We're thinking about this all wrong.
There probably isn't life on our other planets, but what if there could be?
We should be colonizing them. Not with humans, of course. That would be silly, we're far too complicated. Just colonize them with life.
Bacteria, tardigrades, radiophilic fungi.
Smear it all over the solar system.
Individual species are fragile, but life per se is wily and infinitely adaptable. Start simple, then let it evolve out there. It'll find and exploit those alien niches.
That's what we (as life) do.
Our run as a species will eventually be up, the Earth will turn, geologic time will heave and sigh, mother will slowly sequester our mistakes.
Then, when whatever evolves to replace us begins looking up, perhaps someone will be there to look back and wave.
So let's appropriate the planets. Infect them. Aggressively.
Make our mark.
After every other evidence of our existence has passed, this one monument will remain.
Humanities final fingerprint, cosmic graffiti, the ultimate "we were here." This isn't about science, at heart. Nothing we as a species do ultimately ever is.
It's an art project.
One that makes the great pyramids look like a trapper-keeper doodle. One fit for our spot at the apex of our own long history. This would be the most massive and most fundamentally human thing to do. Ever.
And we may just have time enough left to make the attempt... release the spores.