Venus' atmosphere is notoriously hellish. Its air is corrosive and hot enough to melt lead. Its billowing clouds are poisonous to humans. Sometimes, it rains acid. But researchers just discovered that, sandwiched between layers of toxic gas, this inhospitable atmosphere contains a thin layer of molecular oxygen.

Historically, Venus has received far less scientific attention than Earth's other neighbor, Mars. Recent reports that the organic compound phosphine may (or may not) exist in the Venusian clouds, however, have sparked new interest in studying the planet.

The new measurements come courtesy of NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA), a Boeing 747 that the agency retrofitted with a 2.7-meter (8.9 feet) infrared telescope. A team of German astrophysicists pored through data from SOFIA, focusing on 17 positions in Venus' atmosphere, on both the planet's dayside and nightside. They detected molecular oxygen — a gas composed of nonbonded oxygen atoms — in all of them. The results were published Nov. 7 in the journal Nature Communications.

But that doesn't mean astronauts would be able to breathe oxygen on Venus just as they would on Earth. Molecular oxygen is distinct from the oxygen that we breathe on our planet: Whereas breathable oxygen consists of two bonded oxygen atoms, creating the molecule O2, molecular oxygen is a soup of single, free-floating oxygen atoms. If we tried to breathe it, it would react too easily with the tissues in our lungs and wouldn't make it to our bloodstream.

Oxygen had been previously observed on the nightside of Venus, but this marks the first time researchers have detected it in the day-lit regions as well. The researchers suspect that the molecular oxygen builds up as the sun's heat breaks down carbon dioxide and carbon monoxide molecules. Winds high in the atmosphere then whisk it over to the planet's nightside, where the free oxygen atoms gradually react with other elements.

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The molecular oxygen layer also probably has a slight cooling effect on the upper layers of Venus' atmosphere. This modest cooling isn't enough to offset the planet's runaway greenhouse effect, but it does hint at Venus' milder, more pleasant past.

The finding also highlights how much scientists still have to learn about Earth's hostile "twin." With two upcoming NASA missions, as well as one helmed by the European Space Agency, Venus is about to receive a lot more attention, which may mean more discoveries in the near future.