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Posted by: JRehling Oct 31 2005, 05:49 PM

Press Release Source: NASA


NASA's Hubble Reveals Possible New Moons Around Pluto
Monday October 31, 12:30 pm ET


WASHINGTON, Oct. 31 /PRNewswire/ -- Using NASA's Hubble Space Telescope to view the ninth planet in our solar system, astronomers discovered Pluto may have not one, but three moons.
If confirmed, the discovery of the two new moons could offer insights into the nature and evolution of the Pluto system; Kuiper Belt Objects with satellite systems; and the early Kuiper Belt. The Kuiper Belt is a vast region of icy, rocky bodies beyond Neptune's orbit.

"If, as our new Hubble images indicate, Pluto has not one, but two or three moons, it will become the first body in the Kuiper Belt known to have more than one satellite," said Hal Weaver of the Johns Hopkins Applied Physics Laboratory, Laurel, Md. He is co-leader of the team that made the discovery.

Pluto was discovered in 1930. Charon, Pluto's only confirmed moon, was discovered by ground-based observers in 1978. The planet resides about 3 billion miles from the sun in the heart of the Kuiper Belt.

"Our result suggests other bodies in the Kuiper Belt may have more than one moon. It also means planetary scientists will have to take these new moons into account when modeling the formation of the Pluto system," said Alan Stern of the Southwest Research Institute, Boulder, Colo. Stern was co-leader of the research team.

The candidate moons, provisionally designated S/2005 P1 and S/2005 P2, were observed approximately 27,000 miles away from Pluto. The objects are roughly two to three times as far from Pluto as Charon.

The team plans to make follow-up Hubble observations in February to confirm the newly discovered objects are truly Pluto's moons. Only after confirmation will the International Astronomical Union consider names for S/2005 P1 and S/2005 P2.

The Hubble's Advanced Camera for Surveys observed the two new candidate moons on May 15, 2005. The candidates are roughly 5,000 times fainter than Pluto. Three days later, Hubble looked at Pluto again. The two objects were still there and appeared to be moving in orbit around Pluto.

The team looked long and hard for other potential moons around Pluto. "These Hubble images represent the most sensitive search yet for objects around Pluto," said team member Andrew Steffl of the Southwest Research Institute. "It is unlikely that there are any other moons larger than about 10 miles across in the Pluto system," he said.

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.


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

http://hubblesite.org/news/2005/19

For information about NASA and agency programs on the Web, visit:

http://www.nasa.gov/home




--------------------------------------------------------------------------------
Source: NASA

Posted by: ElkGroveDan Oct 31 2005, 06:38 PM

Posted by: imran Oct 31 2005, 06:57 PM

Another reason to get excited about New Horizons!

Posted by: JRehling Oct 31 2005, 07:51 PM

If this holds up, and I guess it will, what kind of complications does this raise for the Closest Approach instrument pointing? I assume that the nominal plan is completely packed with observations, and you can't add an image without subtracting another one from the plan. Is it possible to add C/A images of the new satellites without losing some of Pluto/Charon?
Proactively, would it be possible to alter the time of arrival by some integer number (eg, 1) of Pluto revolutions to acquire alternative geometries WRT the new satellites while keeping Pluto/Charon geometry the same? It would seem that a very small change in velocity enacted in 2007 could tweak arrival by 6.4 days, if desired.

That's assuming that the new satellites aren't orbiting in synchrony with Charon...

New, larger, light-bucket telescopes on the ground should be able to outperform HST in gathering more data on these bodies long before NH arrives...

Posted by: remcook Oct 31 2005, 09:09 PM

very interesting!

http://www.spaceflightnow.com/news/n0510/31plutomoons/

Posted by: Mariner9 Oct 31 2005, 09:38 PM

I doubt this will cause any problems on the encounter planning, because they haven't even launched the vehicle yet. The exact launch date plays a part in which potential arrival dates are possible... so since we don't know exactly when in the launch window the actual launch will take place, I would be willing to bet that there is no firm approach plan in existance yet. I'm sure they have outlines, but minute by minute planning simply is not in existance yet.

And besides, even if it were, they would have ten years to tweak it a bit. That hardly seems like a major problem. I suspect the bigger problem will be in coming up with an approach timing and trajectory that gives them at least a moderate distance approach to one of the new sattelites, and still gets them their desired Pluto and Charon encounters.

Posted by: RNeuhaus Oct 31 2005, 09:46 PM

I thought the same as to you. Perhaps, I am afraid it would be another surprise, with any more moons or any invisible asteroide from Kiuper belt spining around Pluto. It would be a good advise that the NH would have more propellents for main and mini-thrusters than planned to manouver any obstacle since our best telescope still does not look clearly any drifts roaming around Pluto.

Rodolfo

Posted by: Myran Oct 31 2005, 10:10 PM

Once again Hubble proves it value.
Its been speculated there might be more moons at Pluto. Sometimes I wonder if some astronomers got a shrewd intuition.

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

Posted by: JRehling Oct 31 2005, 10:16 PM

I respectfully suggest that you really ought to familiarize yourself with some of the basics here -- there are at least four reasons why this scenario is science fiction.

One, there is no way to change the spacecraft at this point -- add mini-thrusters?! The time to make major design alterations came and went a long time ago.

Two, and equally important, you are VASTLY overestimating the hazard, in particular from large objects (observable and steer-around-able). There is a power law that relates the number of impactors WRT size -- if there was a nonnegligible threat of impact with a large object, then there would be a virtual guarantee that the craft would be destroyed by a "rain" of small, but still deadly, particles. Given that we have no reason to fear that (see below), there is virtually zero concern WRT large objects.

Third, while any spacecraft could be destroyed at almost anytime, by a pellet of tiny size, the probability of this is low anyplace in interplanetary space with very rare exceptions. The density of near-Pluto space is lower than that of the asteroid belt, and seven spacecraft have flown through there without incident. Two Pioneers and two Voyagers have flown through the Kuiper Belt, also without incident. Indeed, the various Mars orbiters face a greater threat from debris, and go on year after year -- without incident. In fact, Earth-orbiting spacecraft stand a pretty good example of the low degree of impact menace. And this is already orders of magnitude greater than the threat in near-Pluto space.

Fourth, with the enormous round-trip time for radio signals, any steer-around plan would only make sense for hazards detected well in advance -- and hazards detected well in advance would be, in many cases, detectible from Earth; and in many more cases -- realistically speaking, in almost ALL cases (see above) invisible to the craft until the moment they hit.

The new satellites are estimated to be about 140 km in diameter with orbits 100,000 km across. That is, if a football field were the size of these orbits, the moons themselves would be about the size of a fist. And any undiscovered moons would be more the size of a fingernail. It's really not a great threat that any craft would strike them.

I know that the spirit of this board is in a lot of good fun, but it wouldn't hurt to do a *LITTLE* fact checking before dispensing "good advise".

Posted by: alan Nov 1 2005, 12:28 AM

New moons in resonance with Plutos rotation?
Charon's period is 6.387 days: 6.387 * 4 = 25.6 days ; 6.387 * 6 = 38.3 days

Posted by: Rob Pinnegar Nov 1 2005, 12:53 AM

Just a couple of points concerning this exciting new discovery:

(1) The orbital periods given for the satellites, 38.2 days and 25.5 days, are really close to the Charon 6:1 and 4:1 resonances. (Of course, those periods have some error associated with them; when more precise values are available, we'll have a better idea of this.)

Here's a question for the classical dynamicists in the audience: since Pluto and Charon are both significantly displaced from their mutual barycentre, would an object orbiting that barycentre in the Charon 4:1 or 6:1 resonances have a stable non-elliptical orbit due to three-body effects? What I mean is, could its distance from the system's barycentre reach several maxima and minima per orbit, instead of just one, if the overall ellipticity of the orbit were low enough to start with?

(2) Just running through some quick Matlab calculations: Seen from Pluto's surface, the two new moons should both have total magnitudes in the neighbourhood of -1 or so. So they should be quite visible. If they're in the neighbourhood of 100 to 150 km across, then, as seen from Pluto, they'd both show disks maybe a fifth to a third the size of the Moon as seen from Earth.

If one of them is 150 kilometres across, it could appear as large as the Moon in the Earth's sky as seen from the other, during mutual closest approach (~15000 km).

[Edit: Corrected an ambiguity.]

Posted by: Alan Stern Nov 1 2005, 01:16 AM

See www.boulder.swri.edu/plutonews for a great deal more info.

-Alan

Posted by: Rob Pinnegar Nov 1 2005, 02:54 AM

I'm confused here: On the website cited above, the estimates for the diameter of S/2005 P1 are 160 km if its albedo is 0.04, and 110 km if its albedo is 0.35.

But shouldn't the estimated diameters of the new moons vary roughly as 1/sqrt(albedo)? I would've thought that a ninefold increase in reflectively would decrease the estimated diameter by a factor of about three, since the total brightness has to stay the same.

Using 16.8 as apparent M_v for Charon, and 23.0 as apparent M_v for S/2005 P1 as given on the website, and assuming both bodies have the same albedo, I get a diameter about one-seventeenth of Charon's, or ~70 km, for 2005 P1. Have I got something wrong?

Posted by: jamescanvin Nov 1 2005, 04:45 AM

Thanks for the update Alan and congratulations on your teams discovery.


Just to make an obvious point,

Recently on this board we have discussed how NH would have to be very lucky to fly by two Kuiper Belt objects after Pluto-Charon. Now we get two for free! Should get a sample of five now, NH just became even better value!

James

Posted by: djellison Nov 1 2005, 08:11 AM

Many thanks, and above all, Congratulations!
Doug

Posted by: DEChengst Nov 1 2005, 12:03 PM

I'm not sure the two moons are as interesting for learning more about differences between Kuiper belt objects as two seperate objects would be. The two moons may have been formed together with Pluto itself so may be very much like Pluto composition wise. The other options ofcourse is that it are captured objects which would be just as interesting as flying by two seperate objects

Posted by: odave Nov 1 2005, 04:04 PM

Add my congrats to the pile as well. This is fantastic news!

I also greatly appreciate Alan and John's participation here in UMSF. As we all well know, the Internet is full of kooks, trolls, and all sorts of other miscreants. The fact that members of NH and other mission teams (Jason Perry, Mike Caplinger, et. al.) actively post here is a testament to the quality of the members, moderators, and discussion found in this forum!

Posted by: Ames Nov 1 2005, 04:22 PM

Now let's see - Hmmmm. Name just one object in the solar system that when we looked a little closer at it, nobody said "Woa!" "Wow!" "What The?"
Everything we look at is amazing, and the closer we look the better it gets.
The sheer multitude of landforms, colours, shapes, alignments, hotspots... seem endlessly beautiful and strange.

I can guarantee Pluto et al will not disappoint.

Nick

Posted by: john_s Nov 1 2005, 04:47 PM

No, you don't have anything wrong- we goofed on the web site, though we got the diameter right for the lowest albedo. Thanks for catching the error- we'll fix it! The correct numbers should be something like 160 km for an albedo of 0.04 and 52 km for an albedo 0.35.

Posted by: Rob Pinnegar Nov 1 2005, 05:03 PM

Glad I could help. And by the way -- congratulations to your team.

Posted by: Rakhir Nov 1 2005, 10:18 PM

If NH is launched during the secondary launch window and if the OWL project is accepted and meet the current schedule, a 60-m class telescope would be available as soon as 2016-2017. It could then be used for the arrival of NH in 2019-2020.
The full 100-m OWL capability would be available too late for NH, in 2020.

Rakhir

Posted by: RNeuhaus Nov 2 2005, 03:00 PM

Many thanks to JRehling with your very good explanation. Now, I can feel it more realistic after knowing your details. Sorry of my first reaction since I am a novel of astronomy science. Little by little I will be better off on that.

Taking the advantage of this post, congratulations to Alan and his team for this great news.

Rodolfo

Posted by: Rob Pinnegar Nov 2 2005, 04:04 PM

I just ran through some simple calculations concerning the orbit of the inner new satellite (the one for which a~49000 km).

If this moon were traversing a perfectly circular path around the system's barycentre, with the orbit in the same plane as Charon's, then the total acceleration due to gravity it would experience at closest approach to Charon should be about 5% stronger than the acceleration it experiences when it is farthest away from Charon. So one could conclude from this that the orbit can't really be a perfect circle.

I'm no expert at classical dynamics, but from an intuitive standpoint it's difficult to see how the orbit could be stable under these circumstances unless the moon were in the 4:1 resonance.

My semi-educated guess is that, to first approximation, the moon's distance from Pluto probably varies with an angular frequency that is exactly three times the angular frequency of its revolution about the system's barycentre. For the outer moon it would be five times the revolution frequency.

The only other satellite in the solar system that is in a similar position is Hyperion, but somehow I doubt that the effects are anywhere near as large in Hyperion's case since Saturn's mass is so much greater than Titan's. It will be an interesting problem to solve.

[Edit: ... If it hasn't been solved already, which I'm guessing it has.]

Posted by: JRehling Nov 2 2005, 05:22 PM

A fun additional consideration: The other "moon" that the new ones can synchronize against is Pluto! You calculated a 5% "surge" when the moons are opposite Charon, but 180-deg opposite, there will be another "surge" as Pluto passes, somewhat closer than otherwise.

The Pluto "surge" felt by each outer satellite should be less than the Charon surge by precisely the ratio of their masses. Since that ratio is about 7:1, the Charon surge will be the dominant perturbation, with the Pluto surge lesser but non-negligible.

Posted by: Rob Pinnegar Nov 2 2005, 05:38 PM

This is correct and I actually did take it into account -- the calculation referred to above assumed that the moon was circling the Pluto-Charon barycentre, not Pluto itself. Without the Pluto "surge" the difference would be greater than 5%; when the inner new moon reaches closest approach to Charon, the gravitational influence of Charon is about a third of Pluto's!

Posted by: Rob Pinnegar Nov 2 2005, 06:06 PM

The other neat thing is that the total acceleration vector experienced by the new moons due to the combined effects of Pluto and Charon, usually doesn't point straight at the barycentre. When the line connecting Pluto and Charon is perpendicular to the line connecting S2005 P2 to the barycentre, for example, the acceleration vector leans slightly toward Pluto.

My _suspicion_ is that the two new moons reach their greatest distances from the barycentre simultaneously with closest approach to Charon. After that, they start to fall inwards and also start to lead a bit in their orbit. Closest approach to the barycentre coincides with their closest approach to Pluto, after which they trail in their orbits and move farther away. This is however conjecture and I've not got it supported by mathematics. I could have the leading/trailing bit backwards, for example.

Of course, the two new moons will interact with each other a bit, but that ought to be a higher-order effect. [Edit: Actually it wouldn't be higher-order, just smaller in magnitude.]

[Edit: A quick back of the envelope calculation indicates that these effects could cause the inner new moon's distance from the system's barycentre to change by up to 250 kilometres, three times per orbit. Hope I haven't made any major blunders here -- I've assumed a simple harmonic oscillator, in the radial direction only, and have neglected the skew in the acceleration vector.]

Posted by: tasp Nov 3 2005, 04:29 AM

If correct, all the satellites of Pluto will essentially repeat their relative positions every 77 days or so. This will limit the number of satellite configurations for the mission designers to evaluate. There won't be any point in moving the arrival date beyond a couple of orbits of the outer satellite. The NH craft will have the same views of all the objects.

Posted by: JRehling Nov 3 2005, 12:29 PM

Well, it would allow for 24 distinct configurations of the outer satellites, or whatever fraction of those 24 the "arrival window" allows for -- that seems like a considerable variety of options.

Posted by: Rob Pinnegar Nov 3 2005, 03:27 PM

If we're lucky, the (hypothesized) resonances will turn out to be similar to the Jupiter-Io-Europa-Ganymede system, where periodically all three moons and the central planet arrange themselves in a straight line.

If we're _really_ lucky, this configuration will occur when the moons are all close to the plane of Pluto's orbit around the Sun. If this were the case, New Horizons could make close flybys of all four bodies, concentrating exclusively on one body at a time, during its flyby in '15.

We'll have to see. I guess one approach would be to take two snapshots of the system, 77 days apart. If they turn out to look the same, well, there you have it.

Posted by: tasp Nov 3 2005, 04:11 PM

Like in the Jupiter system, due to the resonance of Io, Europa, and Ganymede, certain configurations of the satellites never occur. Like all three in a straight line on the same side of Jupiter. I was annoyed a little when the mission designers of Voyager II's Uranus flyby stated a particularly appealing configuration of the Uranian moons occured just a few days prior to the earliest possible flyby date that preserved the Neptune option. Hence the fuzzy picture of Umbriel.

Should be easier for the analysts to examine ~77 days of moon configurations than potentially years worth.

Posted by: tedstryk Nov 3 2005, 07:09 PM

Umbriel is an interesting world. But it wasn't worth the loss of Triton and Neptune. Also, no configuration of Uranus's moons in 1986 would be that good. Voyager was approaching like a dart headed straight at a dartboard, so rather than having closest approaches one by one, they were all at once. Also, had they been free of Neptune's constraints, Titania, not Miranda, would have received the close flyby - so they really lucked out!
Here are the best views we got of Umbriel.
Color:
http://img108.imageshack.us/my.php?image=umbsuprescolb6yd.jpg

Black and White:

http://img116.imageshack.us/my.php?image=umbrielsupresgoodc8vq.jpg

Composite of Wunda (The bright feature at the top):

http://img108.imageshack.us/my.php?image=wunda12ek.jpg

Posted by: Phil Stooke Nov 3 2005, 09:26 PM

Ted's pics of Umbriel are, as ever, excellent. I processed the same images as well, using different methods for mainly cartographic purposes. These are the results:

Phil

Posted by: Phil Stooke Nov 3 2005, 09:30 PM

...and here's a mosaic of the entire visible hemisphere in azimuthal equidistant projection.

Phil

Blast! I was just replying to Ted, I didn't notice what thread I was in. This should really be in the historic images thread... oops.

Posted by: JRehling Nov 3 2005, 09:43 PM

Good point. A 1:4:6 resonance actually allows 12 configurations (not 4 * 6 = 24) if we assume that the Charon position were fixed (which I suppose it is, barring an exceptional reason for change). When the outermost moon has made 2 laps around Pluto (or the barycenter), the middle moon will have made 3 -- that defines a cycle in twelve Charon revolutions, equaling, yes, 77 days).

Posted by: tasp Nov 3 2005, 10:34 PM

I very much appreciate the Umbriel pictures. Maybe we get the NH2 to update the Voyager portfolio. And maybe we don't. Sigh.

Rectified Wunda picture is new to me, interesting feature. Still not evident what happened there, though.

Posted by: tedstryk Nov 3 2005, 10:45 PM

It is almost certainly a bright crater rim...the question is WHY it is bright. There is also a bright central peak visible in another crater. I made the image by reprojecting the dataset used to make both images I posted to be from the same angle and at the same scale, and then stacked them. I used a color overlay from the posted image.

Here is a sequence of the best views of Umbriel. I am not at home right now, so I don't have a larger version. However, other than the images I already posted, the images aren't shrunken, so it will serve our purposes!



Phil: I also experimented with processing along the lines you did to bring out topography. The posted view focuses on a natural look. When I am home, I may try processing the same images in a similar way, and then merging the datasets to make a sharper image that brings out topography more.

Posted by: Phil Stooke Nov 3 2005, 11:15 PM

Ted, my interests are really in the area of making the most easily interpreted map images, not so much the natural view we would see if we were there. So my stuff can look a bit odd! I'm starting to think about doing more of this stuff...

Phil

Posted by: mchan Nov 4 2005, 03:25 AM

NH2 did not get funding.

Posted by: tedstryk Nov 4 2005, 03:49 AM

Here is the result of my attempt to merge the two types of processing.

http://img390.imageshack.us/my.php?image=umbcomb9sm.jpg

Posted by: tasp Nov 4 2005, 04:28 AM

More good pictures of mysterious Umbriel.

Does anyone have any idea where the pole is?

Or the equator?

When I look at the upper limb, from about 11 o'clock to Wunda, I see a 'ridgy' looking feature. Artifact of processing near the limb, or something more....interesting?

(enlarge picture to see it)

Posted by: dvandorn Nov 4 2005, 08:26 AM

The "ridgy" feature becomes clear when you look at Phil's cartographic-purposed image. There is a large, very degraded crater (or, rather, a basin) located right in that area. The ridge-like structure (visible more as an albedo difference farther into Umbriel's disk) is a basin ring.

-the other Doug

Posted by: tasp Nov 4 2005, 02:37 PM

Thanx, I do see that now. I thought it odd something like that would be unnoticed in this time frame.

Posted by: Phil Stooke Nov 4 2005, 03:04 PM

I'm posting more images in the historic images thread...

Phil

Posted by: Rob Pinnegar Nov 4 2005, 04:05 PM

Good idea Phil. We have got a bit off the Pluto topic here.

Posted by: tty Nov 4 2005, 06:59 PM

Hmm... I didn't know that and so apparently didn't Robert Heinlein. The big quake in "Farmer in the sky" happened when all 4 galileans lined up.

tty

Posted by: Rob Pinnegar Nov 4 2005, 07:33 PM

Callisto can line up with two of the other three, but the last one will always be out of place.

Posted by: JRehling Nov 4 2005, 07:36 PM

I don't know the details of the Heinlein story, but of course the Galileans can also all line up... but with one of them on the other side of Jupiter. We can also presume that the Galileans were capable of aligning on the same side of Jupiter in the past, before the synchrony was established. Finally, it is possible for all four Galileans to be within 180 degrees of each other, and have it be that from Earth they would appear to be on the same side of Jupiter.

Posted by: dvandorn Nov 4 2005, 07:39 PM

Interesting. I always knew, at some level, that the image from "2001" showing all of Jupiter's moons aligned in a string with the planet itself wasn't possible...

-the other Doug

Posted by: mike Nov 4 2005, 08:23 PM

Yeah, but aligned spheres in space are part of what made 2001 such a great movie. Movies like that are very rarely made, sadly..

Posted by: tasp Nov 4 2005, 10:42 PM

Would a hpothetical observer on Pluto become bored with a too clock like moon parade? Funny to look at it that way, but 'forbidden' configurations of resonant satellites kinda takes some of the pizzaz out of it.

Even if it simplifies NH mission design.

Posted by: JRehling Nov 4 2005, 11:52 PM

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.

Posted by: Gsnorgathon Nov 5 2005, 02:00 AM

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.

Posted by: tasp Nov 5 2005, 03:29 AM

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.

Posted by: Rob Pinnegar Nov 6 2005, 03:24 PM

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?

Posted by: tasp Nov 6 2005, 06:19 PM

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.

Posted by: Rob Pinnegar Nov 6 2005, 07:23 PM

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).

Posted by: tasp Nov 7 2005, 04:21 AM

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)

Posted by: Rob Pinnegar Nov 7 2005, 05:36 PM

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.

Posted by: ljk4-1 Nov 7 2005, 10:19 PM

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?

Posted by: alan Nov 7 2005, 11:15 PM

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.

Posted by: David Nov 7 2005, 11:54 PM

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.

Posted by: Rob Pinnegar Nov 8 2005, 01:20 AM

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.)

Posted by: BruceMoomaw Nov 8 2005, 02:01 AM

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

Posted by: Comga Nov 8 2005, 04:14 AM

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.

Posted by: tasp Nov 9 2005, 01:25 AM

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.

Posted by: JRehling Nov 9 2005, 04:16 AM

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.

Posted by: tasp Nov 9 2005, 05:09 AM

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?

Posted by: edstrick Nov 9 2005, 07:39 AM

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.

Posted by: Gsnorgathon Nov 11 2005, 01:24 AM

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.

Posted by: odave Nov 11 2005, 03:46 AM

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.

Posted by: ljk4-1 Nov 12 2005, 04:00 AM

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

Posted by: JRehling Nov 12 2005, 06:05 AM

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.

Posted by: tasp Nov 12 2005, 03:17 PM

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?

Posted by: Comga Nov 12 2005, 09:52 PM

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?

Posted by: tasp Nov 13 2005, 04:33 AM

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.

Posted by: ljk4-1 Dec 1 2005, 03:36 PM

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)

Posted by: Rob Pinnegar Dec 7 2005, 02:42 AM

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.

Posted by: Comga Dec 17 2005, 09:50 PM

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.