Plutos New Moons Part 2, News ... Options

[SigurRosFan]

Orbits and photometry of Pluto's satellites: Charon, S/2005 P1 and S/2005 P2

http://arxiv.org/abs/astro-ph/0512491

Orbital periods:

Charon - 6.3872304 +/- 0.0000011 days

S/2005 P2 - 24.8562 +/- 0.0013 days

S/2005 P1 - 38.2065 +/- 0.0014 days

Note:

The old thread - http://www.unmannedspaceflight.com/index.p...wtopic=1622&hl=

[elakdawalla]

OK, so I plugged these periods into my calculator and I get:
S/2005 P1 : Charon = 5.9817 : 1
S/2005 P2 : Charon = 3.8915 : 1

That first one is close to a resonant orbit (1:6), but I don't think that "close" counts with resonant orbits, does it? The second one seems pretty far off from 1:4. It seems like it shouldn't be stable to be so close but not quite at a resonant orbit. But then I never studied orbital dynamics so I don't know.

--Emily

[Rob Pinnegar]

Yeah, the error bars on those periods are too far off to make resonance very likely.

Something I hadn't thought of before: Pluto-Charon is of course unique in that both bodies are tidally despun. Shouldn't this mean that Charon's orbit would have stopped evolving some time ago? Its semi-major axis should be exactly the same now as it was when Pluto's tidal despinning completed.

The two newly discovered moons of course should still be evolving outwards from Pluto, but they may not have had time to reach the 4:1 and 6:1 resonances yet, just as Callisto won't hit the 2:1 with Ganymede for another billion years or so. Maybe they'll get there eventually. I wonder if the system will be stable when they do? (Mind you, the Sun may reach red giant stage before that, at which point all bets are off.)

Does anyone know whether the small mass of the Pluto system would retard the outward evolution of moons? Intuitively one would think so, but I'd sooner trust the physics than my intuition.

There's room here for a nice little Icarus paper. Wish I had the know-how to do it myself.

[Rob Pinnegar]

That first one is close to a resonant orbit (1:6), but I don't think that "close" counts with resonant orbits, does it?

Actually, unless I'm very wrong, "close" _can_ actually count, because resonances don't have to involve both bodies coming back to exactly the same locations after a set number of orbits. They can also involve things like the precession of periastron. I think this is called "resonance splitting"?

Since the outer Plutonian satellite has a fairly big orbital eccentricity, and is quite close to the "formal" 6:1 resonance, I'm tempted to wonder whether that moon might be caught in one of these. (However, this would of course have been considered by the authors, and since it doesn't show up in the abstract, it's not likely to be true. It's worth mentioning, though.)

[djellison]

And of course, the ratio doesnt have to be perfect, as whilst the moon orbits the planet, the planet wobbles a little to return the favour, that wobble may take a calculated measurement away from a perfect figure.

Doug

[ljk4-1]

Paper: astro-ph/0512491

Date: Tue, 20 Dec 2005 00:38:58 GMT (219kb)

Title: Orbits and photometry of Pluto's satellites: Charon, S/2005 P1 and
S/2005 P2

Authors: M. W. Buie (1), W. M. Grundy (1), E. F. Young (2), L. A. Young (2),
and S. A. Stern (2) ((1) Lowell Observatory, (2) Southwest Research
Institute)

Comments: 21 pages, 5 figures, 4 tables
\\
We present new astrometry of Pluto's three satellites from images taken of
the Pluto system during 2002-3 with the High Resolution Camera (HRC) mode of
the Advanced Camera for Surveys (ACS) instrument on the Hubble Space Telescope.

The observations were designed to produce an albedo map of Pluto but they also
contain images of Charon and the two recently discovered satellites, S/2005 P1
and S/2005 P2. Orbits fitted to all three satellites are co-planar and, for
Charon and P2, have eccentricities consistent with zero. The orbit of the
outermost satellite, P1, has a significant eccentricity of 0.0052 +/- 0.0011.
Orbital periods of P1, P2, and Charon are 38.2065 +/- 0.0014, 24.8562 +/-
00013, and 6.3872304 +/- 0.0000011 days, respectively. The total system mass
based on Charon's orbit is 1.4570 +/- 0.0009 x 10^22 kg. We confirm previous
results that orbital periods are close to the ratio of 6:4:1 (P1:P2:Charon)
indiciative of mean-motion resonances, but our results formally preclude
precise integer period ratios. The orbits of P1 and P2, being about the
barycenter rather than Pluto, enable us to measure the Charon/Pluto mass ratio
as 0.1165 +/- 0.0055. This new mass ratio implies a density of 1.66 +/- 0.06 g
cm^-3 for Charon and 2.03 +/- 0.06 g cm^-3 for Pluto thus adding confirmation
that Charon is somewhat under-dense relative to Pluto. Finally, by stacking all
images, we can extract globally averaged photometry. P1 has a mean opposition
magnitude of V=24.39 +/- 0.02 and color of (B-V) = 0.644 +/- 0.028. P2 has a
mean opposition magnitude of V=23.38 +/- 0.02 and color of (B-V) = 0.907 +/-
0.031. The colors indicate that P1 is spectrally neutral and P2 is slightly
more red than Pluto. The variation in surface color with radial distance from
Pluto is quite striking (red, neutral, red, neutral) and begs further study.

\\ ( http://arXiv.org/abs/astro-ph/0512491 , 219kb)

[elakdawalla]

I was about to blog this but realized I don't know how to refer to this paper because I don't quite understand what arXiv is archiving. The layout of the paper looks like it has been submitted to a journal. Which journal? Does its appearance on arXiv mean that it is in prep, in press, or what? Does anybody know?

--Emily

[The Messenger]

I was about to blog this but realized I don't know how to refer to this paper because I don't quite understand what arXiv is archiving.  The layout of the paper looks like it has been submitted to a journal.  Which journal?  Does its appearance on arXiv mean that it is in prep, in press, or what?  Does anybody know?

--Emily

Archives is for 'press ready' papers, allowing the author's to get 'first dibs' on the concept. Peer review is not required, but an author must either be established, or recommended by established authors. In general archive papers are not referenced, and you should contact the authors before extracting or publishing -
very often they are awaiting peer review, and sometimes in the notes the authors will list where or when the paper will be published.

They are fair game, though, for discussions such as this.

I don't know where that puts your blog - right in the middle of gray

[Rob Pinnegar]

I was about to blog this but realized I don't know how to refer to this paper because I don't quite understand what arXiv is archiving.

Looks like Alan Stern is on the author list. He may be able to answer this for you next time he drops by.

[Guest_AlexBlackwell_*]

I was about to blog this but realized I don't know how to refer to this paper because I don't quite understand what arXiv is archiving.  The layout of the paper looks like it has been submitted to a journal.  Which journal?

I'm not sure but I think the paper has been submitted to and/or accepted by The Astrophysical Journal (ApJ), which isn't surprising given the subject matter and the apparent fact that the paper is not under embargo. And a close reading of page 11 of the preprint notes that the authors used a particular LaTeX macro that is typically used to prepare manuscripts for AAS journals.

I wouldn't rule out other journals but ApJ or ApJL are safe bets.

[elakdawalla]

Thanks for the various replies. I decided that it seemed firm enough to blog it. What are blogs for but spreading rumors anyway?

--Emily

[nprev]

At the risk of piquing the ire of some, does anybody think that these new moons will influence the IAU's decision about Pluto's planetary status (to say nothing of 2003UB313?)...

[Alan Stern]

Looks like Alan Stern is on the author list. He may be able to answer this for you next time he drops by.

One usually refers to the paper as submitted to the archival journal it will be published in. In this case, AJ, The Astronomical Journal.

[Guest_AlexBlackwell_*]

One usually refers to the paper as submitted to the archival journal it will be published in. In this case, AJ, The Astronomical Journal.

Yeah, that's the one I meant, Alan I always mix up the alphabet soup listing of astronomical and astrophysical journals (e.g., ApJ, ApJL, AJ, etc.).

EDIT: Note the paper is listed as a submission on AJ's "Future Articles" webpage.

This post has been edited by AlexBlackwell: Dec 23 2005, 06:54 PM

[ljk4-1]

Paper: astro-ph/0512599

Date: Fri, 23 Dec 2005 13:42:57 GMT (311kb)

Title: Characteristics and Origin of the Quadruple System at Pluto

Authors: S.A. Stern, H.A. Weaver, A.J. Steffl, M.J. Mutchler, W.J. Merline,
M.W. Buie, E.F. Young, L.A. Young, & J.R. Spencer

Comments: 15 pages, 1 figure
\\
Our discovery of two new satellites of Pluto, designated S/2005 P 1 and
S/2005 P 2 (henceforth, P1 and P2), combined with the constraints on the
absence of more distant satellites of Pluto, reveal that Pluto and its moons
comprise an unusual, highly compact, quadruple system. The two newly discovered
satellites of Pluto have masses that are very small compared to both Pluto and
Charon, creating a striking planet-satellite system architecture. These facts
naturally raise the question of how this puzzling satellite system came to be.
Here we show that P1 and P2's proximity to Pluto and Charon, along with their
apparent locations in high-order mean-motion resonances, likely result from
their being constructed from Plutonian collisional ejecta. We argue that
variable optical depth dust-ice rings form sporadically in the Pluto system,
and that rich satellite systems may be found, perhaps frequently, around other
large Kuiper Belt objects.

\\ ( http://arXiv.org/abs/astro-ph/0512599 , 311kb)