It’s time to go Scientologist on Mars and send bacteria life there to get started. By slowly creating Mars conditions in the lab we could evolve something that could thrive. Possibly Mars did just that to Earth before their SUV emissions destroyed all Martian life.
I have long thought this was a rather cool idea.
If you could get a bacteria to grow in ‘Martian’ conditions - the question would no longer be “Is there or was there ever life on Mars”; it would be “Do we want there to be life on Mars?”.