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More Moons Around Pluto?
JRehling
post Oct 31 2005, 05:49 PM
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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
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ElkGroveDan
post Oct 31 2005, 06:38 PM
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If Occam had heard my theory, things would be very different now.
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imran
post Oct 31 2005, 06:57 PM
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Another reason to get excited about New Horizons!
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JRehling
post Oct 31 2005, 07:51 PM
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QUOTE (imran @ Oct 31 2005, 11:57 AM)
Another reason to get excited about New Horizons!
*


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...
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remcook
post Oct 31 2005, 09:09 PM
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very interesting!

http://www.spaceflightnow.com/news/n0510/31plutomoons/
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Mariner9
post Oct 31 2005, 09:38 PM
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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.
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RNeuhaus
post Oct 31 2005, 09:46 PM
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QUOTE (Mariner9 @ Oct 31 2005, 04:38 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.
*

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
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Guest_Myran_*
post Oct 31 2005, 10:10 PM
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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. tongue.gif

http://www.boulder.swri.edu/plutonews/
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JRehling
post Oct 31 2005, 10:16 PM
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QUOTE (RNeuhaus @ Oct 31 2005, 02:46 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
*


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".
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alan
post Nov 1 2005, 12:28 AM
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QUOTE
Unique orbits cannot be calculated from the available
data, but the measured positions are consistent with nearly circular orbits
in the orbital plane of Pluto I (Charon). On this assumption, preliminary
orbital solutions yield a = 64700 +/- 850 km and P = 38.2 +/- 0.8 days for
S/2005 P 1, and a = 49400 +/- and P = 25.5 +/- 0.5 days for S/2005

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
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Rob Pinnegar
post Nov 1 2005, 12:53 AM
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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.]
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Alan Stern
post Nov 1 2005, 01:16 AM
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See www.boulder.swri.edu/plutonews for a great deal more info.

-Alan
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Rob Pinnegar
post Nov 1 2005, 02:54 AM
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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?
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jamescanvin
post Nov 1 2005, 04:45 AM
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QUOTE (Alan Stern @ Nov 1 2005, 11:16 AM)
See www.boulder.swri.edu/plutonews for a great deal more info.

-Alan
*


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


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djellison
post Nov 1 2005, 08:11 AM
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QUOTE (Alan Stern @ Nov 1 2005, 01:16 AM)
See www.boulder.swri.edu/plutonews for a great deal more info.

-Alan
*


Many thanks, and above all, Congratulations!
Doug
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