When it's warm on Mars

On really warm days on Mars, it can get above freezing. Suppose a future Martian colonist walks outside his habitat on a very warm Martian day wearing just an oxygen mask and tank (like SCUBA gear). What would he/she feel? Would his/her life or health be at risk from the very low atmospheric pressure? How long until he/she would be compelled to run back inside?

The air pressure on mars is only about three percent of that on earth. For purposes of breathing, that’s effectively a vacuum. Your martian colonist would die very rapidly as their lungs ruptured from the difference between the pressure of their breathing-air and the outside air pressure.

How would this work if their mouth and nose were sealed off by the SCUBA gear?

The rest of their body is still exposed to the near-vacuum outside. The pressure differential between the lungs and the vacuum outside will cause the ribcage to expand beyond the capacity of their lungs. Your lungs can only take a few PSI of greater internal than external pressure before rupturing. The air in the lungs will then be forced under pressure into the bloodstream, and you’ll rapidly die from the resulting air embolism.

I see. Thanks very much!

Also the moisture on your skin would boil. That would actually be a pretty fun feeling.

There is little ‘air’ to remove the heat from the body, so temperature alone could be fine, even feel ‘hot’ without much air to remove it and in direct sun.

As stated above the air pressure would be too low, however some suggested terraforming concepts would raise the air pressure to be just high enough to be able to breath 100% O2 from a ‘scuba like’ setup and not need a space pressure suit. The atmosphere would be a high concentration of CO2 which would also add warmth. Or something like that.

To do this, if I got this correctly, we would need air pressure about 1/5th that of earth for this to work, or 20%, instead of the 3%.

An additional fun fact is that the atmosphere of Mars, besides being thin enough to be physically deadly, has a significant amount of carbon monoxide at 0.06%, more than the percentage of all the earth’s trace gases combined, including CO2. Not healthy stuff at all. Too bad, it would be interesting to take a sniff and see what Mars air smells like. The moon certainly has a distinctive smell!

It would be roughly equivalent to taking a space walk, which NASA commented on.

I wonder how long you’d last (and what damage you’d cause) with SCUBA-like gear that delivers pure O2 at say, 1/6 atmospheres. That would deliver a partial pressure of O2 nearly to normal levels, but with only about 2 PSI internal pressure (which would be uncomfortable but tolerable I believe, based on my limited SCUBA experience.)

Saliva on your tongue would boil, and no doubt your eyes would dry up very quickly, without some kind of face mask.

You’d get a nasty case of the bends, unless you’d been breathing nitrogen-free air prior to going outside, or decompressed slowly and then recompressed before long. Perhaps someone with more SCUBA knowledge could comment on the bends with non-nitro air mixes.

More on what they would feel. The explorer has sleeves that can maintain pressure when their gloves/boots are off so exploding lungs are not a problem. They decide to take off their boots and gloves to run barefoot on Mars and run their fingers through the soil. What would happen to their feet and hands?

As a hijack, same scenario on the Moon.

This actually happened in real life. The suit failed to pressurize in one hand. End result after a few hours was painfully swollen hand with no long term ill effects.

Right but would picking up a handful of arean/lunar soil be like dipping your hand into liquid nitrogen? molten lead? ooooh that’s kind of tingly?

Tangentially, I’ve seen a video of someone plunging his hand into melted lead. Oddly enough, it doesn’t burn (immediately). I don’t remember the explanation.

I bet lunar surface dust gets quite warm during daylight, so it would depend on the temperature. I bet it would feel pretty much like the same thing here on Earth, at the same temperature. Only a bit less hot or cold, because there’d be no convection.

But if you hold it or walk on it barefoot it would be conduction and not convection.

Scuba gear is capable of delivering breathing gas at 1-2 psi over ambient pressure, no problem. The difficulty on Mars is that the outside ambient pressure is so low that even if the breathing gas was 100% oxygen it might not be enough at those low pressures to support life.

If there is enough partial pressure of oxygen in the breathing mixture to sustain life you could still skin get a form of the bends. It would most likely be skin bends, occurring due to the process of isobaric counterdiffusion. In such circumstances, even if your breathing gas is at ambient (outside) pressure, if the partial pressure of one component of your breathing gas mixture is different than the ambient partial pressure of that component then that gas component migrates from high to low pressure according to the pressure gradient.

In essence, the dissolved inert gases in your tissues (mostly nitrogen) would migrate out of your body. If your respiratory system could not handle this fast enough then the gases would attempt to migrate out through the skin. As the dissolved gas bubbles coalesce they transition to a gas phase causing medical problems - skin bends.

The issue, as **Learjeff **rightly surmises, can be dealt with by changing the breathing gas prior to moving to the low pressure environment. Astronauts already do this prior to a spacewalk. An explorer on Mars would need to start breathing a gas mixture very low in nitrogen for several hours prior to leaving the habitat in order to avoid this problem.

IIRC, the lowest air pressure humans can survive long-term at is 5psi which would make the O2 partial pressure 1psi.

You should take a look at The Martian by Andy Weir. Basically, a botanist mission specialist on a Mars mission ends up being left for dead by the rest of his crew, and he’s got to survive, alone, for four years 'til NASA can send a rescue. It’s really, really good so far, and will likely answer any questions you have.