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Pluto Predictions, What will NH find?
Rob Pinnegar
post Oct 6 2008, 01:44 AM
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QUOTE (Decepticon @ Oct 5 2008, 07:15 AM) *
PS I expect something totally unexpected as usually. The 2 newer moons I believe with be very interesting.


I'll be really interested to see the details of how Nix and Hydra's orbits work. They should deviate pretty noticeably from ellipses because of the mutual motion of Pluto and Charon.

I understand that some work has already done in this direction (i.e. predicting the orbital paths); it'll be neat to see whether the predictions are accurate. One would think they would be, but we could always get a surprise.

As for Pluto and Charon -- really, we can forget about predicting anything for our first close-up look at a KBO, apart from Triton which is really in a class by itself. If we're spectacularly lucky, we might be able to see some lingering evidence of the impact that created Charon (apart from Nix and Hydra's existence). I think that would be asking a bit much, but you never know.
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Vultur
post Oct 6 2008, 08:56 PM
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I don't know, but I'm sure it will be informative even if it's "just" an ice ball.
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mchan
post Oct 7 2008, 06:02 AM
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QUOTE (dvandorn @ Oct 4 2008, 07:43 PM) *
Um, yeah.... Miranda, that's the ticket...

IIRC, Miranda features like the chevron are from upwelling rather than result of re-assembly of remnants of body disrupted by collision.
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Fran Ontanaya
post Oct 7 2008, 06:55 AM
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Cryovolcanos and a gravity center outside both bodies could produce something interesting. Is it physically possible that moonlets like Nix and Hydra formed by aggregation at the gravity center and then migrated to their current orbits?


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Rob Pinnegar
post Oct 9 2008, 01:08 AM
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QUOTE (Fran Ontanaya @ Oct 6 2008, 11:55 PM) *
Cryovolcanos and a gravity center outside both bodies could produce something interesting. Is it physically possible that moonlets like Nix and Hydra formed by aggregation at the gravity center and then migrated to their current orbits?

No, they couldn't have done that -- the gravity centre (also called the barycentre in technical terms) wouldn't be a good place for aggregation. It's close to Pluto and so anything that tried to clump together there would have ended up falling onto Pluto pretty quickly. Even if something *could* have built up there, it couldn't have migrated outward, as it would have crashed into Charon on the way out.

Aggregation at the Lagrange points probably wouldn't work either. I don't have the math handy but as I recall, Charon is too massive for that to happen.

One current theory for the formation of the Pluto-Charon system, which seems to be in vogue right now, it that it was created by a giant impact early in Pluto's history. Basically, a large object hit Pluto, and some of the "splash" went into orbit and accreted into Charon. Some of the left-overs from this process ended up as Nix and Hydra.

A similar process is thought to have created the Earth-Moon system as well -- though this has been a point of controversy for a very long time in planetary astronomy.
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Juramike
post Oct 9 2008, 04:21 PM
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After such an impact, there must've been an aweful lot of tidal friction generated on both bodies as the system locked up into its current configuration. How much heat would have been generated, and how would this have affected the crust and surface of Pluto?

Even now, how much tidal libration is in the system? (How eccentric is Pluto-Charons orbital couple?) And would this tidal energy get evenly distributed or would there be sub-crustal hotspots at certain points?

-Mike


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Rob Pinnegar
post Oct 11 2008, 02:25 AM
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QUOTE (Juramike @ Oct 9 2008, 10:21 AM) *
After such an impact, there must've been an aweful lot of tidal friction generated on both bodies as the system locked up into its current configuration. How much heat would have been generated, and how would this have affected the crust and surface of Pluto?

Even now, how much tidal libration is in the system? (How eccentric is Pluto-Charons orbital couple?) And would this tidal energy get evenly distributed or would there be sub-crustal hotspots at certain points?

-Mike


Well, ultimately the energy would have had to come from the orbital energy of Pluto and Charon around each other. That would put limits on the available energy. This wouldn't be an Io-like case where the energy source is Jupiter's rotation, which for all intents and purposes is inexhaustible.

Maybe a little energy could come from librational motion, but it's hard to imagine it could amount to much.

One other thing to keep in mind is that Pluto and Charon are mutually tidally locked. That means that Charon shouldn't be moving away from Pluto any more, the way the Moon is gradually moving away from the Earth. Their orbits around each other are fixed, except for solar perturbations, and what little comes from Nix and Hydra and other KBOs, and the giant planets.

Actually, I guess that some information about the past evolution of this system might be obtained by observing that Nix and Hydra don't appear to have been captured into resonances with Charon (at least this was the case last time I read up on it). That implies that there couldn't have been *too* much tidal energy dissipated. If there had been, Charon's semimajor axis would have increased enough for Nix and Hydra to get "grabbed" into resonances at some point.

(Mind you, Charon's so big relative to Pluto that it would take a *lot* of slowing-down of Pluto's rotational period to move it out very far... hmmm, this gets more complicated. Guess I might have to stop speculating, and actually do the math.)
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Rob Pinnegar
post Oct 15 2008, 04:46 AM
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After thinking about this a bit more:

If the giant-impact model of Charon's formation is correct, it's likely that Charon formed quite a lot closer to Pluto than is the case today. This means that it may originally have had an "egg-shaped" profile (similar to Mimas) caused by tidal effects.

Eventually, Charon moved outwards, and the system reached the mutually-tidally-locked configuration. However, with Pluto's mass being so small, I wonder if Charon's orbital evolution could have proceeded slowly enough for the moon to solidify completely before it reached its current distance from Pluto?

If that's the case, Charon may show some features characteristic of relaxation of an initially ellipsoidal solid body to a more circular shape. Sort of a reverse version of what happened to Iapetus, maybe?
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peter59
post May 16 2010, 07:06 PM
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2010 Hydra-Nix Meeting Webcasts May 11-12, 2010
https://webcast.stsci.edu/webcast/searchres...&sortmode=1
Unfortunately, English is not my native language. I have a problem with understanding the spoken english language. Maybe you can find here some interesting information about Nix and Hydra.


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brellis
post May 16 2010, 09:34 PM
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Didn't Hubble see an atmosphere when Pluto was closer to the sun? If so, might NH see evidence of that atmosphere refreezing and recently falling back to the surface?
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Juramike
post May 16 2010, 10:04 PM
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Recent observations indicated that there might be a lag in the freeze out of Pluto's atmosphere. It might be just starting to freeze out as NH buzzes past.

From Pasachoff et al. The Astronomical Journal 129 (2005) 1718-1723. "The structure of Pluto's atmosphere from the 2002 August 21 stellar occultation."
Freely available here. (as html, click for pdf version)

"The current increase in temperature and pressure seems to prolong the period in which the atmosphere will remain detectable before its collapse, making it more likely that New Horizons will be in time for atmospheric studies at Pluto. The current data are consistent with the model of Hansen & Paige (1996, Fig. 11) that shows a cooling beginning in 2015, not far from the spacecraft’s prospective arrival."


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Greg Hullender
post May 17 2010, 01:38 PM
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I hope that doesn't mean we're likely to be there on a cloudy day!

--Greg
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