Atmospheric constituents

How Mars' gasses are fluctuating through its four seasons

When carbon dioxide – the most abundant gas in the Martian atmosphere – freezes over the poles of Mars, pressure drops across the hemisphere. Pressure rises again when the polar caps melt and

CO2 is released. In both cases, gases are redistributed so that they are equalised from hemisphere to hemisphere. Scientists should, therefore, be able to predict the proportion of molecular nitrogen, argon, molecular oxygen and carbon monoxide in proportion to carbon dioxide.

Carbon dioxide – annual average 95 per cent by volume: The barometric pressure on Mars cycles as carbon dioxide freezes and is re-released from the polar ice caps.

Molecular nitrogen – annual average 2.6 per cent by volume: Behaves as expected, following the pressure changes caused by carbon dioxide fluctuations, with a delay and a seasonal variation of ten per cent.

Argon – annual average 1.9 per cent by volume: Behaves as expected, again following the pressure changes, with a delay and a seasonal variation of ten per cent.

Molecular oxygen – annual average 0.16 per cent by volume: Significant seasonal variability that changes year to year. There can be a spring and summer spike of as much as 30 per cent.

Carbon monoxide – annual average 0.06 per cent by volume: Tracks the season trend in argon, but some divergence from the seasonal trend merits further investigation.

Methane – annual average 0.00000004 per cent by volume: Undergoes a seasonable variation by a factor of ~3 from 0.24 to 0.65 parts per billion by volume.