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Pluto seems to be composed of Nitrogen and other ices that would be fluid or gaseous at higher temperatures. So what would happen if an astronaut using an Apollo era space-suit (crucially with that insulation) would land and step out on the surface of Pluto?

Would conduction of heat cause the surface to melt or sublimate, and if so, how fast would this happen? This would be a illustrative example of how different a landing on Pluto would be compared to a landing on the Moon.

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    $\begingroup$ If an astronaut were to land on Pluto, I'm pretty sure she would be wearing a suit explicitly designed for that dwarf planet. $\endgroup$ – Dan Pichelman Jul 6 '16 at 13:45
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    $\begingroup$ I think considering current insulation is interesting, since it gives a feel for how "alien" the planet really is. People ask the question about whether one can land on a gas giant, which is obviously impossible. However, since Pluto is "rocky" one could assume it would be like landing on the moon. But is this really the case? So many of the "rocks" that exist on Pluto would just evaporate nearer to the sun. So I'm trying to get at how much Pluto is actually a planet in more human terms, hence the assumption of insulation of a regular, current-day spacesuit. $\endgroup$ – user1018464 Jul 6 '16 at 13:51
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    $\begingroup$ I'm interested in what would happen if the space suit isn't adjusted to Pluto. It's analogous to the question "what would happen if you stepped on Mars in your t-shirt" to Pluto. E.g. saliva boiling on your tongue gives an indication to how hostile Mars is, I'm wondering to what extent Pluto is an equal step in hostility from, say, the Moon. Of course, this is related to the question of what is needed for an actual Pluto space suit. Only I place the emphasis on the consequences of arriving underprepared and using an existing space suit. I'd welcome suggestions on clarifying the question. $\endgroup$ – user1018464 Jul 6 '16 at 15:10
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    $\begingroup$ This question still needs an answer that addresses the effect of heat leaking from the bottom of an Apollo-era boot upon the surface of Pluto. Would the sublimation be fast enough to produce a little "jet" of gas under the boot? Would this pressure be comparable to the gravitational force holding the astronaut down, so that it made walking more difficult? $\endgroup$ – uhoh Oct 12 '17 at 2:39
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The temperature on the moon varies from about 90 K at night to about 400 K during the day. However, the Apollo missions were all timed so that the astronauts would be on the surface around dawn, when the temperatures were relatively mild. Their boots were insulated, and their space suits were designed to be highly reflective.

Pluto has temperatures varying from about 33 K to 55 K. What matters to the astronaut inside the suit is the temperature difference between the inside of the suit and the outside. The rate of heat conduction is proportional to that temperature difference.

If you compare lunar nighttime to a balmy summer afternoon on Pluto, the temperature difference is 205 K in the first case versus 240 K in the second case. Those two numbers are really in the same ballpark, so a spacesuit that was designed to handle lunar night temperatures would probably be fine on Pluto. However, the Apollo suits were not designed for lunar nighttime. Therefore I suspect that the astronauts' feet would have very rapidly frozen, and after that they would have quickly died of hypothermia.

It's also interesting to speculate about what effect the astronauts' footsteps would have on Pluto's surface. I'm imagining some spectacular evaporation of nitrogen ice. It might be so violent that you wouldn't even be able to walk.

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    $\begingroup$ Your part about the astronaut experience is fairly good, but the final paragraph about the effect on Pluto's surface could be better justified. $\endgroup$ – called2voyage♦ Jul 7 '16 at 18:28
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    $\begingroup$ @called2voyage: Pure speculation, may be totally wrong. $\endgroup$ – Ben Crowell Jul 7 '16 at 20:38
  • $\begingroup$ Right, I understand that - I just wanted to make clear what remained before this question was adequately answered. $\endgroup$ – called2voyage♦ Jul 7 '16 at 20:43
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    $\begingroup$ I really wouldn't want to try to walk on Pluto without very good boot insulation. Can you say "ice skates"? $\endgroup$ – Loren Pechtel Oct 12 '17 at 22:33
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The boots of the Apollo astronauts experienced temperature swings from 355 K in the sun to 166 K in the shade. There were no reports of temperature problems in regards to the suits and/or footwear, though at one point Aldrin reported being cool and adjusted the thermal control on his suit. Given the boots handled these temperature swings without issue I'd extrapolate the insulation is very good. https://www.hq.nasa.gov/alsj/a11/A11_PAOMissionReport.html

Though even with very good insulation if it wasn't designed for those very low temperatures the boots would start dropping in temperature over time and so would their feet. Eventually it would cause frostbite though I do not think hypothermia since the rest of the suit would keep the astronaut relatively comfortable. The suits had cooling systems on them to keep them comfortable which would likely need to be turned off sooner with such weak sunlight. In fact since conduction works by physical contact if they switched from one foot to the other or better jumped periodically in the 1/12 Earth's gravity their feet would spend far less time on the ground to reach the very low temperatures.

The degassing N2 and other volatiles would definitely occur, their boots would be at a much higher temperature having come from the room temperature conditions of the inside of the space craft. Unless of course the exhaust from the landing itself had already cleared the nearby area of any low boiling point volatiles.

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