Re: Could you survive on Pluto or Mercury for any amount of time?

Without a spacesuit, you'd die of suffocation in under a minute on Mercury of Pluto. This is true of every other planet or moon in the solar system. Even the planets that have an atmosphere are full of deadly gases.

A spacesuit can help. A spacesuit does two things: it surrounds your body with breathable air, and it keeps you from getting too hot or cold. Even Space Shuttle astronauts need heaters and refrigerators in their suits to keep them comfortable.

My calculations show that a human in a Space Shuttle spacesuit would last for under an hour if he was on Mercury, and a similar length of time on Pluto. The problem is that space shuttle suits keep the temperature constant by using electricity from batteries, and batteries don't have a whole lot of power. The astronauts could go much longer if they could plug themselves into their spaceship's power supply using an "extension cord".

The way to solve the problem is the same as it is here on earth: wear thicker clothes. By wearing extra layers of insulation, an astronaut can keep the cold out when he's at Pluto, and (surprisingly) can keep the heat out when he's on Mercury. However, you might need so much insulation that the spacesuit would be too bulky to let you move around.

For those interested in technical details, I'm assuming an outside temperature of 480 K on Mercury, and 50 K on Pluto. Heat loss assumed dominated by thermal conductivity through spacesuit material 5 cm thick with thermal conductivity of .03 W/(m K), interior temperature 290 K, surface area 4 m^2, giving 450 watts of heat into the suit on Mercury, 550 watts out of the suit on Pluto. Add 100 watts of body heat. Assume a Carnot refrigerator on Mercury: you need 360 watts of power to stay cool (but for realistic refrigerator efficiencies, it's probably twice that amount) At Pluto, you need 450 watts of heating. Assume 10 kilograms of batteries with specific energy of 30 watt-hours per kilogram, giving 300 watt-hours of power. If you triple the insulation thickness, power requirements go down to 160 watts on Mercury, 80 watts on Pluto. However, the suit's arms are now at least 40 cm in diameter...