When Apollo 17 commander Eugene Cernan flew to the Moon in 1972, he was struck by the powerful feeling of gazing back at the Earth.

"You look back home and say to yourself, 'That's humanity, love, feeling, and thought,' " Cernan recalled in my book, The Overview Effect: Space Exploration and Human Evolution. "You don't see the barriers of color and religion and politics that divide this world. You wonder, if you could get everyone in the world up there, wouldn't they have a different feeling—a new perspective?"

Astronauts have described how gazing at the Earth from space creates the Overview Effect—a cognitive shift in worldview. It offers a symbol of unity for our species. Now we are entering a new Space Age, with the goal of visiting Mars and other far-flung destinations. As humanity travels farther out into the solar system, the Earth will become, in the words of Carl Sagan, "a pale blue dot," and eventually be lost from sight.

What might be the difference between living in space while always seeing the Earth, versus perceiving it as a point of light from the surface of Mars? Some people suggest that two or more very different societies will emerge. This could be a positive step, as we experiment with various ways to survive in an unforgiving environment. It might also have negative consequences, as new forms of competition and conflict emerge.

Elon Musk and Jeff Bezos, two billionaires who helm thriving private space enterprises—SpaceX and Blue Origin, respectively—are making plans that will address this question. They share the dream of taking us off of Earth, but have publicly expressed different ideas about how to do it and why.

Artist's depiction of a pair of O'Neill cylinders. Image: Rick Guidice/NASA Ames Research Center

One vision offered by Bezos recalls the ideas of Princeton University professor and physicist Gerard K. O'Neill. He advocated free-standing space settlements housing up to 10,000 people at a stable point where the gravitational pull of the Earth and the Moon are balanced. He also suggested moving all heavy industry off the Earth to protect the environment.

Bezos, who's also come out in favor of settling the Moon, has said he supports the O'Neill approach as a way to preserve the home planet while also leaving it. "We want to go to space to save the Earth," he said at an event in Seattle in 2016. "We have sent probes to every planet in this solar system, and believe me, this is the best planet."

Musk, on the other hand, advocates creating a self-sustaining city on Mars as an "insurance policy" against some catastrophic event like a meteor strike.

"I think there are really two fundamental paths," Musk has said. "One path is we stay on Earth forever, and then there will be some eventual extinction event. The alternative is to become a spacefaring civilization and a multi-planetary species."

Bezos and Musk have the resources to make their visions real. The question is how different the psychologies of humans following the path of Musk or Bezos might be.

While flying cross-country years ago, I realized that people living in an O'Neill settlement would always have an "overview." Since there were no space settlers then (or now), I began interviewing astronauts to see if they had experienced what I called the Overview Effect.

Read More: Seeing Earth from Space Is the Key to Saving Our Species from Itself

My interviews suggested that the Effect would indeed influence O'Neill settlers of the future—those who may follow the plan charted by Bezos. But what about the changes in awareness that will occur as we settle on planets like Mars?

Nick Kanas, professor emeritus at the University of California, San Francisco, has cited what he calls the "Earth-out-of-view phenomenon," noting that those en route to Mars will see the home planet dwindle from a familiar whole sphere to a tiny object obscured by a field of stars. This takes the human psyche into unknown territory, since our species has never been farther away from the Earth than the Moon.

Kanas told me, "People living in free space near the Earth where they can view the home planet in all its glory will remain Earthlings. People who settle Mars, where the Earth is viewed as an insignificant blue-green dot in space, will become Martians."

In other words, once we leave the Earth, our identity will be shaped more by our immediate environment than our planet of origin.

Terraforming Mars. Image: D Mitriy/Wikimedia Commons

Nick Nielsen, who blogs about the advent of a spacefaring civilization, describes a "Homeworld Effect." This defines our understanding of ourselves before any human had experienced the Overview Effect, and results from the fact that our species emerged on a planetary surface and knows the cosmos initially only from this standpoint.

Nielsen points out that the shock of going into space and looking back at Earth will never be repeated when we travel from here to other planets, because we will approach them from a distance and always have an "overview" as they come into sight. Even so, children raised on Mars or other planets may experience the Overview Effect for the first time once they travel to orbital altitudes and look back at their home.

Nielsen told me, "The residents of O'Neill settlements will continue being more tightly coupled to terrestrial civilization because of the ever-present immediacy of the Overview Effect. Martian parents will indicate a point of light in the sky as Earth to their children, but their lives will be on their new homeworld, Mars."

Annahita Nezami, a counseling psychologist who recently completed her PhD thesis on the Overview Effect, argues that Bezos-style space settlers may feel more at peace, at least initially, than those who live within the Musk model.

"Space settlers still able to see the Earth are more prone to experience the positive aspects of the Overview Effect, such as interconnection, awe, and universalism," she told me. "By contrast, Martian settlers in the earlier phases of adjustment may have to contend with heightened feelings of insignificance, depersonalization, and detachment because all they love is so very far away and they have limited views of the only familiar object in space, the Earth."

Just at the moment when space exploration has provided a unifying symbol with the Overview Effect, solar system migration may foster multiple human societies. One of our tasks in creating a unified solar civilization will be to find a more expansive worldview that encompasses these diverse perspectives.