper:

"A high inclination Trojan on a nearly circular orbit like 2005 TN53 would only spend about 2% of its orbit within the 1.5 degrees of ecliptic latitude that our survey covered. Thus for every high inclination Trojan discovered by our survey, we should expect tens of, i.e. 50(+75)(−35), high inclination Trojans outside this latitude range, assuming Poisson statistics."

This post has been edited by AlexBlackwell: Jun 15 2006, 09:41 PM

[dilo]

John, the statement disappointed me too, considering that first first Neptune trojan was discovered only in 2001 and we know only 4 such object, all in the L4 region.
By reading the full article (yes, I have the access!) "The number of Jupiter Trojans is comparable to the main asteroid belt" (A. Morbidelli, H. Levison, K. Tsiganis, R. Gomes, Nature 435, 462 (2005)). Moreover, based on photometric measurements, the four known Neptune Trojans have radii from about 40 to 70 km when assuming an albedo of 0.05. These sizes are comparable to the largest known Jupiter Trojans and, assuming the Trojans are equally distributed throughout the L4 Trojan cloud with identical albedos, Neptune Trojans are between about five and twenty times more abundant at the large sizes than the Jupiter Trojans.
This brings to the statement we are discussing about; clearly, there are many uncertains because conclusion is based on assumptions on albedo and size distribution argued from a such small sample...

[Rob Pinnegar]

More numerous than Jovian Trojans I can believe. More numerous than main-belt asteroids, though? Bit of an odd conclusion based on four objects.

By the way... the L5 point for Neptune is somewhere on the edge of the Milky Way right now, whereas the L4 point is far away from it. So as far as discovery bias is concerned, it's probably just easier to spot L4 Trojans for the time being. (This being Neptune we're talking about, the "time being" means the next several decades, I guess).

[Guest_PhilCo126_*]

I was more amazed by the article about Earth having extra Moons

[Guest_AlexBlackwell_*]

More numerous than Jovian Trojans I can believe. More numerous than main-belt asteroids, though? Bit of an odd conclusion based on four objects.

True, though Sheppard and Trujillo are pretty clear that they're using a small statistical sample and Poisson statistics to extrapolate and infer a larger disk. It also should be noted that they combine the high-inclination observation of 2005 TN53 with the chaotic "freeze-in" capture mechanism postulated by Morbidelli et al.

[nprev]

Just out of curiousity (and ignorance...I admit it), how many Uranian Trojans are known? Although I know that Uranus & Neptune are hardly close neighbors, it's interesting that the projected population of Neptunian Trojans is so large...can a very distinct line of demarcation for the inner boundary of the Kuiper Belt be drawn thereby, and is the inner KB therefore enormously denser than the asteroid belt given the much larger volume of space to be considered?

[alan]

No Uranus or Saturn trojans have been found so far.

[mchan]

Perhaps because they're not at the boundary of a belt?

[Rob Pinnegar]

Perhaps because they're not at the boundary of a belt?

That's probably part of it. But there's also orbital stability to consider.

I don't claim to know much about this, but running a quick Google search on "saturnian trojans" pops up a few interesting hits. It's been looked at, of course. First glance doesn't show much of a consensus, though.

[nprev]

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

I wonder if anyone's worked out how long a KBO can really survive at that distance from the Sun, given that Chiron has apparently exhibited significant outgassing in some observations...might be an interesting constraint, perhaps the constraint, that explains the apparent scarcity of such objects further in than the orbit of Neptune...?

Of course, with respect to Trojans it seems that most dynamical models portray them as primordial objects that formed--and stayed--in place. Uranus' sparse modern population of Trojans perhaps might be explained by whatever incredible event tipped the planet on its side (you know there had to be a massive orbital perturbation associated with that, whatever it was...did it perhaps also mess up Saturn's original Trojans? That planet has a pretty large axial tilt as well, to say nothing of the rings...makes you think).

Still, random captures should have populated L4 & L5 for both Saturn & Uranus over time, and their absence to me says that unfortunate KB interlopers that get stuck there evaporate over a relatively short time.

[stevesliva]

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