I can't recommend "The Vital Question" by Nick Lane enough for people who are really interested in the question of life elsewhere. It does such a wonderful job of show how mechanically "life" can be started as a way of simply reacting chemicals to a lower energy state. It neatly ties together biochemistry and geochemistry in a very plausible (and testable) way.

Given the analysis, I would expect that bacteria and archaea, are present on any world with liquid water and a threshold amount of heat. Which would include Mars, Europa, and probably Io as well. There are a number of forms of bacteria living in the ionosphere which could be dropped on to Mars and they would do just fine there.

The odd bit comes from the origin of eukaryotes. Which, according to Lane, might arise if archaea were endosymbiotically living inside bacteria. That works but he doesn't offer any suggestion of what caused it to happen the first time. And he makes a reasonably good case that what ever it was that caused it, happened exactly once in the 4+ billion years of the planet and 3+ billion years of bacterial life roaming around.