Lost moons of Neptune, Still out there? |
Lost moons of Neptune, Still out there? |
Apr 27 2006, 02:45 PM
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Member Group: Members Posts: 509 Joined: 2-July 05 From: Calgary, Alberta Member No.: 426 |
Here's something I've been wondering about for a while:
The general feeling regarding the current Neptunian system seems to be that Triton is a captured Kuiper Belt object. When Triton was captured, any previously existing Neptunian satellite system would have been severely disrupted, which is presumably why we don't see many other moons there now. Only Proteus seems to have survived the catastrophe. If we assume that Proteus is the "Miranda" of the original Neptunian system, then (using the Uranian system as a model) Neptune is probably missing about four major moons right now. It is of course possible that some of them could have collided with Neptune, or with Triton. However, given Triton's large mass, it's also likely that some would have been ejected into heliocentric orbits. (In fact, this could have helped slow Triton down a bit during the capture process. Transfer of energy and all that.) Any ejected moons would most likely have made close passes by Neptune within the first few million years after being tossed, which presumably would have caused their orbits to evolve pretty rapidly. I don't claim to understand the subject well enough to predict what would have happened then, but let's suppose for the sake of argument that some mechanism could have gotten them into the Kuiper Belt -- perhaps multiple approaches with KBOs, or something along those lines. It seems very unlikely, but I wonder if any of those old Neptunian moons are still kicking around in the outer Solar System? At Uranus, Titania and Oberon are both over 1500 kilometres across, and Ariel and Umbriel are over 1100 as well. If Neptune's original satellites were of similar size, any survivors in the Kuiper Belt could rank among the largest objects there. Wouldn't it be a hoot if Ixion, Varuna or Quaoar turned out to be an ex-Neptunian moon? Intuitively, I think this probably isn't very likely. Neptune's original companions probably ended up as super-sized Centaurs, and got chucked out of the Solar System by Jupiter and Saturn. And really, this hypothesis isn't particularly useful because it won't be falsifiable in any of our lifetimes. But it's neat to think about, anyways. |
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Apr 28 2006, 03:15 PM
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Funny you should mention Neptunian moons...
Paper: astro-ph/0604552 Date: Wed, 26 Apr 2006 20:27:17 GMT (73kb) Title: A Survey for "Normal" Irregular Satellites Around Neptune: Limits to Completeness Authors: Scott S. Sheppard (Carnegie Inst. of Wash.), David C. Jewitt and Jan Kleyna Comments: 10 pages, 9 figures (6 color), 3 tables; Accepted for the July 2006 Astronomical Journal \\ We surveyed 1.75 square degrees of sky near Neptune to an R-band 50% detection efficiency of 25.8 mags (corresponding to radii of about 17 km for an assumed albedo of 0.04). We discovered one new outer satellite, Psamathe (S/2003 N1), about 20 km in radius and having a distant retrograde orbit and moderate eccentricity. Until 2003 Neptune was only known to have two satellites which exhibited orbital signatures indicative of capture. Both of these, Triton and Nereid, are unusual when compared to the irregular satellites of other giant planets. With recent discoveries of four additional satellites by Holman et al. (2004) it is now apparent that Neptune has a distant ``normal'' irregular satellite system in which the satellites have radii and orbital properties similar to those of the satellites of other giant planets. We find that the satellite size distribution at Neptune is not well determined given the few objects known to date, being especially sensitive to the inclusion of Triton and Nereid in the sample. Finally, we note that Psamathe and S/2002 N4 have similar semi-major axes, inclinations and eccentricities. They may be fragments of a once larger satellite. \\ ( http://arXiv.org/abs/astro-ph/0604552 , 73kb) -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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