Lot of dismissive reactions to these questions, but there actually are non sound related signals we use to detect submarines and there is absolutely research on how to do that from space. This article is great, but just read the "Signal Processing" section if you're interested in space. https://www.aspistrategist.org.au/prospects-for-game-changer...

Not sure if they are, but I do know that the US Navy funded a lot of oceanographic research into predicting and understanding bioluminescence of marine organisms for this very reason. The surface waters of the North Atlantic have massive spring blooms of phytoplankton, which are sometimes bioluminescent, and could certainly give away the presence of a large subsurface vessel, possibly from space.

They're hardly detectable from Earth.

next time you're out on the open ocean check how far down into the water you can see, and then check out this graph [0] of electromagnetic radiation absorption of water: visible light is the best case scenario.

there's a reason sonar is acoustic and not light based

[0] http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.h...

I won't say modern submarines can or cannot be detected from space, but this should give you some ideas about what is publicly known: https://duckduckgo.com/?q=spotting%20submarines%20using%20ma...

This is fairly open secrets to the degree that it is secret at all so it probably also is no big secret that passive and active countermeasures are used to prevent these techniques.

The US Navy has researched the possibility of detecting shallow submarines from space since at least the 1990s by looking for subtle wake turbulence on the surface. The results are classified so we don't know if they were ever successful. It's not completely impossible, but the signal to noise ratio would be extremely low.

Any detection from space would have to use an optics system to detect light bouncing off the submarine. This light could be either the naturally occurring visible light, or some form of active system (probably emitting radar waves). Unfortunately light can't penetrate very far into water, so this idea is a non-starter. Light can barely make it 200m into the ocean (meaning 100m depth for light to make a round-trip and back for detection), and subs can go as deep as 300m.

Any satellite-based detection system would have to rely on catching the sub while on the surface. I'm positive this is being attempted constantly, but catching a sub at depth is an entirely different manner.

Using what technology? I can imagine in some future there being the means, but I find it hard to believe we have that level of tech available to the sort of packages we can aloft into orbit now.

That's not a bad question.

Subs would be detectable using magnetometers, except that they have electromagnets in them to hide their magnetometer footprint. Still, this is not perfect.

Large subs have somewhat detectable gravitometric footprints that could be observed from space, indeed.

Let's hope not - that submarines carrying nuclear weapons are undetectable is the only thing that's keeping the major powers from going to war.

Why do you think they would be detectable from space? That doesn't make any sense.