[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!

[ZLD]

...Tombaugh Regio lies inside what l think is an impact basin roughly 800km wide.

This is an interesting idea and I think theres a few elements that could lend itself to supporting it. However, I think the biggest reason this can't be the case is the lack of cratering. If that size of impact occurred, I would highly expect a ring system to form and as it condensed back to the surface, there would be many many impact craters. This would also deposit mixed elements across the surface and would leave few uniform looking areas, especially as large as Tombaugh Regio.

[John Broughton]

This is an interesting idea and I think theres a few elements that could lend itself to supporting it. However, I think the biggest reason this can't be the case is the lack of cratering. If that size of impact occurred, I would highly expect a ring system to form and as it condensed back to the surface, there would be many many impact craters. This would also deposit mixed elements across the surface and would leave few uniform looking areas, especially as large as Tombaugh Regio.

The curving scarps I circled would be the basin's outer rim. It is equivalent in size relative to Pluto that Mare Imbrium is to the Moon. Mare Imbrium also has an incomplete rim and no trace of inner rings, after being flooded with lava when the floor rebounded. Moderate-sized craters on Pluto can be made out despite having been blanketed under a kilometre or so of ice deposits, but there are none inside Tombaugh Regio. However, there appears to be craters west of that area that haven't been blanketed, particularly on the upper half of the whale's head. If Pluto ever had a thick atmosphere, there could be signs of its effects on the surface in high-resolution images of that region.