Organic chemistry influences the observed seasonal cycle of molecular
oxygen on Mars
Recent measurements collected by the Mars Curiosity Rover at the Gale
Crater revealed an unexpectedly large seasonal cycle of molecular oxygen
(O2). We use a 1-D photochemical model, including inorganic and organic
chemistry, and its adjoint model to quantify the sensitivity of changes
in O2 to changes in inorganic and organic compounds. We show that O2
changes are most sensitive to changes in organic compounds from the
oxidation of methane. We find that an accelerated loss of atmospheric
methane, achieved either by increasing the atmospheric loss or by
imposing an additional surface loss, does not reconcile model and
observed values of O2 but it helps to explain the O2 seasonal variation.
The resulting changes in atmospheric composition are below the detection
limits of orbiting instruments.