New Horizons: Approach Phase, OpsNav - 25 January 15 to 28 June 15 Options

[dvandorn]

While there does appear to be a bright albedo feature at the visible rotational pole, it's good to recall that this pole has also been pointing at Sol for, what, decades? Instead of being a cold trap that causes ice deposition, this would be the spot of highest insolation (such as it is, out in Pluto space) on this dwarf planet.

Maybe dark ices absorb more solar heating than higher-albedo ices at this sol-pointing pole and are selectively driven off, to re-accumulate on the shadowed side. Leaving the higher-albedo ices behind, and thus showing what looks like a "polar ice cap," even though it's a net deflational, not depositional, feature.

I don't insist on this interpretation, but it fits the observed facts...

-the other Doug

[Aldebaran]

Possibly tholins account for some of the darker reddish coloration.

http://adsabs.harvard.edu/abs/2005DPS....37.5502O

[Phil Stooke]

"Maybe dark ices absorb more solar heating than higher-albedo ices at this sol-pointing pole and are selectively driven off, to re-accumulate on the shadowed side. Leaving the higher-albedo ices behind, and thus showing what looks like a "polar ice cap," even though it's a net deflational, not depositional, feature."


Verily, dvandorn, Sire, thou mayst be correct in thy supposing. Let us call it, not a polar cap, but a polar tonsure!

Phil

[elakdawalla]

Cathy Olkin and Leslie Young have been looking at this problem for a long time, and have determined that Pluto very likely has a permanent north polar cap.

[Gerald]

Working a little more systematically:
14 five-image sequences of "OpNav Campaign 3, LORRI 4X4" cleaned and "stacked" by adding up the four most similar corresponding pixel values of each of the five images, and subsequently subtracting 112 to make better use of the available grey values:

CRs should be filtered out that way.
Sums larger that 255 are mapped to white, those smaller than 0 (due to the subtraction of 112) to black.

Next intended processing step: accurate registering; I guess, this will take a few days.

[Gerald]

Registering of OpNav3 LORRI 4x4 sequence is work in progress, thus far up to about 1 pixel, not yet fully accurate, but sufficient for a tentative identification of a second moon (probably Nix) :

[jasedm]

Very nice work Gerald.

[Gerald]

Thanks a lot!

Registering of the 14 cleaned and stacked OpNav Campaign 3, LORRI 4x4, quintuples until 2015-05-01 with good accuracy completed.
Pinhole camera model with assumed infinitesimally small fov angle did the job.

Overview:


Animation:


Album of individual images, contained pngs (4-fold magnified) should be of the best quality I can provide thus far.

Next intended processing step is determining starfield and Pluto/Charon(?) background.

[Gerald]

Stellar ( + Pluto ) background, median-filtered:

(The "Meridian" in the title of the graphics must be a result of lack of sleep. )

Subtracting this image from the 14 stacked images sequence, and 8-fold brightness-stretching, results in the following preliminary animated gif:


The moons get more distinct, but the images can be improved by some more brightness adjustment...

[elakdawalla]

That is very nice work.

[Gerald]

Thanks Emily!

Here some further brightness stretch and adjustment, cropped:


I think, that's now close to the limits of what can be done with "basic" image processing techniques.

[Gerald]

False color animated gif of the dancing moons:

(background blue, very bright variable parts red, subtle objects greenish)

Brightest stars (not too close to Pluto/Charon), and the presumed Pluto/Charon barycenter with crosshairs, cropped:


Background masked, to show only the above marked stars:


List of star pixel positions in the above graphics, and integrated brightnesses:
 lor_0290526027_0x633_sci_8_etc_cleaned_register_median_data.txt ( 2.98K ) Number of downloads: 319


The brightest object should be close to the presumed Pluto/Charon barycenter.
This position is useful to narrow down the parameter space where to look for other moons, and to pin down the orbital parameters of Nix and Hydra.

[Gerald]

Starting with uploads of two processed images to astromomy.net (and this image) following a hint of Emily's very useful TPS blog post, I've obtained the coordinates of the star background.

CODE

Center (RA, Dec):    (270.678, -14.637)
Center (RA, hms):    18h 02m 42.813s
Center (Dec, dms):    -14° 38' 12.604"
Size:    34.9 x 34.9 arcmin
Radius:    0.411 deg
Pixel scale:    1.02 arcsec/pixel
Orientation:    Up is -159 degrees E of N

Then I've the assembled a blink gif between a map obtained from Google Sky as a reference, and a roughly brightness adjusted version of the filtered and merged OpNav Campaign 3, LORRI 4x4, images (until 2015-05-01):


Besides the bright Pluto/Charon barycenter, I found two subtle, but significant differences:
1 - could be a glitch in the reference map, or a variable object,
2 - unclear, could be a variable star, or a TNO / moon; I can rule out a processing artifact almost with certainty, as well as an incompletely filtered CR hit, since the feature is present in several LORRI images.

[Fred B]

Here's my take on moon IDs. Sigma clipped & aligned the last four quints in Maxim DL. No sign of Styx or Kerberos yet but it shouldn't be much longer. Click for animated GIF:

[Gerald]

Great!
I get more and more the impression, that Nix and Hydra are rather non-spherical, and rotating.