A recent analysis finds up to 1,000 times more molecular oxygen than can be explained by prevailing theories about where it comes from.
https://www.cnet.com/science/space/jupiters-moon-callisto-has-a-whole-lot-of-oxygen-scientists-struggle-to-explain/?utm_source=dlvr.it&utm_medium=blogger#ftag=CAD590a51e
https://www.cnet.com/science/space/jupiters-moon-callisto-has-a-whole-lot-of-oxygen-scientists-struggle-to-explain/?utm_source=dlvr.it&utm_medium=blogger#ftag=CAD590a51e