Fifty years ago today, the United States, the Soviet Union, and the United Kingdom opened a treaty for signature that would become the backbone for international space law. It was a United Nations-approved agreement called the Outer Space Treaty, and 104 nations have become parties to the document since it was signed and enacted in 1967. Since then, the treaty has helped ensure the peaceful exploration of space, as well as provide a lasting framework for how nations are supposed to behave in Earth orbit and beyond.

A list of principles for what nations can and cannot do in space and on other worlds

In reality, the “Outer Space Treaty” is just a nickname. The document’s full title is the “Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies.” It’s a lengthy name, but it sums up the essence of the treaty well: it’s a list of principles for what nations can and cannot do in space and on other worlds. For example, nations can’t claim an asteroid as theirs, and they also should prevent contaminating foreign planets.

But the hallmark of the Outer Space Treaty is that it isn’t too detailed. “It doesn’t solve every problem,” Henry Hertzfeld, a research professor of space policy and international affairs at George Washington University, tells The Verge. The document is just 17 short articles in length; as a comparison, the Law of the Sea Treaty — a set of rules governing the use of the world’s oceans — spans hundreds of articles in length.

The Outer Space Treaty was never intended to be comprehensive, though. Created when space travel was in its infancy, the agreement was meant to address issues that could arise as space technology advanced. So it is somewhat flexible in its interpretation, as well as limited. But the treaty has still acted as the foundation for every piece of space legislation that has been created in the past half century. “It’s essentially the most important and most fundamental source of international space law,” Christopher Johnson, the space law adviser for the Secure World Foundation, tells The Verge. “All international space law follows from it and all national space activities fall under the treaty.”

Here are some of the biggest impacts the Outer Space Treaty has had in its 50-year history:

Space is for everyone — but you can’t claim it

Right away, the Outer Space Treaty establishes that all nations should have free access to space, and that exploration of the cosmos should be a peaceful enterprise. Such exploration should also be done “for the benefit and in the interests of all countries,” quickly setting up the importance for international cooperation in the realm of space travel.

But immediately after creating this “fair use” of space, the treaty makes one important caveat: space and celestial bodies cannot be appropriated by a nation. That means a country can’t claim the Moon as its own, for instance. The motivation was to prevent space land grabs, similar to the territorial claims that plagued the exploration of Antarctica in the first half of 1900s.

But in recent years, space law experts have been debating its interpretation as more and more companies express interest in mining space objects for resources. Private company Moon Express, which hopes to launch its first spacecraft to the Moon this year, has a long-term goal of mining the lunar surface for water, while Planetary Resources and Deep Space Industries are aiming to extract water and other resources from asteroids in the future. Given these ambitions,

Questions have arisen over whether or not companies can keep what they take from space

In 2015, Congress passed the US Commercial Space Launch Competitiveness Act, which ensured that US-based companies would get the rights to anything they collected from space. The United States basically argues that such actions are not expressly prohibited by the Outer Space Treaty. While many experts feel this is a reasonable interpretation, it’s still possible that other countries may feel differently and claim that such extraction is in violation of the treaty. And its passing has definitely stirred up some controversy.

“That’s still an international open argument,” says Hertzfeld. “Even though we have resolved it within our country and said it’s within our treaty obligations, not everyone may agree internationally.”

No weapons of mass destruction in orbit

In 1967, when the Outer Space Treaty was signed, the Cold War was in full swing. Both the US and the Soviet Union wanted to prevent the expansion of the nuclear arms race into a completely new territory. And as space technologies became more advanced, there was a concern that Earth orbit and beyond provided a whole new area from which weapons of mass destruction could be launched. That’s why an article in the treaty prohibits countries from putting nuclear weapons in orbit or on other planetary bodies.

Space, however, hasn’t been completely free of weaponization. Earth orbit has become an important foothold for militaries across the globe when it comes to communications, surveillance, and the control of weapons here on Earth. But the part of the treaty forbidding nuclear weapons — which made the deal a non-armament measure — has never been violated and has enabled space to be a peaceful region of exploration.

“That benefit is often maybe overlooked,” says Johnson. “All the things we do in space — they are allowed to happen because we have a treaty in place that prevents conflict from even being staged. That’s the real payoff.”

Planetary protection

The Outer Space Treaty tasks countries with “avoiding the harmful contamination” of celestial bodies. Additionally, countries have to make sure that any space materials they bring back to Earth won’t harm the planet. These obligations have become the basis for something called planetary protection — an effort to protect the Solar System from contamination of Earth life, as well as protect Earth from any potential alien life. It’s become an important aspect of all the planetary missions that NASA and other space agencies’ undertake.

The impetus for adding this provision was to help the scientific community answer an important question: is there life outside of Earth? The framers of the treaty knew it would be difficult to identify an extraterrestrial organism on Mars, for instance, if we had already spread Earth life on the planet. Conversely, scientists didn’t know if there was alien life on the Moon or elsewhere, and they didn’t want to run the risk of space agencies bringing back a deadly space microbe that had never been seen before.

The Outer Space treaty doesn’t specify the ways in which countries should prevent this cross contamination

The Outer Space Treaty doesn’t specify the ways in which countries should prevent this cross contamination. But most countries try to adhere to guidelines set forth by the Committee on Space Research, or COSPAR. It’s an international organization of scientists that comes up with standards for how to clean a spacecraft depending on where the vehicle is going in the Solar System. It also has standards for how to handle space samples that are brought back to Earth, to ensure nothing dangerous is spread.

Holding nations responsible for their space actions

The Outer Space Treaty may be an agreement between nations, but its provisions also cover what private companies do in space. A line in the treaty says that nations must be held responsible for their actions in space, including those from non-governmental activities. That means that countries have to oversee whatever the private sector does in space and can be held liable for the actions of commercial companies if they don’t adhere to the articles of the treaty. “The Soviets had wanted to ban non-governmental activity in space, and the US insisted, ‘No, we’re a market economy,’” Matt Schaefer, the co-director of the space, cyber, and telecom law program at the University of Nebraska-Lincoln, tells The Verge. “So the treaty allows for commercial activity in space, but part of that tradeoff was the government took an obligation to supervise commercial actors in space.”

Since then, space commercialization has become incredibly advanced. Various telecommunications companies have put numerous satellites in orbit around Earth, while companies have emerged that are dedicated to remote sensing — using satellites to scan the Earth and gather information about objects on the planet’s surface. Meanwhile, the US has developed a number of ways to regulate the launch and operation of these commercial satellites. The Federal Aviation Administration is responsible for issuing launch licenses for rockets carrying satellites into space, as well as making sure that these launches don’t harm the public. And the Federal Communications Commission helps to regulate the radio spectrum on which satellites can transmit.

The problem now is that companies are becoming even more ambitious

The problem now is that companies are becoming even more ambitious, with many hoping to move beyond just launching satellites into space. Moon Express wants to send private spacecraft to the Moon, something that has only ever been done by national governments before; Bigelow Aerospace wants to create private space stations in orbit, another endeavor that’s only been achieved by government agencies. At the moment, there is no regulatory framework that allows the US government to oversee these specialized missions in space and make sure that companies adhere to the articles of the Outer Space Treaty.

Lawmakers are working on legislation that would provide a regulatory framework. It’s a prime example of the role the Outer Space Treaty has played in the past 50 years. The treaty has merely laid out a minimum set of rules for countries to follow. How those rules are executed is decided by each nation that’s signed the treaty. “It does allow flexibility for how you would meet the obligation,” says Schaefer. “And the way we get further detail is through national space legislation.”