Are non-terrestrial ecologies possible?

Question

I'm working on a story where interplanetary travelers occasionally have to deal with space spore contaminating their ships.  It's a very old form of life, and has spread throughout much of the galaxy.  The system from which the spore originates, therefore, shouldn't fit the traditional -mold- (Thank you, I'll be here all week!) of an alien planet.  More of a habitable nebula.

I require a rich and diverse ecology within an environment with the following constraints:

• Near enough to vacuum conditions many forms of life can survive or spend a cycle of life in empty, interstellar space.

• A large cohesive volume of without the confines of gravity, yet still have pressure gradient capable of producing liquids, solids, and gases.

• physically possible.

My original idea was to have a supermassive blackhole surrounded by a huge nebular cloud.  An entire life-filled habitat would exist within the cloud, at some orbital distance and the material.  Rather than collapse into a planet or protostar, the material remains spread across the orbital plane. The atmosphere, oceans, and landmasses can be made of anything, (hydrocarbons, tholins, etc) so long as they can exist at all.  I would allow 'shepherd planets' to keep everything in line, so long as life originates and flourishes in the nebula.  Could material in orbit attain the density required without having to aggregate?  Is such an environment even feasible?

Answer 1

The idea of an alien spore or even an entire alien creature wreaking havoc on Earthly organisms or ecosystems is very unlikely.

All creatures evolve based on the environments they are in, so the first objection is alien planets, environments or ecosystems are in fact alien, so the creatures that evolve there will have few, if any, points of similarity to the creatures that have evolved in the Earthly ecosystem.

The second objection is that predation, parasitical or even symbiotic relationships are also defined by the environments, since creatures could only have these sorts of relationships with other creatures that have evolved closely together. Humans do not catch Dutch Elm Disease, nor do trees catch colds, for example.

Finally, even the local environment has a lot of influence in how creatures will interact with each other. Replacing all the lions in Kenya with great white sharks does not mean that the sharks will become the top predators of the region. Creatures evolved in alien environments will probably not be able to survive in an Earthly environment.

I will offer one "out"; a life form which is not interactive with the alien environment. In Olaf Stapledon's "Last and First Men", the planet Mars is inhabited, but the Martians are virus sized particles which do not achieve sentience unit a sufficient mass of them have gathered. To operate effectively, they tend to coat flat surfaces to allow them to gather solar energy, while linked together for thinking. When the Martians eventually invade Earth, they are pleasantly surprised to discover so many convenient flat surfaces to gather on, without stopping to wonder where these surfaces came from in the first place....

In terms of your scenario, alien life forms which evolve in a free fall environment will have a great deal of difficulty in adapting to environments with gravitational or psudo gravitational forces at work, and will also be exposed to a high radiation environment, so the relatively weak radiation environments inside spaceships will be very difficult for them, especially if they have evolved life processes which require a constant exposure to radiation to survive. If there is any place they might be able to survive, it might be similar to the Martians of "Last and First Men", living as a coating on the exterior surfaces of a visiting ship, so long as the ship itself remains in free fall in a high radiation environment.