How many lifeforms there are like Jenova, whether the creature ever encountered as much resistance as on FFVII's planet -- or, indeed, whether Jenova had ever attacked another planet successfully -- are all questions I'd rather not see answered.
As with the alien in John Carpenter's "The Thing" (which Jenova seems to be based on), the mystery is infinitely more creepy than the facts could ever be. The prequel to that movie almost killed some of that with showing us the inside to the creature's ship, but I think it stopped just shy of touching the untouched corners that should not be touched.
And I assume the meteorite that Jenova arrived on was the husk of a planetoid she had her way with? I don't know if that was ever explicitly stated besides Sephiroth attempting that very thing in Advent Children.
This has always been my thought. Either this or that Jenova is an Omega-like lifeform, and was just doing what the Phantom Gaia tried to do to Earth in The Spirits Within after it arrived on debris from its homeworld.
I don't think Jenova's like Omega. It's been stated that she's a parasite. Even at it's worst, the Planet has never been shown to consume anything. If anything, it gives life more often then it takes it.
To another planet, however, what would an invading Omega or Gaia be but a parasite?
FFIX's dying world of Terra survived by literally eating other planets, Lifestream and all. When it encountered a planet too strong to eat in a direct fashion (Gaia), Garland set about weakening its cycle of souls via the Iifa Tree so as to allow Terra's spirit to become strong enough to consume the other world's.
Similarly, in The Spirits Within, the Phantom homeworld's Gaia was consuming Earth's spirit one piece at a time via its inhabitants, converting their energy into its own until it became strong enough to directly infect the Earth's own Lifestream. That's almost exactly what happened in FFIX, and is exactly what Sephiroth was doing with geostigma.
So, yeah, I don't think there's necessarily a difference between Omega and a parasite once you get offworld from the planet where the Omega originated.
Obsidian said:
Keep in mind that the Omega we see in DoC is not the true Omega the way it's supposed to be formed. Omega is only supposed to be formed when a large amount of life dies unexpectedly. It's real purpose is to take the Lifestream (mako) from the Planet (the rock) if the Planet can't support the Lifestream, otherwise, it doesn't have a reason to even form. It seems logical to me that the ideal situation for Omega would be to find a Planet that doesn't have a Lifestream force attached to it, in order for the Lifestream to begin functioning normally
Would the planet be so kind? It doesn't even care about its own inhabitants beyond the overall survival of the cycle of souls system, so why would it care about another world's inhabitants? Terra didn't. The Phantom homeworld didn't either.
Obsidian said:
Jenova on the other hand, need life (a Lifestream) to feed off of in order to get more energy to travel through the stars. She doesn't have an internal cycle the way the Lifestream does.
While possibly true, this hasn't been confirmed in canon. For all we know, if Jenova were another planet's Omega, she could have been doing exactly what she was supposed to in order to establish herself/her dead world at the center of a new cycle of souls -- just as Sephiroth intended to.
I do think there's a case to be made for Jenova sucking up Lifestream given her similarities to Sin, which was constantly sucking up ambient pyreflies, but -- unlike Sin -- I'm not convinced that Jenova wasn't trying to *become* FFVII's planet, just like Sephiroth ultimately tried to do once he (quote from his 10th Anniversary Ultimania profile) "inherited Jenova's will to destroy/rule the planet."