Venus upper atmosphere I'd say, if you can find a surface to stand on, e.g. on the outside of a floating habitat, if we have built them by then.
The surface of course is deadly, but at the cloud tops, then the Venus atmosphere has the same temperature and pressure as Earth, and it has protection from UV radiation and cosmic radiation like Earth. You would be falling of course, but have tens of kilometers to fall and the higher pressure will mean you can hold your breath and so can survive longer.
If caught in a vacuum, in space or Mars, you mustn't hold your breath because the outwards pressure would tear your lungs. But if falling in the Venus upper atmosphere you could. You could survive a couple of minutes in a vacuum, if you don't hold your breath, though you'd be unconscious for much of it. Survival in Space Unprotected Is Possible--Briefly
If you can hold your breath, that adds an extra minute or so - however long you can hold your breath.
If you have a floating habitat to stand on, and are just stuck outside of it without protection, then your only problems are the sulfuric acid in the air and a supply of oxygen and nitrogen (for a buffer gas) to breathe.
In the Venus cloud tops, if falling, you are 50 kilometers up. Assuming terminal velocity similar to Earth, of 56 meters per second, then that's about 1000 seconds to fall ten kilometers. Or about sixteen minutes. So you would still survive far longer than on Mars or in space, even if falling in the Venus upper atmosphere.
No benefit in Mars at all as far as I can see. It's a laboratory vacuum, and anyway carbon dioxide is poisonous to humans, above the trace amounts in our atmosphere - even at the 1% level in the Mars atmosphere - though you wouldn't survive long enough for that to make a difference. You would not survive with just supplementary oxygen on Mars - no more than you would if floating outside the ISS without a suit and with supplementary oxygen. The moisture lining your lungs would boil in the low pressure.
Or - in the subsurface ocean of Europa. But the water would be at a high pressure there like the floor of the Earth's oceans, so your lungs would be crushed to almost nothing.
Titan, and a suitable level of the atmosphere of Saturn would be the right pressure and acceptable gravity - but would be too cold. Still - they might have some advantages for short term surviving over sulfuric acid. I'm not sure though.
You'd be unconscious quickly, so depends what you mean by survive. And whether you hope someone will revive you. And whether you mean heart beat stopped, or dead to the extent there is no chance you could be revived.
If the aim is to stay conscious for as long as possible, I think your best chance here is suffocating in an atmosphere of CO2 and burning through sulfuric acid. Not a pleasant way to go, but you'd survive a few minutes more I'd imagine.
But you'd be badly burnt if you could be revived. Unless you can protect yourself. Even - like a coat or something to throw over your face and hands would protect you from being burnt by the acid in the short term.
It doesn't really help much to survive an extra few minutes unless there is a chance of someone rescuing you. But if that is your reason, then that changes the situation a bit.
On Titan or Saturn, you'd be very cold. If you get so cold the water in your blood vessels freeze and the individual cells are damaged, then you can't be revived.
Some people have been revived however, after a long time unconscious in cold conditions. Hours certainly, and in one case, possibly for weeks, though it's not sure how he survived. Some sort of hibernation reflex possibly. If you are lucky - very lucky - that is.
If you have good insulation, nice warm clothes, and you get rescued before the ice in your cells freezes, you might have a chance. So maybe on reflection, Saturn upper atmosphere is better. You'd be falling in a hydrogen atmosphere. But as for Venus, and more so, you'd last far longer, because you can hold your breath. It depends how long you can survive your heart stopping etc.
Perhaps best though, standing on Titan? With warm clothes and good padded warm shoes. You could hold your breath, that adds an extra minute perhaps, even more if you happen to be trained in holding your breath. You should stay warm enough I think to last out your last breath of air, then collapse to the surface and maybe your rescuer gets to you in time to revive you. And with the lower gravity it is probably easier for them to land on Titan and take off than to rescue you from the upper atmosphere of Saturn.
This goes a bit beyond the original question, but it's a natural follow up I think.
With a supply of oxygen and nitrogen for breathing, for instance, an aqualung, you could survive in the Venus upper atmosphere as long as your oxygen lasts - so long as you also have a sulfuric acid resistant suit and somewhere to stand on, because if you are falling to the surface you have no chance.
Which may seem like cheating - but that is far lower tech than a 10 million dollar months to make spacesuit.
So - if you phrase it another way - where is the place you can survive for longest with the lowest cost equipment - say you have $100,000 for equipment and that's your limit, Venus wins hands down so long as you have an airship type habitat to stand on, and are caught outside it, not just falling through the atmosphere.
I have absolutely no idea how much an aqualung and an acid resistant full body suit would cost, but probably not that much - perhaps you could get it for less than $10,000? I'm sure you'd have lots of change from $100,000. While you can't build a spacesuit for under $10 million as far as I know.
You could then last for as long as your air supply lasts.
You could even, if you have a habitat there already - potentially build new habitats by growing trees and plants using just materials in the atmosphere, and using the wood to build new habitats. It would be strong enough, easily, as the pressure is the same inside and outside the habitat.
See Will We Build Colonies That Float Over Venus Like Buckminster Fuller's "Cloud Nine"?
If you don't have a Venus habitat to stand on, then we are back to Titan again. So long as you can keep warm, again, you just need an air supply that is tightly closed enough about your face to keep out the ethane and methane, and need to keep warm. But don't need protection from vacuum. So again relatively low tech would let you survive for a longish time. Warm gear such as climbers use for Mount Everest, and air supply tightly sealed around your face, would last you pretty well. Main thing is how good the insulation is you can get.
Or if in the depths of space, well, if you don't need mobility, you need a very strong plastic bag, one strong enough to hold in tons per square meter of outwards pressure, and an air supply, and CO2 scrubber, would last you for a while.
Like one of these
Personal Rescue Enclosure
I don't know if there is any chance of getting together materials to build a low tech version of one of those strong enough to last out in space for your $100,000.
Russian 1970s idea to colonize the Venus cloud tops
The surface of course is deadly, but at the cloud tops, then the Venus atmosphere has the same temperature and pressure as Earth, and it has protection from UV radiation and cosmic radiation like Earth. You would be falling of course, but have tens of kilometers to fall and the higher pressure will mean you can hold your breath and so can survive longer.
If caught in a vacuum, in space or Mars, you mustn't hold your breath because the outwards pressure would tear your lungs. But if falling in the Venus upper atmosphere you could. You could survive a couple of minutes in a vacuum, if you don't hold your breath, though you'd be unconscious for much of it. Survival in Space Unprotected Is Possible--Briefly
If you can hold your breath, that adds an extra minute or so - however long you can hold your breath.
If you have a floating habitat to stand on, and are just stuck outside of it without protection, then your only problems are the sulfuric acid in the air and a supply of oxygen and nitrogen (for a buffer gas) to breathe.
In the Venus cloud tops, if falling, you are 50 kilometers up. Assuming terminal velocity similar to Earth, of 56 meters per second, then that's about 1000 seconds to fall ten kilometers. Or about sixteen minutes. So you would still survive far longer than on Mars or in space, even if falling in the Venus upper atmosphere.
No benefit in Mars at all as far as I can see. It's a laboratory vacuum, and anyway carbon dioxide is poisonous to humans, above the trace amounts in our atmosphere - even at the 1% level in the Mars atmosphere - though you wouldn't survive long enough for that to make a difference. You would not survive with just supplementary oxygen on Mars - no more than you would if floating outside the ISS without a suit and with supplementary oxygen. The moisture lining your lungs would boil in the low pressure.
Or - in the subsurface ocean of Europa. But the water would be at a high pressure there like the floor of the Earth's oceans, so your lungs would be crushed to almost nothing.
Titan, and a suitable level of the atmosphere of Saturn would be the right pressure and acceptable gravity - but would be too cold. Still - they might have some advantages for short term surviving over sulfuric acid. I'm not sure though.
You'd be unconscious quickly, so depends what you mean by survive. And whether you hope someone will revive you. And whether you mean heart beat stopped, or dead to the extent there is no chance you could be revived.
If the aim is to stay conscious for as long as possible, I think your best chance here is suffocating in an atmosphere of CO2 and burning through sulfuric acid. Not a pleasant way to go, but you'd survive a few minutes more I'd imagine.
But you'd be badly burnt if you could be revived. Unless you can protect yourself. Even - like a coat or something to throw over your face and hands would protect you from being burnt by the acid in the short term.
WHAT IF THERE IS A CHANCE OF RESCUE?
It doesn't really help much to survive an extra few minutes unless there is a chance of someone rescuing you. But if that is your reason, then that changes the situation a bit.
On Titan or Saturn, you'd be very cold. If you get so cold the water in your blood vessels freeze and the individual cells are damaged, then you can't be revived.
Some people have been revived however, after a long time unconscious in cold conditions. Hours certainly, and in one case, possibly for weeks, though it's not sure how he survived. Some sort of hibernation reflex possibly. If you are lucky - very lucky - that is.
If you have good insulation, nice warm clothes, and you get rescued before the ice in your cells freezes, you might have a chance. So maybe on reflection, Saturn upper atmosphere is better. You'd be falling in a hydrogen atmosphere. But as for Venus, and more so, you'd last far longer, because you can hold your breath. It depends how long you can survive your heart stopping etc.
Perhaps best though, standing on Titan? With warm clothes and good padded warm shoes. You could hold your breath, that adds an extra minute perhaps, even more if you happen to be trained in holding your breath. You should stay warm enough I think to last out your last breath of air, then collapse to the surface and maybe your rescuer gets to you in time to revive you. And with the lower gravity it is probably easier for them to land on Titan and take off than to rescue you from the upper atmosphere of Saturn.
WHAT ABOUT SURVIVING WITH A MINIMUM OF EQUIPMENT
This goes a bit beyond the original question, but it's a natural follow up I think.
With a supply of oxygen and nitrogen for breathing, for instance, an aqualung, you could survive in the Venus upper atmosphere as long as your oxygen lasts - so long as you also have a sulfuric acid resistant suit and somewhere to stand on, because if you are falling to the surface you have no chance.
Which may seem like cheating - but that is far lower tech than a 10 million dollar months to make spacesuit.
So - if you phrase it another way - where is the place you can survive for longest with the lowest cost equipment - say you have $100,000 for equipment and that's your limit, Venus wins hands down so long as you have an airship type habitat to stand on, and are caught outside it, not just falling through the atmosphere.
I have absolutely no idea how much an aqualung and an acid resistant full body suit would cost, but probably not that much - perhaps you could get it for less than $10,000? I'm sure you'd have lots of change from $100,000. While you can't build a spacesuit for under $10 million as far as I know.
You could then last for as long as your air supply lasts.
You could even, if you have a habitat there already - potentially build new habitats by growing trees and plants using just materials in the atmosphere, and using the wood to build new habitats. It would be strong enough, easily, as the pressure is the same inside and outside the habitat.
See Will We Build Colonies That Float Over Venus Like Buckminster Fuller's "Cloud Nine"?
If you don't have a Venus habitat to stand on, then we are back to Titan again. So long as you can keep warm, again, you just need an air supply that is tightly closed enough about your face to keep out the ethane and methane, and need to keep warm. But don't need protection from vacuum. So again relatively low tech would let you survive for a longish time. Warm gear such as climbers use for Mount Everest, and air supply tightly sealed around your face, would last you pretty well. Main thing is how good the insulation is you can get.
Or if in the depths of space, well, if you don't need mobility, you need a very strong plastic bag, one strong enough to hold in tons per square meter of outwards pressure, and an air supply, and CO2 scrubber, would last you for a while.
Like one of these
I don't know if there is any chance of getting together materials to build a low tech version of one of those strong enough to last out in space for your $100,000.
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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