Now then:
Currently, the goal of most space agencies around the world is to colonize Mars. The surface of Mars, as far as we can tell, is an arid wasteland devoid of life, ripe for colonization by Humans. There may be water underground, but right now we think it's safe to assume that there's no life there.
In the solar system, there are a few moons that are considered prime candidates for life. There are the moons that are believed to have sub-surface oceans; Ganymede, Callisto, Europa, and Enceladus, and then there's Titan, the only moon in the solar system with a thick atmosphere.
Now, according to NASA, the next best place to colonize after Mars would be Callisto. But before that, we will likely send a probe there to explore it's theorized ocean like we want to do with Europa. My question for you all is, if we find life there, should humans colonize it, or should we be forbidden from doing so? Lets face facts, if we don't destroy ourselves, eventually humans will develop the means to travel between worlds in a small amount of time. If we find life anywhere in the solar system, do you think humans should make that moon or planet a protected zone where nobody can land, or should we disregard the alien life and colonize it? Mars wont be able to satisfy us forever, after all.