Early explorers risked their lives to reach the ends of the world, but not purely for the advancement of mankind. In reality, their bravery was motivated by one very powerful prospect: the possibility of wealth, be it treasure or land.

Today, Mars is our land beyond the horizon — a territory that can only be reached by plunging off the edge of our flat, incomplete map. But just like setting sail to the unknown West, sending a human to Mars is enormously expensive, not to mention dangerous, perhaps even deadly.

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But even with the clear risks, people are sinking millions into private Mars colonization projects. Will they eventually pull a King Ferdinand and claim Martian land as their own?

One Treaty That Holds the Cards

"There aren't really any laws that have been tested and widely adopted with respect to extraterrestrial land ownership or even ownership of the stuff that we bring back," says Andrew Rush, a space lawyer who regularly works with emerging aerospace companies.

Rush says the most applicable piece of law we have regarding real estate outside of Earth is the Outer Space Treaty, which has served as the basic framework for international space law since 1967. More specific, Article II of the treaty addresses claiming ownership of extraterrestrial property:

Outer space, including the moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means.

However, Rush tells Mashable any attorney could poke holes in the Outer Space Treaty because there are a lot of loose ends. It all comes down to vague phasing, starting with the term "celestial bodies," which isn't defined.

"The question is what is a celestial body? Is it a tiny asteroid? Does it include Mars? That's an open question," says Rush.

The second phrase that stands out is "national appropriation." To understand why, you must first put the Outer Space Treaty into context: It was written and signed before man ever went to the moon. The main reason for its creation stemmed from fear that the United States would plant a flag on the moon and claim ownership. The treaty was an effort to avoid fighting over territory.

"When considering both the literature and the time surrounding the formation of this treaty, it's pretty clear that they weren't trying to exclude private ownership," Rush says. "It was addressed towards government bodies."

However, Bas Lansdorp, head of private Mars colonization venture Mars One, disagrees with Rush's translation of Article II.

"As far as we know, which is confirmed by our experts, it is not possible to claim ownership of Mars land. Article II of the outer space treaty forbids appropriation," he tells Mashable via email. "What goes for governments also goes for individuals in those governments."

Although Lansdorp intends to send humans on a one-way mission to Mars in 10 years, he says that doesn't mean he will own the land. After all, "colonization" implies populating, cultivating and sharing a territory.

To illustrate his point, Lansdorp points to Dennis Hope, an entrepreneur who claimed ownership of the moon, then in 2009, maintained he had sold more than 2.5 million one-acre lunar plots for about $22 each. Hope said the Outer Space Treaty — which is quarterbacked by the United Nations — did not apply to him because he was an individual, not a country.

Hope, who heads the Lunar Embassy Corporation, then went on to establish his own Galactic Government, complete with a constitution, congress and its own currency. He fought to receive official recognition and argued that because the Galactic Government was not part of the UN, any agreements regarding the moon were irrelevant. So far, he has not been successful.

"The position of the Galactic Government is that we're not trying to distance ourselves from other governments. We just want recognition so we can work together," Hope told National Geographic in 2009.

When it comes to the moon, another piece of law called the 1979 Moon Treaty creates much more red tape for lunar entrepreneurship. The stringent treaty explicitly excludes national and personal ownership of the moon. But there's a catch: Only 15 countries have ratified it, and none of those are space-faring nations.

"It's like a landlocked territory dictating how a coastal territory uses its port," says Rush.

"But We Were Here First!"

It isn't entirely fair to equate future Mars explorers with Hope, who has never been in orbit, let alone set foot on the moon. If Hope had poured money into a successful trip to the lunar surface, he may have had a better case. In theory, that same notion applies to private Mars colonization projects.

However, Tanja Masson-Zwaan, deputy director of International Institute of Air and Space Law and one of Mars One's legal experts, says the law won't bend, even for someone who does complete a successful Mars mission.

"Landing there does not change anything. States cannot appropriate, neither can their citizens," she tells Mashable via email. "It would be too easy to say, 'My government cannot use a nuclear weapon, but I as a citizen am not bound by any treaty provision that my government accepted, so I am free to do as I like.' This argument simply does not fly."

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If all goes according to plan for Lansdorp and his Mars One venture, a group of at least 30 humans will settle on Mars in 2023. The colony will expand every few years as another group arrives to spend the rest of its participants' lives on the Red Planet. And as that settlement grows, more and more Martian land will be used.

As Earth's own colonization history has proved, placement and subsequent expansion of a settlement has essentially led to ownership of that land. But Lansdorp disagrees.

"It is allowed to use land, just not say that you own it," he says. "It is also allowed to use resources that you need for your mission. Don't forget that a lot of these rules were made long ago, when a human mission to Mars was not within reach."

Regarding resources, Lansdorp doesn't have concrete plans to send a return flight home with Martian matter, due to cost and technological constraints.

"Even if you would find a solid rod of gold or a big diamond, it would cost more to ship it to Earth than you would make selling it," he says.

Mars One operates as a non-profit entity, and the money raised will be used to fund its $6 billion mission. However, Lansdorp says if Mars One can sift through the regulations of sending materials from Mars to Earth, he may be interested in bringing home Martian rocks "for research, but also for our business case."

"Imagine how many people would be interested in a grain of sand from the New World!" he says. In that case, Lansdorp, who maintains that Mars One will not work with federal agencies in order to avoid politics, says he'll make those materials available — but not for free.

"Any research institute, including NASA, would be able to purchase parts of what we bring back to Earth," he says.

The Apollo program set a precedent that would make this possible. When astronauts brought back samples from the moon, the U.S. government entered into a bilateral deal with the USSR to share those samples (albeit without a fee, in the name of science). That agreement established if you go to a celestial body and dig something up, you can claim ownership.

"But that doesn't mean if you land on a planet you can claim the entire body," Rush points out.

If the mission is a success, the allocation of resources and colony expansion won't be an issue for Mars One in the beginning. The trouble will come when follow-up private ventures land on Mars. In that case, we can only assume that territories of some kind will have to be established.

"Let's see that when we get there," says Masson-Zwaan. "I assume at some point these settlers will become more and more detached from Earth, and will live by their own rules. I am not in favor of putting everything in stone too long in advance."

When that time comes, Rush says these settlers will have a strong voice in a courtroom on Earth.

"At the end of the day, if you put the money together to land on Mars, the law is unclear about whose law applies to you," says Rush. "It's sort of a Field of Dreams mentality. In this case, you're probably going to have your way when it comes to law."

Image by Mashable, Bob Al-Greene