Recently, Elon Musk, founder of SpaceX and prolific tweeter, has tweeted that he expects one hundred thousand people to travel between Earth and Mars when the two planets are closest together in the effort to make human life multiplanetary. The journey, however, will not be cheap, with expected costs anywhere from $100,000 up to $500,000. To pay for this journey, Musk suggests taking out loans, to be paid for by employment on Mars. As Business Insider points out, critics of the plan see it as approximating indentured servitude. A scheme relying on indentured servants would be in violation of the U.S. Constitution and law. SpaceX, however, might argue that U.S. law does not apply on Mars. After all, SpaceX’s Starlink service, which provides satellite internet, has asserted in its Terms of Service that “no Earth-based government has authority or sovereignty over Martian activities.” This begs the question: Who, if anyone, has legal jurisdiction over a Mars colony?
International law, as well as U.S. law, make it clear that Mars, even though no human has yet set foot on the planet, is not a lawless place; this area of law, however, is not fully defined and complications will need to be addressed if, and when, humanity becomes interplanetary.
The Outer Space Treaty of 1967 (or OST), some experts have noted, forecloses the idea that the law governing the nations of Earth does not apply to Mars. The OST, as Article I of the treaty states, specifically deals with “the moon and other celestial bodies,” a classification which Mars unambiguously falls into. Outer space, according to the treaty, is “the province of all mankind” and to be used to benefit all countries. International law, then, extends to outer space. Nor can states claim Mars for themselves – Article II forbids “national appropriation by claims of sovereignty, by means of use or occupation, or by any other means.” Furthermore, while it is ambiguous whether or not non-State-Parties are able to violate the non-appropriation clauses, Article VIII of the OST maintains that “A State Party to the Treaty on whose registry an object launched into outer space is carried shall retain jurisdiction and control over such, and over any personnel thereof, while in outer space or on a celestial body.” U.S. federal code would require Mars colonists to register their craft with the FAA;  the U.S. would thus be able to exercise jurisdiction under Article VIII of the OST. Because of registration requirements, those colonizing Mars, under international law, would still be under the jurisdiction of the places from which they launched. For example, prospective colonists, launched from SpaceX’s South Texas site, would be under the jurisdiction of the United States.
U.S. law reinforces the OST. Under 18 U.S.C. 7, the special maritime and territorial jurisdiction of the United States applies to “any vehicle used or designed for flight or navigation in space,” while in flight, from the moment of embarkation to disembarkation on Earth. This jurisdiction furthermore extends to “any place outside the jurisdiction of any nation with respect to an offense by or against a national of the United States.” 18 U.S.C. 7 is an extension of the concept in international law of “flag jurisdiction,” and also goes one step further than the OST by allowing the United States to exercise jurisdiction over non-U.S. nationals who injure U.S. nationals. Furthermore, Space-X is subject to the authority of the United States by virtue of incorporation. As a result, under current legal framework, Space-X is legally incorrect that no government has authority or sovereignty over Martian activities. Both International and U.S. law would apply.
This framework is relatively satisfactory for the current level of space exploration and research on celestial bodies being performed. The OST, however, has issues which will need to be resolved before any significant colonization effort takes place. As some legal scholars writing on international law have noted, there is a great deal of ambiguity in the OST. It is unclear, for example, what exactly is meant by space being “the province of all mankind,” what exactly constitutes mankind’s “common interest” in the area, and to what degree commercial exploitation violates these principles. The current use and appropriation of celestial bodies, which has focused on exploration and research, seems clearly within the bounds of the OST, which explicitly allows for and envisions these activities. It’s also unclear at which point commercial exploitation violates the principle that Mars is res communis, meaning the planet is not subject to title by any nation, which animates the OST. There are also issues regarding criminal jurisdiction between various nationalities.
Various legal regimes have been suggested to supplement the OST. “Sustainable development” has been offered as an interpretive lens for the OST’s focus on preserving the common interest of mankind which leaves celestial bodies as substantially unimpaired. This would preclude much commercial development which would significantly alter celestial bodies. An alternative is to replace the legal regime of res communis with a regime incorporating notions derived from English property law, allowing for private ownership in order to incentivize productive use of the red planet. Real property could, for example, be allocated according to landfall and pre-negotiated agreements.
The 1998 International Government Agreement (IGA) regarding the International Space Station (ISS) shows one potential improvement. The agreement, which provides a dispute and jurisdictional resolution mechanism by way of state-to-state consultation, provides a sample for more complex jurisdictional agreements, allowing for a positive determination of criminal jurisdiction. Some law students have argued that this therefore avoids the problems which may arise where jurisdiction is blurrier, as is the case in space.
While a step in the right direction, this solution may not be adequate given the complexity and possible extent of colonization. The 1998 IGA was drafted for the ISS, a project much smaller than Musk’s hope for Mars, and all parties sought to “work toward a common goal.” A Mars colony, in contrast, may not have this same “common goal” animating the decisions of parties and its larger size will likely lead to increased conflict (both because of lower professionalism and discipline as well as increased opportunities for conflict). Furthermore, the jurisdictional elements of the agreement have not been tested, and it is possible that parties may be reluctant to actually allow foreign powers to exercise jurisdiction over their nationals.
There are other complications. Travel to Mars is likely to take at least six months. Extradition and enforcement would be difficult for the United States; it might be logistically impossible for certain nations to achieve justice for their nationals who are injured aboard a Mars colony. While this does not legally change whether or not a state will have jurisdiction, it does suggest that an alternative which does not rely on distant entities to exercise control may be preferable.
Another complication arises regarding the nationality of those born en-route to, and on, Mars. International law suggests that births on aircraft and ships are treated similarly to those of the state whose flag the ship flies, but makes no mention of spacecraft. This should be extended to registered space objects. International law also provides a mechanism for determining a child’s nationality depending on a child’s parents when it cannot otherwise be determined. Jurisdiction can thus flow from these determinations of nationality.
These complications illustrate one central difficulty with the current legal jurisdictional regime: it depends upon identity and not location. During space flight and on Earth satellites, this regime makes sense. For a small Mars colony, and where there is a uniformity of nationalities, such a regime is workable. However, if a Mars colony ever gains a significant diversity of nationalities, it will likely prove much more cumbersome than jurisdiction based on local or territorial sovereignty. As a result, while SpaceX is wrong in asserting that Mars is free from the control of nations on earth, it may be prudent to continue the search for alternatives which can accommodate what will likely be a diverse population on a distant planet.
 See, for example, Tan’s discussion in the Yale Journal of International Law https://digitalcommons.law.yale.edu/yjil/vol25/iss1/4/
 Tan also discusses the ways in which the principle of res communis is interpreted. https://digitalcommons.law.yale.edu/yjil/vol25/iss1/4/
 The first alleged crime on the I.S.S. was between two U.S. nationals (one on Earth, one on the I.S.S.) during divorce proceedings. As a result, how this jurisdictional provision will play out in practice remains unclear. See: https://www.space.com/who-investigates-space-crime.html.
 The U.S. recently refused to extradite Diplomat Sacoolas’ wife after she killed a British teenager, citing diplomatic immunity, and a U.K. judge has refused to extradite Julian Assange. See https://www.politico.eu/article/us-denies-uk-extradition-request-for-diplomats-wife/ and https://www.cnbc.com/2021/01/04/wikileaks-founder-julian-assange-cannot-be-extradited-to-us-judge-rules.html.
 This can be problematized: What if the child is a “foundling,” with unknown parents? International law provides that it is assumed the child’s nationality is related to the territory in which he or she is found. There may be constructs on mars not easily attributable or under the control of one nation; determining nationality, and thus jurisdiction, in this case, would be difficult.