alright here's the criteria that a ben 10 exobiology post will assess:
what does the alien look like? what's under it's skin/exoskeleton/outer layer? could this be explained with earthly biological principals? how does the organism gain energy? how do their superpowers work?
there is so much diversity in forms and adaptations of life here on Earth. nearly all the aliens in the omnitrix are humanoid though because the show generally designs sentient species that way.
does this celestial object sound like it could exist? what are the conditions like? could the species in question really live here?
conditions are really important for life to flourish - on Earth the temperatures are in the range which allows for water, the perfect solvent. also the oxygen is in concentrations which are ideal for respiration of air (although not always the case). extremophile species do exist which can handle higher temperatures and anoxic conditions but these are prokaryotes, not multicellular and have looser requirements for survival. i may feel an alien may have different requirements to most life on Earth as well.
could the planet's conditions allow life to arise? would it be more feasible to have come from somewhere else?
the best working theory for how life arose on Earth is from underwater alkaline hydrothermal vents. it isn't hot enough to kill most life and the porous rock provides pockets of isolation and metal catalysts for biological reactions. The difference in pH between these and the environment allows for favourable reaction of CO2 and water to create organic molecules. through the accumulation of these and competition between molecules, living cells may have been able to froth out the vents. i highly recommend reading the vital question by Nick Lane if you're interested.
basically, i'm looking for liquid water, heat and mineralised rock in one place.
another "theory" of life on Earth is panspermia where it arrived from elsewhere in the universe on an asteroid but that just defers origin of life to a different planet.
how do we go from cells to a large multicellular organism (which all the aliens are afaict)?
i'll likely skip over the multicellularity step since that only requires advantage in colony formation and specialisation within the colony. Same for biomineralisation which is what really allows for explosion of diversity. on Earth this happened in the Cambrian after glacier meltwater enriched the oceans.
The addition of bones and exoskeletons allows for evolution of predator-prey dynamics, competition and selective pressures.
what selective pressures could have led to the rise of the morphology we see today?
if we're lucky then we'll be given some biodiversity by the show to play with dynamics, but it's likely not close to the amount we should see on a planet with multicellular life. obviously the showrunners aren't going to pump out that many designs but the only in-universe explanation would be that the dominant species drove all the others to extinction :p
how egregious is this alien in terms of plausibility? do i like them anyway?
i'm guessing most of the time this will be "it's not the worse they could've come up with" and "of course! i love ben 10!"
