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A new class of life-friendly exoplanet? The Hycean ocean world.


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https://www.cam.ac.uk/research/news/new-class-of-habitable-exoplanets-are-a-big-step-forward-in-the-search-for-life

 

https://arxiv.org/abs/2108.10888

 

https://www.cam.ac.uk/research/news/large-exoplanet-could-have-the-right-conditions-for-life

 

Hello.  :)

 

The above articles caught my attention lately and set me thinking about how intelligent life might evolve on these ocean worlds.  Here are my thoughts.

 

 1.      The Oxygen Problem. 

 

Given that electrical discharges (lightning) are common to planets in our solar system with radically different atmospheres it seems likely that Hycean weather systems will also have storms and lightning.  Venus has a carbon dioxide atmosphere and powerful lightning displays.  Jupiter and Saturn both have atmospheres of Hydrogen and Helium, plus a smattering of other gases and lightning too.  But free, gaseous oxygen is notably absent from all of these planets in out solar system.  The problem with oxygen is that when mixed with hydrogen and exposed to electrical energy an explosion is the inevitable result.  Think of the Hindenburg disaster.  So, would a process like evaporation on a Hycean planet release sufficient oxygen into the hydrogen / helium atmosphere to cause the risk of massive explosions?   Any chemists want to comment?

 

2.     Marine Mammals?  Probably not.

 

Aquatic intelligence on Earth seems to be dominated by marine mammals; dolphins, porpoises, whales, seals and sea lions.  But there seem to be two reasons to argue against this happening on Hycean water worlds.  Firstly, all marine mammals are air breathers who must come to surface to inhale oxygen.  But if there is no free oxygen in the hydrogen / helium atmospheres of Hycean planets, then aquatic animals in these oceans would be obliged to take in their oxygen via gills or some similar method.  The second reason is that on Earth aquatic mammals evolved from land-based mammals which took to a sea-going life later on.  But Hycean planets have no solid land at all and oceans that could be dozens or hundreds of miles deep.  Therefore, that evolutionary pathway could never occur.  If intelligence did arise in the sea life of these planets it could not be mammalian as we understand mammals.

 

3.     Material technologies?  Unlikely.

 

Given the absence of continents, islands or any kind of solid land, Hycean planets have all of their minerals stored under dozens or hundreds of miles of water.  So, if intelligent aquatic life were to try and develop any kind of physical technology, they would have very limited options indeed.  The oceanic ecosystems we see on Earth rely on the interplay between the land and the sea.  Nutrients from the land are delivered to the sea by rivers and coral reefs require solid surfaces upon which to grow.  Neither of these are possible on Hycean worlds.  There is no land and any solid surfaces are, at best, dozens of miles deep, far from the reach of sunlight and the possibility of photosynthesis. 

 

On the other hand, unless the terrific pressures of a hundred-mile deep water column prevent it, I don't see why hydrothermal vents couldn't populate the ocean floor of Hycean planets.  We seem to have detected the possibility of hydrothermal vents under the ice-covered ocean moons Enceladus and Europa that orbit Saturn and Jupiter, respectively.  But could the nutrients and minerals brought up from these vents find its way from these abyssal depths to the shallower, near-surface regions of the oceans?   That seems like a big ask, given the distances and pressure-changes involved.

 

On the surface, there could be drifting colonies of sea creatures which seaweeds, sponges and corals (or their equivalents) could attach themselves.  But if the raw materials for these colonies themselves didn't come from the ocean depths, then they would have to come from the bodies of other sea creatures found in the uppermost few layers of the oceans.  There seems to be little evolutionary benefit in having to dive a hundred miles from the surface to bring various materials back up from the depths.  The problem of having to adapt to the immense and crushing pressures is another massive hurdle to be overcome.  Could an organism that lives on or near the surface really cope with such changes?  I realize that Sperm whales do this, diving to a depth of 3,300 feet in search of squid.  But on a Hycean ocean planet we aren’t talking about diving to less than a mile – we are talking about diving 126,720 feet if the ocean floor is 24 miles from the surface.  And that's an optimistic estimate, given that Hycean oceans could be hundreds of miles deep.

 

Of course, given the diversity and adaptability of life that we see on Earth, I could be limiting what life is capable of on other worlds.  Perhaps I'm being too unimaginative or too pessimistic.  What do you think?

 

Thank you.

 

Walter.

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  • 2 weeks later...

It's still all Cool stuff with future possibilities for us.

 

I see two problems. One is that bigger planets are harder to escape from and go out and about, and planets that are more than 10.000 light years away will take 20,000 years for any back-and-forth communications with us based upon speed-of-light communications. Closer exoplanets  would be much better --the closest possibilities being about 4 light years away.

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