Of course, because Pluto's rotation is locked on Charon, that means there is no apparent motion of Charon, although if these outer moons tug at Charon a bit, there may be slight motion of Charon WRT Pluto. In fact, note that there was, years ago, some evidence that Charon's orbit was somewhat elliptical, which had prompted the hypothesis that a recent impact may have caused it. It remains to be seen if the smaller moons may have tugged Charon into a slightly elliptical orbit.

All this talk of resonance and opposition surges makes me wonder - are the masses of the two moons enough to result in any geological activity on any of the four bodies in the Pluto system?

I'm also wondering - I know the new moons were imaged in 2002; is there any chance that they show up in any of the data from the 1985 - 1990 Pluto/Charon mutual occulatations? My first guess is they'd be buried in the noise, but hope springs eternal.

Yes, excellent point, the mutual occultation data may show something IF the observations, sync-ed to Charon, happened to sync up with the 2 'outies'.

Now, how everything was 'phased' out in that time period is a big???

Any data though would reveal diameter and oblateness, help pin down i and e, and perhaps mutual perturbations (if they occur in resonant relationships, if they are resonant) that might help derive masses for the two little guys. If you get diameter, you can figure albedo too. Color data during a mutual event would be great for narrowing down surface composition.

I believe data was taken as Pluto eclipsed Charon, and vice versa. How much data was recorded in between, I dunno.

Stellar occultation data from that time may show something too, if we get lucky, and the more data to go through, the better the chances get.

Ummm... I could be wrong about this, but doesn't that occultation data consist of measurements of the Pluto-Charon system's apparent magnitude, rather than images?

Yes, and if one of the two new guys pops into or out of either Pluto or Charon's shadow, or if either transits Pluto or Charon, the brightness of the whole system changes.

Amazing if we have such data on hand waiting to be analyzed.

Well, maybe. After a bit of looking, I found an equation that gives an estimate of the total rate of tidal energy dissipation in a satellite in an elliptical orbit about a planet (Murray and Dermott's book, page 173). Using e=0.0076 and assuming that Pluto and Charon's bulk physical characteristics are similar to Triton's, I get dE/dt~7*10^7 watts for Charon.

Comparing this with the predicted wattage for a few other moons, given in the same reference (keep in mind that this is total power over the whole satellite, not power pound-for-pound):

3e12: Io
1e11: Europa
4e10: Titan
3e08: The Moon, Mimas
7e07: Charon
2e07: Ariel
1e07: Enceladus
3e06: Miranda

It's fairly evident that this equation isn't infallible, since it predicts that Mimas should be more active than Enceladus; of course, that's ignoring secular changes in eccentricity (and probably a lot of other things too).

Left out something:

It may be possible for either or both new objects to cast a shadow on Pluto or Charon, at various times during the Plutonian year. An observer on Pluto in the shadow would be experiencing a total solar eclipse. (I worked this out in my head, think both satellites should be large enough to eclipse sun). From earth's vantage point, the object casting the shadow upon Pluto (or Charon) would not necessarily simultaneously transit the disk of Pluto (or Charon).

But at some point it could. (I'm getting dizzy watching this happen in my head, yoiks)

Yup... and if their orbits are coplanar with Charon's, the next set of eclipses of this type should start in about a hundred and ten years.

Has anyone gone back in the astronomical records to see if Pluto's two "new" moons were imaged before this year?

I know that was the case with Charon going back to 1965 at least and for Pluto going back to 1915 or so.

While I am wondering, if there are other KBOs out there bigger than Pluto, and assuming they are not ridiculously far away, how did they escape detection before 1992? Or do some of them also exist on older astrophotos hidden away in some dusty file cabinet of some university observatory?

The last three large KBO's found were later found (precovered is the term used) on plates from the 50's taken as part of the Deep Sky Survey.

This sort of thing is apparently the rule for "newly-discovered" bodies, rather than the exception. Uranus, discovered in 1781 by Herschel, was first recorded in 1690 by Flamsteed. Neptune, discovered in 1846 by Galle, was first sighted as early as 1613 by Galileo! I don't know if Ceres appears on any astronomical charts before 1801, but I wouldn't be surprised.

Depends how bright they are, of course. It's not surprising that bodies like Uranus, being of the sixth magnitude, would show up in a few star charts (actually, one would think that Vesta should have made a few appearances, too). But once you get a few magnitudes below the limit of naked-eye visibility, there are so many stars that a practical limit to what can be catalogued by hand starts rearing its ugly head.

By the 1840's, astronomical photography started getting to be pretty decent in quality; this is the reason for the big spike in asteroid discoveries that happened at about the same time Neptune was found. For bodies like Pluto, "Xena" and most of the asteroids out there, this would be the farthest back we could reasonably expect to find records of their positions. (Galileo's recording of Neptune really is an amazing coincidence.)

Well, Chiron (NOT Charon), after its 1977 discovery, turned up on photographic plates going all the way back to 1895!

From
http://www.boulder.swri.edu/plutonews/

the new moons are 23rd magnitude and 23.5 or so, more than a factor of 100 less bright than Pluto, and lie less than three arc-second from Pluto. Perhaps only Hubble can resolve them. However, from the same web site

Marc Buie and Eliot Young located faint images of both satellites in HST ACS data taken for a Pluto mapping project they spearheaded in 2002.

So yes, they have been "precovered" but only from another dedicated Hubble search using the Advanced Camera for Surveys. It would seem unlikley that they will be found in any other archive.

As to finding old data on eclipses, Elliot Young may have been one of those involved with the Charon-Pluto mutual occultations some time ago or so, when the Earth passed through the plane of their mutual orbits. If there is data for the little moons there, there, he would be the one to find it. On the other hand the moons are about 5% the diameter of Pluto. Assuming similar albedos, the decrease in brightness would be a part in 400. It would be hard to believe that such a small change would have been resolvable, even if they had been watching between the mutual events, whose timing was well known.

Wow! What a good question!

Pluto and Charon are known to have differing surface compositions, Pluto more methane, Charon more water ice.

Consider Io, depleted of light elements, presumably from tidal heating effects.

And now we are looking at Charon, seemingly depleted of a more volatile compound compared to nearby Pluto.

Seems reasonable that by what ever process created Charon, it was not in tide lock at inception. As Pluto and Charon tidally interacted, power dissapated in Charon 'boiled' off the methane. Also, I think Charon would have receded from Pluto while this was occuring (Pluto not tide locked to Charon at that time either, and it would have accelerated Charon in its orbit as earth is doing to our moon even now). While Charon is receding from Pluto, its' resonances will move outward with it and "snag" outer satellites as we now observe.

All this seems to fit together, resonant orbits, tide locking, tidal recession, and surface chemistry.

That was a really good question, Gsnorgathon.

Historians need not take note, but as an amateur, I spotted Vesta when it was very near Venus, and only much later realized that it was Vesta. Thank heavens for the ecliptic, making those coincidences likely.

Additional:

Perhaps the Io analogy needs to be pressed a little further. A tidal effect sufficient to 'demethanize' Charon should leave a lasting relic on the presumably now permanently frozen surface.

The phrase 'widespread and recurrent {methane} volcanism' in regards to Charon springs to mind. Once the tidal effects died down, Charon would have froze up and preserved the geological manifestations of this period.

Geysers or volcanoes? Tar pits or artesian springs?

What would such a modified object look like?

Tasp: "The phrase 'widespread and recurrent {methane} volcanism' in regards to Charon springs to mind. Once the tidal effects died down, Charon would have froze up and preserved the geological manifestations of this period."

Before Cassen, Reynolds and Peale use dthe phrase "widespread and recurrent volcanism" to predict the result of tidal heating on Io in an abstract and then paper published shortly before Voyager 1 blew us away with "Plumes and Pizza", the most reasonable model of Io's strange colors and spectral properties and observed sodium torus was a model of early volcanic activity with significant water leaching salts to the surface, depositing them in vast salt-flats, followed by loss of the water and geologic "shut-down". It was perfectly reasonable till CR&P predicted just how bogglaceous the tidal heating might be.

Aww, shucks! Thanks, tasp. One of my main contributions to maintaining the site's high signal to noise ratio is not posting, but occasionally I can at least think of something interesting to ask!

Re: Vesta: A quick googling indicates that Vesta is only visible to the naked eye *sometimes*. Does anyone have an idea how much of the time that would be? And if there are any even dubious claims of pre-telescopic sightings?

Galileo's seeing Neptune in 1613 has made me wonder if there's a comprehensive listing somewhere of discoveries that includes an "earliest known observation" column along with the "discovery" column.

I did a quickie run through with my older version of "The Sky", considering magnitudes of less than 6 as naked eye:

Mag Date
----- ------------
5.40 14-Jul-2000
5.87 27-Mar-2003
5.44 01-Jun-2007
5.63 05-Aug-2011
5.74 15-Apr-2014
5.33 20-Jun-2018
5.85 23-Aug-2022

So it looks like Vesta could be reasonably "naked eye" every 3 to 4 years, given good eyes and a fairly dark site.

Contact: Carolina Martinez (818) 354-9382

News Release: 2005-163

November 11, 2005

Free Lectures on Exploring Pluto

Two free public programs in Pasadena will offer an overview of the upcoming NASA mission to Pluto. Pluto is the only planet in our solar system not yet studied by a robotic explorer, but not for long.

Dr. Bonnie Buratti, a New Horizons science team co-investigator from NASA's Jet Propulsion Laboratory, Pasadena, Calif., will talk about the mission on Thursday evening, Nov. 17, at JPL and on Friday evening, Nov. 18, at Pasadena City College.

Now at the NASA Kennedy Space Center in Florida, the spacecraft is scheduled for launch on Jan. 11, 2006. JPL will provide the communications coverage for the mission via NASA’s Deep Space Network.

Buratti’s major interest is in whether there has been geologic activity on Pluto in the recent past and whether Pluto has seasons. She is also interested in the surface composition and texture of Pluto and the Kuiper Belt Objects, millions of asteroid-like bodies from outside the orbit of Pluto, which scientists hope to observe.

A native of Pennsylvania, she holds a bachelor's degree in earth and planetary sciences from the Massachusetts Institute of Technology, Cambridge, Mass., and a Ph.D. in astronomy and space sciences from Cornell University in Ithaca, N.Y. She is currently a science team member on the Cassini-Huygens mission to Saturn.

NASA's New Horizons mission will be the first to visit Pluto and its largest moon, Charon. The compact spacecraft carries seven science instruments for examining the geology, composition, surface, temperature and atmospheric structure of the planet and its main moon. The science team is studying whether New Horizons will be able to obtain data on the two recently discovered smaller moons of Pluto. The Johns Hopkins Applied Physics Laboratory in Laurel, Md., manages the mission and will operate the spacecraft for NASA.

Both lectures will begin at 7 p.m. Seating is first-come, first-served. The Thursday lecture will be in JPL's von Karman Auditorium. JPL is at 4800 Oak Grove Dr., off the Oak Grove Drive exit of the 210 (Foothill) Freeway. The Friday lecture will be in Pasadena City College's Vosloh Forum, 1570 E. Colorado Blvd. For more information, call (818) 354-0112.


Thursday's lecture will be webcast live at

http://www.jpl.nasa.gov/events/lectures/nov05.cfm

Vesta would have been a better possibility than Uranus, most likely. It moves much faster in the sky. On the other hand, it also fades out, while Uranus is almost constant in its dim visibility, which I have seen just once without a telescope -- but I of course knew where to look.

Musings I did years ago on Uranus concluded that almost certainly no one discovered it before, and I would submit the same of Vesta. Essentially, someone would have had to compile a star map of stars down to the 6th magnitude with careful noting of the positions. They could have simply commited to memory a very small part of the sky, yes, and gotten lucky, but the rigor would still have been necessary. The sky is very crowded with 6th magnitude objects.

Of course, we'll never be able to prove that it didn't happen sans "publication", not once but thousands of times. Maybe some shepherd looked up and picked a random corner of the sky, memorized it, and noticed the next time that it had changed. In fact, perhaps an owl discovered Uranus/Vesta. We'll never know.

How conclusively do the occulatation derived studies of Pluto and Charon rule out rings around either object?

Discussion:

My thinking is, for the portion of the data derived when Pluto and Charon were directly aligned (center line of both bodies aligned with earth), the possible rings would have been exactly edge on to us and far below the resolving power of the occultation technique.

As the alignment of Pluto and Charon approach and recede from this condition, however, any rings would have been more open to our view, and would have affected the data being taken.

Noticeably?

Bright rings should have 'skewed' the light curves, but what about dark Uranian style rings?

Would the effect have been just a subtle darkening of the disk to either side of the center line? Would this have been noted?

The possible rings of either object would start ingress well ahead of the disk of the respective body, but this would have started as much as the length of time of the main occultation itself. Since the occultations occured every ~6 1/3 days, and this was known to high accuracy, would anyone have started data collection that far in advance?

Additional:

Would long term stability of rings around Pluto be more likely considering such rings would have resonances across their width from Charon? (and to a lesser extent from the new moons) Such 'curbs' may have restrained material from processes that tend to dissipate rings (such as dynamical ring spreading) and left them for us to discover.

Would dark tenuous rings be excluded by the existing stellar occultation data? I have no info on the geometry of those encounters, and I don't know if there were more than 2 or 3 recorded.

So do we have a 'toe in the door' to hope for rings in the Plutonian system?

There are others who have read the papers by Young et al and know more about this than I do, but the basic geometry of the occultations is where the Earth passes through the plane of the oribit of Charon and Pluto about their mutual center of mass. Any rings would almost have to be in the same plane, and edge on during the occultation, just as you say. If so, they would appear as a constant offset of the signal in the occultations. These observations do not geometrically resolve the bodies. These are radiometric, power measurements so to speak. If so, they would not be seen.

(There must have been at least a dozen of these occultation events, judging soley from the resolution of the map of Pluto that was generated.)

The gravitational fields around Saturn and Neptune are fully dominated by the massive planets. We have recently seen in Cassini images the effects of even small bodies on the rings, as small moons leave wakes in the outer rings. Charon, on the other hand, is massive enough to have the center of mass of Pluto outside of it. Now we know of two more, which also seem to be coplanar and resonant. It would seem unlikely that rings could form in such an uneven gravitational field, with all the tidal forces that must exist. There must be some theoretical work on the impact of a relatively massive moon on the stability of rings. Does anyone know of any such work?

In re to Comga's post:

(I'm speculating here) For thin Uranian style rings would effects of a nearby mass (such as Charon) be mostly in bumping up the eccentricity of each ring? If that was the extent of the effect, not sure we see a big hit in ring longevity in this possibility. (I assume between each narrow ring would lie a strong resonance from Charon)

For broad Saturn style rings (with ring particles 'cheek by jowl') having the particles experiencing strong effects from Charon becomes, perhaps, more interesting. The dynamical ring spreading mechanism would seem to be enhanced in this scenario. Every orbit around the primary, all the ring particles bump more vigorously and transfer momentum across the ring plane. Would such effects 'overpower' the resonance 'curbs' in the ring system? Perhaps.

Then we are in a scenario where, due to the strong momentum transfer across the ring system, we see a large effect 'pushing' the lower edge of the ring downward and the upper edge outward.

This does not seem compatible with long ring retention, but, once the (possible) ring material thins out, you may approach the Uranian model, and perhaps get to see some skinny dark rings in 2014?

Are there other 'damaging' effects of a nearby Charon on rings of Pluto other than increased orbital eccentricity? Inclination changes seems unlikely.

Possible 'demethanization' of Charon from tidal heating would imply a slight degree of atmosphere interacting with the ring system when Charon passes between the sun and Pluto. Such an effect would not persist after tide lock, but atmosphereic drag and ring systems don't seem to go together.

Paper: astro-ph/0511837

Date: Wed, 30 Nov 2005 19:37:52 GMT (124kb)

Title: New Constraints on Additional Satellites of the Pluto System

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

Comments: 18 pages including 4 figures
\\
Observations of Pluto and its solar-tidal stability zone were made using the
Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) on UT
2005 May 15 and UT 2005 May 18. Two small satellites of Pluto, provisionally
designated S/2005 P 1 and S/2005 P 2, were discovered and are reported by
(Weaver et al. 2005). These observations also provide strong constraints on the
existence of any additional satellites of Pluto. We place a 90%-confidence
lower limit of V=26.2 (V=27.1 for a 50%-confidence lower limit) on the
magnitude of undiscovered satellites >5" from Pluto. Assuming an albedo of
p_v=0.04 (similar to cometary nucleii and a reasonable lower limit), this
corresponds to a limiting diameter of 37 km at 90%-confidence (25 km at
50-confidence). For an assumed albedo similar to Charon, i.e p_v=0.38, the
magnitude limit corresponds to a limiting diameter of 12 km at 90%-confidence
(8 km at 50%-confidence). At distances <5" from Pluto, scattered light from
both Pluto and Charon degrades the sensitivity of our search, such that at 1.7"
from Pluto the 50%-confidence magnitude limit is V=25.3, corresponding to a
limiting diameter of 57 km for an object with p_v=0.04.

\\ ( http://arXiv.org/abs/astro-ph/0511837 , 124kb)

It's good to see that some abstracts are starting to come out of the two new Plutonian moons.

Not to harp on this too much, but I'm still *really* interested to see how much Charon perturbs their orbits. A few weeks back (in this thread) I tried to figure out a rough estimate of this effect, but my attempt was ridiculously oversimplified as it didn't take into account the rotating frame of reference (as seen from 2005 P1 and P2). It'll be neat to see the real solution.

The article in the link and the original one both indicate that the new moons are in resonant orbits with Pluto-Charon and their 6.3 day rotation. They may be in the fourth and sixth harmonic orbits. (I don't have the original article to repeat the calculation.) Whether you can say that Charon "perturbs" the orbit or "regulates" them is semantics, but the system isn't chaotic. As for your simple model, determining how large the libration swings can be would require some real sophistication.