What would happen to its two satellites, Jorge?

The same thing, basically. They'd partially evaporate and would remain only whatever rock they have. If Pluto was to replace the Earth, the outer satellites might also be lost due to gravitational interference by other bodies, since the inner system is much more packed than the Kuiper Belt. Perhaps. I can't know for sure, because I don't know how much mass Pluto would have without its volatiles, so I can't say how tightly it'd grab Charon, Nyx and Hidra…

If Pluto was in a habitable orbit around the Sun would it be an ocean covered planet?

No. It's too small for that. Water would sublimate and be blown to interplanetary space, leaving behing only its rocky core.

I still have doubts, though.

The temperature and kinetic energy of a particle do affect how they behave in the atmosphere, but it isn't just a matter of 'they have high KE and hence can shoot up higher' – the mean free distance of a molecule in air is very short, so they tend to diffuse only fairly slowly.

On Earth, as on any other planetary body with a thick atmosphere, sure, but I don't know about something as thin as the atmosphere of Pluto… or Earth's upper atmosphere, for that matter. I must admit my ignorance as to what kind of pressures would be needed for a gas molecule to become basically free to travel anywhere, though.

However, this says nothing about convection! Indeed – hot parcels of air do rise on Earth all the time due to their collective high KE – the constituent molecules have more kinetic energy and hence the gas becomes relatively less dense than that surrounding. They accordingly rise , but when they do the atmospheric pressure rapidly drops, and hence the air does work on it's surroundings by expanding adiabatically – and the temperature of the parcel of air drops very quickly as a result!

Hm… yes, that's true. The result would be an atmosphere which is hotter near the surface and colder higher up. However, in Pluto there is very little heat coming from the Sun to power that kind of system, which is probably also involved in the explanation of this "reversed" heat gradient they've observed out there.

I very much doub't it's only one thing.

"There's one thing I don't get. Knowing that the temperature is a measure of the average kinetic energy of some material's constituent particles. wouldn't it be expected that, in the absence of surface irradiation of heat and/or layers opaque to infrared radiation, the higher you get the higher the temperature, since those molecules found there would be the ones fast enough to get that high?"

The temperature and kinetic energy of a particle do affect how they behave in the atmosphere, but it isn't just a matter of 'they have high KE and hence can shoot up higher' – the mean free distance of a molecule in air is very short, so they tend to diffuse only fairly slowly. However, this says nothing about convection! Indeed – hot parcels of air do rise on Earth all the time due to their collective high KE – the constituent molecules have more kinetic energy and hence the gas becomes relatively less dense than that surrounding. They accordingly rise , but when they do the atmospheric pressure rapidly drops, and hence the air does work on it's surroundings by expanding adiabatically – and the temperature of the parcel of air drops very quickly as a result!

Hence, in a very (over) simplified model, thermal heating from the ground causes the atmosphere in close proximity to heat up and rise, which then cools by adiabatic expansion (look up orographic lift as an example of this process), and so the temperature profile decreases as we move higher in the atmosphere.

Maybe.

Does anyone know what state Pluto's atmosphere will be in when New Horizons arrives? Will it befrozen? Sublimated? Somewhere in-between?

It will not be frozen. Pluto is on the outward bound part of it's orbit, but it's atmosphere is not expected to be significantly frozen out for some time to come – I read it in an interview with Alan Stern. NH may glimpse the start of the process, but it won't all be sitting in a heap of snow on the surface.

ideally, yes…. and with about 42 years in between each pair of missions… it'll require some patience!

Why? no planetary criteria have changed.

Does anyone know what state Pluto's atmosphere will be in when New Horizons arrives? Will it befrozen? Sublimated? Somewhere in-between?

We may have to sent three "New Horizons" to view Pluto in each state to get a good understanding of the dwarf planet.

On Pluto, where the Sun is barely brighter than other stars, theres probably not enough energy for the gas to decompose..

The reason that methane on Mars caused such a stir is because there was data that suggested it was being replenished somehow. Pluto, on the other hand, most likely has a more fixed amount, so it isn't as exciting.

Where does the methane on Pluto come from? Does it work differently there than on Mars?

On Earth, under normal circumstances, the temperature decreases through the atmosphere by about 6 degrees per kilometer.

Only in the troposphere. The temperature profile is more complicated than that above 10 km altitude. In fact, in the thermosphere, the temperature skyrockets, if you forgive me for the bad pun.

There's one thing I don't get. Knowing that the temperature is a measure of the average kinetic energy of some material's constituent particles. wouldn't it be expected that, in the absence of surface irradiation of heat and/or layers opaque to infrared radiation, the higher you get the higher the temperature, since those molecules found there would be the ones fast enough to get that high?