hi Laird,


from the caption of the picture

In a "big surprise," scientists have found lots of oxygen on Comet 67P/Churyumov–Gerasimenko, captured by the European space probe Rosetta an hour before its closest approach to the sun on August 13, 2015


the oxygen is found IN the coma surrounding the comet by the Rosetta orbiting the comet
not by the lander ON the comet

so there is no confirmation that this oxygen is coming from the comet
being a charged body flowing through space
it is likely that the comet is attracting the oxygen (and all the other gases) to it
(a giant "static cling" mop sweeping through space)