i am currently working on a CG Short for my Portfolio. It takes place in a Binary system and just tells the Story of a Pilot on one of the Planets.

Anyways, my question for today is how we could expect life to be on both Planets. Some data for context:

The Binary system consists of Hela and Vesna. They Orbit each other at a Distance of 40536,252km with a Orbital Periode of 14,9hr. The Orbit itself is, for all intents and purposes, circular. Meaning that there no tidal forces from one Plant to the other. Which of course also means they are locked to each other.

Hela has a Radius of 5636,492km and a Surface Gravity of 8,68m/s². The Atmosphere is Co² Rich and Dense. Around 60% of the Surface is covered in Oceans. The rest of the Planet´s Surface is mostly covered in "Jungles" with some Deserts scattered inbetween. The Life on Hela takes 4 Forms. Vertebrates which are almost exclusively Airborn, Invertebrates which dominate the Surface and the Oceans, then we have Plant life and lastly Placeholder Name. The idea for them is that they are Planets but also not really. A Combination of Plants and Animals.

So far so good

Vesna has a Radius of 7457km and a Surface Gravity of 11,51m/s². Her Atmosphere is very Similar to Hela´s but less Dense. When it comes to Gases, Vesna has more Oxygen then Hela. 78% of the Planets surface is covered in Oceans. The rest is of the Surface has a lot of very high Mountains. Meaning there are almost no Flat planes.

And now we come to the question, finally. How could the life look like ?

As far as i understand it, if one Planet has life, the other one will have it too. Now the Evolution can still be different. The Atompshere is different, the Gravity and Geo but just how similar would the life be ? Can i go all Crazy ? Or could it be that duo to constant Matter exchange between the Planets (be to throw Asteroids or whatever) the general Evolution on both stays the same ?

Thank you very much for your answer !

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    $\begingroup$ You may call it "constant matter exchange," but I call it "mass-extinction-causing bombardment." The dominant life on both might resemble bacteria or algae, possibly animals as large as corals if protected by the sea, as larger forms keep getting killed off by the side-effects of those pesky matter exchanges. $\endgroup$ – user535733 Sep 16 at 0:17
  • $\begingroup$ if one Planet has life, the other one will have it too There's no scientific basis for that idea - certainly not observation and as we have no observations, no accepted theory. $\endgroup$ – StephenG Sep 16 at 0:27
  • $\begingroup$ @StephenG -- Since we know of only one planet that actually has life, I'd say your position has no basis for acceptance. We're told that this is a double planetary system with life on both worlds. That's a given. It's our job to apply reason and creativity to coming up with an answer. Remember, folks: this is Worldbuilding! $\endgroup$ – elemtilas Sep 16 at 0:44
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    $\begingroup$ @StephenG, i get that this may seem a bit much in terms of assuming things. My reasoning is that the Planets are really close and, when they formed, had moons. So for a long time, big Impacts where nothing out of the order. So the moment one planet Sparks life, the other one gets it eventually. Think about how much ash a single erruption can put into Orbit. And with a 2nd planet not that far away a larg enough event could bring life from Hela to Vesna. This would however take its sweet time. So we might see that one planet has a delayed evolution ? $\endgroup$ – Erik Hall Sep 16 at 1:25
  • $\begingroup$ @elemtilas The OP is the one linking the life on one planet to the other with the word "...if...". I'm simply pointing out that this rational has no scientific basis. Your first sentence seems illogical to me - having only one planet as an example surely means we cannot have any way to accept a theory as to what happens when we this scenario. Does life evolve on each independently (not unreasonable, IMO) or somehow transfer from one to the other - seems less likely to me ? $\endgroup$ – StephenG Sep 16 at 1:54