[opportune]

>It's pretty much our only opportunity to see if life emerged twice in the same planetary system under similar conditions.

Well there's also Titan, Enceladus, and Europa right? Titan is by far the most exotic but it could serve as an example of what happens when life evolves under a radically different environment. It has some complex organic molecules there and a very interesting/varied geology and topology. Enceladus and Europa could exhibit very similar conditions to those of the deep sea on Earth as well, which could very well be where life originated. Also at one point even Earth could have became a "snowball" planet and still able to sustain life: https://en.wikipedia.org/wiki/Snowball_Earth