Colonizing Mars is often talked about in the context of preventing the extinction of humanity. This has led to the unfortunate misconception that colonization results in the abandonment of Earth. I’d like to take the time to explain why this doesn’t happen.

Before we explore just why Earth wouldn’t be abandoned, it will be useful to review the extinction risk argument for colonizing another planet. The argument starts by noting that out of all species to ever live on Earth, 99.9% have gone extinct. It then goes on to point out how most of these extinctions occurred in planet-wide events called mass extinctions. Thus, establishing a species on another planet would be a good way to increase its chances of survival. If a cataclysmic event wipes the species off one planet, it is simply a matter of waiting for the dust to settle before reintroducing them from the other planet.

One detail of this plan is extremely important: so long as no such event has occurred, it is essential that the species be well-established on both planets. Once the species is wiped off one planet, it becomes as vulnerable as it used to be until its presence on that planet is restored. Abandoning the species’ home planet in favor of a newly colonized one thus completely fails to increase the species’ survival rate.

The misconception stems from the idea that once Mars is colonized, Earth will become unnecessary to the survival of the human race. Since the end of humanity on Earth no longer means the end of humanity, we are free to abandon it whenever we want. But this ignores that the whole purpose of colonizing Mars was to have two planets instead of one. Mars may be essential to the plan, but so is Earth.

But won’t having Mars as a backup mean we put less effort and resources toward preventing a catastrophe on Earth? No, because there will still be plenty of people living on Earth, and their lives will be as valuable as ever. Humanity will be wiped off the face of the Earth only if no way exists to prevent it.

However, if Mars is colonized, then Earth can actually be re-inhabited, given enough time. Therefore, colonizing Mars is actually the opposite of abandoning Earth; it is a means by which to remain on Earth. That is why many people see it not as the abandonment of our home, but as an important step to take for protecting both it and humanity.