Amongst the mountains, strange terrain and young surface that we’ve already interpreted for the Plutonian surface, those reviewing the images have picked out what they believe to be nitrogen or methane flows on the surface. Contrasting that with the other major finding of 3000 m water-ice mountains on Pluto – does it leave you wondering why ice can form mountains on Pluto, but methane flows?

Pitcher: Pluto and it’s moons (Charon, Nix and Hydra) scaled next to Australia.

….Known as the ‘hydrogen’ bond, the interaction between hydrogen and oxygen atoms in water still puzzles scientists to this day, and is the main reason for some of the special properties of ice. One of which is making it really strong, especially at 44 K. At these temperatures ice is held together by a rigid framework of water molecules held together by hydrogen bonds, like a steel frame supporting a skyscraper. This means you can build mountains.

These mountains don’t flow like on Earth because it’s too cold. Glaciers on Earth move in a number of ways, one of which is by the ‘creep’ of defects in the structure of the ice. This can only happen if the water molecules have enough energy to vibrate a little – which they don’t really have at the chilly condition of Pluto.

So ice is strong. But methane has hydrogen in it (CH4) so why can’t it form hydrogen bonds to make it strong? The issue here is that methane has too many hydrogen atoms, and they take up all the ‘stickyness’ of the carbon atom in the middle. This means that the structure of methane is pretty simple. We all remember the fun we had in ball pools at children? If your ball pool was square and, for a moment, didn’t have a ton of kids playing in it the balls would arrange themselves in a structure we call ‘close packing’. And that’s the structure that solid methane forms. The methane molecules are unable to stick to any of its neighbours, so find themselves spinning about. If you ‘rotationally disorder’ a tetragonal methane molecule it ends up looking a lot like a sphere – like the balls in your pool! The only force that is holding them together is the weak Van de Waals interaction, sort of like gravity for atoms.

This means that solid methane is quite like jelly! We actually called it a plastic solid because if you prod it, it won’t return to its original shape. And because there’s no framework holding the methane molecules together then even at the frozen temperatures of Pluto it can flow.

Nitrogen is pretty similar to methane – in its solid forms it forms molecules of pairs of nitrogen atoms. These N2 pairs also spin making them pack like spheres and again forming a plastic solid.

Full article: http://theconversation.com/what-flows-on-pluto-46380

> The methane molecules are unable to stick to any of its neighbours, so find themselves spinning about. If you ‘rotationally disorder’ a tetragonal methane molecule it ends up looking a lot like a sphere – like the balls in your pool! The only force that is holding them together is the weak Van de Waals interaction, sort of like gravity for atoms.

> This means that solid methane is quite like jelly! We actually called it a plastic solid because if you prod it, it won’t return to its original shape. And because there’s no framework holding the methane molecules together then even at the frozen temperatures of Pluto it can flow. Nitrogen is pretty similar to methane – in its solid forms it forms molecules of pairs of nitrogen atoms. These N2 pairs also spin making them pack like spheres and again forming a plastic solid.

Nice, that makes a lot of sense. But Pluto does have water ice on the surface – we knew that even before the New Horizons spacecraft got anywhere near Pluto. Further, these large flow features must be extremely recent (in geological terms) because of the lack of craters, and not just lack of craters on these “flow zones” so there must be some subsurface heating and convection.

A bit technical, but interesting. Last revised 24 Jul 2015.

An atmospheric general circulation model for Pluto with predictions for New Horizons temperature profiles
http://arxiv.org/pdf/1501.02848v5.pdf

Results are presented from a 3-D Pluto general circulation model (GCM) that includes
a subsurface model and volatile cycle. Conductive heating and cooling, non-local thermodynamic
equilibrium (non-LTE) heating by methane at 2.3 and 3.3 microns, non-LTE
cooling by cooling by methane at 7.6 microns, and LTE CO rotational line cooling
are used. This Pluto model advances the work of its predecessors because it has both
detailed subsurface and atmospheric model components.

The following charts are predicted temperatures (in Kelvin)

and wind speeds (in m/s) in Pluto’s atmosphere.

New news on New Horizons at Pluto is so nonexistent that there haven’t even been any tweets for 3 days. And no new images released for a whole 23 days. Tracking stations are still getting signals from the spacecraft.