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=

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

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.

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.)

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

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)

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

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

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.

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

--Emily

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?)...

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.

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)

With the nes period findings, the NH mission disign still remains rather uncomplicated with regards to satellite placement during the flyby. Granted the configuration of the satellites does not repeat exactly every ~70 days or so, with the near resonance exhibited, the 2 new sats will still be constrained in their posible positions. (working this out in my head) it seems the sats will be slightly short of their last position every ~70 days. (imagine the whole system lining up slightly earlier every time the objects 'reclock')

For an apparently narrow range of possible arrival dates (assuming a nominal launch, evaluating the arrival dates consistent with Pluto and Charon optimal positions for good views of the new satellites still should not devolve to a plethora of possibilities.

New paper:

http://arxiv.org/abs/astro-ph/0601018 - The Discovery of Two New Satellites of Pluto

Our discovery team is beginning to debate names. Suggestions for P1 and P2 are welcome. Here are
some groundrules: the names must come from Roman mythology and they must have a logical
connection to one another and to either Pluto or Charon (or both).

-Alan

Cerberus and Orthrus?

The five rivers of the underworld are mentioned in the Aeneid: Acheron, Phlegethon, Styx, Cocytus, and Lethe. Styx and Acheron are traditionally associated with Charon. That leaves you with three more names in case new moons are discovered.

Well, to get some discussion going, here are some possibilities and non-possibilities:

Names already taken by asteroids or KBOs:

6239 Minos
38083 Rhadamanthus
1865 Cerberus (darn!!!)
3361 Orpheus
75 Eurydike

Names that don't seem to be taken yet:

Aeacus (unpronounceable)
Styx
Tartarus
Erebus
Hecate
Thanatos

Myself, I like "Thanatos" for one of them. (Thanatos was more or less the Grim Reaper of Greek mythology.) Perhaps Tartarus and Erebus ought to be kept in reserve to be used as names of features on Pluto. Maybe Styx as well, thought it's difficult to imagine that any rivers will be found there.

[Edit: "Orthrus" seems to be open. Too bad about Cerberus being taken -- Cerberus and Orthrus would've been perfect.]

There's at least one overlaps between moons and asteroids: for example, 593 Titania and the moon of Uranus. Are these grandfathered or something?

Probably... there's also an asteroid called Europa and it's one of the early ones.

There's a Ganymed, too, but that's different because it has a different spelling than Ganymede.

(While hunting through the asteroid list, I was pleased to discover four named after Moe, Larry, Curly and Shemp. Nyuk, nyuk, nyuk!)

Probably "Tityas" would be appropriate, too. He was a Titan-like figure sent as a prisoner to Tartarus, Pluto's realm, as a punishment for having tried to rape Leto, mother of Apollo and Artemis.

"Phlegeton" is considered to be the river that forms the border of Tartarus. It is the "river of fire" and was supposed to burn without consuming fuel. Others describe it as beeing made of boiling blood. So the color red would possibly fit P2.

Rob has already listed the other names that came to my mind, too.

Michael

Or as potential names for 2003 UB313...

These are perfect names for large Kuiper Belt objects.

Yes, alternate spellings for kids names is quite trendy these days - note that there are at least 155 ways to spell Caitlin. Why couldn't this work for solar system bodies?

Serberus
Aurfeeus
Mynohs



Any chance the IAU could be convinced to allow Cerberus and Orpheus to be doubled as well? I mean, technically the asteroids come with a number first...

I would be very disappointed if one of the moons isn't named Cerberus, despite the fact an asteroid has the same name (lest we for get 85 Io, 52 Europa, 55 Pandora, 106 Dione, 1810 Epimetheus, and 4450 Pan, just to name a few). I second Orthrus as well, though I other than being a brother of Cerberus, I can't find a connection to Pluto/Hades (my Greek mythology here coming from Wikipedia though).

It's just EE-uh-kuss. Not so bad. Orthrus is more nearly a tongue-twister!

Perhaps all trans-Plutonian planets should be called names starting with 'P', and their satellites should all have names starting with 'C'...

Bob Shaw

Cerberus had a BROTHER? What happened? Did he flunk Obedience School or something?

No one's mentioned Proserpina, Queen of the Underword and Pluto's wife. Even though the names have already been given to asteroids, I think Cerberus and Proserpina are the most appropriate.

One name that hasn't been given to an asteroid but which would result in some amusing double-takes is Mors (death).

Probably the reason nobody's mentioned Proserpina or Persephone is that many people are figuring that those names are first in line for 2003 UB313. That's why I didn't mention them, at least.

[Edit: Yeah, Bruce, Cerberus and Orthrus were brothers. Orthrus only had two heads, though. Budget cuts.]

The first few were named before anything like the current IAU regime, but weren't the Saturnian satellites Epimetheus and Pan named after the Voyager flybys? So that's clear modern precedent for recycling of asteroid names. Eat that, IAU Commission 20!

Doubling up is probably an appropriate response, but it would be tempting to push for a total "steal" of some of these names. It's just silly to have an asteroid named Europa.

It seems to me there are a couple of objective functions here, where one is how often a world will ever be mentioned and then how intrinsically desirable a name is, and ideally the two would align. Give Jupiter a high-profile name (check!) and give some 7 km rock in the middle of the asteroid belt the name Mildred. Where glaring discrepancies exist, I'd just as soon see us "harvest" the best names, and deal with the (exceedingly) rare case that someone in 2017 would have trouble finding a paper on 7868 Mildred because they didn't know that it used to be called 7868 Odin. If the premise is that these worlds are rarely mentioned, then the harm is minimized.

Fight the power!

Hmmm. I suppose that it wouldn't be difficult to add "A" to the end of some of those asteroid names, to distinguish 52 Europa A from Jupiter's moon Europa. Or something along those lines.

On the subject of moon names: if there was one I could change, it'd be Iapetus. No other moon in the solar system deserves the name "Janus" more.

The same problem applies to naming planetary features. For many of the outer solar system satllites, they've used up the most important names in their naming schemes for what was visible in Voyager images. So if the IAU is consistent, we'll end up with bottom-of-the-barrel names for the most prominent craters on Dione and Iapetus, not to mention interesting non-craters like the belly band and the tiger stripes.

...that might be confusing for some Canadians

[ducks and runs]

^Ouch! Below the belt!







ahun ahun...

That's 878 Mildred and 3989 Odin. You see, you can't come up with a name so ridiculous that it hasn't been taken by an asteroid!

In my opinion, the numerical prefix is a sufficient distinction: 52 Europa is one body, Europa is another. To be fair, in 1858 when 52 Europa was named, it was probably felt that "Europa" was an abandoned name for "Jupiter II", and hence reusable. At that point Jupiter's satellites were still merely featureless points of light in a telescope, and it was not foreseen that they would eventually be seen as worlds deserving of unique names. One could argue that such an argument goes doubly for most of the asteroid belt.

Geez, last night I had a dream where these moons turned out not to be real (they weren't visible in newer Hubble images). Oh the disappointment!

The Weaver et al. and Stern et al. papers reporting the discovery are finally being published in the February 23, 2006, issue of Nature. See also the accompanying News and Views piece by Richard Binzel.

Related press release: Pluto's New Moons Likely Born with Charon; Pluto May Even Have Rings

EMBARGOED UNTIL: 1:00 pm (EST) February 22, 2006

PHOTO NO.: STScI-PRC06-09

HUBBLE CONFIRMS NEW MOONS OF PLUTO

Astronomers using NASA's Hubble Space Telescope have confirmed
the presence of two new moons around the distant planet Pluto.
The moons were first discovered by Hubble in May 2005, but the
Pluto Companion Search team probed even deeper into the Pluto
system with Hubble on Feb. 15 to look for additional satellites
and to characterize the orbits of the moons. In the image, Pluto
is in the center and Charon is just below it. The moons,
provisionally designated S/2005 P 1 and S/2005 P 2, are located to
the right of Pluto and Charon. The initial discovery is being reported
today in this week's edition of the British science journal Nature.

Credit: NASA, ESA, H. Weaver (Johns Hopkins University/Applied Physics
Laboratory), A. Stern (Southwest Research Institute) and the HST Pluto
Companion Search Team

For images and additional information about this research on the Web,
visit:

http://hubblesite.org/news/2006/09
http://www.jhuapl.edu/newscenter/pressrele...2006/060222.asp
http://www.boulder.swri.edu/recent/

For more information, contact:

Donna Weaver, Space Telescope Science Institute, Baltimore, Md.,
(phone) 410-338-4993, (e-mail) dweaver@stsci.edu or

Hal Weaver, The Johns Hopkins University Applied Physics Laboratory,
Laurel, Md., (phone) 443-778-8078, (e-mail) hal.weaver@jhuapl.edu.

The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency. The Space Telescope Science
Institute in Baltimore conducts Hubble science operations. The Institute
is operated for NASA by the Association of Universities for Research in
Astronomy, Inc., Washington.

Pluto Might Have Rings
By Ker Than
Staff Writer, Space.,com
posted: 22 February 2006
01:03 pm ET

Question of the Day: Should rings or other forms of debris around Pluto be
proven true, is New Horizons capable of detecting and avoiding them on its own?

Possibility exists for elongated craters on Pluto for orbitally decayed former satellites. (some theories for the similar craters on Mars cite this).

The deep but very thin Plutonian atmosphere will have had a considerable effect on any past rings of Pluto.

I don't think between atmospheric effects and the dynamical ring spreading process we have any hope of seeing currrent rings around Pluto.

That there may be some smallish satelllites interior of Charon seems feasible, but nothing close to Pluto.

I haven't seen any current estimates, but atmospheric drag effects up to the top of the Plutonian Roche limit seem quite likely.

As to a ring system in the past, why not? (well, more on that shortly) Any impact scenario that can loft Charon is most likely to have been a 'messy' process. Recent density measurements of Charon, to me, imply Charon may be substantially 'de-volatized', not unlike earth's moon.

A ring system eroded from atmospheric effects will be an interesting process to think about. Unlike Iapetus (if you think the equatorial structure is an orbitally decayed ring system), the material would be essentially evenly distributed around the equator. And during its' deposition, would be subject to cross winds (seasonal breezes?) too. A 'blunter' structure may be expected.

Additionally, if the impact that birthed Charon (should that be the case) did release a large quantity of volatiles that persisted in the Plutonian vicinity, the formation of a ring system (the collapse of randomly inclined orbit debris to the LaPlacian plane) was most likely disrupted.

Funny how my thinking changed while typing this out.

Atmospheric drag effects on an existing ring system are one thing, but drag effects during the formation of the ring system seem to be quite a hurdle for any ring scenario at Pluto.


Now as to rings around Charon . . . .

I did...along with Libera. Emily quoted my exact e-mail in her blog.

http://www.amazon.com/gp/product/081253014...glance&n=283155

LOL!

Thanx!

According to Hubble, the two moons have the same color as Charon

http://www.jhuapl.edu/newscenter/pressrele...2006/060310.asp