My question is: would there be any special or unusual technical challenges to performing Scuba or deep technical diving in one of these oceans or seas? Assuming the diving technology, for the sake of the question, was roughly equivalent to what we have available today.
I’m a naif when it concerns the subject. But the issues I can at least imagine might be relevant would be A) lower gravity, B) water pressure (I have no idea how much this would be effected by gravity, different atmospheric pressure, etc), C) composition of the water itself, with the salinity levels different from Earth sea level, depending on how the world was terraformed, and for how long, D) atmospheric pressure at “sea level,” and even atmospheric composition, which might be at least different, depending on the methods and goals of terraforming),
Like I said, I’m a novice, and I know but that I know nothing. Can anyone enlighten me?
The simple question would be - what are you breathing?
Here we generally breathe an oxygen-nitrogen mix. (Deep sea divers IIRC use helium mix instead). At a certain pressure, depressurizing too fast the nitrogen forms bubbles that can cause painful joints, embolisms, and other fun facts. (In one of Tom Clancy’s novels, the protagonist tortures someone by putting him in a pressure chamber and then releasing pressure). At a certain level, nitrogen becomes toxic (nitrogen narcosis) so that puts a definite limit on normal diving. On Mars, unless the atmosphere has been magically transformed, you can (must) put whatever mix you chooose in your tank. Plus, the atmospheric pressure on Mars will be a factor too. IIRC, at one point, (Apollo?) the capsules were going to be 5psi but pure oxygen, no nitrogen. Our bodies can only tolerate a certain level of oxygen pressure too.
I presume one of the fun facts would be that at 2/5 earth gravity (actually, 38%), the pressure would not increase as rapidly with depth. Rule of thumb IIRC from long ago scuba lessons, here on earth pressure would increase 1atm/33feet. So on Mars presumably that would be 1atm/87feet. (1atm is about 14.7psi) All those scuba tables about when to stop to decompress would apply at 87-foot intervals I suppose.
Another factor is the recommendation is not to fly - ie. get to even lower atmospheric pressure - for 24 hours after. On Mars, even with terraformed atmosphere, unless we pull off a major miracle, our Mars inhabitants will probably be wandering from one closed environment to another and maintaining approximately the same pressure will be an issue.
At any given depth, water pressure is proportional to gravity. More precisely, water pressure is depth times the gravitational field times the density of water. More precisely yet, you also have to add on atmospheric pressure, but at any significant depth, that quickly becomes irrelevant.
Of course, on Mars, you might well be diving deeper, both because you can (pressure is mostly what limits dive depth, here on Earth), and because Mars has some seriously deep terrain features.
Martian seawater probably would have a different mix of salts than Earth (depending on the terraforming process, of course), and that would in principle mean a different density, but probably not a very large difference in density.
It would be interesting how far one could safely go. Going deeper means going further, which needs more air if one traveled at the same speed. But one should be able to decent and accent faster considering the change of pressure is much less. In diving you are suppose to go up or down slowly due to changing pressure, and also it becomes uncomfortable or even painful to change depths too quickly. However on mars I suspect it would be far easier to do, so in diving quick descents and accents may be the norm, and perhaps even swimming down (as there is not much gravity to assist). On the way up there is less buoyancy too, so swimming up may be a thing there.
So one can go deeper, and humans being humans will do so, though OTOH it may be difficult to go down fast after all, and likewise may be hard to go up fast, which would require more air, or less time at depth. IDK which would be a bigger factor.
The risk I see is it’s going to take longer to come up from a deeper depth, And perhaps inflation of a buoyancy device won’t get you that speed boost you were hoping for so air management could be a larger factor, as well as keeping a good energy level for a more rapid accent.
The pressure is of course relevant to the weight of the water above - 15psi is the weight of 15 pounds of water in a 1"x1" column. On Mars you can go 2.6 times deeper. So if the effecive depth you can dive on Earth is about 200’ then perhaps on Mars, about 520’.
I forgot about the salt factor. That can add significantly to the weight of the water, as anyone who has floated in the Dead Sea can attest. (You start to float when when you are about mid-chest deep) That would make the maximum depth less. However, as I can tell you about the Dead Sea - you do NOT want to get the water in your eyes. It stings like crazy.
One alleged danger of Mars 9and the moon) is fine dust. Assuming this is composed also of some salts, the dust would blow into the open oceans and help get them to high salinity if the local ocean floor was not enough.
500 feet is a long way down, but I doubt it would take significant time to return to the surface directly. The major time delay would be decompressing, and that time with normal 80% nitrogen air supply, would be the same times and stop points (times 2.6) as diving on Earth to 200 feet. You can probably change this with a different mix (less nitrogen) but there’s also the limit of oxygen pressure too. I’m assuming “scuba” like on Earth means you are experiencing the ambient pressure of the water around you.
One other issue is the nature of Martian regolith [soil cover]. Our oceans have sparkly white, yellow or darker sand because of aeons of water action, which removes finer particles and leaves grains of a minimum particle size. Turning a rift valley into a sea will release silt and clay-sized particles which will remain in suspension for very long periods [prob longer than Earth without tidal effects to drive water sorting].
You are likely to have thick water with negligible visibility for a decade or more. Until that silt and clay flushes out of the system you are unlikely to get good conditions for the first stages of aquatic life. So while you could go scuba diving, you could just put a bucketful of soil from your garden into a full bath and stick your head in for a similar experience.
One issue might be the boat the diver is diving from; as I understand it in low gravity waves will be larger, so the boat would need to be designed to handle rougher seas than average on Earth. Also it would make getting on and off the boat itself more difficult and dangerous since it would be moving so much.
But presumably in much lower gravity, the boat’s motion (and waves) would move slower because the force (gravity) pulling waves and floating object back down is less.
Sort of like how the astronauts on the moon appears to be hopping in slow motion.
With lower gravity and therefore lower pressure at different depths than on earth, you ought to be able to snorkle at greater depth than on earth.
As I’ve noted before on this Board, I tried snorkling in my pool as a kid and was surprised at how rapidly the pressure increased with depth. With Martian gravity, though, you might be able to practice that trope of breathing through a tube while completely submerged that people use in so many old movies.
The recreational dive limit on Earth for air-breathers is 130 feet, so figure about 340 feet on Mars.
I’ll note that divers would probably have lighting issues. For starters, Mars is 1.5X farther from the sun, so only gets 44% as much solar flux at the surface. I’ve been down past 100 feet here on Earth, and can say that with decent water clarity, there’s enough light to see around you pretty well. But if you’re 100 feet underwater on Mars, you’ve got a only 44% as much light to work with, so you’ll probably want a flashlight or two. And if you’re 340 feet underwater on Mars, it’s gonna be real dark: you’ll have less than 0.5% of the surface light down there, so less than 0.22% of what you get on the Earth’s surface.
The depth of the water not only affects the colors of light that are noticeable underwater, it also affects the intensity , or amount of light. Within the first 10 m, water absorbs more than 50 percent of the visible light energy (Fig. 9.9). Even in clear tropical water only about 1 percent of visible light—mostly in the blue range—penetrates to 100 m.
Needing a flashlight isn’t an issue. I’ve been on dives on earth where due to cloud coverage, latitude and season there was not very much natural light at hte surface and nt great visability meant that below 20-25m it was essentially torch light only. Lots of people also go cave diving.
I would go back to md-2000’s question, what are you breathing?
Lower gravity means lower atmospheric pressure. We need Oxygen to be at a partial pressure of about 0.16 to 1.4 / 1.6 to breath safely. To survive on the surface we would therefore need the “air” to be at least 50% O2. 56% would give us the 0.21 bar partial pressure we are used to.
If we dive 56% Oxygen the maximum depth we can go and keep the partial pressure below 1.4 bar would be 57m (186ft) the same as on earth. We could dive deeper with a gas with less oxygen but we would also need to carry a seperate bottle with enough oxygen for shallow depths.
The 130ft recreational limit to diving is not due to oxygen pressure below 130ft the time you can stay down without needing to do mandatory deco stops becomes to small for a dive to be feasible. The risks of narcosis causing dangerous behavior also increases but many divers do go 160ft or more on air (with deco stops)
NDL as set by the Partial pressure of Nitrogen in the breathing gas, if on mars we are breathing 56% Oxygen that become much less of an issue.
For Narcosis if we are breathing an N2 / O2 mix you would get a similar effect on Mars at 260 ft as on earth at 100ft.
In fact would we be breathing any nitrogen at all? If we were breathing an Oxygen Helium mix NDL times would increase enormously. As Helium has virtually no narcotic effect this would increase the maximum depth (providing you reduce the oxygen percentage as you go deeper otherwise you would be limited to about 56m due to Oxygen toxicity)
Note: I am a recreational diver with a tiny bit of knowledge of technical diving so a technical diver might be able to explain better or even correct some of the things I have said
I’ll have to dig out my copy of Stephen Dole’s Habitable Planets for Man. I believe he gives a few charts of acceptable partial pressures for oxygen, nitrogen etc. and describes the basic effects of too much partial pressure.
No doubt there are plenty of cave divers out there, but I suspect the average earth-bound recreational scuba diver has not invested in a flashlight that’s rated for the air-breathing recreational depth limit. On Mars, just about every scuba diver would need a flashlight.
I am not sure about who the “Average” earth bound recreational diver is but most recreational divers will at least have used a flashlight while diving. Many recreational divers have not invested in essentials such as a tank and regulator but instead hire them when they need them so investing in is quite a high hurdle.
I would suspect the large marority of qualified scuba divers will have done at least one night dive where if they do not own a flashlight they would hire one.
A significant number of recreation divers dive where visibility isn’t the best places like the UK coast and a flashlight is essential to make sure you do not lose your buddy.
Underwater photographers, at least the more serious ones have lighting rigs to illumiate their subjects and enhance their vibrancy (Colours are all very blue underwater as longer wavelength colours disappear after a few meters)
Even if a flashlight isn’t essential it can enhance the dive, lots of creatures hide in holes in the rock or in the shadows without a flashlight you are likely to swim past without noticing them. I take a torch on all by dives for this reason.
