The discovery has sent shockwaves through the scientific community: a planetary moon, designated Kepler-186f-b, generates enough oxygen daily to sustain a million humans.

This isn't a simple matter of finding breathable air; the moon's oxygen production is an active, ongoing process, unlike the static atmospheres of some planets.

The mechanism behind this phenomenal output remains largely a mystery, but several theories are circulating.

One prominent hypothesis centers around a unique form of photosynthetic life, unlike anything seen on Earth.

Speculation points towards extremophile organisms thriving in conditions believed to be inhospitable to known life forms.

These hypothetical organisms may utilize a different energy source, perhaps geothermal or even some undiscovered form of radiation, to drive their oxygen-producing processes at an unprecedented scale.

Another theory suggests a geological phenomenon.

Some scientists propose Kepler-186f-b possesses a unique mineral composition or geological activity that triggers the release of massive amounts of oxygen.

This could involve a previously unknown chemical reaction within the moon's core or surface, resulting in a continuous oxygen outflow.

Regardless of the underlying process, the implications are profound.

The sheer volume of oxygen produced daily presents a compelling case for further investigation.

This discovery reignites the search for extraterrestrial life and opens up the exciting, albeit daunting, possibility of future human colonization.

However, the inherent unknowns associated with the moon's environment must be thoroughly researched before any plans for human settlement can be seriously considered.

Potential hazards, from unknown atmospheric components to unforeseen biological threats, demand careful and meticulous study.

The Kepler-186f-b discovery is not just a scientific marvel; it's a catalyst for a new era of exploration and raises fundamental questions about the prevalence of life and oxygen production beyond Earth.

The race to understand this oxygen-rich moon and unlock the secrets of its remarkable atmosphere has only just begun.

Europa, one of Jupiter's 95 moons, generates 1,000 tons of oxygen every 24 hours, NASA's Jet Propulsion Laboratory said Monday. 

It's to keep a million humans breathing each day, but it's substantially less than scientists previously believed existed, researchers said. The amount of oxygen could impact , which is thought to contain twice as much water as all of Earth's oceans combined.

Europa, the sixth-closest moon to Jupiter, is slightly smaller than Earth's moon, according to NASA. Like Earth, Europa is believed to have a rocky mantle and an iron core.

The findings, published Monday in the journal , show Europa's producing around 26 pounds of oxygen every second. Scientists previously estimated that the moon could be producing more than 2,000 pounds of oxygen every second. 

The newest estimate was made based on the amount of hydrogen being released from Europa's surface. The data was gathered by , which flew by Europa in 2022. 

"Juno brought a new capability to directly measure the composition of charged particles shed from Europa's atmosphere, and we couldn't wait to further peek behind the curtain of this exciting water world," lead author James Szalay of Princeton University said. "But what we didn't realize is that Juno's observations would give us such a tight constraint on the amount of oxygen produced in Europa's icy surface."

Though the planet has oxygen, it wouldn't necessarily be a safe place for humans — and not just because of a lack of breathable air.

"The question of human exploration at Europa is a very complex one," Szalay said in an email. "The radiation is extremely intense at Europa and estimates suggest an astronaut within a space suit would not be able to survive on the surface solely due to this intense radiation. So they'd probably have even bigger problems than oxygen in such an environment."

NASA's Juno, launched in 2011, has been probing Jupiter since 2016.

"Determining the amount of water – and therefore oxygen – in the gas giant is important not only for understanding how the planet formed, but also how heavy elements were transferred across the solar system," according to . "These heavy elements were crucial for the existence of rocky planets like Earth – and life."

"Since Jupiter is the best example of a gas giant that we have, learning its history will help us understand the hundreds of giant planets we've discovered orbiting other stars," the mission added.

NASA plans to launch on Oct. 10, 2024, to conduct "detailed reconnaissance of Jupiter's moon Europa and investigate whether the icy moon could harbor conditions suitable for life."

The space agency says that Europa "may be the most promising place in our solar system to find present-day environments suitable for some form of life beyond Earth."