Fig. 1. Time series of a potential Pluto-Charon–forming impact yielding a planet-disk system (run 70 in table S1 with N 0 120,000 particles). Results are shown looking down onto the plane of the impact at times t - 1.3, 3.2, 7.5, 11.8, 14.5, and 24.6 hours; units shown are distance in 103 km. Color indicates material type (blue, water ice; orange, dunite; red, iron), with all of the particles in the 3D simulation overplotted in order of increasing density.
The impacting objects are identical--both are predifferentiated into 40% ice mantles and 60% rock cores by mass with initial surface temperatures set to 150 K, increasing with depth (7) to a central temperature ,800 K. After an initially oblique impact in the counterclockwise sense (A), the two objects separate (B and C) before recolliding. After the second collision, the denser cores migrate toward the center, as a bar-type mode (36) forms in the rapidly rotating merged objects (D). From each end of the bar emanate spiral structures (D and E), whose self-gravity acts to transport angular momentum from inner to outer portions. The arms wrap up on themselves and finally disperse to yield a ring (36) of material (whose differential motion would on a longer time scale produce a disk), together with the central planet (F).
This differentiated model with a 40% rock core mass and 40% ice mantle fail
Impactor's with solid cores
This is Robin's impact model of two bodies with differentiated (solid) cores prior to collision. I suspect this is where the other scientist's model's failed. Colors are temperature gradients and seem to indicate blue is cold ice, red is iron and orange is Dunite rock >90% olivine.
Impactors beginning with solid core's like these two bodies, merge into one and leave a ring of debris (F). Robin explains, this is why you can't use a model based on two planets with differentiated (solid) cores. The planets must be uniform prior to impact.
Conclusion - for the collision model to work Pluto and Charon had to be uniform at the time of impact or Robin's collision model simply doesn't work.
According to this paper titled
"Ocean worlds in the outer solar system"
By F. Nimmo and R. T. Pappalardo at AGU Pub.
For a silicate core >1000 km in radius the heat diffusion timescale is longer than the age of the solar system, so large silicate cores provide a long-term reservoir of energy which can potentially maintain a subsurface ocean. Conversely, for bodies with small silicate core radii like Enceladus or Tethys, (and I include Pluto at 875km) ancient heat cannot be stored in this manner.
Francis Nimmo is saying that for planets with a core radius smaller than 1000 km, ancient radioactive core heat is not possible and for core radius' greater than 1000 km it is only potentially possible.
Quote from this paper
Thermal evolution of Pluto and implications for surface tectonics and a sub-surface ocean.
By Guillaume Robuchon, Francis Nimmo
Pluto’s ice/rock+ice ratio is supposed to be about 0.65 (McKinnon et al., 1997) and for a differentiated Pluto the silicate core would be roughly 40% of the volume.
The radiogenic heating provided by the core can potentially melt the mantle ice and form a subsurface ocean (Hussmann et al., 20 06; McKinnon, 2006)
This is Robin's collision model of two bodies that have uniform cores prior to impact. This model worked
Solid blue shows temperatures between 0 and 50K and subsequently appears to mean any existing rock is suspended in rock hard ice.
The larger body represents Pluto. In Robin's paper she points out (in this image) how you can see Charon does not get heated above 35K remaining blue while a small portion of Pluto does get warm. A small portion heats to 200K (-73C or -100F) while most of the heated material is in the yellow green temperature range which is between 60K and 150K (-213C to -123C, -352F to -190F).
The other thing noted here is that much less than half of Pluto was heated to higher temperatures in this model perhaps 30% to 40%, however, her paper does not specify the portion that heats but the image shows a small yellow green section approximately one third the size of the planet.
The natural conclusion from this model is that Charon did not heat and remained uniform while less than 40% of Pluto heated to temperatures that could result in differentiation. This means Robin's collision model necessitates Pluto having a partially not fully differentiated core.
A fully differentiated core's radius would only be 875km based on Bill McKinnon's estimates which state only 40% the volume of Pluto is rock.
Being generous by saying this partially differentiated core is 40% of a full core (875km) means the partial core's radius would at best be 350km (875km X .40). This is far, far too small to still be hot after 4 billion years.
Quote from Robin's collision model paper
In moon-producing impacts, the satellite material experienced little heating (Temp = 30 K), because it had for the most part avoided direct impact with the planet, whereas the target was heated more substantially (Fig. 2).
Fig. 2. Time series of a potential Pluto-Charon–forming impact yielding a planet-moon system (run 20 in Table 1 with N 0 20,000 particles). Results are shown at times t0 0.9, 3.2, 5.9, 7.5, 11.2, and 27.5 hours; distances are shown in units of 103 km and color scales with the change in temperature in kelvin. The impacting objects have uniform serpentine compositions. After an initially very oblique impact with a 73- impact angle (A), the two objects separate (B and C) and during this period the smaller impactor receives a net torque from the distorted figure of the target.
After a second, even more grazing encounter (D), an additional portion of the impactor is accreted onto the planet, while the rest self-contracts into an intact moon containing 12% of the central planet’s mass that is again torqued by the ellipsoidal figure of the target (D and E) onto a stable orbit with a semimajor axis of 6.5 Rp and an eccentricity of e 0 0.5. The final moon in (F) is described by 2232 SPH particles.
A uniform undifferentiated model is the only one that can potentially succeed.
Even using Robin's model, Charon and Pluto were always uniform planets with different compositions and Charon could not have formed from a debris field.
Charon and Pluto were two distinctly different objects.
This remains true whether they impacted or didn't because if it remains true under an impact scenario then it certainly is true for a non impact scenario.
In other words, this collision scenario doesn't relate to that of our Moon's collision with Earth as our Moon is supposed to be the crustal material from Earth that was turned molten and ejected into space to later coalesce.
Robin's impact model scenario is one in which Charon delivered a slight and slow glancing blow on Pluto surviving mostly in tact just as it was prior to the impact remaining cold and uniform and compositionally different.
Since an errant fully differentiated core idea was firmly entrenched for 10 years in everyone's mind, a hot core concept naturally followed which B. McKinnon also proposed claiming it was heated by the radioactive decay of AL26.
How long did accretion take and what are the implications (i.e. how long for Pluto to grow up)? If we have an accretion time (10’s of million years), there is time enough to form Aluminum-26, which provides a form of heat through its decay. Heat then can melt ices and create a differentiated body (i.e., rocky core, icy mantle) and also drive water out.
McKinnon’s best guess: Pluto formed rapidly and early.
Bill McKinnon made the above statement in 2006, 1 year after Robin Canup made her collision model yet Bill is suggesting Pluto accreted in the first tens of millions of years of the solar system's formation (lets say 50 million) and was at that time a fully differentiated planet with a radioactively hot core which at its largest could only be 875km which means it would be cold today according to Nimmo.
However, according to Robin, Pluto and Charon couldn't have been differentiated if and when they collided as her model won't work if they were.
Back in 2002 Bill wrote a paper called "On the initial thermal evolution of Kuiper Belt Objects" (excerpt on the right) in which he seems to argue against Al26 as a possible heat source for KBO's but uses Al26 as a potential heat source at LPSC 2016.
Wikipedia has this to say about Aluminum 26 in our solar system.
26Al is only present today in solar system materials as the result of cosmic reactions on unshielded materials at an extremely low level. Thus, any original 26Al in the early Solar system is now extinct.
In addition, NASA scientist Kelsi Singer is trying to convince us via 3 impacts on Hydra and 11 on Nix that Pluto and Charon collided 4 billion years ago which would have been after their Pluto formation period. Conflicts, conflicts conflicts.
The above chart has 3 diagonal lines indicating surface age.
purple= 2Gyr surfaces.
Hydra's 3 blue triangles fall between 2.5 billion years and about 2.75 billion years
Nix's red/pink diamonds depending on the camera used ranges from 3 to 4.5 billion years.
So the range of potential ages for these moons based on NASA's chart is anywhere from 2.5 to 4.5 BILLION years that's a 2 billion year slop factor in a 4.5 byr time frame or a 45% slop factor. Yet NASA claims this as proof that the moons are 4 billion years old.
This chart to the left from a New Horizons team paper called "The Small Satellites of Pluto as Observed by New Horizons" shows the Nix impacts (pink & red diamonds) not shown in the above chart. These impact examples don't fit as nice and neat into this 4 billion year old theory so they were left out of the chart above which was used at the 47th LPSC press conference in Texas.
The LORRI camera (pink diamonds) puts some of Nix's impacts at around 2.5 billion years and MVIC puts some at less than 3 billion years yet this is proof of 4Gyr old moons from impact dating.
The black chart above was used publicly to demonstrate how the moon's impacts placed this system's age at 4 Gyr but it only displayed 9 of the 19 impact data points.
It seemed interesting to me that NASA would leave out half of the data from their original paper so I decided to use all 19 impacts and draw the diagonal lines to see how things lined up.
My magenta line is 4 Gyr the blue is 3 Gyr and the red is 2 Gyr. This chart runs from .1 kilometer diameter crater to 1000 this is why the diagonal lines appear steeper.
Since there are more data points on this chart using the three diagonal lines renders some interesting results.
Four impacts are less than 2 billion years and 7-9 fall between 2 and 3 billion years.
My conclusion about this chart remains the same, it is an unreliable method for age dating the moons and does not support a 4 byr age for the small moons.
Based on the ocean of water idea the existence of 5% ammonia antifreeze became necessary.
Likewise, out of the ocean theory, a positive gravity anomaly developed to explain Sputnik Planitia's alignment with Charon along with an impact theory which caused true polar wonder.