Obviously the definition of life is not the appropriate framing for the conversation, especially within the context of a single celled organism on mars.
I'm sure you would also concede that a spider, a mosquito, a cow, and aging family pet, or a mouse would be considered "life." We do not debate these intentional life-endings with nearly the same furor. Ironically, if you were to correlate political ideologies, the people who are against the murder of non-human-animal "life' are equally for the protection of abortion. But that's because the environmental movement is more anti-human than it is pro-earth. Tangent.
Each side of the abortion debate is trying to frame it using precisely chosen words to bolster their argument. Every single person knows exactly what the debate is about. Killing a fetus. It doesn't matter what we would do on Mars with a single cell. It also doesn't matter that a fetus can't function on its own. Debate the issue, not the semantics.
And in case it seems like I'm waffling, I'm personally against all abortions that aren't for rape or health concerns for the mother or child. However I concede, as an atheist, that my views are based on a personal analysis of humanity and not some magical graybeard in the sky telling me what to do. In such instances where the population is clearly split, the tie goes to the citizen. So I would make abortion legal up the the point of viability (currently hovering around 22 weeks, so let's call it 25 for now). After viability only serious risk to the mother or child would be ground for an abortion. A middle ground solution to a deeply divided issue.
But like so many conversations in American politics today, we now spend more time talking about the semantics of the issues than the issue itself.