Is there oxygen in space? Facts and hypotheses

29th Dec 2022
Is there oxygen in space? Facts and hypotheses

People need two basic elements to live: water and air. On Earth, neither is a problem, but what about astronauts in space? At first, water and oxygen supplies were carried onboard with each mission, but later, we learned how to produce both directly on a spacecraft. However, if we want to colonize other planets, we will need much more of these vital resources. Scientists have found that water in space is present as ice and are already looking for a way to extract and process it. But is there oxygen in space, and will we be able to breathe as we do on Earth? Let’s find out.

Atomic vs. molecular oxygen

You will be surprised, but oxygen is the third most abundant element in the universe after hydrogen and helium. However, this is not quite the oxygen that we need. About 96% of all oxygen in space exists in the form of atomic oxygen O(3P). It is a chemical element, a free radical, that has an unpaired electron, which makes it highly reactive. As a result, this atom cannot exist in the natural environment,  whereas in space, it participates in the corrosion of metals.

The oxygen we need to breathe is called molecular oxygen (O2). It is a diatomic compound that exists in the atmosphere as a colourless gas. So, when considering the question is there oxygen in space, this difference should be taken into account.

Why do we need oxygen and where it comes from on Earth?

The Earth’s atmosphere contains 78.084 % nitrogen, 20.948 % oxygen, 0.934 % argon, 0.0314 % carbon dioxide, negligible other gases, and a large amount of water vapour. In the course of evolution, our respiratory system has adapted to this composition, and now we breathe freely. When we breathe, we take in oxygen that enters the atmosphere as a result of photosynthesis occurring in plants, and in return, we release carbon dioxide and a small amount of other metabolic products.

Oxygen oxidizes nutrients in the body, giving us energy, and is also responsible for important biochemical processes in tissues and organs. Insufficient oxygen consumption disrupts these processes, causing hypoxia and suffocation. And if one does not inhale oxygen, a person loses consciousness in a minute. And after 3-4 minutes, the brain cells will start to die. Should the oxygen supply be absent for 5-7 minutes, a person will not be brought back to life.

How do we know there is no oxygen in space?

People traveling in the mountains noticed that the higher they climb, the more difficult it is to breathe. The scientist Blaise Pascal got interested in this phenomenon and conducted an experiment in 1646. His ascent to the top of a mountain with a mercury barometer made it possible to observe a decrease in atmospheric pressure as he moved away from the Earth’s core.

The reason why this happens was explained by Isaac Newton, who formulated his famous law of gravity in 1687. Gravity not only keeps us on Earth by pulling us down; it also attracts the atmosphere, creating the atmospheric pressure necessary for breathing and, thus, life. Atmospheric pressure decreases with altitude, the air becomes rarefied, and breathing becomes difficult.

The studies of Pascal and Newton, the experimental balloon flights of the Montgolfier brothers, laws of Boyle, Charles, Avogadro and many others, discovered until the beginning of the 18th century, made us question: is there any oxygen in space, which eventually led to the assumption that space is a vacuum.

Where does oxygen go in space?

Oxygen is concentrated in the lower layers of the atmosphere and is held by the Earth’s gravitational field. But at a certain distance from the Earth’s core, the force of gravity ceases to act, and nothing more holds the oxygen atoms. As a result, they fly far apart from each other, cling tightly to stardust, and do not merge into O₂ molecules that a person could breathe. Simply put, molecular oxygen turns into atomic oxygen and dissipates in the vast vacuum of space.

Why is there no oxygen in space?

Oxygen atoms can theoretically separate from stellar dust and combine to form molecular oxygen. But studies of the silicate and water ice that make stardust particles have shown that when oxygen atoms remain stuck to stardust, they combine with hydrogen atoms to form water ice. This ice can later become part of asteroids, comets and planets, setting the stage for the creation of life.

In the 1970s, astronomers predicted that molecular oxygen would be the third most abundant interstellar molecule, after molecular hydrogen (H₂) and carbon monoxide (CO). But they were wrong. Astronomers could only find molecular oxygen only in the nebula around the star Rho Ophiuchus and in the Orion nebula. And even in these clouds, the number of hydrogen molecules is millions of times greater than the number of oxygen molecules.

If there is no oxygen in space how does the Sun burn?

We know that the combustion process is impossible without oxygen. Rocket engines operate in space because rocket fuel contains oxygen as an oxidizing agent. But how can stars burn in space without oxygen?

The thing is, stars like our Sun are giant gas balls where thermonuclear reactions of hydrogen conversion into helium occur. They heat the gases to a glow resembling a flame.


So, is there oxygen in space? Sadly, not in a form breathable for us. Its atoms, away from the Earth’s gravitational field, bind to stardust and fly far apart, making it impossible to create O₂ molecules in the necessary amount.

But modern technology makes it possible to provide astronauts with oxygen. International Space Station and other manned spacecraft are equipped with special facilities to produce oxygen from water by electrolysis. Similarly, scientists plan to obtain air from local water ice and on future lunar and Martian bases. And in the distant future, humanity will probably even be able to terraform Mars.

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