This link was sent in by Gary – www.dailymail.co.uk/sciencetech/article-7680651/ … NASA scientists are said to be baffled after a portable chemistry lab on the Curiosity Rover (sampling the air) detected fluctuations in oxygen levels on Mars. The oxygen levels vary from one season to the next (over a 3 year period) and scientists now think that it is not the atmosphere of Mars that is fluctuating, as such, but somewhere in the vicinity there is an oxygen sink (or oxygen is leaking on to the surface). If so it is currently an unknown source of oxygen.
The portable chemistry lab has confirmed the atmosphere of Mars is primarily made up of carbon dioxide (almost 95% of it) with much smaller quantities of nitrogen, argon, oxygen, and carbon monoxide. This is itself somewhat peculiar.
The same story is at https://wattsupwiththat.com/2019/11/13/with-mars-methane-mystery-unsolve… …which has the benefit of lots of comments – and the odd gem.