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New Horizons: Approach Phase, OpsNav - 25 January 15 to 28 June 15
nprev
post May 9 2015, 11:51 PM
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Nonspherical is obviously highly probable for both moons, and of course they're rotating. Be interesting if they're not rotationally locked with respect to Pluto, though, or if there's some sort of odd harmonic relationship as we've seen elsewhere.


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Paolo
post May 10 2015, 07:05 AM
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speaking of which, are there any ideas of the rotation status of the minor moons? I guess a classical spin-orbit resonance would be difficult to achieve in such a binary system, as it would be like orbiting around a highly non-spherical primary. would a spin resonant with Pluto's spin and Charon's orbit be more likely?
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Phil Stooke
post May 10 2015, 07:20 AM
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I think a standard spin orbit resonance is still most likely, with perhaps larger physical librations than we are accustomed to. The Saturn system is very complicated, but I think only Hyperion is in an unusual rotation state.

Phil


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elakdawalla
post May 10 2015, 04:15 PM
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Well, Mark Showalter at least thinks they could be chaotic rotators, but not everyone is convinced.


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pitcapuozzo
post May 10 2015, 06:18 PM
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QUOTE (Aldebaran @ Apr 30 2015, 09:13 AM) *
It could be Nitrogen ice.


As we understand it, Pluto's surface is a mixture between bedrock and N2, CH4, CO and C2H6 ices cover, plus the atmospheric gasses freezing on the surface (N2, CH4, CO, Ar, higher hydrocarbons (acetylene, diacetylene) and nitriles (hydrogen cyanide, dicyanoacetylene) ), so the situation is much more complex than just simple nitrogen (N2).
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pitcapuozzo
post May 10 2015, 06:21 PM
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By the way, here is some info on Pluto's and Charon's Sun occultations, in case someone hasn't posted them already.

"For both ingress and egress, far-ultraviolet solar occultations will be observed with the Alice instrument (wavelength bandpass: 52-187 nm) and uplink radio occultations will be observed with the REX instrument (X band wavelength: 4.2 cm), for both Pluto and Charon. The solar and radio occultations mostly overlap in time (since the Earth and Sun are very close together (0.24°) as seen from Pluto); the Pluto occultations are about an hour after closest approach (e.g., we will observe the solar ingress at Pluto from 12:16-12:49 UT on July 14th, and expect the Sun to set at about 12:47 UT; closest approach to Pluto is expected at 11:50 UT). The Charon occultations occur about an hour after the Pluto occultations. Besides all these occultations (we also observe the occultation by Pluto of a bright UV star with Alice, starting about 4 hours after closest approach), we use the Alice instrument to look for “airglow” (a faint glow at certain UV wavelengths, mostly due to processes related to UV sunlight; e.g., a UV photon from the Sun ionizes an N2 molecule, the emitted electron may be energetic enough so that when it hits another N2 molecule it breaks it apart and excites one of the N fragments to emit a photon at 134 nm). The particle instruments will indirectly study atmospheric escape by measuring ions formed when solar wind protons collide with escaping N2 molecules and steal an electron – the N2+ ions are swept up into the solar wind and are called “pickup ions”. We’ll also use the LORRI and MVIC imagers to look for clouds and hazes, or even plumes (as were seen at Triton, a near twin of Pluto)."

From an email conversation I had with Randy Gladstone, atmospheric lead scientist on New Horizons.
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Aldebaran
post May 11 2015, 03:04 AM
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QUOTE (pitcapuozzo @ May 10 2015, 06:18 PM) *
As we understand it, Pluto's surface is a mixture between bedrock and N2, CH4, CO and C2H6 ices cover, plus the atmospheric gasses freezing on the surface (N2, CH4, CO, Ar, higher hydrocarbons (acetylene, diacetylene) and nitriles (hydrogen cyanide, dicyanoacetylene) ), so the situation is much more complex than just simple nitrogen (N2).


I was talking about the polar ice cap specifically and for what it's worth, I was quoting the article. Solid Nitrogen and Carbon Monoxide are perhaps more likely to be transient. Methane is more likely to be constantly frozen with perhaps a smaller proportion in the lower atmosphere. The remainder including Argon, higher hydrocarbons and of course thiolins would be almost permanently frozen. Hydrogen cyanide would have negligible vapour pressure and may be likely to be found in association with thiolins in more ablated regions, although over time it tends to hydrogenize even in the solid phase. I would add methanimine (CH2NH) to your prospective list.

Either way, a lot of this is speculation, but we only have to wait a couple of months to find out more.
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Gerald
post May 11 2015, 11:10 AM
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Starting from manually determined positions of Nix and Hydra

in 17 (until 2015-05-06) of the OpNav Campaign 3, LORRI 4x4, cleaned, stacked and star-background-subtracted image quintuples I've tried to simulate the positions by manually adjusting parameters of assumed circular orbits:

This simulation can be extrapolated:

After narrowing down the orbital plane I've transformed the processed LORRI images, such that objects orbiting in a circular way around the Pluto/Charon barycenter are mapped to almost constant position; phase angle as x, radius as y-axis:

Here an example of the last eight of this image sequence stacked to reduce noise:


Versions on less

and more processed images:


For small radii the method is very sensitive to the barycenter.

Nix and Hydra are apparent, Styx and Cerberus not yet evident (to me), despite this excessive processing.
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pitcapuozzo
post May 11 2015, 01:35 PM
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QUOTE (Aldebaran @ May 11 2015, 05:04 AM) *
Either way, a lot of this is speculation, but we only have to wait a couple of months to find out more.


I agree, it's definitely speculation, but it's not like we can do much more before July 14th biggrin.gif Yes, the purpose of my comment was just to say that reducing it to one element may lead you to misunderstand the broader picture. Your comment is absolutely fine! Plus, like you say, with the few data we have it's impossible to say anything with certainty. Can't wait for July!!
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Ian R
post May 11 2015, 01:56 PM
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Stellar image processing, Gerald. Really enjoying your work.


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Fred B
post May 11 2015, 03:35 PM
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I just noticed that the image metadata files have the expected X,Y coordinates of all the objects in each raw image. For example:

http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x633_eng_1.txt lists:

PLUTO;X=127;Y=126
CHARON;X=128;Y=137
NIX;X=119;Y=99
HYDRA;X=116;Y=156
KERBEROS;X=152;Y=122
STYX;X=107;Y=126

These seem to have the Y origin at the bottom of the image, and I needed to subtract a pointing offset from all of them equally to get things to line up. But this could help with spotting Styx and Kerberos, perhaps doing a manually shifted stack on the expected XY. Strip the URL back to /info/ for a directory of the files.
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pitcapuozzo
post May 12 2015, 08:57 PM
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Finally, Kerberos and Styx!

http://www.nasa.gov/image-feature/nasa-s-n...est-known-moons
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ElkGroveDan
post May 13 2015, 02:26 AM
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QUOTE (Ian R @ May 11 2015, 06:56 AM) *
Stellar image processing, Gerald.


Planetary, actually.


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0101Morpheus
post May 13 2015, 10:31 AM
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All five this early, awesome.

That is all the known moons down. Now we keep watch for the unknowns (if they exist).
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Gerald
post May 13 2015, 03:57 PM
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First congrats to the New Horizons team, and particularly to John Spencer and his image processing team, for accomplishing this milestone!
At least with the published jpegs until 1st of May that's exceedingly difficult.

QUOTE (Fred B @ May 11 2015, 05:35 PM) *
I just noticed that the image metadata files have the expected X,Y coordinates of all the objects in each raw image.
... I needed to subtract a pointing offset from all of them equally to get things to line up.


The coordinates seem to be relative to the barycenter of the system.
I tried to adjust for this by adding the displacement needed to register stars:
Attached Image

But there is an increasing error build-up. I've been pondering for a while for the reason; my best explanation thus far is a changing parallax of the Pluto/Charon barycenter with respect to the starfield background during the OpNav Campaign 3.
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