[X] My Assistant

[Nafnlaus]

I was just going to say that those chunks of ice look like floating icebergs on some fluid but I was thinking it was a silly idea and maybe it is.

It's not silly at all - see my post above about eutectics. Especially if there's neon there (neon makes it almost too easy to have liquids at Pluto temperatures), but even if there's not. Examples:

* There's various mixtures of N2/CO/CH4/O2, without any neon, that have lower melting points than any of them have individually, including down to nearly 50K (Pluto is commonly said to get up to 55K)
* The temperature could easily get higher than the commonly cited temperature range for Pluto - that's based on very simplistic equilibrium-heating calculations. I'm sure the mission will give us far more accurate data on how hot Pluto actually gets - or at least, how hot it is right now.
* Local variations in temperature can occur in a body, for example, due to differences in albedo. Liquids could flow like "groundwater" from one area to another.
* There could be geothermal heating from within Pluto
* There could be heat from subduction of ices.
* There could be heat from transition between ice phases

And so forth. Beyond temperature, what's needed for liquids is pressure. Nitrogen needs about 18 meters of N2 ice (more if it's "fluffy" (probable) or mixed with other ices). Neon needs about 3x the pressure.

But the basic point is, if you hit the eutectic's triple point, even if the stuff originally fell as snow, it will melt on the bottom.

[Webscientist]

My first impression was that the bright heart (made of frozen CO and not CO2...) looked like a "banquise" or an ice pack.

The black patches along some limits of the polygons seem to be in line with my initial assumption according to which there is a layer of liquid hydrocarbons (methane, ethane...) beneath this bright uniform crust.

At what depth?...

Possibly the largest reservoir of liquid hydrocarbons is hiding beneath this intriguing area! Who knows?

That's my bet!

[Paolo]

Mike Brown (aka @plutokiller) had a couple of interesting tweets yesterday on the subject of Pluto being geologically active:

In current hallway conversations with planetary scientists most are unconvinced by the evidence that "Pluto is geologically active"

covered in frost. frost redistribution is not the same as internal geological activity

[serpens]

Mike Brown (aka @plutokiller) had a couple of interesting tweets yesterday on the subject of Pluto being geologically active:
'In current hallway conversations with planetary scientists most are unconvinced by the evidence that "Pluto is geologically active"'

Yes, I can see a lot of tectonic changes taking place before the system became tidal locked but once tidal energy dissipated the surface should have been stable. While just one possibility, the mountain in a moat does does seem akin to the remnant of a collapsed tidal bulge. One thing I had forgotten and was reminded of in an old Dobrovolskis paper on the Pluto Charon binary system was that tidal dissipation would also cause the equatorial planes of the two bodies to realign to the [edit] orbital plane. The tidal bulge would become static as distance between the bodies increased but probably well before Charon became completely tidal locked, So after collapse it would potentially be displaced from the equatorial plane - just like the mountain in a moat. Yeah sheer speculation on my part but probably less speculative than geological activity or impact to explain the strange topography of the mountain in a moat. The upper bounds of the time taken for tidal locking for the system seems to be in the region of 100 Mya so the tidal locking is not in any way an indication of extended age and associated expectation of extensive impact craters.

[marsbug]

... The upper bounds of the time taken for tidal locking for the system seems to be in the region of 100 Mya so the tidal locking is not in any way an indication of extended age and associated expectation of extensive impact craters.

I didn't quite follow that Serpens, do you mean that tidal locking could have occured within the last 100,000,000 years and so the surface was being reshaped within that time, hence the surface is stable now and yet relatively craterless? That would place the formation of the Pluto/Charon system relatively recently, would it not?