Juno fly-by detects lower levels of oxygen on Europa than expected

Less abundant molecular oxygen narrow chances of life being found on Jupiter's icy moon

Jupiter's moon Europa has a lot less free oxygen than previously thought, narrowing the odds that life may have evolved in this remote orb.

Long thought to be one of the solar systems best bets for hosting extraterrestrial life, Europa witnessed a fly-by from NASA space probe Juno in 2022, giving scientists the opportunity to test scientific models predicting the levels of free oxygen and hydrogen close to the moon’s surface.

Under its frozen surface crust, Europa has an internal liquid ocean of salty water, possibly including volcanic activity similar to hydrothermal vents in the Earth's oceans. The combination has enticed researchers to consider it a strong candidate for hosting extraterrestrial life, but the presence of the necessary free oxygen has been the subject of debate.

Frozen water on Europa's surface is split into oxygen and hydrogen by a bombardment of radiation from space. Scientists have used remote observations and modeling to predict the abundance of free oxygen (molecular O2), but these estimates of the rate of oxygen production varied wildly. Before Juno’s transit of Europa, model-driven estimates for the total Europa-genic O2 source extended over two orders of magnitude from 5 to 1,100 kg per second.

The flyby of space-bound research hardware in the form of Juno offered researchers the opportunity to narrow down these predictions.

Princeton space physics research scientist Jamey Szalay led a research team analyzing the data produced by Juno when it skimmed 353 km above Europa's surface. The probe carried the Jovian Auroral Distribution Experiment (JADE), designed to pickup ions - charged particles resulting when radiation or other particles break up neutral particles.

The total production of oxygen at the surface of Jupiter's icy moon Europa may be less than previously assumed, a paper published in Nature Astronomy now suggests. The findings have implications for the potential habitability of Europa’s ocean.

Using data from the experiment, Szalay and his team calculated about 12 kilograms of free oxygen is made at Europa’s surface every second, very much at the lower end of the previous estimates based on modeling.

“Unless Europa’s oxygen production was significantly higher in the past, the O2 production rates found here of less than the 18 kg s−1 available to be retained in Europa’s surface ice provide a narrower range to support habitability than previous model-driven estimates,” the authors note in a paper published in Nature Astronomy.

However, those hoping for moon-based subsurface oceans harboring life need not give up just yet. Scientists have been adding to the list of ice orbs which may host them. Researchers recently discovered that Saturn’s moon Mimas is likely to have liquid water sloshing below its icy surface.

Meanwhile, carbon dioxide, one tell-tale sign of life, has been found of the surface of Europa, according to a paper published September last year. ®

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