In space, no one can hear you scream, and as every grade school student knows, it's because there's no air to carry sound waves. Since around 350 BC, we've suspected — and more recently confirmed — that space is a vacuum. But what happens to oxygen in space?

Although NASA and other space agencies were well-prepared with spacesuits before sending astronauts into space, determining what happens to oxygen in space has been less clear. However, the study of the atmosphere — or, more correctly, the lack of atmosphere — in space has recently shown that molecular oxygen does exist there, but only in two locations so far.

Clearly, despite it being the third most abundant element in the universe, breathable oxygen is in extremely short supply once you leave our planet. But are the implications of this? And what can we learn from this fact?

Oxygen in space

Early Study of the Atmosphere Predicted the Void of Space

What happens to oxygen in space could not be confirmed by direct observation at first, as crewed spaceflight did not happen until the latter half of the 20th century. Instead, the lack of oxygen in space was initially predicted by deduction, observation and a lot of climbing.

Our planet is surrounded by a shell of atmosphere. Layers of air comprising nitrogen, carbon dioxide and other gases, such as oxygen, support life on the planet. The University Corporation for Atmospheric Research (UCAR) describes how early scientists measured the change in the atmosphere as you get farther from Earth's surface.

In 1648, two scientists, Blaise Pascal and his brother-in-law Florin Perier, carried a one-meter glass column of mercury to the top of a mountain. This early Torricelli barometer showed them that air pressure decreased with altitude. In 1787, further research carried out by another researcher who risked altitude sickness on Mont Blanc, Europe's highest mountain, showed that, along with the drop in air pressure, temperature also decreased.

These findings suggested that our atmosphere was breaking free of gravity and vanishing into a vacuum of space, which was further confirmed with daring balloon flights higher and higher into the atmosphere. Risking death, early scientists demonstrated not only that air pressure was lower at higher altitudes but also that oxygen levels four miles up into the atmosphere were so reduced that they were almost incompatible with life.

Further study of the atmosphere at greater elevation, carried out with uncrewed weather balloons, confirmed that there's less oxygen in the upper layers of our atmosphere and the air pressure is lower there.

Where Does Oxygen Come From?

Oxygen is the third most abundant element in the universe, so in theory, space should be full of it. However, the space between the planets, stars and other celestial bodies is only thinly populated with dust, gas and radiation. Despite decades of astronomy, molecular oxygen (the stuff you can breathe, comprising two atoms, O₂, joined together) is almost nonexistent. As Science.org notes, in space, hydrogen molecules, H₂, outnumber O₂ by a million to one.

On Earth, O₂is abundant. It's formed by plants, algae and phytoplankton during photosynthesis as they take in CO₂ and convert it into energy. Breathable oxygen forms around 20% of the atmosphere, and gravity keeps it closely bound to the planet, but in the upper layers, the pull isn't so strong, and the vacuum of space hoovers it up. Oxygen floating off into space at altitude is why most mountaineers need to carry reserves with them to summit Everest.

Oxygen does exist in space, though the Goddard Space Flight Center notes that it wasn't formed during the Big Bang. Instead, it arrived due to nuclear fusion reactions in the newly formed stars. As the stars consumed hydrogen and helium, they created carbon and oxygen. At the end of a star's life, these elements — the building blocks of carbon-based life — are hurled into space.

So, yes, we do come from stardust, but it's also stardust that's hoarding the oxygen molecules out in space.

What Happens to Oxygen in Space?

Oxygen was discovered in the 1770s, but astronomers have only recently discovered where to find it in space. And the reason for it being so elusive is stardust.

NASA reported in 2015 that infrared detectors at the European Space Agency's Herschel Observatory found molecular oxygen in only two places in the universe: the Orion Nebula and the Rho Ophiuchi cloud. The reason for this scarcity could be that oxygen is much stickier than it was once thought to be.

A recent study that simulated space dust cloud conditions here on Earth found that the binding energy for elemental oxygen is around twice as strong as expected. In the clouds of stardust, this strong attachment means that the oxygen atoms themselves are not free to combine and form breathable O₂. When they're tightly bound to the grains of space dust, they join with hydrogen instead to form H₂O, or water, which then freezes.

Although individual oxygen atoms are common around the stars that create them, stardust quickly gathers them up and doesn't easily let go. When you look up at the stars at night, remember this fact, and it may give you some comfort knowing a little more about how our universe works and what happens to oxygen way up there.

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study of the atmopshere

What Happens to Oxygen in Space?

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